RSNA Soft-Tissue Sarcomas of the Abdomen and Pelvis (PDF)

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This copy is for personal use only. To order printed copies, contact [email protected] 797 GASTROINTESTINAL IMAGING | Soft-Tissue Sarcomas of the Abdomen and Pelvis: Radiologic- Pathologic Features, Part 2— Uncommon Sarcomas1 Angela D. Levy, MD Maria A. Manning, MD Soft-tissue sarcomas occurring in the abdomen and pelvis are an ­ Markku M. Miettinen, MD uncommon but important group of malignancies. Recent changes to the World Health Organization classification of soft-tissue tumors FROM THE RADIOLOGIC PATHOLOGY ARCHIVES Abbreviations: GIST = gastrointestinal stro- include the movement of gastrointestinal stromal tumors (GISTs) mal tumor, MPNST = malignant peripheral into the soft-tissue tumor classification. GIST is the most com- nerve sheath tumor mon intraperitoneal sarcoma. Liposarcoma is the most common RadioGraphics 2017; 37:797–812 retroperitoneal sarcoma, and leiomyosarcoma is the second most Published online 10.1148/rg.2017160201 common. GIST, liposarcoma, and leiomyosarcoma account for the Content Codes: majority of sarcomas encountered in the abdomen and pelvis and are discussed in part 1 of this article. Undifferentiated pleomorphic 1 From the Department of Radiology, Medstar Georgetown University Hospital, 3800 Reser- sarcoma (previously called malignant fibrous histiocytoma), der- voir Rd NW, Washington, DC 20007 (A.D.L., matofibrosarcoma protuberans, solitary fibrous tumor, malignant M.A.M.); the American Institute for Radio- logic Pathology, Silver Spring, Md (M.A.M.); peripheral nerve sheath tumor, rhabdomyosarcoma, extraskeletal and the Center of Cancer Research, National chondro-osseous sarcomas, vascular sarcomas, and sarcomas of Cancer Institute, Bethesda, Md (M.M.M.). uncertain differentiation uncommonly arise in the abdomen and Received October 31, 2016; accepted Janu- ary 10, 2017. For this journal-based SA-CME pelvis and the abdominal wall. Although these lesions are rare activity, the authors, editor, and reviewers sarcomas and their imaging features overlap, familiarity with the have disclosed no relevant relationships. Ad- dress correspondence to A.D.L. (e-mail: locations where they occur and their imaging features is important [email protected]). so they can be diagnosed accurately. The anatomic location and Supported by the American Institute for Radio- clinical history are important factors in the differential diagnosis logic Pathology, the Joint Pathology Center, and of these lesions because metastasis, more-common sarcomas, bor- the Uniformed Services University of the Health Sciences. The views expressed in this article are derline fibroblastic proliferations (such as desmoid tumors), and those of the authors and do not necessarily re- endometriosis have imaging findings that overlap with those of flect the official policy or position of the Depart- ment of Defense or the U.S. Government. these uncommon sarcomas. In this article, the clinical, pathologic, and imaging findings of uncommon soft-tissue sarcomas of the abdomen and pelvis and the abdominal wall are reviewed, with an SA-CME LEARNING OBJECTIVES emphasis on their differential diagnosis. After completing this journal-based SA-CME activity, participants will be able to: Discuss the classification of soft-tissue sarcomas. Introduction Describeand illustrate the radiologic and pathologic features of undifferenti- Soft-tissue tumors are a diverse group of tumors of mesenchymal or ated pleomorphic sarcoma, dermatofi- neuroectodermal origin with biologic behavior that ranges from benign brosarcoma protuberans, solitary fibrous to malignant. Benign tumors are extremely common and are encoun- tumor, and MPNST. tered in daily clinical practice by physicians of all specialties. In contrast, Identify the imaging findings that are sarcomas are malignant soft-tissue tumors that are rare, especially when most important for establishing an accu- compared