ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES. Dr. M. VENU MADHAV

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1 ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES By Dr. M. VENU MADHAV DISSERTATION SUBMITTED TO THE RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, KARNATAKA, BANGALORE In partial fulfillment of the rules and regulations for the award of M.D. DEGREE IN RADIO - DIAGNOSIS Under the Guidance of Prof Dr. V. VENKATARATHNAM MDRD DEPARTMENT OF RADI0 - DIAGNOSIS, DR.B.R.AMBEDKAR MEDICAL COLLEGE AND HOSPITAL BANGALORE

2 DECLARATION BY THE CANDIDATE I here by declare that this dissertation titled ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES is a bonafide and genuine research work carried out by me under the guidance of Dr V.VENKATARATHNAM, Professor, Department of Radio-Diagnosis, Dr.B.R Ambedkar Medical College and Hospital, Bangalore. Date: Place: Bangalore Signature of the candidate Dr. M. VENU MADHAV Post Graduate in Radiodiagnosis Dr.B.R Ambedkar Medical College and Hospital Bangalore- 45 Rajiv Gandhi University of Health Sciences, Karnataka, Bangalore. II

3 DEPARTMENT OF RADIO DIAGNOSIS DR. B.R.Ambedkar Medical College, Bangalore. CERTIFICATE BY THE GUIDE This is to certify that this dissertation titled ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES is a bonafide work done by Dr. M.VENU MADHAV, in partial fulfillment of the requirement for the award of M.D. Degree in Radio-Diagnosis. Date: Place: Bangalore Dr. V. VENKATARATHNAM, MDRD Professor Department of Radio Diagnosis DR.B.R.Ambedkar Medical College Bangalore 45 Rajiv Gandhi University of Health Sciences, Karnataka, Bangalore. III

4 RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, KARNATAKA ENDORSEMENT BY THE HOD, PRINCIPAL This is to certify that the dissertation entitled ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES is a bonafide research work done by Dr. M.VENU MADHAV, under the guidance of Dr V. VENKATARATHNAM, Professor, Department of Radio-Diagnosis, D r. B. R A m b e d k a r Medical College and Hospital, Bangalore Seal and Signature Dr. RAJAN.B MDRD, DNB, DMRD Professor and Head, Department of Radio Diagnosis Dr. B. R. Ambedkar Medical Seal and Signature Dr. B.R.SHIVAKUMAR. MD (GEN MED) Principal, Dr. B. R. Ambedkar Medical College, Bangalore College, Bangalore Date: Place: Bangalore Date: Place: Bangalore IV

5 COPY RIGHT DECLARATION BY THE CANDIDATE I hereby declare that the Rajiv Gandhi University of Health Sciences, Bangalore, Karnataka, shall have the rights to preserve, use and disseminate this dissertation entitled ROLE OF COMPUTED TOMOGRAPHY IN EVALUATING MEDIASTINAL MASSES in print or electronic format for academic / research purpose. Date : Place : Bangalore Dr. M. VENU MADHAV Post Graduate in Radiodiagnosis Dr.B.R Ambedkar Medical College and Hospital Bangalore- 45 Rajiv Gandhi University of Health Sciences, Karnataka V

6 ACKNOWLEDGEMENTS I primarily express my earnest gratitude and feelings of proud indebtedness to Dr.V.Venkatarathnam, Professor, Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, for his priceless guidance, valuable suggestions, supervision and the support that he had extended during the course of this study. I Convey my deepest regards and heartful gratitude to Dr. Rajan. B Professor and Head of the Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, who provided to be a source of consistant inspiration and for his valuable suggestions and supervision. I express my gratitude to Dr.MD Amen Gawai, Assistant professor, Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, for his immense help, supervision and suggestions. I express my gratitude to Dr.Harish B S, Dr Mahesh. H, Dr Madhav Hegde, Assistant professors, Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, for their immense help and suggestions. I am thankful to Dr. Nazir. S F B, Dr Shabeer Ahmed & Dr. Aslam pasha, Senior residents, Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, for their valuable advice and help during the studies. VI

7 I owe much to Dr. Greeta Mathews, senior Resident, Department of Radiodiagnosis, Dr.B.R.Ambedkar Medical College, who provided to be a source of constant inspiration. I express my heartful gratitude to colleague friends of Department of Radiodiagnosis who have been walking along side me, aiding in the successful completion of the study. My thanks to all the staff of the Radiographers and all the staff of department of Radiodiagnosis who held me during the studies. I thank my father and mother and my family for their care and support for me in my life and for my studies. Lastly, my sincere thanks to all the patients, who with their excellent cooperation became the backbone of this dissertation. Date: Place: Bangalore Dr. M. VENU MADHAV Post Graduate in Radiodiagnosis VII

8 LIST OF ABBREVIATIONS Ca cm CT GCT GI HU IVC LM MLN MRI NB PET SD SVC TB Tc yrs carcinoma Centimetres Computed Tomography Germ Cell Tumour Gastrointestinal Hounsfield Unit Inferior vena cava Leiomyoma Metastatic Lymph Node Magnetic Resonance Imaging neuroblastoma Positron Emission Tomography Standard Deviation Superior Vena Cava Tuberculosis Technetium Years VIII

9 ABSTRACT BACKGROUND & OBJECTIVES : The Objective of this study is to determine the accuracy of the diagnosis of mediastinal masses by Computed Tomography and to correlate its findings with histopathology. This study reviews the variety of the disease processes involving the mediastinum. Emphasis is based on illustrating the specific diagnostic CT features and its correlation with histopathology findings that allow one to distinguish between the different types of mediastinal masses. MATERIALS AND METHODS Total Number of 30 cases referred to the department of Radio-Diagnosis for clinically suspected Mediastinal masses at Dr.B.R. Ambedkar Medical college and Hospital over a period of two years were included in the study. Technique : In all cases pre-contrast study was followed by post-contrast study, image acquisition was done with intermittent suspended inspiration. For post-contrast study, ml of dynamic intravenous injection of Diatrizoate-meglumine (Trazograf 76%; Urograffin 76%, 60%) at a dose of 300mg of Iodine / Kg body weight (in children) was given and axial section were taken from thoracic inlet to the level of suprarenals. The pre and post contrast attenuation values, the size, location of the mass, presence of calcification, mass effect on adjoining structures and others associated findings were studied. IX

10 RESULTS : In our study, anterior mediastinum was the most commonly involved compartment, followed by superior mediastinum,posterior mediastinum and middle mediastinum. Lymphoma is most common lesion in anterior mediastinum and superior mediastinum, Teratoma in middle mediastinum and Schwannoma in posterior mediastinum. In our study, isolated compartmental involvement is common in posterior mediastinum followed by superior, middle and anterior mediastinum. However the anterior mediastinal is most commonly involved in trans-compartmental lesions. Therefore anterior mediastinum was collectively the most common compartment involved, followed by superior mediastinum, posterior mediastinum and middle mediastinum. In the study, Lymphoma 37.5%, Lymphoma and Thymic masses 31.25%, Ca. esophagus and Schwannoma were the most common mediastinal masses in the anterior, superior, middle and posterior mediastinal compartments respectively. CONCLUSION : From the above results, we conclude that computed tomography definitely has a major role to play in the evaluation of a mediastinal mass regarding the compartmental distribution, mass effect upon adjacent structure and provisional diagnosis. X

11 TABLE OF CONTENTS Sl No Particulars Page No 1 INTRODUCTION 1 2 AIMS & OBJECTIVES 2 3 REVIEW OF LITERATURE 3 4 EMBRYOLOGY, GROSS & CT ANATOMY 5 CLASSIFICATION & DIFFERENTIAL 5 DIAGNOSIS 20 6 MATERIALS AND METHODS 55 7 RESULTS 58 8 IMAGES 77 9 DISCUSSION CONCLUSION BIBLIOGRAPHY CASE PROFORMA KEY TO MASTER CHART 98 XI

12 LIST OF TABLES Sl. No. Tables Page No. 1 Classification of mediastinal masses based on the 20 location 2 Normal measurements of the thymus on CT: Mean 25 values 3 Differentiation of thymoma and normal thymus (CT 27 criteria) 4 Age and sex distribution 58 5 Clinical symptoms Distribution 59 6 Compartmental distribution of mediastinum masses 60 7 Superior Mediastinal Lesions distribution 61 8 Anterior Mediastinal Lesions distribution 62 9 Middle mediastinal Lesions distribution Posterior mediastinal masses distribution Thymic masses distribution Neural tumors distribution Lymph nodal masses distribution Definition of mediastinal masses Density of mediastinal masses on non-contrast study Degree of contrast enhancement Pattern of contrast enhancement Other attenuations in mediastinal masses Mass effect on adjoining mediastinal structures Metastasis CT Diagnosis Histopathology diagnosis Symptoms Distribution Compartmental distribution Individual mass distribution (based on the tissue of origin) 85 XII

13 LIST OF CHARTS Sl. No. Charts Page No. 1 Age and sex distribution 58 2 Clinical symptoms Distribution 59 3 Compartmental distribution of mediastinum masses 60 4 Superior Mediastinal Lesions distribution 61 5 Anterior Mediastinal Lesions distribution 62 6 Middle mediastinal Lesions distribution 63 7 Posterior mediastinal masses distribution 64 8 Thymic masses distribution 65 9 Neural tumors distribution Lymph nodal masses distribution Definition of mediastinal masses Density of mediastinal masses on non-contrast study Degree of contrast enhancement Pattern of contrast enhancement Other attenuations in mediastinal masses Mass effect on adjoining mediastinal structures Metastasis 74 XIII

