Cerebellopontine angle masses: MRI technique, positive and differential diagnosis

Transcription

1 Cerebellopontine angle masses: MRI technique, positive and differential diagnosis Poster No.: C-1517 Congress: ECR 2012 Type: Educational Exhibit Authors: C. Scheau, I. G. Lupescu, G. Popa, E. M. Preda ; Bucharest/ RO, BUCHAREST/RO, Bucuresti/RO Keywords: Anatomy, Neuroradiology brain, Vascular, MR, MR-Angiography, Contrast agent-intravenous, Technical aspects, Tissue characterisation, Arteriovenous malformations, Cerebrospinal fluid DOI: /ecr2012/C-1517 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 25

2 Learning objectives The aims of this presentation are to describe the current and particular MRI techniques of the cerebellopontine angle (CPA) and to list the MR semiological signs used in the characterization and differentiation of cerebellopontine masses. The pathology of the CPA can arise from the different structures in its anatomy and vecinity, like the cisterns, arteries, meninges, nerves, skull base, and last but not least, the cerebellum ventricle, therefore, special attention must be paid to leading the examination towards describing the point of origin, and making a positive diagnosis. In this poster, we will review the most frequent lesions of the CPA, as well as point out certain distinctive features in each case. Background The cerebellopontine angle is the anatomic space between the cerebellum and the pons ( Fig. 1 on page 3 ). Borders: - Medial - Lateral surface of the brainstem - Lateral - Petrous bone - Superior - Middle cerebellar peduncle & cerebellum - Inferior - Arachnoid tissue of lower cranial nerves - Posterior - Cerbellar peduncle Content: CSF, arachnoid tissue, cranial nerves and their associated vessels (and possibly embryologic remnants). [1] Various anatomic structures may be involved in CPA pathology ( see Table 1 on page 4 ). CPA lesions do not manifest with specific symptoms related to the disease but rather to their location in the brain. Masses arising in the CPA typically are manifested by either cranial neuropathies or signs of posterior fossa mass effect. There is always a posibility to mistake an anatomic variant for a lesion. The most common pseudolesions of the CPA are [3]: Page 2 of 25

3 Asymmetric cerebellar flocculus ( see Fig. 2 on page 5 ) Asymmetric choroid plexus Marrow foci around internal auditory canal (IAC) Usually, a correctly lead MRI examination is sufficient for an accurate diagnosis. Using sequences specially designed for the investigation ( Fig. 3 on page 7 ) of the various structures involved, basically every compartment can be assesed. The constructive interference in steady state (CISS) sequence is highly specific and gives great detail, but should not be used exclusively in screening for masses of the CPA [4] but rather alongside the other standard sequences, and with contrast media administration when necessary. At times, a CT examination may provide useful information regarding the bone involvement and possible calcifications ( Fig. 4 on page 7 ). Images for this section: Page 3 of 25

4 Fig. 1: Schematic representation of the CPA region Page 4 of 25

5 Table 1: Possible lesions of the cerebellopontine angle and their respective points of origin Page 5 of 25

6 Page 6 of 25

7 Fig. 2: MRI exam. Asymmetric cerebellar flocculus in an otherwise normal brain. Fig. 3: 3D FSE sequence centered on the CPA in a normal patient. Note the good bilateral deliniation of the nerves VII (anterior) and VIII (posterior). Page 7 of 25

8 Fig. 4: Normal CT scan of the posterior fossa viewed in bone window. Page 8 of 25

9 Imaging findings OR Procedure details Study population: Retrospective study between 2001 and 2011 of 40 cases (M/F: 15/26), aged 25 to 84 with cerebellopontine angle pathology Clinical examination: The patients reffered to our clinic, first underwent a clinical examination performed by a neurologist; the most common symptoms in the study population, correlated with the structures involved were: Asymmetric sensorineural hearing loss, tinnitus (nerve VIII-cochlear) Dysequilibrium, vertigo (nerve VIII-vestibular) Facial weakness (nerve VII) Facial numbness (nerve V) Headache, visual loss (brainstem) Wide gait, falling to side of lesion (cerebellum) Examination protocol: Exploration by MRI, using a 1,5 T system and a adapted protocol for the cerebellopontine angle evaluation (T2 3D FSE, 3D FSPGR with and without Gd-DTPA, 3D TOF, diffusion, T1 without and with Fat Saturation). Additional cerebral CT investigations with thin bone filter reconstructions were available, according to the case. Results: Retrospective analysis of the cases showed a predominance of the schwannoma (10 cases) followed by meningioma (8 cases), arachnoid cyst (7 cases) and epidermoid cyst (3 cases). Other entities were vascular abnormalities: vasculo-nervous conflicts and venous drainage anomalies, (5 cases each), lipoma of the IAC (one case) and ependymoma (one case). Also, we featured proximity lesions with secondary involvement of the CPA Based on the MRI appearance and specific semiology, we propose grouping the pathology in the following categories: Solid masses Schwannoma Meningioma Cystic masses Arachnoid cyst Page 9 of 25

