Imaging Evaluation of Malignant Chest Wall Neoplasms 1

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1 This copy is for personal use only. To order printed copies, contact Imaging Evaluation of Malignant Chest Wall Neoplasms CHEST IMAGING Brett W. Carter, MD Marcelo F. Benveniste, MD Sonia L. Betancourt, MD Patricia M. de Groot, MD John P. Lichtenberger III, MD Behrang Amini, MD Gerald F. Abbott, MD Abbreviations: DFSP = dermatofibrosarcoma protuberans, FDG = fluorine 18 fluorodeoxyglucose, MM = multiple myeloma, MPNST = malignant peripheral nerve sheath tumor, SPB = solitary plasmacytoma of bone, UPS = undifferentiated pleomorphic sarcoma RadioGraphics 2016; 36: Published online /rg Content Codes: 1 From the Department of Diagnostic Radiology, Division of Diagnostic Imaging, University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1478, Houston, TX (B.W.C., M.F.B., S.L.B., P.M.d.G., B.A.); Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences, Bethesda, Md (J.P.L.); and Department of Radiology, Massachusetts General Hospital, Boston, Mass (G.F.A.). Recipient of a Certificate of Merit award for an education exhibit at the 2014 RSNA Annual Meeting. Received June 29, 2015; revision requested December 10 and received January 29, 2016; accepted February 8. For this journal-based SA-CME activity, the authors B.W.C. and J.P.L. have provided disclosures (see end of article); all other authors, the editor, and the reviewers have disclosed no relevant relationships. Address correspondence to B.W.C. ( bcarter2@mdanderson.org). Neoplasms of the chest wall are uncommon lesions that represent approximately 5% of all thoracic malignancies. These tumors comprise a heterogeneous group of neoplasms that may arise from osseous structures or soft tissues, and they may be malignant or benign. More than 50% of chest wall neoplasms are malignancies and include tumors that may arise as primary malignancies or secondarily involve the chest wall by way of direct invasion or metastasis from intrathoracic or extrathoracic neoplasms. Although 20% of chest wall tumors may be detected at chest radiography, chest wall malignancies are best evaluated with cross-sectional imaging, principally multidetector computed tomography (CT) and magnetic resonance (MR) imaging, each of which has distinct strengths and limitations. Multidetector CT is optimal for depicting bone, muscle, and vascular structures, whereas MR imaging renders superior soft-tissue contrast and spatial resolution and is better for delineating the full extent of disease. Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT is not routinely performed to evaluate chest wall malignancies. The primary functions of PET/ CT in this setting include staging of disease, evaluation of treatment response, and detection of recurrent disease. Ultrasonography has a limited role in the evaluation and characterization of superficial chest wall lesions; however, it can be used to guide biopsy and has been shown to depict chest wall invasion by lung cancer more accurately than CT. It is important that radiologists be able to identify the key multidetector CT and MR imaging features that can be used to differentiate malignant from benign chest lesions, suggest specific histologic tumor types, and ultimately guide patient treatment. RSNA, 2016 radiographics.rsna.org RSNA, 2016 SA-CME LEARNING OBJECTIVES After completing this journal-based SA-CME activity, participants will be able to: Delineate the strengths and limitations of multidetector CT, MR imaging, and FDG PET/CT in the evaluation of chest wall malignancies. Identify the key imaging features that can be used to distinguish malignant from benign neoplasms and suggest specific tumor types. Discuss the basic treatment strategies used in the clinical management of chest wall malignancies. See Introduction Chest wall neoplasms are uncommon lesions that represent approximately 5% of all thoracic malignancies (1) and are encountered less frequently than are osseous and soft-tissue tumors that occur elsewhere in the body (2,3). More than 50% of chest wall neoplasms are malignant and typically result from direct invasion by or metastasis from thoracic tumors; however, these lesions may also arise from the chest wall as primary tumors (4,5). Most of these rare lesions are malignant, and because they are uncommon, radiologists may be unfamiliar with their typical clinical manifestations and imaging features. As malignant chest wall tumors represent a heterogeneous group of lesions, several different classification schemes have been proposed and may be used in clinical practice. In most schemes, malignant chest wall neoplasms are divided into categories that are based on their site of origin (bone and cartilage, or soft tissue) and tissue composition.

2 1286 September-October 2016 radiographics.rsna.org TEACHING POINTS Several key features of chest wall neoplasms may be useful in formulating a diagnosis and treatment approach: lesion prevalence and clinical features (ie, presenting signs and symptoms, patient demographic information), site of chest wall involvement, presence and pattern of mineralization at imaging, and correlation between imaging and histopathologic findings. Given the superior soft-tissue contrast achieved with MR imaging, as compared with CT, it is the optimal imaging modality for delineating extent of chest wall soft-tissue involvement and enables the differentiation of malignancy from normal chest wall structures and nonneoplastic disease processes such as infection and inflammation. Although the role of FDG PET/CT in characterizing chest wall masses is limited, it may be used to distinguish high-grade soft-tissue sarcomas from benign neoplasms, the former of which tend to have higher mean and maximal standardized uptake values. However, FDG PET/CT cannot enable reliable differentiation of benign tumors from low- and intermediategrade soft-tissue sarcomas. The imaging appearance of liposarcoma depends primarily on the tumor s histologic features and internal composition. Well-differentiated liposarcoma is composed of 50% 75% adipose tissue, resulting in predominantly fat attenuation (between 40 and 120 HU) on multidetector CT images. At MR imaging, this tumor shows high signal intensity on T1-weighted images and low signal intensity on T2- weighted images. At multidetector CT and MR imaging, the most common findings of radiation-associated malignancies include bone destruction and a soft-tissue mass. Approximately 20% of chest wall tumors may be detected initially at chest radiography (6). However, the ability to completely characterize these abnormalities by using radiography is limited, and cross-sectional techniques such as multidetector computed tomography (CT) and magnetic resonance (MR) imaging are the imaging modalities of choice. In many cases, the diagnosis can be strongly suggested by using key features seen at one or more imaging examinations. In other cases, although the radiologic features may be nonspecific, a combination of clinical features, imaging characteristics, and histopathologic findings usually enables the differentiation between malignant and benign chest wall neoplasms and the formulation of a useful differential diagnosis to subsequently guide further patient treatment (7,8). In this article, we review the pathophysiologic characteristics and classification of malignant chest wall tumors of osseous and softtissue origin, and the role of cross-sectional imaging techniques, principally multidetector CT and MR imaging, in the evaluation of these lesions. Emphasis is placed on distinguishing radiologic features and basic treatment strategies. Classification of Chest Wall Malignancies Malignant neoplasms of the chest wall represent a heterogeneous group of lesions, and no specific classification scheme is universally accepted for use in clinical practice. In most proposed classification systems, these tumors are divided into several groups that are based on specific features such as the tumor s site of origin (bone and cartilage, or soft tissue) and tissue composition (Table 1). In the 2002 World Health Organization classification system for soft-tissue neoplasms, the following nine categories are recognized: adipocytic, vascular, fibroblastic-myofibroblastic, fibrohistiocytic, smooth muscle, pericytic, skeletal muscle, chondro-osseous, and tumors of uncertain differentiation (9). Nam et al (8) have suggested a different scheme for classifying soft-tissue tumors that includes adipocytic, vascular, fibroblastic-myofibroblastic, and fibrohistiocytic categories, as well as categories such as peripheral nerve sheath and cutaneous neoplasms, which will be described in this review (8,10) (Table 1). Malignant chest wall tumors with secondary origins, including metastatic disease, invasion by lung cancer and other thoracic malignancies, lymphoma, and radiationinduced malignancies, also will be reviewed. Evaluation of Chest Wall Malignancies When a chest wall abnormality is first identified, a multidisciplinary approach to the workup is necessary to differentiate malignant from benign tumors, narrow the differential diagnosis, and guide further management. Several key features of chest wall neoplasms may be useful in formulating a diagnosis and treatment approach: lesion prevalence and clinical features (ie, presenting signs and symptoms, patient demographic information), site of chest wall involvement, presence and pattern of mineralization at imaging, and correlation between imaging and histopathologic findings (8). As stated previously, more than 50% of chest wall neoplasms are malignant, and most of these malignancies represent direct invasion by or metastasis from adjacent tumors of the lung, breast, pleura, and mediastinum. The most common primary malignancies of the chest wall are sarcomas, 45% of which arise from soft tissue and 55% of which arise from bone. Patients with chest wall neoplasms may be symptomatic or asymptomatic at the time of presentation. In contrast to patients with benign chest wall tumors, the majority of patients with malignant chest wall neoplasms are symptomatic, and the most common symptom at presentation is chest pain (11 13). In the setting of malignancy, chest wall associated pain is suggestive of osseous involvement, and the possibil-