14 LIST OF IMAGES Sl. No. Image Page No. 1 CT and Histopathology images of Lymphoma 77 2 CT and Histopathology images of thymoma 78 3 CT images of Carcinoma thyroid with mediastinal extension 79 4 CT image of Osteoclastoma 79 5 CT and Histopathology images of Schwannoma 80 6 CT and Histopathology images of Teratoma 81 7 CT and Histopathology images of Metastatic Lymphadenopathy 82 XIV

15 INTRODUCTION The aim of this study is to determine the accuracy of the diagnosis of mediastinal masses by Computed Tomography and to correlate its findings with histopathology. This study reviews the variety of the disease processes involving the mediastinum. Emphasis is based on illustrating the specific diagnostic CT features and its correlation with histopathology findings that allow one to distinguish between the different types of mediastinal masses. The multitude of diseases affecting the mediastinum varies considerably, ranging from tumors (benign to extremely malignant), cysts, vascular anomalies, lymph node masses and mediastinal fibrosis. Hence every possible effort has to be made to arrive at a specific diagnosis at the earliest. Computed Tomography has revolutionized in the diagnosis of mediastinal lesions. It is one of the finest non-invasive imaging modalities available for imaging of the thorax. Computed Tomography has good spatial resolution and shorter imaging time, besides being less expensive and being more widely available. It is capable of defining the precise anatomical details and characterizing the nature, site and extent of the disease. Co-existing lung abnormalities and calcification within the lesions are better appreciated on CT. CT gives much more detail of extent and involvement of disease. This also underlines the importance of close cooperation with the histo-pathologist and the clinicians in diagnosis and management. The additional role of CT in performing CT guided biopsies of lesions cannot be over emphasized. 1

16 AIMS AND OBJECTIVES 1. To study the characteristics and determine the differential diagnosis of Mediastinal masses by Computed Tomography. 2. To study the distribution of mediastinal masses. 3. To determine the accurate delineation and extensions of the tumours. 4. To correlate the histo-pathological diagnosis to the findings of CT scan where possible. 2

17 REVIEW OF LITERATURE 1971 Mayo clinic review Wychulis et al [1] of 1064 cases identified over 40 years period, 60% constituted neurogenic neoplasms, thymomas and benign cysts; and majorities were adults. 80% were younger than 15 years of age at diagnosis Benjamin et al [2] in their CT study of 214 cases found neural tumours as the commonest mediastinal mass constituting 22.9% of the total McLoud et al [3] in their CT study showed hilar mediastinal lymphadenopathy in 2-3% of cases were secondary to extra thoracic malignancy Baron, Richard L [4] showed that CT scanning can differentiate vascular from avascular causes of mediastinal widening Baron, Richard L [5] showed that CT is the method of choice when suspected thymic abnormality requires further evaluation; CT differentiates benign thymic cysts from solid tumors Webb WR [6] showed that CT allows the differentiation of mediastinal mass from normal mediastinal structures, characterization of its density, its localization and discrimination of vascular and avascular lesions. 1987Sones PJ, et al [7] showed the effectiveness of CT in evaluating intrathoracic masses Davis et al [8] in their study of 400 consecutive patients with mediastinal masses found thymic tumors as the commonest mediastinal mass comprising 17%. 3

18 1988 Chen et al [9] in their study on 34 patients with CT diagnosis of Thymic masses. Thymoma constituted 91%, thymic cyst 2.9% Cohen et al [10] in their study of 230 cases reported 16.9% were neural tumours, 24.3% were thymic tumor 20% benign cysts Im et al [11] in their study on Tuberculosis lymphadenopathy, 52% of the TB lymphadenopathy showed rim enhancement with central areas of low attenuation. Right Para tracheal lymph nodes were commonly involved in 87% Morgenthaler et al [12] in their study showed that thymoma constitutes 15% of primary mediastinal masses Strollo et al [13] showed the middle and posterior mediastinal masses constituted nearly 50% of primary mediastinal masses Kim JH et al [14] showed that mesenchymal neoplasms account for about 55% of mediastinal tumours and the radiological pattern of these masses are quite characteristic Lee K.H et al [15] in their retrospective study of 46 patients showed 54% were purely cystic masses and 46% were cystic tumours with solid portion in the anterior mediastinum compartment. 4

19 EMBRYOLOGY The mediastinum is embyrologically complex, anatomically diverse and yet remarkably compact. Therefore, it is subjected to development of various pathological lesions. The septum transversum is a thick plate of mesodermal tissue occupying the space between the thoracic cavity and the stalk of the yolk sac. This septum does not separate the thoracic and abdominal cavities completely leaving large openings, the pericardioperitoneal canals on each side of the foregut. With the rapid growth and expansion of the lung buds the mesoderm of the body wall is split into two components as:- 1. Definitive wall of the thorax 2. Pleuropericardial membranes which with the descent of the heart and positional changes of the sinus venous result in the formation of the pericardial cavity and two pleural cavities. The brachial arches and primitive foregut forms the lungs, heart, great vessels and esophagus. Additionally the thymus, thyroid and parathyroid glands migrate to their respective positions. The complexity of these changes in the foetus facilitates frequent errors in development [16]. 5

20 GROSS ANATOMY A. Boundaries: Mediastinum is the extra pleural space within the thorax between the two pleural spaces. It extends from the sternum anteriorly to the vertebral column posteriorly. The upper limit is formed by the thoracic inlet and the lower limit by the diaphragm. B. Mediastinal Compartment: The mediastinum is often divided into many compartments in an attempt to develop a differential diagnosis. Many methods are put forward and are: 1. Anatomical classification: An imaginary plane extends from the sternal angle to the lower border of the fourth dorsal vertebra dividing the mediastinum into superior and inferior divisions. The inferior compartment is further subdivided into a. Middle mediastinum, which contains the pericardium and its contents as well as the major vessels and airways; b. Anterior mediastinum, which lies anterior to the middle mediastinum and posterior to the sternum; and the c. Posterior mediastinum, which lies posterior to the middle mediastinum and anterior to the thoracic vertebral column. 6

21 (Shanks and Kerley) [17] 2. Felson s classification: Mediastinal compartments are ascertained from the lateral roentgenogram as follows: An imaginary line is drawn upward from the diaphragm along the back of the heart and front of the trachea to the neck. This divides anterior from middle mediastinum. A second imaginary vertical line connects a point on each of the thoracic vertebra 1cm behind its anterior margin. This divides middle from posterior mediastinum [18]. Felson classification of mediastinum 7

22 3. Fraser and Pare classification: According to Fraser and Pare the mediastinum is divided into three compartments, Anterior, middle and posterior. The anterior mediastinal compartment is bounded anteriorly by the sternum posteriorly by the pericardium, aorta, and brachiocephalic vessels. The posterior mediastinal compartment is bounded anteriorly by the pericardium and the vertical part of the diaphragm, laterally by the mediastinal pleura, and posteriorly by the bodies of the thoracic vertebrae (although for practical purpose, the para vertebral gutters are included).the middle mediastinum lies in between the anterior and posterior mediastinal compartment [19]. Fraser modified classification of mediastinum 4. Heitzmann classification [20] : The normal mediastinum is divided into six anatomic regions: a. Thoracic inlet b. Anterior mediastinum c. Supra azygos d. Supra aortic 8

23 e. Infra azygos f. Infra aortic C. Contents of mediastinum (based on anatomical division): 1. Superior Mediastinum: Vessels: Innominate veins, SVC, aortic arch, great vessels, thoracic duct, azygos vein and upper hemiazygos vein. Nerves: Vagi nerves, left recurrent laryngeal nerve and both phrenic nerves, thymus and Lymph nodes, trachea and upper thoracic oesophagus. 2. Anterior mediastinum: Vessels: Ascending aorta, internal mammary arteries, lower part of thymus and Lymph nodes. 3. Middle mediastinum: Vessels: Aortic root, IVC lower ½ of SVC terminal part of azygos vein, pulmonary arteries and veins. Nerves: Phrenic nerve Cardia with pericardium, hila of lungs, tracheal bifurcation and tracheo bronchial lymph nodes. 4. Posterior mediastinum: Vessels: Descending thoracic aorta, intercostals vessels, peribronchial and oesophageal vessels, thoracic duct, azygos vein and hemiazygos vein. Nerves: Autonomic nerves (vagus and splanchnic nerves). Lower thoracic oesophagus, Para vertebral lymph nodes. 9

24 NORMAL CT ANATOMY The cross sectional anatomy of the mediastinum is easily separated into a set of basic slices or levels, which can be conveniently described based on the major structures at each level [21]. CT of normal mediastinum. Five 1-cm thick sections have been selected to show the important anatomical features (A E). The level of each section is illustrated in the diagram. A.Ao = ascending aorta, AV = azygos vein, D.Ao = descending aorta, IA = innominate artery, LCA = left carotid artery, LIV = left innominate vein, LPA = left pulmonary artery, LSA = left subclavian artery, MPA = main pulmonary artery, Oes = oesophagus, RIV = right innominate vein, RPA = right pulmonary artery, SVC = superior vena cava, T = trachea, RA = right atrium, LA = left atrium, RVO = right ventricular outflow tract. 10

25 Axial CT scans of thorax showing normal mediastinum at various levels at illustrated in the diagram IMAGING OF MEDIASTINUM Imaging plays an important role in the evaluation of the mediastinum. It is been widely used for investigating the location and the extent of the mediastinal masses. 11