with other cancers. The estimated number of new cancer rate differential diagnosis for soft-tissue masses in the abdomen and pelvis. cases in the United States in 2016 is 1 685 210. Of those, only 12 310 cases (0.7%) are soft-tissue sarcomas (1). Despite the rarity of soft- See www.rsna.org/education/search/RG. tissue sarcomas, they are an important group of tumors to understand and accurately recognize so they can be diagnosed as early as possible. Soft-tissue sarcomas arise most commonly in the extremities, fol- lowed by the trunk wall, retroperitoneum, and head and neck (2). In part 1 of this article, we reviewed (a) the anatomic locations in which sarcomas arise in the abdomen and pelvis; (b) the updated 798 May-June 2017 radiographics.rsna.org TEACHING POINTS Classification of Soft-Tissue Sarcomas Occur- Twenty percent of soft-tissue sarcomas show no lines of dif- ring in the Abdomen and Pelvis on the Basis of ferentiation and are classified as undifferentiated sarcomas. the 2013 WHO Classification of Tumors of Soft These lesions are most often undifferentiated pleomorphic Tissue sarcoma (previously known as pleomorphic malignant fibrous Categories of Soft-Tissue Tumors, with the Sarcomas histiocytoma). Classified in Each Category On CT and MR images, dermatofibrosarcoma protuberans is in the skin and may extend into the subcutaneous fat, with Adipocytic tumors occasional deep lesions. Dermatofibrosarcoma protuberans Well-differentiated liposarcoma demonstrates soft-tissue attenuation on CT images, with vari- Dedifferentiated liposarcoma able enhancement after intravenous contrast material admin- Pleomorphic liposarcoma istration. At MR imaging, the lesion is isointense or hyperin- tense relative to skeletal muscle on T1-weighted MR images Myxoid liposarcoma and is isointense or hyperintense relative to the adjacent fat Fibroblastic/myofibroblastic tumors on T2-weighted MR images. Fat-suppressed T2-weighted se- Dermatofibrosarcoma protuberans quences or short inversion time inversion-recovery sequences Solitary fibrous tumor are helpful in the identification of the extent of the lesion be- cause of its high signal intensity on MR images obtained with Fibrosarcoma these sequences. Linear extensions into the skin and satellite Myxoid fibrosarcoma nodules may also be seen. So-called fibrohistiocytic tumors After administration of intravenous contrast material, large Malignant tenosynovial giant cell tumor and often tortuous vessels may be seen along the periphery of solitary fibrous tumor on arterial phase contrast-enhanced Smooth muscle tumors images. Leiomyosarcoma In patients with neurofibromatosis type 1, it may be difficult Pericytic (perivascular) tumors to differentiate MPNST from coexisting plexiform neurofibro- Malignant glomus tumor mas because both have similar imaging features, including Skeletal muscle tumors bone erosion and heterogeneity. Embryonal rhabdomyosarcoma The differential diagnosis for deep lesions of the abdominal wall includes desmoid tumor, endometriosis, and metastatic Alveolar rhabdomyosarcoma disease. Pleomorphic rhabdomyosarcoma Spindle cell/sclerosing rhabdomyosarcoma Vascular tumors of soft tissue World Health Organization classification of soft- Epithelioid hemangioendothelioma tissue sarcomas, which included the movement of Angiosarcoma gastrointestinal stromal tumors (GISTs) into the Chondro-osseous tumors classification; and (c) the most common soft-tissue Extraskeletal osteosarcoma sarcomas occurring in the abdomen and pelvis GISTs (Table) (3). Liposarcoma, leiomyosarcoma, and Malignant GISTs GIST are the three most common sarcomas in the Nerve sheath tumors abdomen and pelvis. Although the remaining soft- Malignant pleural nerve sheath tumor (MPNST) tissue sarcomas are not common in the abdomen Ectomesenchymoma and pelvis, it is important to have knowledge of them so they can be considered in the differential Tumors of uncertain differentiation diagnosis of masses arising in the abdomen and Synovial