3 RG Volume 36 Number 5 Carter et al 1287 Table 1: Classification of the Most Common Osseous and Soft-Tissue Chest Wall Malignancies Malignancy Group Osseous malignancies Chondrosarcoma Myeloma Osteosarcoma Ewing sarcoma Soft-tissue malignancies Adipocytic tumor Vascular tumor Peripheral nerve sheath tumor Fibrohistiocytic tumor Cutaneous tumor Secondary tumor Specific Tumor* MM SPB Osseous osteosarcoma Extraosseous osteosarcoma Ewing sarcoma of bone Extraosseous Ewing sarcoma Askin tumor Liposarcoma Angiosarcoma Kaposi sarcoma MPNST UPS DFSP Metastasis Chest wall invasion by intrathoracic malignancy Lymphoma Radiation-associated malignancy *DFSP = dermatofibrosarcoma protuberans, MM = multiple myeloma, MPNST = malignant peripheral nerve sheath tumor, SPB = solitary plasmacytoma of bone, UPS = undifferentiated pleomorphic sarcoma. ity of invasion must be investigated. In addition, in contrast to benign neoplasms, malignant tumors tend to appear as larger lesions and grow much more rapidly (11,14). At presentation, older patients tend to have large, aggressive malignant chest wall neoplasms, whereas younger patients tend to have small, benign abnormalities (6). Chest wall neoplasms originating as primary or secondary extrathoracic lesions are more likely to manifest as a growing palpable mass than are intrathoracic lesions extending into the chest wall (5). Role of Imaging Chest well neoplasms may be identified initially at chest radiography, given the widespread availability and use of this modality. Approximately 20% of these lesions are visible on chest radiographs, which can be beneficial in demonstrating the location, size, and growth rate of chest wall malignancies (6,13). The radiographic features of malignant chest wall tumors are typically nonspecific, and differentiation of the various histologic tumor types may not be possible. Small lesions may not be visible at radiography, whereas a large tumor can result in a focal opacity projecting over a portion of the thorax (Fig 1). In many cases, the incomplete border sign, which is char- acterized by both well-defined and ill-defined tumor margins and indicates an extrapulmonary tumor location, may be present (Fig 2). Dedicated views of specific structures such as the ribs and sternoclavicular joints help to identify the tumor s site of origin. Radiography may also reveal evidence of cortical destruction, which indicates extracompartmental extension (15). Although mineralization such as calcification or ossification may be present, the high-kilovoltage technique used for radiography is not optimal for detecting small deposits of bone and calcium; however, the lowkilovoltage techniques used for bone radiography can better reveal small foci of mineralization and enable better delineation of soft-tissue planes (7). Dual-energy subtraction chest radiography, a technique that enables one to take advantage of differences in the degree to which body tissues attenuate low- and high-energy photons, has been shown to aid in the detection and diagnosis of many thoracic abnormalities. Two major advantages of using this technique are its high sensitivity in the detection of calcification within lesions and its utility in the identification of osseous abnormalities. Specifically, on dual-energy bone-selective images, osseous lesions such as primary malignancies and metastases are more conspicuous than they would normally be on conventional chest radiographs (16,17).

4 1288 September-October 2016 radiographics.rsna.org Figure 1. Non-Hodgkin lymphoma of the chest wall in a 58-year-old man who presented with right-sided chest pain. (a) Posteroanterior chest radiograph shows an ill-defined opacity (arrows) projecting over the right hemithorax; this finding was interpreted as pneumonia, given the presenting symptom of chest pain. (b) Axial coned-down contrast material enhanced multi detector row CT image obtained at the level of the aortic valve after the presumed pneumonia failed to resolve shows a lenticular mass (*) in the right anterior chest wall. Biopsy revealed non-hodgkin lymphoma. Approximately 20% of chest wall neoplasms are detected on chest radiographs, and these lesions can appear as a focal opacity projecting over a region of the thorax, as in this case. Figure 2. Metastatic renal cell carcinoma in a 51-year-old woman. (a) Posteroanterior chest radiograph shows an opacity (arrow) projecting over the right hemithorax, with an incomplete border sign, which is suggestive of an extrapulmonary lesion. (b) Axial coned-down contrast-enhanced multi detector row CT image obtained at the level of the left atrium shows a soft-tissue mass (*) in the right anterior chest wall, with regions of internal enhancement and vascularity (arrows). Biopsy confirmed the presence of metastatic renal cell carcinoma. Many chest wall malignancies demonstrate the incomplete border sign, which is characterized by both well-defined and ill-defined tumor margins and indicates an extrapulmonary tumor location such as the chest wall or pleura. Cross-sectional imaging techniques, including multidetector CT and MR imaging, enable much more accurate identification and characterization of chest wall malignancies. Multidetector CT readily reveals a lesion s presence, site and tissue origin (bone and cartilage, or soft tissues such as muscle, fat, or skin), morphologic features, and internal components, such as fat and mineralization (11,12). The intravenous administration of contrast material can be used to identify tumor vascularity (7). Disadvantages of multidetector CT include the use of ionizing radiation and the reduced soft-tissue contrast that may be encountered in emaciated patients. Given the superior soft-tissue contrast achieved with MR imaging, as compared with CT, it is the optimal imaging modality for delineating extent of chest wall soft-tissue involvement