10 Epidermoid cyst Lipomatous masses Lipoma Dermoid cyst Cholesterol granuloma Flow void masses Vascular conflict Venous drainage anomalies VB, PICA, AICA aneurysms A. Solid Masses: Schwannoma The schwannoma ( Fig. 5 on page 13, Fig. 7 on page 15 ) is a benign tumor, composed entirely of Schwann cells. The neurofibroma is a well-differentiated nerve sheath tumor composed predominantly of Schwann cells and, to a lesser extent, fibroblasts and perineuralcells. In small lesions, the parent nerve can be detected within the tumor; in larger tumors the relationship between the nerve and the tumor becomes obscured.[5] Diagnostic elements: Centered on Porus Acousticus "Ice cream on cone" pattern (intracanalicular extension) Acute angles to petrous bone Often involves the IAC Homogeneous enhancement No dural tail No calcifications [2,6] Meningioma Meningiomas ( Fig. 6 on page 14, Fig. 7 on page 15 ) are well-circumscribed, globular or lobulated, vascular, non-glial tumors of the central nervous system arising from arachnoidal cells, clearly demarcated from the brain [12] Diagnostic elements: Arise from surface of petrous bone Page 10 of 25

11 Obtuse angles to petrous bone Uncommonly involves the IAC Frequently with "dural tail" sign (linear enhancement along the dura matter on either side of the tumor) Calcifications common Pial vessel flow voids [7] B. Cystic Masses: Arachnoid cyst Loculated collections of CSF within a reduplication of arachnoidal membrane. Erosion of the adjacent calvarium is often present. ( Fig. 8 on page 16 ) Diagnostic elements: Avascular cystic mass Nonenhancing Smooth regular shape Homogeneous, identical signal to CSF in all weightings No calcifications FLAIR sequence shows intense signal suppresion Diffusion weighting will show a hipointensity (no restriction of diffusion) [2,7] Epidermoid cyst Extra-axial lesions which typically spread along the basal surface. Rupture can produce aseptic meningitis. Overwhelmingly benign. ( Fig. 9 on page 17 ) Diagnostic elements: May dumbell into middle fossa or contralateral cistern Nonenhancing (25% mild peripheral enhancement [5]) CT usually shows a mass hypodense to CSF Inhomogeneous lesion, highly variable in shape with a cauliflower surface appearance T1 - hipo-isointense; T2 - hiperintense (if it has a high protein content, it may have high signal on T1 and low signal on T2 MR sequences = "white epidermoid." [7]) FLAIR sequence shows iso-hiperintensity Page 11 of 25

12 Diffusion weighting will show a characteristic moderate intensity (restriction of diffusion) C. Lipomatous Masses: Lipoma Anomalously developed masses that arise from abnormal differentiation of the meninx primitiva [2] Signal intensity similar to that of fat on all sequences -> high signal on T1-weighted images; would be of intermediate signal on T2-weighted images, similar to subcutaneous and marrow fat; and would not be visible, "disappear," on fat-saturated sequences [5] Nonenhancing (thick peripheral capsule that may enhance) [8] Dermoid cyst Midline lesions that rarely invade the CPA laterally, contain elements from all layers of the skin [2] FLAIR, CISS and DWI certify diagnostic MR appearance depends on the amount of fat present, although generally they are of increased signal on both T1- and T2-weighted images [5] Cholesterol granuloma Results from the chronic obstruction of air cells and accumulation of secretions Expansile lytic lesions of the temporal bone Central region of high signal intensity and a peripheral hypointense rim on both T1- and T2-weighted images Nonenhancing [9] D. Flow void masses: Vascular loop syndrome Affected nerves may by V (at root entry zone) or VII (at root exit zone) Vessel may by atherosclerotic - serpiginous, irregular MR Angiography - source images are most helpful Page 12 of 25

13 Vertebrobasilar dolichoectasia ( Fig. 10 on page 18 ) may be one of the causes (atherosclerotic finding especially in the elderly) [3] Venous anomaly Various developmental anomalies, which may involve the CPA as a drainage route, but rarely with clinical impact ( Fig. 11 on page 19 ) 2D and 3D Time of Flight sequences are useful for evaluating the vascular axes Contrast administration shows more detail VB, PICA, AICA aneurysms Non-neoplasic lesions, but with mass effect Thrombosis associates hiperintensity in T1 (methemoglobin); possible enhancement of the thrombus Pulsation artifacts may also be present in cases of aneurysm.[10,11] Secondary involvement: Glomic tumor ( Fig. 12 on page 20 ) Sphenoid mengingioma ( Fig. 13 on page 21 ) Lymphoma Ependymoma Choroid plexus papiloma Images for this section: Page 13 of 25

14 Fig. 5: RIGHT ICA NEUROFIBROMA of the VIII nerve: mass lesion with inhomogeneous enhancement due to small necrotic areas, developed in the right CPA centered on the IAC with intracanalar extension associating slight enlargement (confirmed by CT scan) Page 14 of 25