26 Imaging modalities used are: a) Radiography b) Fluoroscopy c) Ultrasound d) CT scan e) MRI f) PET scan 1. Radiography: It is the initial modality used in patient with chest complaints. Depending on the changes in the various mediastinal lines and with the presence of various signs the mediastinal mass can be put in various compartments. Mediastinal lines: These lines represent pleural reflections delineated by air in the adjacent lungs. The chest film must be well penetrated and the pleural lines optimally oriented for their demonstration [18]. The right paraspinal line: Runs from the thoracic inlet to the diaphragm, a millimeter or two from the right border of the thoracic spine. It is produced by the normal soft tissues covering the bone. The left paraspinal line: Lies medial to the lateral border of the descending aorta and is seldom seen above the aortic knob The right paraesophageal line: It is a concave line in the right upper thorax extending from the pulmonary apex down to about the level of the right main stem bronchus. The upper segment of this line is visible through the trachea in about 10% of adults and 50% of children. 12

27 The left paraesophageal line: Less often seen as the adjacent descending aorta obliterates it. The left para aortic lines: Lies parallel to the left paraspinal line alongside the lateral border of the aorta. The lower end of the right para aortic line may sometimes be seen just above the diaphragm on a well penetrated film. The posterior junction line: Lie between the two lungs behind the esophagus, it is difficult or impossible to distinguish from the paraesophageal lines without barium. The anterior junction line: Lie between the two lungs usually near the midline. It is seen in about 20% of chest as a 'V' shaped structure only 2 to 3 inches in length extending downward from the level of the angle of Louis. This line is seldom apparent in infants because of the thymus. The right Para tracheal line: Is visible in 63% of normal chest films. The Left pericardial line: Is sometimes demonstrated as it obliquely crosses the aortic knob and is continues with the left heart border. 13

28 Diagrams illustrating the mediastinal boundaries and junction lines. (A) Section just above the level of the aortic arch; (B) section through the aortic arch; (C) section through the heart [21]. 14

29 Signs of mediastinal masses: A. Silhouette sign: An intrathoracic lesion touching a border of the heart, aorta or diaphragm will obliterate the border whereas; an intra-thoracic lesion not anatomically contiguous with a border of these structures is distinctly seen separately. Anterior mediastinal masses: Cause obliteration of a part or whole of the heart border and right border of ascending aorta. The opacity of an anterior mediastinal mass will overlap the left border of aortic knob but not obliterate it, since aortic knob lies posteriorly its border are seen through the opacity. Posterior mediastinal masses: Obliterate the left border of the aortic knob. The same opacity will overlap the cardiac border but does not obliterate it. B. Hilum overlay sign: It is used to differentiate opacity of an anterior mediastinal mass from that of an enlarged heart. The proximal segment of the visible left pulmonary artery lies lateral to the cardiac shadow or just within its outer edge in over 98% of normal individuals. In the remainder it lies slightly more than 1 cm within the cardiac silhouette. The opacity of an anterior mediastinal mass may closely resemble that of an enlarged heart or pericardial sac, but the opacity will overlap the main pulmonary artery which will be well seen within the margins of the mass. If the pulmonary artery is seen lateral to the opacity, enlarged heart or pericardial sac is indicated. Failure of Hilum overlay sign: However, certain types of congenital heart disease, especially among infants, may result in a lateral bulge anterior to the pulmonary 15

30 trunk, causing the left pulmonary artery to appear well within the left border of the cardiac silhouette. C. Hilum convergence sign: If the pulmonary artery branches converge towards the mass, rather than toward the heart then it is an enlarged pulmonary artery. The reverse indicates mediastinal mass. D. Cervicothoracic sign: This sign is based on the fact that if a thoracic lesion is in anatomic contact with the soft tissues of the neck, its contiguous border will be lost. The cephalic border of the anterior mediastinum ends at the level of the clavicles, whereas that of the posterior mediastinum extends much higher. Hence a lesion clearly visible above the clavicle on the frontal view must be posteriorly situated and be entirely within the thorax. If anterior, the cervical soft tissues could have obscured its upper border. E. Thoracoabdominal sign: Convergence of the lower margin of the mass towards the spine indicates that the lesion is probably entirely intrathoracic whereas divergence indicates an abdominal mass. The Thoracoabdominal sign is seen in aneurysm, neoplastic conditions, and azygos continuation of the inferior venacava. F. Other signs: Interface of a mediastinal mass with adjacent mediastinal structure will usually be an obtuse angle. Whereas, the lung lesions against the mediastinum will often makes an acute angle. Posterior mediastinum is continuous below the diaphragm with the retrocrural region. Thus masses, that extend with above and below the diaphragm usually lie in the posterior mediastinum [22]. 16

31 2. Fluoroscopy: It assists in evaluating the effects of the mediastinal mass on diaphragm movement. As in the evaluation of phrenic nerve paralysis - "sniff test" may be performed to determine paradoxical elevation of the diaphragm. 3. Ultrasound: Used via transthoracic (transcutaneous) or transesophageal routes and can identify masses overlying the heart. It generally tells whether the mass is solid or cystic. 4. MRI It has several advantages over CT in imaging the heart and mediastinum like: Ability to produce orthogonal views Ability to image vessels and moving blood as flow voids. Thus obviate iodinated contrast material. Ability to image masses adjacent to the heart and paraspinal region. Ability to distinguish mass and fibrous tissue in a patient with treated lymphoma or carcinoma in whom tumor recurrence may be present [23]. 17

32 INDICATIONS FOR THE CT EVALUATION OF THE MEDIASTINUM [7, 19} 1. To define and characterize a mediastinal abnormality suspected or diagnosed on plain radiographs, Mass differentiation: cystic, fatty or solid in nature and also localization to other mediastinal structure. Mediastinal widening: assessment of the cause - pathological or anatomical variation. Hilum: differentiate an enlarged pulmonary artery from a mass. Paraspinal widening: distinguish between lymph node enlargement, tumor, infection or vascular cause 2. To evaluate the mediastinum in patients who have normal chest radiographs yet a clinical reason to suspect mediastinal disease. Eg: - search for Thymoma or Ectopic parathyroid adenoma in a Myasthenia gravis or surgically resistant Hyperparathyroidism patients respectively. 3. Radiation treatment planning and follow up 4. Aid biopsy or drainage procedures. 18

33 APPROACH TO THE DIAGNOSIS OF MEDIASTINAL MASS ON CT SCAN The differential diagnosis of a mediastinal mass on CT is usually based on its location, identification of the structure from which it is arising, whether it is single, multifocal or diffuse, its size and shape, its attenuation, the presence of calcification and its character and amounts, and its opacification following contrast administration. Based on CT attenuation masses can be categorized as a. Fat attenuation. b. Lowattenuation, having density greater than fat but less than muscle. c. High attenuation, withdensity greater than that of muscle. d. Enhancing, showing significant increase inattenuation following contrast administration. Following determination of location and density other CT characteristics of mediastinal masses are considered in improving specificity of the differential diagnosis such as shape, edge, sharpness, contour, relation to normal structures, effect on adjacent structures (especially displacement) and the presence of other abnormalities including those visible in the lung and abdomen as well as those remote from the mass in the mediastinum. Clinical information including age and sex of the patient is often as useful as any imaging parameter in achieving a logical and useful differential diagnosis list 19

34 CLASSIFICATION OF MEDIASTINAL MASSES Table 1: Classification of mediastinal masses based on the location [24] Common lesions Tortuous brachiocephalic Vein Rare lesions Aneurysm of brachiocephalic artery Lymph node enlargement Retrosternal goiter Fat deposition Thymic tumour Germ cell Lymphangioma Parathyroid adenoma Sternal mass Lipoma Hemangioma Epicardial fat pad tumours Morgagni hernia Anterior mediastinum Diaphragmatic hump Pleuropericardial cyst Lymph node enlargement Aneurysm arch aorta Tracheal lesions Cardiac tumours Enlarged pulmonary artery Middle mediastinum Dilated superior vena cava, Bronchogenic cyst 20

35 Neurogenic tumours Hiatus hernia Neuroenteric cyst Pseudocyst of pancreas Aneurysm of descending Artery Oesophageal masses Sequestration lung Thoracic duct cyst Dilatation of azygos vein Bochdalek hernia Posterior Mediastinum Para vertebral mass Extramedullary haemopoiesis Thoracic aorta passes through all the divisions of mediastinum. Hydatid cyst can occur most commonly in the middle and posterior mediastinum. Masses situated in all mediastinal compartments are lymphoma and sclerosing mediastinitis DIFFERENTIAL DIAGNOSIS OF MEDIASTINAL MASSES BASED ON COMMON SITES OF ORIGIN [23] 1. Pre vascular masses a. Thymic masses i) Hyperplasia ii) Thymoma iii) Thymic carcinoma iv) Thymic cyst v) Thymic carcinoid tumor vi) Thymolipoma 21

36 vii) Thymic lymphoma viii) Metastasis b. Germ cell tumor i) Seminoma ii) Teratoma iii) Non-seminomatous GCT c. Thyroid abnormalities d. Parathyroid abnormalities e. Lymph node masses f. Vascular abnormalities (aorta and great vessels) g. Mesenchymal abnormalities (e.g., lipomatosis, lipoma) h. Foregut cyst i. Lymphangioma and hemangioma 2. Cardiophrenic angle a. Lymph node masses (particularlylymphoma and metastases) b. Pericardial cyst c. Morgagni hernia d. Thymic masses e. Germ cell tumours 3. Pretracheal space a. Lymph node masses i) Lung carcinoma /Sarcoidosis 22

37 ii) Lymphoma (particularly Hodgkin disease) iii) Metastases iv) Infections (e.g., TB) b. Foregut cyst,tracheal tumour c. Mesenchymal masses (e.g., lipomatosis, lipoma) d. Thyroid abnormalities, e. Vascular abnormalities (aorta and great vessels) f. Thymic mass or germ cell tumour 4. Aorticopulmonary window a. Lymph node masses i. Lung carcinoma ii. Sarcoidosis iii. Lymphoma iv. Metastases b. Mesenchymal masses (e.g. Lipomatosis, lipoma) c. Vascular abnormalities (aortaor Pulmonary artery) d. Foregut cyst 5. Subcarinal space, azygoesophageal recess a. Lymph node masses i) Lung carcinoma ii) iii) Lymphoma Metastases b. Foregut cyst 23