5 RG Volume 36 Number 5 Carter et al 1289 Figure 3. MR images obtained in a 33-year-old woman after resection of a posterior chest wall sarcoma. (a) Axial coned-down T2-weighted MR image obtained at the level of the carina shows a hyperintense postoperative fluid collection (*) consistent with seroma in the posterior chest wall at the site of surgical resection. There is an indeterminate ill-defined region of high signal intensity (arrow) in the anterior margin of the fluid collection. (b) Axial contrast-enhanced coned-down T1-weighted fat-suppressed MR image obtained at the same level shows a prominent enhancing component (arrow) in the seroma (*), consistent with residual or recurrent disease. Superior soft-tissue contrast and spatial resolution make MR imaging the optimal modality for evaluating and characterizing chest wall malignancies and identifying residual or recurrent disease following surgical resection. and enables the differentiation of malignancy from normal chest wall structures and nonneoplastic disease processes such as infection and inflammation (7). MR imaging is also helpful in the posttreatment setting, as it enables better identification of the sites of residual or recurrent disease than does multi detector row CT (Fig 3), and intravenous administration of gadoliniumbased contrast material is helpful in this respect. For the evaluation of soft-tissue lesions, images are typically obtained in the axial plane and in a secondary sagittal or coronal plane. T1- and T2-weighted MR imaging sequences are recommended, as published descriptions of most soft-tissue lesions include their depiction with standard spin-echo MR imaging sequences. Fast spin-echo MR imaging sequences may be used to reduce the overall imaging time and minimize motion artifacts. Gradient-echo MR imaging sequences can reveal the characteristic blooming of hemosiderin within lesions. Short t inversion-recovery T2-weighted and chemical shift selective fat-saturated T2-weighted MR imaging sequences can be used to better delineate abnormal tissue that has increased water content (18). In cases of excessive motion, cardiac gating and respiratory compensation can be used (7). Different coils can be used to better evaluate tumors on the basis of their location. Surface coils are helpful in evaluating superficial chest wall neoplasms, and torso coils are used to characterize lesions that have substantial intrathoracic components. One of the primary limitations of MR imaging is its limited utility for assessment of bone involvement and mineralization, which are better evaluated with multidetector CT. Another potential limitation of MR imaging is operator dependence, which may apply to individuals performing the examination and/or those interpreting the examination findings but can decrease as the user s experience with the modality increases. Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT is not routinely performed to evaluate chest wall malignancies, as many primary and secondary neoplasms show increased FDG uptake. The primary functions of PET/CT in this setting include staging of disease, evaluation of treatment response, and detection of recurrent disease. Ultrasonography (US) has a limited role in the evaluation and characterization of superficial chest wall lesions; however, it can be used to guide needle biopsy. In one study, US was found to be superior to CT for identifying chest wall invasion by intrathoracic malignancies: US had a sensitivity of 89% and a specificity of 95%, and CT had a sensitivity of 42% and a specificity of 100% (15,19). Differentiating Malignant from Benign Neoplasms Once a chest wall mass has been identified, the first priority is to determine whether it has a malignant versus benign cause, as this distinction ultimately guides further patient

6 1290 September-October 2016 radiographics.rsna.org treatment. A large soft-tissue mass invading adjacent osseous and/or soft-tissue structures is nearly pathognomonic for a malignant neoplasm. When regions of mineralization are present in such a lesion, consideration should be given to specific entities such as primary chondrosarcoma or osteosarcoma, and metastasis from calcium- or bone-forming tumors such as chondrosarcoma or osteosarcoma arising from other locations. Primary malignancies of osseous origin frequently result in soft-tissue mass formation. In contrast, benign osseous neoplasms do not result in extraosseous soft-tissue masses and typically exhibit unique nonaggressive imaging features. For instance, fibrous dysplasia usually manifests as an expansile lytic or mixed lesion with lytic regions and a characteristic ground-glass matrix affecting the ribs, proximal humerus, or clavicle (7,8,20). Although cortical thinning and scalloping may be present, osseous erosion is not a feature. Enchondroma appears as an osteolytic lesion with the characteristic rings and arcs pattern of internal chondroid calcification (7,8,20). Although expansion of the medullary cavity and endosteal scalloping may be present, osseous erosion is absent. Osteochondroma manifests as a pedunculated or sessile lesion with smooth continuity between the tumor and the medullary cavity and cortex of the affected osseous structure (7,8,20). Evaluation of the associated cartilaginous cap is necessary, as caps measuring greater than 2 cm in adults and greater than 3 cm in children should raise suspicion for malignant transformation (20). At imaging, benign neoplasms of soft-tissue origin often have a distinct appearance that enables them to be differentiated from malignant tumors. For instance, lipoma appears as fat attenuation (between 40 and 120 HU) at multidetector CT, has high signal intensity at T1-weighted MR imaging, and demonstrates uniform loss of signal at fat-suppressed MR imaging (2,21 24). Although well-differentiated liposarcoma is composed of 50% 75% adipose tissue, this malignant neoplasm usually contains other internal structures such as septa or soft-tissue nodules, which may enhance after the intravenous administration of contrast material; these findings are much less common in lipomas (2,21 25). Hemangioma, a benign neoplasm of vascular origin, results in high signal intensity at T2-weighted MR imaging, demonstrates variable amounts of internal fat at multidetector CT and T1-weighted MR imaging, and frequently contains phleboliths at multidetector CT (21,26 28). In contrast, malignant vascular lesions such as angiosarcoma are heterogeneous on T1- and T2-weighted MR images, lack internal fat, demonstrate aggressive behavior such as invasion of adjacent structures, and exhibit findings related to their origin (lymphedema) such as fibrous thickening, soft-tissue nodules, and fluid collections adjacent to the chest wall musculature (8,14). Benign nerve sheath neoplasms such as neurofibroma and schwannoma typically manifest as low-attenuating soft-tissue masses that often contain fat or cystic components. Although pressure erosion of adjacent ribs or other osseous structures may be present, invasion and other types of aggressive behavior are absent. The target sign, characterized by central low signal intensity and peripheral high signal intensity on T2-weighted MR images and central enhancement following the intravenous administration of gadolinium-based contrast material, and the fascicular sign, characterized by heterogeneous low signal intensity with a ringlike pattern on T2-weighted MR images, are frequently visualized (29 31). The split fat sign, characterized by fat attenuation around the soft-tissue mass at multidetector CT, also may be seen. These radiologic signs are typically absent in MPNSTs, which, when compared with benign nerve sheath neoplasms, demonstrate greater heterogeneity and aggressive behavior at multidetector CT and MR imaging and may show increased FDG uptake at PET/CT (14,32,33). The key multidetector CT and MR imaging features of the malignant neoplasms described in this article are listed in Table 2. Although the role of FDG PET/CT in characterizing chest wall masses is limited, it may be used to distinguish high-grade soft-tissue sarcomas from benign neoplasms, the former of which tend to have higher mean and maximal standardized uptake values. However, FDG PET/CT cannot enable reliable differentiation of benign tumors from low- and intermediate-grade softtissue sarcomas (34 37). Diagnosis and Histopathologic Tissue Sampling As the imaging features of chest wall malignancies may be nonspecific, histopathologic tissue sampling with use of a variety of techniques, including fine-needle aspiration, core-needle biopsy, incisional biopsy, and excisional biopsy, may be necessary to establish a diagnosis (1). The chosen approach depends on several factors such as lesion size, extent of resection anticipated at surgery, and whether reconstruction is necessary (5). Excisional biopsy usually is performed to examine chest wall masses measuring less than 5 cm, whereas lesions 5 cm or greater may be sampled by using fineneedle aspiration and/or core-needle biopsy, or with incisional biopsy (5).