sarcoma pelvis and the abdominal wall. Epithelioid sarcoma In the retroperitoneum, well-differentiated Alveolar soft part sarcoma liposarcoma is the most common sarcoma. It Clear cell sarcoma of soft tissue is composed of mature fatty elements. Conse- Extraskeletal myxoid chondrosarcoma quently, the imaging appearance of well-differ- Extraskeletal Ewing sarcoma entiated liposarcoma is readily suggestive of its Desmoplastic small round cell tumor diagnosis. Soft-tissue elements within a fatty Extrarenal rhabdoid tumor retroperitoneal mass are suggestive that the mass Perivascular epithelioid cell tumor (PEComa) is a dedifferentiated liposarcoma. Dedifferenti- Undifferentiated/unclassified sarcomas ated liposarcoma may also be a completely solid Undifferentiated pleomorphic sarcoma (previ- soft-tissue mass, which makes the diagnosis ously called malignant fibrous histiocytoma) more challenging. Leiomyosarcoma, GIST, and Undifferentiated spindle cell sarcoma uncommon soft-tissue sarcomas such as undif- Undifferentiated round cell sarcoma ferentiated pleomorphic sarcomas and malignant Undifferentiated epithelioid sarcoma solitary fibrous tumors also manifest as a solid heterogeneous retroperitoneal mass. Note.—Reprinted from reference 3. RG Volume 37 Number 3 Levy et al 799 undifferentiated sarcomas. These lesions are most often undifferentiated pleomorphic sarcoma (pre- viously known as pleomorphic malignant fibrous histiocytoma). Clinical and Pathologic Features Undifferentiated pleomorphic sarcoma usually occurs in older adults and may arise at any loca- tion in the body. Men account for two-thirds of cases, and undifferentiated pleomorphic sarcoma is more common in white subjects (4). Undifferen- tiated pleomorphic sarcoma is the most common sarcoma to develop at sites of prior irradiation (5). Figure 1. Photomicrograph of undifferentiated pleomorphic Investigators have shown that most patients have sarcoma. The tumor is composed of pleomorphic undifferen- received a radiation dose of 50 Gy or more, and tiated cells showing high mitotic activity. (Hematoxylin-eosin the median time interval between radiation expo- stain; original magnification, 3100.) sure and the development of a radiation-associated sarcoma is approximately 10 years (6). Undiffer- entiated pleomorphic sarcoma may also arise at In the peritoneal cavity, GIST is the most sites of chronic ulceration (7). The extremities are common sarcoma. Because most GISTs arise the most common location. Approximately 15% of from the muscularis propria of the stomach and undifferentiated pleomorphic sarcomas arise in the intestine, finding an attachment to the stomach abdomen and pelvis (8,9). or the intestine is suggestive of the diagnosis. If Clinical signs and symptoms of undif- no attachment can be identified, GIST should ferentiated pleomorphic sarcoma are usually still be considered in the differential diagnosis nonspecific. Fever, weight loss, and abdominal because GIST may be extraintestinal, or it may pain have been reported for those patients with lose its pedicle of attachment and appear separate intra-abdominal lesions. Many investigators from the stomach or intestine. Dedifferentiated have noted that a substantial proportion of liposarcoma, leiomyosarcoma, and uncommon undifferentiated pleomorphic sarcomas in the sarcomas are in the differential diagnosis after abdomen are dedifferentiated liposarcomas. more common diseases such as metastasis, lym- At gross pathologic examination, undifferenti- phoma, and borderline fibroblastic proliferations ated pleomorphic sarcoma is typically a solitary (eg, desmoid tumors) are considered. large lesion, 5–10 cm in diameter, at the time of Any soft-tissue sarcoma may arise in the diagnosis (4). The lesion is multilobulated, with abdominal wall. Such sarcomas may be deep necrosis, degeneration, or hemorrhage on the seated, arising in the abdominal wall muscula- cut surface. In some tumors, extensive hemor- ture, or superficial. Dermatofibrosarcoma