38 6. Paravertebral region a) Neurogenic tumour b) Nerve sheath tumours i) Sympathetic ganglia tumors ii) Paragangliomas c) Foregut cysts d) Meningocoele e) Extramedullary hematopoiesis f) Pseudocyst g) Thoracic spine abnormalities h) Hernias i) Esophageal masses j) Mesenchymal masses(e.g., lipomatosis, lipoma) k) Lymph node masses i. Lymphoma (particularly Non-Hodgkin) ii. Metastases l) Lymphangioma and Hemangioma. 24

39 ANTERIOR MEDIASTINAL MASSES 1. Thymus and related masses: Computed tomography should be the imaging method of choice following plain chest radiograph when suspected thymic abnormality require further evaluation [25]. Table2: Normal measurements of the thymus on CT: Mean values [26] Age AP Diameter Thickness of Craniocaudal Width in in in cm(sd) limbsin cm (SD) length in cm (SD) cm (SD) yrs (0.82) 1.5(0.46) 3.53(0.99) 3013(0.85) (0.88) 1.05(0.36) 4.99(1.25) 3.05(1.17) Of all the measurements i.e. length (measured in the cephalo-caudal dimension), width (measured in the transverse dimensional) and thickness (perpendicular to the length), the thickness is most helpful value for thymic size assessment. Under age 20, a thickness of 1.8 cm is considered maximum allowable value whereas 1.3cm being maximum normal value in older subjects [23]. a. Thymic hyperplasia Most commonly associated with myasthenia gravis, it is also seen in other conditions such as thyrotoxicosis, autoimmune diseases like Hashimoto s thyroiditis, Addison s disease, Hemolytic Anemia and Behcet s disease.the thymus may atrophy due to stress or consequence of steroid or anti neoplastic drug therapy. [27, 28, 29] The gland returns to its original position on recovery or cessation of treatment, or may 25

40 become larger than its previous normal size, in the phenomenon known as Rebound Thymic Hyperplasia. b. Thymic cyst: Uncommon lesion, mostly asymptomatic and accounts for 3% of all tumors in the anterior mediastinum. They can be congenital or acquired in origin. Congenital are derived from remnants of thymopharyngeal duct and are typically unilocular, contains clear fluid of water density with a thin wall usually less than 6cm in diameter. In contrast acquired thymic cyst result from an inflammatory process and occurs in patients after thoracotomy, radiation therapy for Hodgkin's disease or in association with Thymic tumors. These are usually multilocular, wall of variable thickness and range in size from 3 to 17cm in diameter, sometimes septations and calcification of the cyst wall may be seen [21]. c. Thymoma: Most common primary tumor of the anterior mediastinum, it accounts for 15% of primary mediastinal mass [23]. These are neoplasms originating from the thymic epithelium and are most common during 5th to 6th decade. 30 to 54% patients with thymoma develop myasthenia gravis. On CT, thymomas appear as homogenous soft tissue density masses, which are usually sharply demarcated and oval, round or lobulated in shape, project to one side of the mediastinum, and do not conform to the normal shape of the thymus. Rarely, cystic with discrete nodular components are seen. Except in patients with cystic masses, thymomas usually enhance homogenously and not uncommonly may contain calcium. Pleural implants may be present which are often unilateral and usually unassociated with pleural effusion. Large tumors have areas of hemorrhage, necrosis or cyst formation. 26

41 Staging of thymoma: Stage I: Intact capsule Stage II: Invasion of adjacent fat only Stage III: Invasion into other mediastinal structures, lung and pleura Table3: Differentiation of thymoma and normal thymus (CT criteria) [23 Thymoma Normal Thymus Age Over 30 Under 20 Shape Spherical or lobulated Elongated with length > width Attenuation More than chest wall muscle Diffusely infiltrated with fat Calcification Present Absent Laterality Unilateral or midline Bilateral soft tissue prominence seen in usual location of right and left lobe d. Thymic Carcinoma: Arises from thymic epithelial cells and accounts for about 20% of thymic epithelial tumors [31]. Age of incidence is around 50 years. Symptoms are usually attributable to the mediastinal mass and superior venacava syndrome may be present. Paraneoplastic syndromes such as Myasthenia gravis, pure red cell aplasia are uncommon. Thymic carcinoma cannot be distinguished from thymoma on CT unless enlarged lymph nodes are visible in the mediastinum or distant metastases are evident. On CT, it is seen as homogenous soft tissue mass or heterogeneous with areas of cystic necrosis. Calcification is seen in 10-40% of cases. Obliteration of fat planes and extension into pericardium and pleura is usually seen [32]. 27

42 e. Thymolipoma: It is a rare, benign well encapsulated thymic tumor, consisting primarily of mature adipose tissue and variable amounts of thymic tissue. It can arise within the thymus or be connected to the thymus by a pedicle. It is most commonly seen in the children and young adults. CT shows a fatty mass with varying amounts of intermixed soft tissue representing thymic tissue. Sometimes it is predominantly fatty so that it is impossible to distinguish a thymolipoma from a mediastinal lipoma. On MRI, fatty component shows high signal on T1W with soft tissues having intermediate signal intensity. 2. Germ Cell Tumours: Primary germ cell tumors account for about 10% to 15% of primary mediastinal masses as well as 10% to 15% of all anterior mediastinal masses [33]. Presumably they arise from primitive germ cells that have arrested their embryologic migration in the mediastinum. They are most common in the anterior mediastinum. Only about 5% originate in the posterior mediastinum. Most germ cell tumors present during the second to fourth decades of life (mean age 27 years). Germ cell tumors include benign and malignant teratoma, seminomas, embryonal carcinoma, endodermal sinus (yolk sac) tumor, choriocarcinoma and mixed types. Most malignant germ cell tumors (> 90%) occur in men, whereas benign lesions occur with equal sex incidence. Benign tumors are often asymptomatic and commoner in women whereas malignant tumors are more likely to cause symptoms. Confirmation that these lesions are primary to the mediastinum requires that there be no evidence of a testicular or retroperitoneal tumor. 28

43 Teratoma:- They contain elements of all germinal layers. Teratomas are classified as mature, immature and malignant [33]. Dermoid cysts are said to contain derivatives of only the ectodermal layer, specifically skin and its appendages, but small rests of endodermal and mesodermal cells are often present; they are benign. Mature teratomas are common accounting for 70% of germ cell tumors in childhood and 60% of mediastinal germ cell tumors in adult. Regardless of their histology, CT often shows combination of fluid filled cysts, fat, soft tissue and areas of calcification. Calcification seen in 20% to 80% of cases, it may be focal, rim like, or rarely representing teeth or bone. A fat fluid level is particularly diagnostic. Cystic teratoma characteristically has a thick wall, internal septations and in-homogenous areas approaching fatty attenuation values, within a predominantly near water density mass; differentiates from other benign cysts [5]. Seminoma: Mean age of presentation is 26 years [34]. They constitute 40% of malignant germ cell tumors. Approximately 10% with pure seminoma have evidence of elevated beta human chorionic gonadotropin (HCG) levels, but never elevated alphafetoprotein (AFP) levels. Typically, primary mediastinal seminomas are large, smooth or lobulated, homogenous soft tissue masses, although small areas of low-attenuation may be seen. Obliteration of fat planes is common and pleural or pericardial effusion may be present. 29

44 Non-seminomatous germ cell tumors: Includes embryonal carcinoma, endodermal sinus tumor, chariocarcinoma and mixed types up to 80% of affected patients have elevated levels of AFP and 54% have elevated levels of bhcg. Up to 20% of affected patients have Klinefelter's syndrome. There exists an association with hematological malignancies as well. On CT, these tumors usually show heterogeneous opacity, including ill-defined areas of low attenuation secondary to necrosis and hemorrhage or cystic areas. They often appear infiltrative, with obliteration of fat planes and may be spiculated calcification may be seen. Thyroid masses: Mediastinal involvement by thyroid masses is most often anterior and is due to down ward extension of either a multi nodular colloid goiter, or occasionally an adenoid or carcinoma. Intrathoracic thyroid masses usually have a well-defined outline which may be spherical or lobular. Rounded or irregular, well defined areas of calcification may be seen in benign areas, whereas amorphous cloud like calcification is occasionally seen within carcinomas [28]. CT is at greatest value in defining the morphologic extent. Marked irregularity of the gland contour, loss of distinct mediastinal fascial planes and / or presence of cervical or mediastinal adenopathy should signal potential malignancy. Although scintigraphy can defect mediastinal goiters, the uptake of technetium or iodine is variable. The CT appearance of a mediastinal goiter is variable, but the goiter can confidently diagnose when continuity of the mass with the thyroid is visible [28]. 30