7 RG Volume 36 Number 5 Carter et al 1291 Table 2: Key Multidetector CT and MR Imaging Findings of Osseous and Soft-Tissue Chest Wall Malignancies Malignancy Multidetector CT Findings MR Imaging Findings Osseous malignancies Chondrosarcoma Well-circumscribed mass arising from anterior chest wall and composed of soft tissue and mineralization Ring, arc, and/or stippled patterns of calcification Myeloma MM appears as multiple lytic lesions SPB appears as a single expansile lytic bone lesion; focal soft-tissue mass may or may not be present Osteosarcoma Soft-tissue mass with variable amounts of matrix mineralization Calcification or ossification is dense, cloudy, or ivory like; greatest centrally; and decreased peripherally Ewing sarcomas Heterogeneous soft-tissue mass due to necrosis, Soft-tissue malignancies hemorrhage, and/or cystic changes Calcification is rare Cartilage background is heterogeneous but often iso- to hypointense to muscle on T1- weighted images, and is hyperintense to muscle on T2-weighted images Regions of mineralization are hypointense to muscle on T1- and T2-weighted images Untreated tumor is hypointense to muscle on T1-weighted images, hyperintense to muscle on T2-weighted images, and shows enhancement on postcontrast images Treated tumor has heterogeneous signal intensity on T1- and T2-weighted images and heterogeneous enhancement on postcontrast images Inactive disease is hyperintense on T1-weighted images, hypointense on T2-weighted images, and nonenhancing on postcontrast images Soft-tissue mass of extramedullary plasmacytoma has low signal intensity on T1-weighted images, has high signal intensity on T2-weighted images, and enhances on postcontrast images Soft-tissue component is hyperintense to muscle on T1-weighted images, iso- to hyperintense to muscle on T2-weighted images, and heterogeneously enhancing on postcontrast images Matrix mineralization is hypointense on T1- and T2-weighted images Lesion has heterogeneous signal intensity (iso- or hyperintense to muscle), with high-signal-intensity hemorrhage, on T1-weighted images; is heterogeneous and hyperintense to muscle on T2-weighted images; and has intense enhancement on postcontrast images Liposarcoma Heterogeneous mass containing fat and soft tissue Thick internal septa may be seen Angiosarcoma Heterogeneous mass with internal necrosis, hemorrhage, and vascularity Vascular structures may enhance Imaging features depend on the histologic subtype Well-differentiated liposarcoma has high signal intensity on T1-weighted images, low signal intensity on T2-weighted images, and heterogeneous enhancement of nonadipose tissue on postcontrast images Thick septa may enhance Myxoid liposarcoma has moderately high signal intensity on T1-weighted images and high signal intensity on T2-weighted images Soft-tissue mass has heterogeneous signal intensity on T1- and T2-weighted images, intense enhancement on postcontrast images, and internal vessels Associated features of lymphedema include fibrous thickening, soft-tissue nodules, and fluid collections adjacent to chest wall muscles (continues)

8 1292 September-October 2016 radiographics.rsna.org Table 2: Key Multidetector CT and MR Imaging Findings of Osseous and Soft-Tissue Chest Wall Malignancies (continued) Malignancy Multidetector CT Findings MR Imaging Findings MPNST Large soft-tissue mass adjacent to one or more peripheral nerves May invade adjacent osseous structures DFSP Well-defined lesion in subcutaneous tissues Highly variable attenuation due to hemorrhage, necrosis, and/or cystic changes UPS Soft-tissue mass in deep fascia or skeletal muscle Heterogeneous contrast enhancement Peripheral mineralization following treatment Metastatic disease Multidetector CT is superior to MR imaging for depiction of osseous metastases Lesions frequently demonstrate imaging characteristics specific to the primary malignancies from which they are derived: sclerotic lesions in breast or prostate cancer, lytic and expansile lesions in renal cell carcinoma, and lytic lesions in MM Chest wall invasion Loss of normal fat and soft-tissue planes Osseous destruction Lymphoma May appear as infiltrative soft tissue with spread around bone and cartilage, or as a focal mass Radiation-associated malignancy Multidetector CT is superior to MR imaging for delineation of osseous destruction Invasive mass is iso- or hyperintense to muscle on T1-weighted images, hyperintense to muscle on T2-weighted images, and heterogeneously enhancing on postcontrast images Heterogeneity is due to internal necrosis, hemorrhage, and/or cellularity With transformation of benign nerve sheath neoplasm to MPNST, there is loss of target, fascicular, and split fat signs; a sudden change in the size of the benign nerve sheath neoplasm; and heterogeneous signal intensity due to necrosis and/or hemorrhage and to invasion of adjacent tissues Lesion is hypointense to muscle on T1-weighted images and hyperintense to fat on T2- weighted images Highly variable signal intensity is due to hemorrhage, necrosis, and/or cystic changes Mass has low signal intensity and is isointense to muscle on T1-weighted images, and has intermediate to high signal intensity and is iso- to hyperintense to fat on T2- weighted images High collagen content has low signal intensity at all MR imaging sequences Myxoid components have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images Hemorrhage has variable signal intensity at all MR imaging sequences MR imaging is good for evaluation of soft-tissue metastases Lesions frequently demonstrate imaging characteristics specific to the primary malignancies from which they are derived: enhancing metastases in vascular malignancies (thyroid and renal cell cancers, melanoma, some sarcomas, choriocarcinoma) MR imaging is superior to multidetector CT for identifying chest wall invasion MR imaging findings of invasion include infiltration or disruption of the normal extrapleural fat plane on T1-weighted images, high signal intensity of the parietal pleura and other chest wall structures on T2-weighted images and short inversion time inversion-recovery images, and lesion attachment to the chest wall at cine MR imaging during breathing Lesion is typically isointense to mildy increased in signal intensity on T1-weighted images and hyperintense on T2-weighted images MR imaging is superior to multidetector CT for evaluating soft-tissue mass and infiltration of adjacent structures Soft-tissue mass is usually present and can enable differentiation of radiationassociated malignancy from benign osseous changes after radiation therapy

9 RG Volume 36 Number 5 Carter et al 1293 Figure 4. Chondrosarcoma of the chest wall in a 29-year-old woman who presented with focal right anterior chest pain. (a) Posteroanterior coned-down chest radiograph demonstrates an ill-defined opacity (arrow) that has internal mineralization and is projecting over the medial right lower lung zone. (b) Lateral chest radiograph confirms the position of the lesion (arrow) in the anterior chest wall. (c) Axial coned-down contrast-enhanced multidetector CT image obtained at the base of the heart shows a soft-tissue mass (arrow) with extensive calcification in the right anterior chest wall. Biopsy revealed chondrosarcoma. Although variable in composition, most chondrosarcomas demonstrate rings, arcs, and/or stippled patterns of calcification, which are best visualized on multidetector CT images. Primary Malignant Osseous Tumors Chondrosarcoma Chondrosarcoma is the most common primary osseous malignancy of the chest wall, representing 30% of all primary malignant osseous lesions and 33% of all primary rib neoplasms (38,39). In addition to developing as a primary tumor, chondrosarcoma has also been associated with malignant degeneration of benign chondromas, trauma, and thoracic radiation therapy (3,6,39). Approximately 10% of chondrosarcomas occur in the chest wall, and most of them are identified in the anterior chest wall, in the superior five ribs, adjacent to costochondral junctions, or in the paravertebral regions (14). Chondrosarcoma originating from soft tissues has been reported but is uncommon (40). Although chondrosarcomas may be seen in individuals of any age, those affected are usually in their 4th to 7th decades of life, and men are affected more frequently than are women (8). Most patients present with a palpable and painful anterior chest wall mass. The 5-year survival rates for patients with chondrosarcoma range from 60% to 90%. Factors indicating a poor prognosis include high grade of the primary tumor and presence of pulmonary metastases, which are seen in 10% of cases at the time of diagnosis. The typical appearance of chondrosarcoma on multidetector CT images is a well-circumscribed mass of variable composition arising from the anterior chest wall. Most lesions contain a combination of soft tissue and mineralization, and several patterns of calcification, such as rings, arcs, and/or a stippled pattern, have been described (8) (Fig 4). Invasion and destruction of adjacent osseous structures are common. At MR imaging, the cartilage background of chondrosarcoma is heterogeneous but frequently iso- to hypointense to muscle on T1-weighted images and hyperintense to muscle on T2-weighted images. Regions of mineralization, including the highly characteristic rings and arcs configuration that may be seen on multidetector CT images, are hypointense to muscle on T1- and T2-weighted MR images (8). Following the intravenous administration of gadolinium-based contrast material, enhancement is usually heterogeneous, especially at the