protu- rhage can be present. Although the border of the berans is a superficial sarcoma that arises from tumor may appear well defined at gross patho- the skin and may extend into the deeper layers logic examination, microscopic spread along of the abdominal wall when its development is muscle fibers and fascial planes is often present. advanced. Microscopically, tumor cells with variably pleo- This article reviews the clinical, pathologic, morphic nuclei are characteristic (Fig 1) (10). and radiologic features of uncommon soft-tissue There is no characteristic immunohistochemical sarcomas arising in the abdomen and pelvis and profile. Immunohistochemical analysis is used the abdominal wall. These lesions are sarcomas to help exclude other tumors that may have a that cannot be differentiated or classified, fibro- pleomorphic appearance. blastic/myofibroblastic malignancies, MPNSTs, skeletal muscle sarcomas (rhabdomyosarcomas), Radiologic Features vascular sarcomas, chondro-osseous sarcomas, Undifferentiated pleomorphic sarcomas may and sarcomas of uncertain lineage. arise at any soft-tissue site in the abdomen and pelvis. On CT images, these lesions are well-cir- Undifferentiated/ cumscribed, multinodular, or infiltrating masses Unclassified Sarcomas of soft-tissue attenuation. Undifferentiated pleomorphic sarcomas are often large at the Definition time of diagnosis and invade adjacent anatomic Twenty percent of soft-tissue sarcomas show structures (Fig 2). Centrally within the tumor, no lines of differentiation and are classified as areas of low-attenuation necrosis, hemorrhage, 800 May-June 2017 radiographics.rsna.org Figure 2. Radiologic features of undifferentiated pleo- morphic sarcoma in two patients. (a, b) Undifferentiated pleomorphic sarcoma in a 57-year-old man with left leg swelling: Axial (a) and coronal (b) contrast-enhanced CT images show mostly homogeneous enhancement of a well-circumscribed soft-tissue mass (straight arrow) invading the left anterolateral abdominal wall and oblit- erating the left external iliac vein. A reactive lymph node (curved arrow on b) is depicted in the left inguinal re- gion. (c–e) Undifferentiated pleomorphic sarcoma in a 64-year-old man with vague right upper quadrant pain. (c) Axial contrast-enhanced CT image shows areas of low attenuation reflecting necrosis (*) within a sharply marginated, heterogeneously enhancing mass (arrow). (d, e) Axial half-Fourier acquisition single-shot turbo spin-echo (HASTE; Siemens, Erlangen, Germany) (d) and equilibrium phase contrast-enhanced T1-weighted fat-suppressed (e) MR images of the same patient as in c better show infiltration into the adjacent liver (arrow), as well as areas of necrosis (*). or myxoid change can be seen on CT images. pattern or coarse and chunky (9). After ad- The tumor may appear cystic with a rim of ministration of intravenous contrast material, peripheral enhancement when marked intrale- the enhancement pattern is variable, although sional hemorrhage is present (11). Calcification regions of marked contrast enhancement and from osseous or chondroid metaplasia occurs large intratumoral vessels may be seen. Hemo- in approximately 16% of cases (12). Calcifica- peritoneum from tumoral hemorrhage has been tions may be small and punctate in a speckled reported (13). RG Volume 37 Number 3 Levy et al 801 Recurrent and Metastatic Disease and may extend into the subcutaneous fat, with Undifferentiated pleomorphic sarcoma may recur occasional deep lesions. Dermatofibrosarcoma locally or as metastatic disease. The lesion usu- protuberans demonstrates soft-tissue attenuation ally recurs within 12–24 months after the initial on CT images, with variable enhancement after diagnosis (4). Lung, bone, and liver are the most intravenous contrast material administration (Fig common sites of distant metastasis. Similar to the 3) (17). At MR imaging, the lesion is isointense or metastases from other sarcomas, metastases to hyperintense relative to skeletal