45 Parathyroid Adenoma: Anterior mediastinal parathyroid glands are thought to result from islands of parathyroid tissue that are carried into the anterior mediastinum by the descending thymus during embryologic development. Primary hyperparathyroidism is seen in 85% cases. They may be searched for by USG, angiography, CT scan, combined Thallium 201/ 99mTc pertechnate imaging or MRI. When visible on CT, they usually appear homogenous in density. In anterior mediastinum, they may be indistinguishable from small thymic remnants, small thymomas or small lymph nodes and are usually found in the expected location of the thymus. CT correctly identified parathyroid adenomas preoperatively in 81 % of patients [35]. Primary Mediastinal Lymphoma : It constitutes about 20% of all mediastinal neoplasms in adult and 50% in children [36]. A mediastinal mass is also a frequent manifestation of lymphoma. The most common cause for such primary disease are Hodgkin's disease, large cell lymphoma and b lymphoblastic lymphoma; other forms are infrequent. Many of these primary mediastinal tumors appear to originate in the thymus 19. Hodgkin s Lymphoma is a more common cause and occurs in older group (Median age 55years) [23]. The typical presentation consists of an anterior mediastinal mass often associated with enlarged nodes in the middle and posterior mediastinum and hila. PML often affects extra thoracic sites at time of diagnosis particularly abdomen, head and neck. On CT Hodgkin's lymphoma is characterized by the presence of a discrete anterior superior mediastinal mass with surface lobulations. Surface lobulations of 31

46 main mass is due to involvement of multiple nodes and coalescence. Masses typically exhibit homogenous soft tissue attenuation, while large tumours may exhibit heterogeneity with complex low attenuation representing necrosis, hemorrhage and cystic degeneration. It commonly involves cervical, mediastinal, hilar and Para aortic nodes [37]. Non-Hodgkin s lymphoma comprises of mediastinal large 8-cell lymphoma and lymphoblastic lymphoma and is more common in children than Hodgkin's lymphoma. Large cell lymphomas are typically confined to the mediastinum and contiguous nodal areas initially without showing extrathoracic disease at presentation. It may present with hematogenous spread to kidney, liver, ovary, adrenal gland, GI tract and central nervous system during disease progression or at recurrence. CT demonstrates mediastinal mass without surface lobulations, often associated with vascular involvement and pleural or pericardial effusion. Lymphoblastic lymphoma is characterized by mass without surface lobulations involving vascular structures often associated with pleural or pericardial effusion. Systemic involvement is in the form of involving cervical, axillary, paraaortic, mesenteric and inguinal nodes and by hepatomegaly and splenomegaly [38]. Morgagni Hernia: They are mostly asymptomatic; it is due to incomplete attachment of diaphragm anteriorly to the sternum. It may contain omental fat or gut. On X- ray opacity is seen in the right cardiophrenic angle. Barium studies show a portion of gut in the hemi thorax. CT demonstrates the herniated fat or the gut. 32

47 Epicardial Fat Pad: Deposition of fat in either cardiophrenic angles is not uncommon, particularly in obese patients and can simulate a mass. CT can demonstrate the fatty nature of the mass. Pleuropericardial cyst: It constitutes 6% of mediastinal mass. They result from aberrations in the formation of coelomic cavities. Pericardial cysts are invariably connected to the pericardium. The majority of them arises in the anterior cardiophrenic angle, more frequently on the right, but can be seen as high as the pericardial recesses at the level of the proximal aorta and pulmonary arteries [39]. CT shows thin walled unilocular water density (O-20HU) cystic structure. Wall may calcify. Lymphangiomas: Are rare, benign congenital malformation, constitutes 0.7% to 4.5% of all mediastinal tumors. Majority are discovered during first 2 years of life. They are most common in the neck and axilla, and about 10% extend into the mediastinum. CT usually shows a smooth, lobulated mass, which may mould to or envelop, rather than displace, the adjacent mediastinal structures. They are either unilocular or multilocular with near water density. Calcification is rare. Thin enhancing septations within the mass may be seen [39]. 33

48 MIDDLE / POSTERIOR MEDIASTINAL MASSES Foregut duplication cysts: It includes bronchogenic, neuroenteric and oesophageal duplication cysts. Bronchogenic cyst: Bronchogenic cysts are congenital lesions thought to result from abnormal budding of the embryonic foregut. Most cysts are located in the mediastinum, near the tracheal carina predominantly in the middle mediastinum (79%) less commonly may occur within the lung parenchyma, pleura or diaphragm (15%) according to McAdam's series [40]. On CT, typically shows sharply marginated thin walled mediastinal mass of homogenous soft tissue or water attenuation. Rarely, calcification of the cyst wall is present. When dense, bronchogenic cysts may be difficult to distinguish from solid lesions. An important clue can be their lack of enhancement following contrast administration [41]. Neuroenteric cysts: These rare lesions are connected to the meninges through a midline defect in one or more vertebral bodies and are composed of both neural and gastrointestinal elements. A connection with the esophagus is often present. CT appearance is same as that of other duplication cyst, but the presence of vertebral abnormality points to the diagnosis, vertebral anomalies are present in half of the cases. 34

49 Oesophageal duplication cysts: They are lined by gastrointestinal tract mucosa and are often connected to the esophagus. 60% are found in the lower posterior mediastinum, adjacent to the oesophagus, and are sometimes found within its wall. On CT it is indistinguishable from bronchogenic cyst except for the location [ 30]. Rare middle mediastinal masses include: Tracheal tumours: These are carcinoma, cylindroma, plasmacytoma, tracheobronchomegaly (Mounier-Kuhn syndrome) and tracheomalacia. They may cause widening of mediastinum carcinoma spreads through the Para tracheal space and invades lymph nodes. Metastatic bronchial carcinoma also gives similar appearance. POSTERIOR MEDIASTINAL MASSES Neurogenic Tumours: They account for about 9% of primary mediastinal masses in adults, although they are more prevalent in children, constituting 29% of mediastinal tumours [42]. Tumours are divided as follows: Nerve sheath tumours: Neurofibromas, Schwannoma, Malignant peripheral nerve sheath tumours, Neurofibrosarcoma. Ganglion cell tumours: Ganglioneuroma, Ganglioneuroblastoma, Neuroblastoma. Paragangliomas: Chemodectomas - Aortic body tumour, Sympathetic chain tumours, Pheochromocytoma. 35

50 Nerve Sheath Tumors: The Schwannoma is the most common intra thoracic nerve sheath tumour. In their classic form, they are eccentric and encapsulated and have no nerve fibers. Almost all intra thoracic nerve sheath tumours arise either from the intercostals, or the sympathetic nerves, the rare exception being Neurofibromas or Schwannoma of the phrenic or vagus nerves. Many arise close to the spine and may extend through the neural exit foramina into the spinal canal the so-called "Dumb bell tumour". Nerve sheath tumours are rare in patients below age 20 and virtually nonexistent in patients who are less than 10 years old except in patients with neurofibromatosis [22]. Malignant nerve sheath tumours are infrequent. They may cause pain and are usually associated with neurofibromatosis. Ganglion cell tumours form a spectrum with Neuroblastoma at the malignant end and Ganglioneuroma at the benign end, Ganglioneuroblastoma being an intermediate form. Neuroblastoma and Ganglioneuroblastoma may occasionally mature into a more benign form. The mediastinum is the second most common primary site after the adrenal gland. Primary mediastinal neuroblastoma appears to have a better prognosis than those that arise primarily in the abdomen. Neuroblastoma and ganglioneuroblastoma are essentially tumours of childhood, fewer than 10% seen in patients older than 20 years of age. Ganglioneuroma is seen in age range of 1 to 50 years. Urinary vaniyllmandelic acid and homovanillylmandelic acid levels may be raised in Neuroblastoma and Ganglioneuroblastoma. 36

51 Common imaging features of neurogenic tumours: They are well defined mass with a smooth or lobulated outline. Most neurogenic tumors are approximately spherical, but some ganglion cell tumours are elongated. It is possible to distinguish between a ganglion cell tumour and a nerve sheath tumour by observing. a. The shape of the mass, since the base of ganglion cell tumour may show a tapered interface with the adjacent chest wall or mediastinum, whereas nerve sheath tumours tend to show sulfurs at their margins. b. Ganglion cell tumours arise slight more anteriorly with their epicenter against the vertebral body, whereas nerve sheath tumours are centered on the exit foramina, or are plastered against the chest wall. Calcification may be seen in all types of neural tumours. In neuroblastoma the calcification is usually finely stippled, whereas In ganglioneuroblastoma and ganglioneuroma, it is denser and coarser occurring most frequently in the larger benign lesions. Nerve sheath tumours calcify only occasionally. Pressure deformity and displacement of the adjacent ribs and vertebrae are common and absence of these changes in a larger lesion is a pointer against the diagnosis of neurogenic tumour. Pleural effusion is a sign of a malignant tumour. At CT, many neural tumours have mixed density, including low attenuation region, On non-contrast enhanced CT Schwannoma often demonstrate lower attenuation than skeletal muscle because of their high lipid content, interstitial fluid and areas of cystic degeneration. Neurofibromas are often more homogenous and show higher attenuation than schwannomas because they have fewer of these histologic features. These lesions may heterogeneously enhance following contrast administration. 37

52 Mediastinal Paragangliomas: They are rare, forms only 2% approximately [43]. One third of mediastinal pheochromocytomas are non-functioning and asymptomatic, the remainder present with symptoms, signs and laboratory findings of catecholamine overproduction. Imaging: Rounded soft tissue masses which are usually extremely vascular and therefore enhance brightly. MRI is particularly advantageous in intracardiac pheochromocytomas. Lateral intrathoracic Meningocele: It is a protrusion of the spinal meninges through an intervertebral foramen. It is usually detected in patients between 30 and 60 years of age. Approximately 2/3rd associated with neurofibromatosis. CT shows uniform low attenuation of CSF value. CT myelography confirms the diagnosis, showing contrast entering the meningocoele. PARAVERTEBRAL LESIONS It includes traumatic compression of a vertebral body with hematoma formation, pyogenic or tuberculous paraspinal abscess, multiple myeloma, disseminated lymphoma, extra medullary hematopoietic tissue and metastatic carcinoma with paraspinal extension. Radiological features of paravertebral lesions - Inflammatory lesions produce narrowing of disc space as well as bone destruction, whereas, neoplastic lesions produce only bone destruction. In metastatic lesions pedicles are usually affected. 38