10 1294 September-October 2016 radiographics.rsna.org Figure 5. SPB involving the right hemithorax in a 52-year-old man. (a) Axial coned-down T2- weighted MR image obtained at the level of the pulmonary arteries demonstrates a large hyperintense mass (*) arising from the right chest wall and extending into the right lung. (b) Axial contrast-enhanced coned-down T1-weighted fat-suppressed MR image obtained at the same level shows diffuse enhancement (*) of the abnormality. Biopsy confirmed the presence of SPB. (c) Axial coned-down FDG PET/CT image obtained at the same level demonstrates intense FDG uptake (*) within the mass. Although the superior soft-tissue contrast achieved with MR imaging enables better delineation of the disease extent than does multidetector CT, FDG PET/CT facilitates better demonstration of the metabolic activity of myelomatous lesions. tumor periphery (41 43). Markedly high signal intensity in myxoid chondrosarcomas, which do not contain foci of mineralization, may be seen on T2-weighted images (14). Myeloma Neoplasms comprised of malignant plasmacytes include MM, SPB, and extramedullary plasmacytoma, which involve different patient characteristics, affected structures, and clinical symptoms at presentation. MM is most common in patients years of age, whereas SPB and extramedullary plasmacytoma affect slightly younger patients those around the age of 50 years (14). MM and SPB affect bones with active hematopoiesis, including the skull, thoracic skeleton, spine, pelvis, proximal humeri, and femora. Although extramedullary plasmacytoma may involve any soft-tissue structure, most of these neoplasms arise from the upper aerodigestive tract (44). Symptoms reported at presentation typically include bone pain, renal failure, and anemia in association with MM; focal pain at the tumor site in association with SPB; and epistaxis and rhinorrhea in association with extramedullary plasmacytoma (44). At multidetector CT, MM manifests as multiple lytic lesions, whereas SPB appears as a single expansile lytic bone lesion. Focal soft-tissue masses may or may not be identified; when present, however, they typically demonstrate heterogeneous enhancement after intravenous contrast material administration (14). Regardless of the site of origin, extramedullary plasmacytoma manifests as a focal soft-tissue mass with attenuation characteristics similar to those of muscle. The MR imaging characteristics of MM and SPB depend on whether the lesions have been previously treated and are metabolically active. For instance, nontreated lesions are hypointense to muscle on T1-weighted images, hyperintense to muscle on T2-weighted images, and enhance after intravenous administration of gadolinium-based contrast material (Fig 5). Treated disease results in heterogeneous signal intensity on T1- and T2-weighted images and heterogeneous enhancement on

11 RG Volume 36 Number 5 Carter et al 1295 Figure 6. Advanced chest wall osteosarcoma in a 47-year-old man. (a) Axial coned-down contrast-enhanced multidetector CT image (soft-tissue window) obtained at the level of the aortic arch demonstrates a large softtissue mass occupying the entire left hemithorax, with invasion of the adjacent chest wall (*) and mediastinum (arrows). A large focus of mineralization is present centrally. (b) Findings on axial coned-down contrast-enhanced multidetector CT image (bone window) obtained at the same level confirm the presence of extensive internal ossification in this patient. The ossification or calcification in osteosarcomas may be dense, cloudy, or ivory like. Unlike in chondrosarcoma, in osteosarcoma, ossification or calcification is greatest in the central part of the neoplasm and decreased toward the periphery. postcontrast images. Inactive disease is hyperintense on T1-weighted images, is hypointense on T2-weighted images, and demonstrates no enhancement on postcontrast images (45). The soft-tissue masses of extramedullary plasmacytoma demonstrate low signal intensity on T1-weighted images, high signal intensity on T2-weighted images, and enhancement on postcontrast images. FDG PET/CT is beneficial in the assessment of disease burden, identification of extramedullary involvement, and evaluation of response to therapy (45) (Fig 5). Decreased or absent FDG uptake is characteristic of treated disease. Osteosarcoma Osteosarcoma is a high-grade malignant mesenchymal tumor that accounts for 10% 15% of primary malignant chest wall neoplasms (6,14). Two different forms of osteosarcoma based on age peak have been described: an osseous form affecting young adults and a less common extraosseous form seen in individuals older than 50 years (3). The osseous form may arise from the ribs (costochondral junction), manubrium, sternum, scapulae, and clavicles, whereas the extraosseous form originates from soft tissues, without attaching to bone or periosteum. In both groups, a rapidly enlarging, painful chest wall mass is usually identified at presentation. At multidetector CT, osteosarcoma manifests as a soft-tissue mass with variable amounts of matrix mineralization. Calcification or ossification, which can be dense, cloudy, or ivory like, is greatest in the central part of the neoplasm and decreased toward the periphery (Fig 6). Internal heterogeneity can be seen in the setting of hemorrhage and/ or necrosis (3,14). At MR imaging, the soft-tissue component of osteosarcoma is often hyperintense to muscle on T1-weighted images and iso- to hyperintense to muscle on T2-weighted images. Matrix mineralization is hypointense on both T1- and T2-weighted images (3,8). Heterogeneous enhancement following the intravenous administration of gadolinium-based contrast material is typical. On FDG PET/CT images, osteosarcomas demonstrate heterogeneous FDG uptake. Predominantly peripheral FDG uptake can be seen in the setting of central necrosis or after chemotherapy (37). Telangiectatic osteosarcoma rarely affects the chest wall but may manifest as a completely lytic bone lesion. Ewing Sarcoma Tumors The Ewing sarcoma family of tumors is a group of malignant neoplasms that includes Ewing sarcoma of bone, extraosseous Ewing sarcoma, and Askin tumor (or peripheral primitive neuroectodermal tumor arising from the chest wall). These malignancies are postulated to arise from embryonal neural crest cells (14), and all of them are highly aggressive (46,47). All of the tumors in this group contain the identical balanced, reciprocal translocation between

12 1296 September-October 2016 radiographics.rsna.org Figure 7. Ewing sarcoma of the right chest wall in a 37-year-old man. (a) Axial coned-down contrast-enhanced multidetector CT image obtained at the level of the carina at presentation shows a heterogeneous mass (*) arising from the chest wall. Internal regions of low attenuation represent necrosis. Note the peripheral mineralization (arrow). (b) Axial coned-down FDG PET/CT image obtained at the same level shows FDG uptake in the mass (*) similar to the radiotracer uptake in the mediastinal background. At multidetector CT, Ewing sarcomas appear as heterogeneous soft-tissue masses due to the presence of internal necrosis, hemorrhage, and/or cystic changes, which typically demonstrate little or no FDG uptake at FDG PET/CT. (c) Image obtained at US-guided biopsy enables good visualization of the chest wall mass (*) and the passage of the biopsy needle (arrow) into the lesion for tissue sampling. chromosomes 11 and 22, t(11;22) (q24;q12) (48,49). Ewing sarcomas typically arise from the ribs, scapulae, clavicles, and sternum, and most commonly affect individuals between the ages of 20 and 30 years (14). These lesions represent the most common primary malignant chest wall neoplasms seen in children and young adults and the third most common cause of primary chest wall malignancy (7). At multidetector CT, neoplasms in the Ewing sarcoma family of tumors manifest as heterogeneous soft-tissue masses due to necrosis, hemorrhage, and/or cystic changes (2,14) (Fig 7). In contrast to the calcification seen in other primary osseous malignancies of the chest wall, calcification within these neoplasms is rarely seen. Tumors may invade adjacent structures such as the pleura, mediastinum, and lung. Heterogeneous signal intensity, with lesions usually iso- or hyperintense to muscle and regions of high-signal-intensity hemorrhage on T1-weighted MR images, and heterogeneous high signal intensity on T2-weighted images are most common. Most lesions demonstrate intense enhancement following the intravenous administration of gadolinium-based contrast material. Small neoplasms tend to be homogeneous, whereas large tumors are more likely to demonstrate regions of heterogeneity due to hemorrhage and/or necrosis (14). At FDG PET/CT, increased FDG uptake is typical, although decreased radiotracer uptake may be seen in regions of necrosis (50) (Fig 7). Primary Malignant Soft-Tissue Neoplasms Adipocytic Neoplasms After UPS, liposarcoma is the second most common chest wall malignancy of soft-tissue origin. Although this tumor accounts for 15% of all sarcomas affecting the chest wall, only 10% of them originate from this site (14). Liposarcoma is most common in men aged years, but it may affect any group (7). Histologically, this tumor is composed of lipoblasts that range from poorly differentiated round cells to mature adipose