muscle on T1- the lymph nodes from undifferentiated pleomor- weighted MR images and is isointense or hyper- phic sarcoma are rare. intense relative to the adjacent fat on T2-weighted MR images (18). Fat-suppressed T2-weighted se- Fibroblastic/Myofibroblastic Tumors quences or short inversion time inversion-recovery The sarcomas classified as fibroblastic/myofi- sequences are helpful in the identification of the broblastic tumors display histologic, immuno- extent of the lesion because of its high signal inten- histochemical, and ultrastructural features of sity on MR images obtained with these sequences fibroblasts or myofibroblasts, as well as elements (19). Linear extensions into the skin and satellite of an extracellular matrix such as collagen. In this nodules may also be seen. section, we cover dermatofibrosarcoma protuber- ans and solitary fibrous tumor. Recurrent and Metastatic Disease.—Dermatofi- brosarcoma protuberans has a high local recur- Dermatofibrosarcoma Protuberans rence rate, up to 45% if the lesion is not excised with a wide margin (3 cm) (20). Those lesions Definition.—Dermatofibrosarcoma protuberans resected with wide margins have a 10%–20% is a locally aggressive superficial neoplasm arising chance of recurrence. The recurrence rates after in the dermis or subcutis. Mohs surgery are lower because of the ability to estimate the location of microscopic tumor Clinical and Pathologic Features.—Dermato- with this technique (21). Distant lung metastases fibrosarcoma protuberans most often occurs in from dermatofibrosarcoma protuberans are not young to middle-aged adults and is more com- common but may occur with fibrosarcomatous mon in blacks and in women. The increased transformation. occurrence in blacks is most exaggerated in the 45–49-year-old group, in which dermatofibro- Solitary Fibrous Tumor sarcoma protuberans is 3.5 times more common compared with other racial groups (14). The Definition.—Solitary fibrous tumor (including trunk wall (50%) and proximal extremities are tumors previously called hemangiopericytomas) the most common locations. is a fibroblastic tumor that often has a prominent Dermatofibrosarcoma protuberans grows hemangiopericytoma-like vascular pattern. slowly and indolently during several years be- fore beginning a rapid-growth phase. During Clinical and Pathologic Features.—Solitary fi- the rapid-growth phase, the tumor develops its brous tumor typically arises in deep soft tissues, characteristic protuberant appearance. Progres- such as those of the thigh, retroperitoneum, sion to fibrosarcoma occurs in 10%–15% of pelvis, and pleura. Solitary fibrous tumor has cases (15,16). Patients come to medical attention no gender predilection and is most common in because of an enlarging dermal mass. At gross adults aged 20–70 years (15). Clinically, the le- pathologic examination, dermatofibrosarcoma sion is a slow-growing painless mass. Less than protuberans is a nodular or plaquelike mass that 5% of patients may present with hypoglycemia may contain a protuberant cutaneous compo- (Doege-Potter syndrome) (22). The biologic nent. Histologically, dermatofibrosarcoma protu- behavior of the majority of solitary fibrous tu- berans is typically infiltrative in the subcutaneous mors is unpredictable, but frankly sarcomatous fat and is composed of uniform fibroblasts often examples are also recognized. At gross patho- arranged in whorling patterns. Development of logic examination, solitary fibrous tumor often a fascicular histologic appearance, often with an appears as a circumscribed firm mass, which is increased mitotic rate, indicates fibrosarcomatous pale gray to yellowish at sectioning. Hemorrhage transformation. The tumor cells are positive for and necrosis may be present. Histologically, CD34, which can be lost in fibrosarcomatous the tumors can be hypercellular or hypocellular transformation (16). with areas of dense collagen and hyalinization. A mitotic rate of more than four mitoses per 10 Radiologic Features.