15 Fig. 6: LEFT PCA MENINGIOMA: nodular lesion with intense enhancement and extraaxial topography developed in the left CPA, with a broad base and obtuse angles to the petrous bone. Page 15 of 25

16 Fig. 7: NEUROFIBROMATOSIS TYPE II: bilateral acoustic schwannoma; left CPA meningioma. Page 16 of 25

17 Fig. 8: RIGHT PCA ARACHNOID CYST: cystic lesion at the level of the right CPA, with identical signal to the CSF in all weightings, with slight mass effect on the right cerebellar hemisphere. Right side cranial nerves VIII and VII appear enveloped in the cysternal segment, but with no significant course alteration. Page 17 of 25

18 Fig. 9: LEFT PCA EPIDERMOID CYST: well deliniated lesion, which involves the left prepontine cystern and CPA, with slight mass effect on the left pons, and engulfing of the cranial nerves V to VIII on the left side, in the cysternal segment. The lesion has a fluidtype signal, slighly hererogenous, but with important water diffusion restriction. Page 18 of 25

19 Fig. 10: NEURO-VASCULAR CONFLICT: megadolico-vertebral and basilar arteries, with significant mass efect on the pons, which appears displaced medially and to the posterior. Note the segmentary contact with the left-side VII and VIII cranial nerves, in the cysternal segment, with their slight displacement to the posterior. Page 19 of 25

20 Fig. 11: CAVERNOMA and VENOUS DEVELOPMENT ANOMALY of the left middle cerebellar peduncule. Left cerebellar venous development anomaly made of a series of small venules with deep topography which converge to a venous collector, in the immediate vecinity of the described cavernoma, which then crosses the left CPA cystern to connect through a left temporal cortical vein to the left transvers sinus. Page 20 of 25

21 Fig. 12: AGGRESSIVE PARAGANGLIOMA (*) with invasion of the right CPA. Page 21 of 25

22 Fig. 13: GIANT MENINGIOMA of the left sphenoidal region, with multiple extensions to both sphenoidal sinuses, posterior ethmoidal cells, engulfing the left internal carotid artery, and with extension to the posterior fossa (left CPA) including nerves V, VI, and VII on the left side. Page 22 of 25

23 Conclusion A strong knowledge of the anatomy, and pursuit of a correct MRI examination protocol lead to establishing the diagnostic of the most frequent pathology-schwannoma, followed by meningioma and to delineate rarer entities such as: arachnoid or epidermoid cysts, vasculo-nervous conflicts, as well as distinguishing lesions with different origin and secondary involvement of the CPA. Personal Information C. Scheau, Ioana G.Lupescu, G.A.Popa, Emi M.Preda Radiology and Medical Imagistics Clinic, Fundeni Clinical Institute, Bucharest, Romania (258 Fundeni St) cristianscheau@gmail.com Images for this section: Page 23 of 25

24 Fig. 14: Fundeni Clinical Institute, Bucharest Page 24 of 25

25 References 1. Cerebellopontine Angle Masses Alan L. Cowan, MD, University of Texas Medical Branch, June 2, 2004 Lecture 2. Bonneville F, Sarrazin JL, Marsot-dupuch K et-al. Unusual Lesions of the Cerebellopontine Angle: A Segmental Approach, March 2001 RadioGraphics, 21, Anne Osborn, Susan Blaser, Karen Salzman, Diagnostic Imaging: Brain, 2004, AMIRSYS 4. Einar Goebell, Thorsten Ries, Thomas Kucinski - Screening for cerebellopontine angle tumors: is a CISS sufficient?, Eur Radiol (2005) 15: Antonios Drevelegas, Extra-axial brain tumors, Eur Radiol (2005) 15: Fabrice Bonneville, Julien Savatovsky and Jacques Chiras, Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extraaxial lesions, Volume 17, Number 11, , Smirniotopoulos JG, Yue NC, Rushing EJ, Cerebellopontine Angle Masses: Radiologic-Pathologic Corelation, Radiographics Sep;13(5): Fabrice Bonneville, Julien Savatovsky and Jacques Chiras, Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extraaxial lesions, Volume 17, Number 11, , Jan W. Casselman, The skull base: tumoral lesions, Eur Radiol (2005) 15: Dhakshina Ganeshan, Deepa Anand, Radiological Reasoning: Cerebellopontine Mass Causing Hemifacial Spasm, 2010, AJR: Fabrice Bonneville, Julien Savatovsky and Jacques Chiras, Imaging of cerebellopontine angle lesions: an update. Part 1: enhancing extra-axial lesions, European Radiology Volume 17, Number 10, , Ewa I#ycka-#wieszewska, Edyta Szurowska, Wojciech Kloc. Cerebellopontine angle tumours: radiologic-pathologic correlation and diagnostic difficulties, Folia Neuropathol 2006; 44 (4): Page 25 of 25