13 RG Volume 36 Number 5 Carter et al 1297 Figure 8. Liposarcoma of the left chest wall in a 51-year-old man who presented with left shoulder pain. Axial contrast-enhanced multidetector CT image demonstrates a large mass (*) in the left teres major muscle. Although the mass comprises predominantly fat, regions of internal soft tissue and septa (arrows) are present. Histopathologic findings at the time of surgical resection were consistent with well-differentiated liposarcoma. Factors favoring the diagnosis of liposarcoma rather than lipoma include size larger than 10 cm, internal septa thicker than 2 mm, nodular regions of nonadipose tissue, and adipose tissue accounting for less than 75% of the tumor s total content. tissue. Five pathologic subtypes of liposarcoma are recognized by the World Health Organization: well differentiated, dedifferentiated, myxoid, pleomorphic, and mixed (21). Well-differentiated liposarcoma is the most common subtype and represents 50% of all of these lesions. The imaging appearance of liposarcoma depends primarily on the tumor s histologic features and internal composition. Well-differentiated liposarcoma is composed of 50% 75% adipose tissue, resulting in predominantly fat attenuation (between 40 and 120 HU) on multidetector CT images (Fig 8). At MR imaging, this tumor shows high signal intensity on T1-weighted images and low signal intensity on T2-weighted images. Depending on the volume of fat in the tumor, it may be difficult to distinguish well-differentiated liposarcoma from lipoma. Several imaging features that are suggestive of well-differentiated liposarcoma have been identified and can help differentiate it from lipoma: size larger than 10 cm, internal septa thicker than 2 mm, nodular regions of nonadipose tissue, and adipose tissue accounting for less than 75% of the tumor s total content (23) (Fig 9) (Table 3). After intravenous gadolinium-based contrast material administration, the nonadipose tissue components demonstrate variable enhancement (16). Irregularly thick septa tend to enhance intensely, whereas thin septa often show faint enhancement (24). The other histologic subtypes of liposarcoma generally contain less fat (25). For instance, pleomorphic sarcoma may contain no visible fat. Owing to its low fat content, myxoid liposarcoma demonstrates moderately high signal intensity on T1-weighted MR images and high signal intensity on T2-weighted images. If regions of low signal intensity on T1-weighted images, high signal intensity on T2-weighted images, and enhancement on postcontrast images are seen within a well-differentiated liposarcoma, then a diagnosis of dedifferentiated liposarcoma should be considered. Vascular Neoplasms Angiosarcoma is the most common primary malignant neoplasm of vascular origin and demonstrates a vasoformative architecture histologically (14). These tumors manifest as large, painful, rapidly enlarging chest wall lesions, and affected patients may present with clinical signs and symptoms such as hemorrhage, anemia, and/or coagulopathy (8,51). Angiosarcoma is most strongly associated with chronic lymphedema (52), especially after mastectomy for breast cancer, although this association exists in only 10% of cases (8). When angiosarcomas arise from the chest wall, the most common location is the breast in patients with a history of breast cancer (14). The imaging features of angiosarcoma depend on the lesion s location and whether it is superficial or deep. Most superficial lesions manifest as a focal soft-tissue mass with associated skin thickening and subcutaneous edema. In contrast, deep lesions tend to manifest as a focal mass without these associated features (53). At multidetector CT, angiosarcomas are heterogeneous with internal regions of necrosis, hemorrhage, and vascularity. After intravenous administration of contrast material, enhancement of the vascular tissue may be seen (Fig 10). At MR imaging, the typical finding is a soft-tissue mass with heterogeneous signal intensity on T1- and T2-weighted images (8). Intense enhancement following the intravenous administration of gadolinium-based contrast material is common. Discrete vessels may be identified at the tumor periphery. Features such as fibrous thickening, soft-tissue nodules, and fluid collections adjacent to chest wall muscles are often

14 1298 September-October 2016 radiographics.rsna.org Figure 9. Liposarcoma of the left chest wall in a 49-year-old woman who presented with chest pain. (a) Axial coned-down T1-weighted MR image demonstrates a large mass that is heterogeneously hypointense to the adjacent fat. Regions of internal high signal intensity represent adipose tissue. (b) Axial contrast-enhanced coned-down T1- weighted fat-suppressed MR image demonstrates extensive enhancement within the mass. (c) Axial coned-down T2-weighted MR image shows regions of high signal intensity consistent with cystic components and necrosis. The imaging appearance of liposarcoma depends on the composition of the tumor (fat, soft tissue, mineralization), which is reflected by the histologic subtype. present owing to the association with lymphedema (14). At FDG PET/CT, angiosarcoma demonstrates increased FDG uptake, although the uptake pattern may be heterogeneous owing to the presence of hemorrhage and/or necrosis. Nerve Sheath Neoplasms MPNST is a spindle cell sarcoma of nerve sheath origin that involves large and mediumsized nerves and has previously been referred to as malignant schwannoma, neurofibrosarcoma, or neurosarcoma. These neoplasms account for 5% 10% of all soft-tissue sarcomas and are most common in patients aged years (8). MPNST is associated with neurofibromatosis type 1 and is the leading cause of cancer-related death in patients with this disorder. The lifetime risk of developing MPNST in the setting of neurofibromatosis 1 is approximately 10% (54). Malignant transformation of a benign nerve sheath neoplasm should be suspected when a patient with neurofibromatosis type 1 presents with a new onset of pain (14). At multidetector CT, MPNST manifests as a large soft-tissue mass that is adjacent to one or more peripheral nerves and may invade adjacent osseous structures. At MR imaging, MPNST appears as an invasive mass that is iso- or hyperintense to muscle on T1-weighted images and hyperintense to muscle on T2-weighted images (14). The heterogeneity is due to internal necrosis, hemorrhage, and/or cellularity (32) (Fig 11). After the intravenous administration of contrast material, enhancement is typically heterogeneous (33). With transformation of a benign nerve sheath neoplasm to MPNST, radiologic signs such as the target sign, fascicular sign, and split fat sign typically are absent. Other imaging findings suggestive of malignant transformation include a sudden change in the size of a benign nerve sheath neoplasm, heterogeneous attenuation at multidetector CT and heterogeneous signal intensity at MR imaging due to necrosis and/or hemorrhage, and the invasion of adjacent tissues (14,32,33). At FDG PET/CT, MPNST demonstrates heterogeneous FDG uptake owing to the presence of necrosis and/or hemorrhage. Although the utility of FDG PET/CT in distinguishing benign nerve