—On CT and MR images, high-power fields has been considered a sign for dermatofibrosarcoma protuberans is in the skin risk of malignant behavior (23). 802 May-June 2017 radiographics.rsna.org Figure 3. Dermal and deep dermatofibrosarcoma protuberans in two patients. (a–c) Dermatofibrosarcoma protu- berans in a 61-year-old woman with a painful, rapidly enlarging mass on her anterior abdominal wall. (a, b) Axial (a) and sagittal (b) contrast-enhanced CT images show a well-circumscribed multinodular soft-tissue–attenuation mass extending from the skin surface into the subcutaneous fat (arrows), without involvement of the anterior abdominal wall musculature. (c) Photograph of the resected specimen shows the dermal mass protruding from the skin, with central ulceration (arrow) at the skin surface. (Scale is in centimeters.) (d) Dermatofibrosarcoma protuberans in a 40-year-old man with a painful right lower chest wall mass: Axial contrast-enhanced CT image shows a heterogeneous subcutane- ous mass inseparable from the anterolateral abdominal wall musculature (arrows). Radiologic Features.—On CT and MR images, located in the extremities. Local recurrence and solitary fibrous tumor may be single or may form distant metastases to the lung, bone, and liver multiple masses. Solitary fibrous tumor is seen as may be seen (27). a sharply marginated round or oval mass. After administration of intravenous contrast material, Malignant Peripheral large and often tortuous vessels may be seen along Nerve Sheath Tumor the periphery of solitary fibrous tumor on arte- rial phase contrast-enhanced images (Fig 4) (24). Definition The tumor may show intense enhancement in the MPNST is typically a high-grade sarcoma that arterial phase and persistence of enhancement in usually arises in a neurofibroma or a nerve trunk, the portal venous and delayed phases of contrast often in patients with neurofibromatosis type enhancement (25,26). The pattern of enhancement 1 (15). MPNST was previously known as neu- has been correlated to highly vascular cellular areas rofibrosarcoma, malignant schwannoma, and within the tumor (24). Cystic areas of degeneration neurogenic sarcoma. and intratumoral necrosis may be present, such that the lesion resembles a GIST or leiomyosarcoma. Clinical and Pathologic Features Approximately 50% of MPNSTs occur in patients Recurrent and Metastatic Disease.—Solitary with neurofibromatosis type 1, 10% of MPNSTs fibrous tumors in the retroperitoneum and pelvis are radiation induced, and the remainder of them tend to behave aggressively compared with those occur sporadically (28). The mean age at diagno- RG Volume 37 Number 3 Levy et al 803 Figure 4. Solitary fibrous tumor in a 69-year-old man with long- term lower urinary tract symptoms and back pain radiating to the right leg. (a, b) Axial (a) and coronal (b) contrast-enhanced CT images show marked heterogeneous enhancement of a sharply marginated lobulated solid mass (straight arrow) in the right pel- vis. A prominent peripheral blood vessel (curved arrow) drapes over the superior margin of the mass. (c) Photograph of the cut surface of the resected specimen shows the encapsulated pink-tan soft-tissue mass. (Scale is in centimeters.) Radiologic Features On CT and MR images, MPNST is characteris- tically a large aggressive tumor with well-defined or ill-defined margins. MPNST is typically heterogeneous on both nonenhanced and intra- venous contrast material–enhanced CT and MR images because of necrosis within the tumor (31). MPNST may invade and infiltrate into adjacent organs and tissues and erode adjacent bone (Fig 5). In patients with neurofibromatosis type 1, it sis is 35 years in the general population, compared may be difficult to differentiate MPNST from with 26 years in patients with neurofibromatosis coexisting plexiform neurofibromas because both type 1 (28,29). MPNST is seen in a variety of loca- have similar imaging features, including bone tions, including the head and neck and the