53 Tuberculous paravertebral lesions: The vertebral column is the most common site of osseous tuberculous involvement comprising in most series about 50% of cases. The lower dorsal and upper lumbar vertebrae are most frequently affected. The spread of tuberculosis of the spine is usually by hematogenous route by perivertebral arterial or venous plexus, or rarely by extension form a paraspinal infection. The infection typically commences at the superior or inferior anterior body corner adjacent to the discovertebral junction, and spreads then by sub ligamentous extension and penetration of the subchondral plate. Advanced disease may demonstrate abscess tracking along the fascial planes. Plain film evaluation of the tuberculous spondylodiscitis may demonstrate loss of vertebral height or disk interval, erosions, in distinction of the end plates, paravertebral masses and sequestrate. Over 50% of the trabecular bone is lost before a lesion is conspicuous on plain film; this process may take up to 6 months. In the thoracic spine visualization of a paravertebral abscess requires an adequately penetrated view. Scalloping of the anterior vertebral contour (aneurysmal appearance) is more commonly seen with children. Plain film is limited in the evaluation of the posterior arch, particularly in the thoracic spine. CT scan is excellent for visualization of end plate destruction, fragmentation of the vertebrae, and paravertebral calcifications. Inflammatory collections and masses are best seen after the contrast administration. Small necrotic foci are recognized by CT scans and they are difficult to find in the radiographs i.e. foci less than 1.5 cm in diameter are not demonstrable in a conventional radiograph. Extension into the canal of epidural abscesses and bony fragments are well demonstrated on 39

54 axial CT images. CT is also used for guiding percutaneous biopsy and post drainage follow up. Multi planar capability and optimal tissue contrast make MR imaging the optimal modality for spondylodiscitis. The entire spine and canal can be visualized. MR imaging has higher sensitivity for early infiltrative disease including end plate changes and marrow infiltration than bone scan and plain film. MR imaging affords excellent definition of epidural, paravertebral and intra osseous abscesses and extent of cord compromise [44, 45]. Extramedullary haemopoietic tissue: One of the thoracic manifestations of extra medullary haemopoiesis is a paravertebral mass. It is a compensatory phenomenon seen most commonly in congenital hemolytic anemia (e.g., thalassemia and sickle cell anemia). It has been also found in myelosclerosis, carcinomatosis, chronic nephritis, haemochrornatosis, lead poisoning and chronic infections. Marrow is formed in areas outside the normal haemopoietic system. Histologically, resemble splenic tissue. CT features - are well-defined margins and have soft tissue attenuation. Extramedullary haemopoietic tissues are low density masses due to fat content [46]. Diaphragmatic Hernia: Abdominal organs or retroperitoneal fat can herniate through areas of congenital or acquired diaphragmatic weakness or tears and manifest as a mediastinal mass on chest radiographs. Common nontraumatic sites of herniation include the anterior parasternal hiatus, the esophageal hiatus and the posterior pleuroperitoneal hiatus. Hiatus hernia 40

55 is a common cause of a mediastinal mass in the lower thorax. The diagnosis is easily made if air or contrast material is seen within the hernia. Herniation through the posterior pleuroperitoneal hiatus (Foramen of Bochdalek) is the most common cause of congenital diaphragmatic hernia in infants. In adults, the lesions are usually small and asymptomatic and occur more commonly on the left (65%) than on the right (35%). They are particularly common in patients over 70 years of age. They are typically found posteriorly some 4 to 5cm from the posterior attachment of the diaphragm. They contain herniated retroperitoneal fat, sometimes kidney or a portion of Spleen. CT demonstrates the fatty nature of the hernial contents and often shows the accompanying muscle defect in the diaphragm [47]. MEDIASTINAL LYMPH NODES AND LYMPH NODE MASSES Mediastinal lymph node abnormalities can be seen in any mediastinal compartment, although they most commonly involve middle mediastinal regions [23]. Thoracic lymph nodes are usually grouped into parietal and visceral, depending on their location and drainage. The parietal lymph nodes primarily drain structures of the chest wall and are classified as internal mammary, diaphragmatic or paracardiac and intercostal. Visceral node groups include intrapulmonary, bronchopulmonary, tracheobronchial, paratracheal, paraesophageal and anterior mediastinal nodes. Anterior Lymph Nodes: Internal mammary lymph nodes are located in a retrosternal position, at the anterior ends of the intercostals spaces, near the internal mammary artery and veins, 41

56 they are considered to be part of the parietal lymph node group. They drain the anterior chest wall, anterior diaphragm, medial breasts, and freely communicate with pre vascular lymph nodes. Most often enlarged as a result of lymphoma or metastatic breast cancer. Prevascular lymph nodes lie anterior to the aorta and in relation to the great vessels. These nodes drain most anterior mediastinal structures including the pericardium, thymus, thyroid, pleura and the anterior hila. They represent visceral nodes. They communicate with the internal mammary chain of nodes anteriorly and paratracheal and aorticopulmonary lymph nodes posteriorly. They may be involved in a variety of diseases, notably lymphoma and granulomatous diseases, but their involvement in lung cancer is relatively uncommon. Diagram showing AJCC UICC classification of regional lymph nodes 42

57 AJCC UICC classifications of regional lymph nodes [21] 1. Highest mediastinal nodes lie above a horizontal line at the upper rim of the brachiocephalic (left innominate) vein. 2. Upper Para tracheal nodes lie above a horizontal line drawn tangential to the upper margin of the aortic arch and below the inferior boundary of No 1. nodes 3. Prevascular and retrotracheal nodes may be designated 3A and 3P: midline nodes areconsidered to be ipsilateral. 4. Lower Para tracheal nodes lie to the right or left of the midline of the trachea between a horizontal line drawn tangential to the upper margin of the aortic arch and a line extending across the right or left main bronchus at the upper margin of the ipsilateral upper lobe bronchus. 5. Sub aortic (aorto-pulmonary window) nodes lie lateral to the ligamentumarteriosum or the aorta or left pulmonary artery and proximal to the first branch of the left pulmonary artery and lie within the mediastinal pleural envelope 6. Para-aortic nodes (ascending aorta or phrenic) lie anterior and lateral to the ascending aorta and the aortic arch or the innominate artery, beneath a line tangential to the upper margin of the aortic arch. 7. Subcarinal nodes lie caudal to the carina of the trachea, but not associated with the lower lobe bronchi or arteries within the lung. 8. Paraesophageal nodes (below carina) lie adjacent to the right or left of the midline, excluding subcarinal nodes. 9. Pulmonary ligament nodes lie within the pulmonary ligament, including those against the posterior wall and lower part of the inferior pulmonary vein. 43

58 10. Hilar nodes lie distal to the mediastinal pleura reflection and the nodes adjacent to thebronchusintermedius on the right 11. Interlobar nodes lie between the lobar bronchi 12. Lobar nodes lie adjacent to the distal lobar bronchi 13. Segmental nodes lie adjacent to the segmental bronchi 14. Subsegmental nodes lie around the sub segmental bronchi NB. Stations 1 through 9 nodes lie within the mediastinal pleural envelope, whereas station 10 through 14 nodes lie outside the mediastinal pleura within the visceral pleura. Paracardiac or cardiophrenic angle 'lymph nodes lie anterior to or lateral to the heart and pericardium on the surface of the diaphragm. They communicate with the lower internal mammary chain and drain the lower intercostals spaces, pericardium, diaphragm and liver. Most commonly enlarged in lymphoma and metastatic breast carcinoma. Prepericardiac nodes are located posterior to the xiphoid process and slightly lateral to it. Normal lymph nodes on CT are generally visible as a. Discrete and surrounded by mediastinal fat b. Round, elliptical or triangular in shape c. Soft tissue attenuation. The short axis or least diameter of a lymph node is generally used when measuring size.based on 3 study [48] short axis measurement of 12mm is the upper limits of normal for subcarinal lymph nodes, 10mm for right tracheo-bronchial and low paratracheal lymph nodes, and 8mm for all other lymph nodal groups. According 44

59 to Glazer et al [49] study suggests that the optimum size in patients suspected of malignancy should exceed 10mm except in the subcarinal region. DIAGNOSIS OF LYMPH NODE ABNORMALITIES: Are based on a. Lymph node enlargement b. Lymph node morphology c. Lymph node attenuation d. Lymph node enhancement Lymph node enlargement: Lymph nodes having a short axis of 2cm or more often reflect the presence of neoplasm, such as metastatic tumor or lymphoma, sarcoidosis or infection and should always be treated as potentially significant. Whereas in variety of non infectious and non-granulomatous inflammatory diseases they are usually smaller than 2cms [50, 51, 52]. Lymph node morphology: a. Discrete enlarged nodes: This pattern can be seen in association with all causes of mediastinal lymph node enlargement. b. Coalescence of enlarged nodes: Most typical of infection, granulomatous disease and neoplasm. c. Diffuse mediastinal involvement: This diagnosis may be difficult to make unless the attenuation of mediastinal soft tissue is compared to the attenuation of subcutaneous fat on the same scan - they should be similar [23] - suggests lymphoma, undifferentiated carcinoma, generalized infection, or granulomatous mediastinitis. 45