15 RG Volume 36 Number 5 Carter et al 1299 Table 3: Key Imaging Features Used to Differentiate Liposarcoma from Lipoma Imaging Feature Liposarcoma Lipoma Tumor size.10 cm 10 cm Internal septal thickness.2 mm 2 mm Nodular nonadipose tissue present Yes No Adipose tissue component (percentage of tumor s total content),75% 75% Figure 10. Angiosarcoma of the left chest wall in a 59-year-old woman after mastectomy for breast cancer. (a) Posteroanterior chest radiograph demonstrates ill-defined opacity (arrow) projecting over the left hemithorax. Note the surgical clips in the left chest wall, consistent with previous mastectomy. (b) Axial coned-down contrast-enhanced multidetector CT image obtained at the level of the left atrium shows a large heterogeneous mass (*) in the medial aspect of the reconstructed left breast. Several regions of internal enhancement reflect the vascular nature of the tumor. Note the adjacent skin thickening (arrow). Angiosarcomas of the chest wall are most strongly associated with chronic lymphedema related to mastectomy in patients previously treated for breast cancer. sheath neoplasms from MPNST is variable, compared with benign lesions, MPNST tends to demonstrate increased FDG uptake (Fig 12). Cutaneous Neoplasms DFSP is a malignant dermal lesion composed of spindle cells that usually spreads to involve subcutaneous tissues and muscles. Although DFSP is now classified as a primary tumor of the skin by the World Health Organization, it is sometimes considered a soft-tissue malignancy arising from the cutaneous layer (8,9). DFSP is characterized by local invasion and recurrence following therapy. Two specific types of DFSP have been described: a fibrosarcomatous variant characterized by an aggressive course and a more indolent variant. On multidetector CT and MR images, DFSP appears as a well-defined lesion that arises from the subcutaneous tissues and ranges from a small nodule to a large mass. Internal attenuation, signal intensity, and contrast enhancement are highly variable owing to the presence and extent of hemorrhage, necrosis, and/or cystic changes. DFSP is usually hypointense to muscle on T1- weighted MR images and hyperintense to fat on T2-weighted MR images (55,56). Fibrohistiocytic Neoplasms UPS, formerly known as malignant fibrous histiocytoma, is classified as a fibrohistiocytic malignancy and is the most common malignant soft-tissue neoplasm of the chest wall in adults (57). The mean age of patients at the time of diagnosis is 55 years, and women are affected slightly more frequently than are men. UPS originates in the deep fascia or skeletal muscle but only rarely arises from the chest wall as a primary malignancy. Three histologic subtypes of UPS have been described by the World Health Organization: high-grade pleomorphic sarcoma, pleomorphic sarcoma with giant cells, and pleomorphic sarcoma with prominent inflammation (8).

16 1300 September-October 2016 radiographics.rsna.org Figure 11. Findings of MPNST on axial MR images coned down to the right chest wall, obtained in a 39-year-old man with neurofibromatosis type 1. (a) T1-weighted image demonstrates a large, invasive right anterior chest wall mass that has predominantly low signal intensity but also regions of internal high signal intensity due to hemorrhage (arrow). (b) T1-weighted contrast-enhanced fatsuppressed MR image shows extensive regions of internal enhancement. (c) T2-weighted MR image demonstrates internal regions of high signal intensity due to cystic components and necrosis (*). In the setting of neurofibromatosis type 1, imaging findings suggestive of malignant transformation include sudden change in size of a neurogenic neoplasm, heterogeneous signal intensity on MR images due to necrosis and/or hemorrhage, and invasion of adjacent tissues. At multidetector CT, UPS appears as a softtissue mass that involves the deep fascia or skeletal muscle and enhances heterogeneously after intravenous contrast material administration. Involvement of adjacent osseous structures is common. Internal mineralization can often be identified in the peripheral aspect of the lesion after treatment. UPS demonstrates low signal intensity and is isointense to muscle on T1-weighted MR images. On T2-weighted images, UPS has intermediate to high signal intensity and is iso- to hyperintense to fat (Fig 13). Lesions with high collagen content often have low signal intensity at all MR imaging sequences, those with myxoid tissue components may demonstrate low signal intensity at T1- weighted sequences and high signal intensity at T2-weighted sequences, and tumors with internal hemorrhage can have variable signal intensity at all MR imaging sequences (9). Secondary Neoplasms Metastatic Disease Osseous metastatic disease affecting the chest wall is typically encountered in the setting of extensive metastatic disease elsewhere in the body, but it may be seen early in association with aggressive primary malignancies. These lesions can manifest in many different ways, with some metastases demonstrating imaging characteristics specific to the primary malignancies from which they are derived. Some metastases may be predominantly sclerotic lesions from breast or prostate cancer; lytic and expansile lesions from renal cell carcinoma; or lytic lesions from MM (3). Such osseous features are best evaluated with multidetector CT. Soft-tissue metastatic disease typically is seen only in the setting of extensive metastatic disease elsewhere in the body, is considered an indicator of a poor prognosis, and is associated with decreased patient survival rates (58,59). Common patterns of metastatic spread include direct extension, hematogeneous spread, and lymphatic spread (Fig 14). Similar to osseous chest wall metastases, chest wall metastases of soft-tissue origin frequently demonstrate imaging characteristics

17 RG Volume 36 Number 5 Carter et al 1301 Figure 12. MPNST in a 54-year-old man with neurofibromatosis type 1. (a) Axial contrast-enhanced multidetector CT image coned down to the right chest wall demonstrates a large soft-tissue mass (white arrows) arising in the right shoulder and resulting in osseous destruction and fragmentation (black arrow). (b) Axial FDG PET/ CT image coned down to the right chest wall shows intense FDG uptake in the peripheral aspect of the tumor (arrows) and central low FDG uptake (*) due to extensive necrosis. On FDG PET/CT images, MPNST demonstrates heterogeneous patterns of FDG uptake due to the presence of necrosis and/or hemorrhage. Although the utility of FDG PET/CT for distinguishing benign neurogenic neoplasms from MPNST is variable, most MPNSTs, as compared with benign lesions, tend to demonstrate increased FDG uptake. Figure 13. UPS of the left pectoralis muscle in a 51-year-old man who presented with left-sided chest pain and had normal contrast-enhanced multidetector CT findings. (a) Axial T1-weighted contrast-enhanced fatsuppressed MR image coned down to the left chest wall demonstrates ill-defined enhancement (arrow) within the left pectoralis muscle at the site of the pain reported at physical examination. (b) Axial T2-weighted MR image coned down to the left chest wall shows regions of high signal intensity in the muscle and more focal regions of high signal intensity (arrow) that represent cystic components of the neoplasm. specific to the primary neoplasms from which they are derived. For instance, vascular malignancies may result in enhancing metastases that can hematogenously spread to the chest wall (Fig 14). Chest Wall Invasion by Thoracic Malignancy The chest wall may be directly invaded by aggressive thoracic malignancies typically lung cancer, breast cancer, pleural tumors, or mediastinal neoplasms. Although MR imaging and multidetector CT have been shown to have similar utility in the detection of chest wall invasion by lung cancer, MR imaging is considered to be superior owing to better soft-tissue contrast and spatial resolution. MR imaging findings of invasion include infiltration or disruption of the normal extrapleural fat plane at T1-weighted sequences and high signal

18 1302 September-October 2016 radiographics.rsna.org Figure 14. Secondary malignancies of the chest wall seen on axial contrast-enhanced multidetector CT images. (a) Image obtained below the level of the right hilum in a 56-year-old woman with lung adenocarcinoma demonstrates a soft-tissue mass (M ) extending from the right upper lung lobe into the right anterior chest wall (arrows), consistent with invasion. Note the enlarged subcarinal lymph node (*) consistent with nodal metastatic disease. (b) Image obtained at the level of the aortic arch in a 49-year-old man with thymic carcinoma shows a large tumor (M ) in the prevascular mediastinal compartment invading the left anterior chest wall and breast (*). The chest wall may be directly invaded by aggressive thoracic malignancies typically lung cancer, breast cancer, pleural tumors, or mediastinal tumors. Figure 15. Chest wall invasion by thoracic malignancy in a 60-yearold woman with large non small cell lung cancer (M) of the left upper lobe of the lung. Sagittal coned-down contrast-enhanced T1-weighted MR image demonstrates extension of the enhancing tumor along the intercostal spaces and into the left chest wall (arrows), consistent with invasion. MR imaging is considered superior to multidetector CT for depicting chest wall invasion, and intravenous contrast material administration may assist in confirming tumor involvement. intensity of the parietal pleura and other chest wall structures at T2-weighted and short t inversionrecovery sequences (60,61). Intravenous contrast material administration is often helpful in confirming chest wall invasion (61) (Fig 15). Additional techniques such as cine MR imaging during breathing can help in the identification of invasion, as attachment of the tumor to the chest wall suggests involvement (62). Lymphoma Lymphoma of the chest wall is relatively rare and typically results from direct invasion by Hodgkin lymphoma or large B cell lymphoma arising from the mediastinum, axilla, or bone. Direct invasion occurs in 6.4% of patients with Hodgkin lymphoma, and primary malignant lymphoma accounts for only 2.4% of primary chest wall tumors (63). Lymphomatous involvement of the chest wall affects 9.6% of patients sometime during the course of their disease (64). Patients with Hodgkin lymphoma and chest wall involvement have been shown to have substantially poorer outcomes than those without chest wall invasion (65). At multidetector CT, lymphomas typically manifest as infiltrative soft-tissue masses in the parasternal soft tissues, with spread around bone and cartilage as a result of direct extension of disease from lymph nodes or masses in the prevascular mediastinal compartment (66) (Fig 16). At MR imaging, lymphoma is usually isointense to mildly

19 RG Volume 36 Number 5 Carter et al 1303 Figure 16. Hodgkin lymphoma of the mediastinum and chest wall in a 38-year-old man who presented with progressive chest pain and shortness of breath. (a) Axial coned-down contrast-enhanced multidetector CT image demonstrates an extensive soft tissue (M ) in the prevascular mediastinal compartment that extends into the anterior chest wall (*). Small bilateral pleural effusions (arrows) also are present. Note the occlusion of the superior vena cava, with dilated azygos and mediastinal venous collateral vessels. (b) Axial coned-down FDG PET/CT image shows intense FDG uptake within these regions of soft tissue. Biopsy revealed Hodgkin lymphoma of the mediastinum, with extension into the anterior chest wall. Lymphomatous involvement of the chest wall is rare, but it usually results from direct invasion by Hodgkin lymphoma or large B cell lymphoma originating in the mediastinum, axilla, or bone and is considered a factor of a poor prognosis. increased in signal intensity on T1-weighted images and hyperintense on T2-weighted images (67). At FDG PET/CT, FDG uptake in lymphomas is variable; it depends on the histologic type of the tumor. However, most invasive lesions demonstrate increased FDG uptake, and PET/CT can be used for tumor staging and restaging purposes (Fig 16). Radiation-associated Malignancies Radiation-associated malignancies may develop after thoracic radiation therapy for leukemia, lymphoma, or solid tumors. The overall risk of developing a secondary chest wall malignancy is similar to the risk of death from surgery or anesthesia (68), and only 0.1% or fewer of individuals who survive 5 years after therapy develop these tumors (69). Secondary malignancies may develop at any time, from 3 to 50 years after therapy, but the average latent period is years. As the majority of these tumors develop within or adjacent to the radiation site, correlating imaging findings with the radiation treatment plan used for previously treated patients is recommended. The histologic features of radiation-associated malignancies are variable and depend on the origin of the tumor. For instance, secondary lesions arising from bone typically represent osteosarcoma, whereas those originating from soft tissue usually represent UPS (70,71). Criteria for diagnosing radiationassociated malignancies have been proposed and include a history of radiation therapy, a neoplasm arising within the irradiated area, a number of years of latency, and histologic proof of sarcoma (69,70). Radiation-associated malignancies, most of which are sarcomas, are aggressive lesions associated with a high recurrence rate and distant metastatic spread (72), and they should be suspected when changes in the appearance of previously irradiated bone occur, especially in the setting of an associated soft-tissue mass (70). At multi detector row CT and MR imaging, the most common findings of radiation-associated malignancies include bone destruction and a soft-tissue mass (73). Infiltration of adjacent structures may be present. As soft-tissue masses are typically present, the absence of this finding can help differentiate extensive benign osseous changes from radiation-associated sarcoma (70). Owing to the aggressive behavior of these tumors, radiation-associated malignancies demonstrate increased FDG uptake at FDG PET/CT (Fig 17). Treatment For most chest wall malignancies, surgical resection is the treatment of choice and can prolong patient survival and provide palliative relief (74). Desirable tumor margins depend on the histologic features of the given tumor and have been shown to be an important predictor of recurrence-free

20 1304 September-October 2016 radiographics.rsna.org Figure 17. Radiation-associated sarcoma of the right posterior chest wall in a 56-year-old man 8 years after combined chemotherapy radiation therapy for non small cell lung cancer. (a) Axial coned-down contrast-enhanced multidetector CT image demonstrates a large, destructive soft-tissue mass arising from the right posterior chest wall, with extension into the spinal canal. Note the marked chest wall venous collateralization from central venous obstruction. (b) Axial coned-down PET/CT image shows intense FDG uptake within the mass. Biopsy revealed spindle cell sarcoma due to prior radiation therapy. (c) Axial CT image obtained as part of the radiation treatment plan shows the port used for thoracic radiation therapy for right upper lung lobe non small cell lung cancer 8 years ago and that the right posterior chest wall received a portion of the radiation dose. Radiation-induced sarcoma usually occurs within or adjacent to the radiation site and manifests as a soft-tissue mass that results in osseous destruction and invasion. patient survival (63). For instance, following surgical resection of chondrosarcoma, the local recurrence rate is 4% in cases of cancer-negative margins and 73% in cases of positive margins (75). For treatment of aggressive malignant neoplasms that can spread along the periosteum, resection of the entire rib is recommended, with costal articulations posteriorly or anteriorly, depending on the location of the tumor (5). For high-grade malignancies, 4-cm resection margins are considered adequate, whereas 1 2-cm resection margins are considered adequate for lowgrade malignancies (5). Adjacent structures such as the soft tissues, skin, pleura, and lung should be resected, if they are involved. Following surgical resection, the need for reconstruction depends primarily on the tumor s size and location. In general, surgical defects measuring less than 4 5 cm and posterior defects covered by the scapula do not require chest wall reconstruction (5). Preoperative chemotherapy may be administered for chemotherapy-sensitive tumors and can reduce the overall tumor burden. For patients with osteosarcoma, Ewing sarcoma, rhabdomyosarcoma, and other small cell sarcomas of the chest wall, it is generally recommended that neoadjuvant chemotherapy be administered and chemotherapy continued postoperatively, depending on the tumor response. Chondrosarcoma and soft-tissue tumors in adults are typically irradiated if negative margins cannot be obtained at surgical resection (5). Conclusion Neoplasms of the chest wall are uncommon lesions that represent approximately 5% of all thoracic malignancies. Therefore, radiologists may be unfamiliar with the typical clinical presentations and imaging features associated with these rare lesions, most of which are malignant in origin and behavior. Approximately 20% of chest wall tumors may be detected at chest radiography. However, these lesions are best evaluated with cross-sectional imaging, principally multidetector CT and MR imaging, each of which has strengths and limitations. As accurate identification and characterization of chest wall malignancies are necessary for formulating treat-