60 Lymph node attenuation [23] : a. Homogenous soft tissue attenuation: Lymphoma: It is primary neoplasms of the lymphoreticular system and is classified into Hodgkin s disease and Non-Hodgkin s disease. b. Calcified lymph nodes: Common: Infectious granulomatous diseases, Tuberculosis, Fungal infections, Sarcoidosis, Silicosis, Hodgkin's disease (following treatment) Rare: Pneumocystis carini pneumonia, Metastases (mucinous adenocarcinoma) Amyloidosis, Scleroderma, Castleman's disease. c. Low density lnecrotic lymph nodes Common: Infectious granulomatous diseases, Tuberculosis, Fungal infections (histoplasmosis), Metastases, Lung cancer, Seminoma, Lymphoma. Rare: Whipple's disease, Sarcoidosis. Lymph node enhancement [23] : Enhancing lymph nodes: Common: Metastases, Castleman's disease Rare: Sarcoidosis, Angioimmunoblastic lymphoma [53]. Hodgkin s disease: Occurs at all ages, but its peak incidence is in the third and eighth decades. Hodgkin's disease has a thoracic predilection in up to 85%, presenting with mediastinal adenopathy. Most commonly involves prevascular and paratracheal lymph nodes [54]. Nodular Sclerosing histology accounts for 50% to 80% of adult Hodgkin's disease [55]. 46

61 In a study by Castellino et al [56] findings shown on CT changed treatment in more than 9% of patients. Nodes are of homogenous soft tissue attenuation in majority of cases. Multiple enlarged lymph nodes are often seen and they can be well defined and discrete, matted or associated with diffuse mediastinal infiltration. It is uncommon to show areas of low attenuation or necrosis. Hodgkin's disease also has a predilection for involvement of the thymus in association with mediastinal lymph node enlargement [54]. Non Hodgkin's Lymphoma : In comparison to Hodgkin's disease, Non Hodgkin s lymphoma is less common cause of thoracic disease and occurs in an older group (median 55 years) [53]. Non Hodgkin's lymphoma is more common than Hodgkin's disease in children [4]. Enlargement of anterior mediastinal, internal mammary, paratracheal and hilar nodes is much less common with non Hodgkin's lymphoma than with Hodgkin's disease. Nonetheless superior mediastinal node involvement remains the most frequently involved site. Rarely, calcification is seen. Extra nodal involvement like lung, pleura, pericardial space and chest wall is common. On CT, large, lobulated anterior mediastinal masses are seen. CT valuable in determining tumour extent, as radiation is usually used; the presence of pleural effusion predicts a poor outcome. Leukemia: Mediastinal lymph node enlargement occurs in about 50% and 67% of cases respectively with acute and chronic lymphocytic leukemia and 35% and 36% of patients with acute and chronic myelogenous leukemia respectively [23]. 47

62 `CT appearance of lymphadenopathy is indistinguishable from lymphomas; hence Clinical correlation is a must to arrive at the correct diagnosis. Metastatic tumour: Metastases to mediastinal lymph nodes from extrathoracic malignancies are uncommon. The extrathoracic tumours most likely to metastasize to the mediastinum are carcinomas of the head and neck, genitourinary tract, breast and malignant melanoma. Lymph node enlargement involving the posterior mediastinal and paravertebral lymph nodes suggests an abdominal location for the primary tumour and superior mediastinal lymph node involvement suggests a head and neck tumour. Internal mammary lymph node metastases are most likely caused by breast carcinoma. Sarcoidosis: Typically, node enlargement involves the hilar as well as mediastinal groups, and it appears bilateral and symmetrical in the large majority which allows differentiation from lymphoma. In the order of decreasing frequency, paratracheal, aorticopulmonary, subcarinal and prevascular lymph nodes are commonly involved [57]. Lymph nodes shows dense or stippled or egg shell calcification and rarely enhance or appear necrotic. Tuberculosis: Hilar and mediastinal lymph node enlargement is commonly seen on CT in active tuberculosis cases, more frequently in children than adults [58]. Lymph node enlargement is usually seen on the side of lung disease, but involvement of contra 48

63 lateral nodes can sometimes be present. Right sided adenopathy usually predominates [58]. On CT, the enlarged lymph nodes usually show central areas of low attenuation on contrast enhanced CT, with peripheral rim enhancement. However these areas of low attenuation are not of water density but range from 40 to 50HU. CT more accurately defines the presence and extent of lymph node enlargement than routine chest radiography in patients with tuberculosis. In some cases, CT can serve as a guide for determining the best sites for node biopsy, and can help determine whether mediastinoscopy or parasternal mediastinotomy is most appropriate. Fibrosing mediastinitis In some patients with granulomatous disease, involving mediastinal lymph nodes and extension of the disease process to involve surrounding mediastinal tissues results in extensive fibrosis. This is termed fibrosing or granulomatous mediastinitis. Symptomatic encasement and/or compression of a number of mediastinal structures, particularly vessels, and the tracheal or oesophagus can result. The most common causes are histoplasmosis, tuberculosis and sarcoidosis; can also be related to autoimmune disease, drugs, retroperitoneal fibrosis, or may be idiopathic. On CT they are manifested by replacement of low density mediastinal fat by higher density fibrous tissue often associated with calcification. Discrete enlarged lymph manifested by replacement of low density mediastinal fat by higher density fibrous tissue, often associated with calcification. Discrete enlarged lymph nodes cannot be identified. Often, compression and/or encasement of the trachea, main 49

64 bronchi or mediastinal vessels [59] are seen.rarely does it affect the posterior mediastinum. Mediastinal lipomatosis It is a benign condition in which over abundant amounts of histologically normal, unencapsulated fat accumulate in the mediastinum. They may be associated with Cushing's syndrome, steroid treatment, or obesity. It is unassociated with symptoms. The excess fat deposition is most prominent in the upper mediastinum resulting in smooth mediastinal widening as shown on chest radiographs, and convex or bulging mediastinal pleural surfaces on CT. Mediastinal lipoma and Liposarcoma Mediastinal lipoma is uncommon, constituting approximately 2% of all mediastinal tumours. Most commonly occur in the prevascular space. Lipomas are soft and pliable and do not result in symptomatic compression of adjacent structures unless they are very large. Mediastinal liposarcoma are rare malignant tumour, composed largely of fat. CT findings include: a. Inhomogeneous attenuation with evidence of significant amounts of soft tissue within the fatty mass. b. Poor definition of adjacent mediastinal structures. c. Evidence of infiltration or invasion of mediastinal structures. 50

65 Esophageal carcinoma Esophageal carcinoma represents approximately 10% of all cancers of the gastrointestinal tract. The CT manifestations include: a. Narrowing of the esophageal lumen or dilatation caused by obstruction. b. Thickening of the oesophageal wall, either symmetric or asymmetric c. Loss of periesophageal fat planes, with or without evidence of invasion of surrounding organs. d. Periesophageal adenopathy. Moss etal [60, 61] proposed classification based on CT findings as: Stage 1: Intraluminal lesions or those that cause localized wall thickening of between 3 and 5mm. Stage 2: Wall thickening greater than 10mm, either localized or circumferential. Stage 3: Wall thickening associated with evidence of contiguous spread of tumour into adjacent mediastinal structures. Stage 4: Any locally definable disease associated with distal metastases. CT aids in assessment of resectabiltiy, accurate means for detecting invasion of the carina and main stem bronchi. CT is of proven value in detecting liver and lung metastases as well as direct extension of tumour into the pleura, lung, or adjacent vertebral bodies. 51

66 Mediastinitis and Mediastinal abscess Acute mediastinal infections are uncommon and are usually related to surgery,esophageal perforation, or spread of infection from adjacent region. CT findings include diffuse or streaky infiltration of mediastinal fat (greater than 25HU), mediastinal widening, localized fluid collections, pleural or pericardial effusion, lymph node enlargement, and compression of mediastinal structures. Gas bubbles in the mediastinum, with or without associated fluid collections is an important finding. Aneurysm of thoracic aorta Aortic aneurysms can result in a mass in the anterior, middle or posterior mediastinum. The classical description of Aortic aneurysm is 'An area of permanent dilatation of the aorta where the dilatation is at least 50% greater than baseline or standardized normal limits [62]. The average diameters are 3.5cms for the ascending aorta, 2.6cm at the proximal descending aorta, 2.5cm at the mid descending aorta and 2.4 at the distal descending aorta with progressive increase with age at approximately 0.1 cm per decade [62]. A true aneurysm involves all three layers of the aortic wall. A pseudoaneurysm represents an area of perforation that is contained by the adventitia or para aortic connective tissue. Non enhanced CT scans are useful for evaluating the mural composition of the aneurysm, such as the morphology, pattern and distribution of wall calcification and thrombus. The classic description is thin, linear mural calcification seen in 40% of luetetic aneurysm [63] and coarse thick and irregular calcification in atherosclerotic aneurysms. Cystic medial degeneration often does not associate with mural calcification. The draped aorta [64] has been described as a CT sign of contained leak 52

67 of aortic aneurysm in the emergent settings, the hyperdensity of the hematoma points to the area of acute injury and the hyper attenuating crescent sign has been shown to represent acute or impending rupture [65]. Dissection of aorta: Is classified as Stanford type A: Ascending aorta is involved and this type requires immediate surgery; Stanford type B: Begin distal to the origin of left sub clavian artery and are generally treated conservatively. CT has a sensitivity of 93.8% (MRI 98.3%) and specificity of 87% (MRI: 97.8%) 28. However the CT has the advantage of showing calcification which may be valuable in detecting intimal displacement. On CT the communicating dissections show a 'double barreled aorta. CT GUIDED BIOPSY Transthoracic needle biopsy of the mediastinum is an accurate, safe and cost effective diagnostic tool for the evaluation of mediastinal masses and lymphadenopathy. The technique is most useful in the staging of carcinoma where it serves as a less expensive and minimally invasive alternative to mediastinoscopy for establishing unresectability. An anterior parasternal approach is preferred for most anterior mediastinal masses, whereas a posterior paravertebral approach is used for posterior mediastinal masses. Midline (substernal) masses can undergo biopsy from a transternal approach. Subcarinal biopsy is occasionally performed using a left parasternal approach by entering the mediastinum via the connective tissue space between the descending aorta and spine [66], whenever possible; a direct mediastinal approach is preferable to a transpulmonary approach, because of the risk of pneumothorax. 53

68 Pneumothorax is the principal complication of CT guided chest biopsy occurring in 25% to 43% of patients [67, 68]. Most patients with pneumothorax require no therapy, but 5% to 18% may require placement of a chest tube, hence equipment for immediate chest tube placement should be available whenever a chest biopsy is performed. Hemoptysis can also occur after CT guided thoracic biopsy (less than 5%) and almost always is self-limited [68]. With recent advances in immunohistochemical and core biopsy techniques, transthoracic needle biopsy has become more accurate for establishing the initial diagnosis for lymphoma and for confirming recurrent disease. Core needle biopsy has improved the accuracy of transthoracic needle biopsy and is particularly useful when fine needle aspiration fails to yield a specific diagnosis, when lymphoma or a non carcinomatous lesion is suspected. 54

69 MATERIALS AND METHODS Source of Data: All cases referred to the department of Radio-Diagnosis for clinically suspected Mediastinal masses at Dr.B.R. Ambedkar Medical college and Hospital over a period of two years were included in the study. Sample size: 30 cases. Type of study: Prospective Study. Inclusion Criteria: Patients with symptoms of clinically suspected Mediastinal Masses investigated by CT scan and subsequently proved by histopathology. Exclusion Criteria: i. Patients with prior treatment elsewhere on presentation. ii. iii. Recurrent mediastinal masses after treatment. Patient with abnormal renal function test and contrast sensitivity. All the cases were studied on a TOSHIBA ASTEION computed tomography machine. 55

70 Preparation of patient: Patients were kept nil orally 4 hrs prior to the CT scan to avoid complications while administrating contrast medium. Risks of contrast administration were explained to the patient and consent was obtained prior to the contrast study. Technique: Routine anteroposterior topogram of the thorax was initially taken in all patients in the supine position. An axial section of 10mm thickness was taken from the level of thoracic inlet to the level of suprarenal. In all cases pre-contrast study was followed by post-contrast study, image acquisition was done with intermittent suspended inspiration. For post-contrast study, ml of dynamic intravenous injection of Diatrizoate-meglumine (Trazograf 76%; Urograffin 76%, 60%) at a dose of 300mg of Iodine / Kg body weight (in children) was given and axial section were taken from thoracic inlet to the level of suprarenals. Sagittal and coronal reconstructions were made wherever necessary. The magnification mode was commonly employed, and the scans were reviewed on a direct display console at multiple window settings (i.e. soft tissue (mediastinal) window, Lung window and Bone window to examine the wide variation of tissue density and also to look for osseous involvement. The pre and post contrast attenuation values, the size, location of the mass, presence of calcification, mass effect on adjoining structures and others associated findings were studied. 56

71 STANDARD IMAGING PROTOCOL Routine chest scanning protocol: Scout image: Anteroposterior Landmark: Slice plane: Sternal notch Axial or spiral Intravenous contrast: ml Oral Contrast: Yes Rate 1.5-2ml/sec for 15 sec Followed by 1 ml/sec, Breath hold: Slice thickness: Suspended Respiration 5mm sections from apices to base of lung Slice interval: Continuous Start location: Strenal notch Because lung cancer may metastasize to the adrenal glands, scanning is often continued through to the adrenals in patients with a history of cancer. End location: Through lung bases 57

72 RESULTS Table 4: Age and sex distribution MALE Age in Yrs FEMALE TOTAL No. % No. % No. % > Chart 1: Graph showing Age and Sex distribution Percentage MALE FEMALE Total >61 Age in yrs 58

73 Table 5: Clinical symptoms Distribution Clinical symptom Number Percentage Cough 24 80% Dyspnea % Chest pain % Fever Chart 2: Graph showing clinical symptoms distribution 59

74 Table 6: Compartmental distribution of mediastinum masses Compartment Number Percentage Superior Anterior 3 10 Middle Posterior Superior and Anterior Anterior and Middle Middle and Posterior Chart 3: Graph showing Compartmental distribution 60

75 Table 7: Superior Mediastinal Lesions distribution Number Percentage Thymoma Thymic Ca Ca. Thyroid Ca. Lung with MLN Lymphoma Teratoma Chart 4: Graph showing Distribution of Superior Mediastinal Lesions 61

76 Table 8: Anterior Mediastinal Lesions distribution No of cases Percentage Thymoma Thymic carcinoma Lymphoma Ca. lung with MLN GCT Teratoma Chart 5: Graph showing Distribution of Anterior Mediastinal Lesions 62

77 Table 9: Middle mediastinal Lesions distribution Number Percentage Teratoma 2 40 Ca. Oesophagus 2 40 LM of Oesophagus 1 20 Chart 6: Graph showing Distribution of middle mediastinal Lesions 63

78 Table 10: Posterior mediastinal masses distribution Number Percentage Schwannoma Neuroendocrine Tumor NB Osteoclastoma LM of Oesophagus Teratoma Ganglioneuroma Chart 7: Distribution of Posterior mediastinal Lesions 64

79 Table 11: Thymic masses distribution Number Percentage Thymoma 3 60 Thymic Ca 2 40 Chart 8: Distribution of thymic masses Thymoma 40 Thymic Ca 65

80 Table 12: Neural tumors distribution Number Percentage Schwannoma 3 60 NB 1 20 Ganglioneuroma 1 20 Chart 9: Distribution of neural tumors: 66

81 Table 13: Lymph nodal masses distribution Number Percentage Lymphoma MLN Chart 10: Distribution of lymph nodal masses: 67

82 CT CHARACTERISTICS Table 14: Definition of mediastinal masses Definition of the mass Number of cases Percentage Well defined Ill defined 9 30 Chart 11: Definition of mediastinal masses 68

83 Table 15: Density of mediastinal masses on non-contrast study Density Number cases of Percentage Hypodense Isodense Hyperdense 0 0 Chart 12: Density of mediastinal masses on non-contrast study 69

84 Table 16: Degree of contrast enhancement Degree Number Percentage Mild Moderate Gross Chart 13: Degree of contrast enhancement 70

85 Table17: Pattern of contrast enhancement Pattern No. of cases Percent age Homogenous Heterogenous Chart 14: Pattern of contrast enhancement 71

86 Table18: Other attenuations in mediastinal masses Other attenuations Number of cases Percentage Calcification Fluid Fat Chart 15: Other attenuations mediastinal masses 72

87 Table19: Mass effect on adjoining mediastinal structures Mass effect Number of cases Percentage Present Absent 9 30 Chart 16: Mass effect on adjoining mediastinal structures 73

88 Table20: Metastasis Metastasis Number of cases Percentage Present Absent Chart 17: Metastasis: 74

89 Table21: CT Diagnosis Mediastinal masses Number of cases Percentage GCT Thymoma 3 10 Lymphoma 6 20 Schwannoma 3 10 Neurogenic tumour Ca. Thyroid NB Ca. Lung MLN 3 10 Thymic Ca Teratoma 3 10 LM of Oesophagus Ca. Oesophagus Ganglioneuroma

90 Table22: Histopathology diagnosis Mediastinal masses Number of cases Percentage GCT Thymoma 3 10 Lymphoma 6 20 Schwannoma 3 10 Neuroendocrine Tumour Ca. Thyroid NB Ca. Lung MLN 3 10 Osteoclastoma Thymic Ca Teratoma 3 10 LM of Oesophagus Ca. Oesophagus Ganglioneuroma

91 IMAGES 1. LYMPHOMA: (a) (b) (c) (d) Axial CT scan of thorax of different patients complaining of cough shows, lobulated, soft tissue attenuating mass at superior and anterior mediastinal compartments appearing hypodense on non- contrast study (a) and (b). On post contrast study (c) it shows homogenous enhancement. Mediastinal vessels encased. 77

92 2. THYMOMA (a) (b) (c) (d) CT scan of thorax of different patients shows, lobulated, soft tissue attenuating mass at superior mediastinal compartment appearing hypodense on non- contrast study (a). On post contrast study (b) it shows heterogenous contrast enhancement. Variable appearance of thymoma as thick walled cyst (c). Histo-pathology image (d) showing thymoma. 78

93 3. Carcinoma THYROID with mediastinal extension: (a) (b) Axial and Coronal images showing, an lobulated, minimally enhancing lesion encasing the trachea. It is arising from the thyroid gland with superior mediastinal extension. 4. OSTEOCLASTOMA (a) (b) Axial Non- contrast Ct scan (a) and (b) shows an well defined, heterogenously contrast enhancing lesion in posterior mediastinum with destruction of adjescent vertebral body.histopathologicaly this lesion proven as Osteoclastoma. 79

94 5. SCHWANNOMA (a) (b) (c) (d) Axial Non- contrast Ct scan (a) shows an well defined, hypodense lesion in posterior mediastinum. Which on post-contrast study (b) shows heterogenous contrast enhancement. Coronal reconstruction (c) shows mass effect on descending thorasic aorta and stomach. This lesion proven as schwannoma Histopathologicaly (d). 80

95 6. TERATOMA (a) (b) (c) CT scan of thorax of different patients shows, lobulated, mass at superior and anterior mediastinal compartments appearing hypodense on non- contrast study with areas of calcification (a) and fat attenuation (b). Histopathology image (c) showing teratoma. 81

96 7. METASTATIC LYMPHADENOPATHY (a) (b) Axial CT scan of thorax (a) showing two ill-defined heterogeneously enhancing lesions in Pre-aortic and Pretracheal regions. Histopathology image (b) showing, adenocarcinomatous metastasis. 82