extremi- erosion and heterogeneity (32). ties. The paraspinal regions of the retroperitoneum are the most common location in the abdomen Recurrent and Metastatic Disease and pelvis. MPNST is most often asymptomatic, al- MPNSTs are highly aggressive sarcomas with though some patients may report neurologic symp- poor survival rates. Forty percent of patients toms in the distribution of the affected nerve (29). have local recurrence, and 40%–60% of patients At gross pathologic examination, MPNST have metastatic disease within 1 year after the often forms an elongated fusiform mass with the initial resection (33). The lung is the most com- ends, representing the nerve of origin, usually mon site for metastatic disease. Liver, adrenal transformed into neurofibroma (30). MPNST gland, brain, and bone metastases may also oc- may be truly encapsulated, reflecting the origin cur. Occasionally, lymph node metastases may from a nerve trunk. Necrosis, hemorrhage, and be seen. cystic change may be present on the cut surface. At histopathologic examination, the tumor is typically Rhabdomyosarcoma composed of spindle cells to pleomorphic cells that demonstrate nuclear atypia and high mitotic activity Definition (28). Divergent differentiation, such as rhabdomyo- Rhabdomyosarcomas are malignant tumors with sarcomatous, angiosarcomatous, or chondro-osse- exclusively skeletal muscle differentiation. They are ous differentiation, may be seen in an MPNST. the most common sarcomas of childhood and are 804 May-June 2017 radiographics.rsna.org Figure 5. MPNST in a 34-year-old woman with low back pain radiating to the left lower extremity. (a–c) Coronal T2-weighted inversion-recovery (a), T1-weighted (b), and contrast-enhanced T1-weighted fat-suppressed (c) MR images show a heterogeneous lobulated left paraspinal mass (arrow) invading the L5 vertebral body medially, the sacrum inferomedially, and the iliac wing inferolaterally. The mass is T1 hypo- to isointense (arrow on b) and T2 hyperintense (arrow on a) relative to skeletal muscle, with avid heterogeneous enhancement (arrow on c). (d) Photograph of the cut surface of the resected specimen shows a multinodular pale yellow–tan mass invading the iliac wing (arrow). rare in adults. It should be noted that many other Pleomorphic rhabdomyosarcoma is the vari- tumors, such as dedifferentiated liposarcoma, ant that is seen almost exclusively in adults. MPNST, and uterine carcinosarcoma, can contain It occurs in older adults, with a mean age at rhabdomyosarcomatous elements and are more diagnosis of 51 years (10). By definition, tumor common than true rhabdomyosarcomas in adults. cells should express desmin, as well as myogenic transcription factors MyoD1 or myogenin, or Clinical and Pathologic Features both (10). Spindle cell/sclerosing rhabdomyosar- The WHO recognizes four distinct subtypes of coma is also uncommon. In adults, it arises in rhabdomyosarcoma: embryonal, alveolar, pleomor- the deep soft tissues of the neck, paratesticular phic, and spindle cell/sclerosing (15). Almost all region, retroperitoneum, and external genitalia embryonal rhabdomyosarcomas and the majority of (35). Microscopically, spindle cell/sclerosing alveolar rhabdomyosarcomas are seen in pediatric rhabdomyosarcomas are composed of elongated and young adult populations and are beyond the spindle-shaped cells in a dense collagenous scope of this review. If found in the abdomen and stroma. The immunohistochemical profile of pelvis of an adult, embryonal and alveolar rhab- spindle cell/sclerosing rhabdomyosarcomas domyosarcomas arise in the paratesticular soft should support skeletal muscle differentiation, tissues, perineum, and retroperitoneum (34). to distinguish them from other sarcomas (36). RG Volume 37 Number 3 Levy et al 805 Radiologic Features grade, with pleomorphism and variable amounts Cross-sectional imaging data with regard to of osteoid, bone, and cartilage. The imaging diag- adult abdominal and pelvic rhabdomyosarcomas nosis is based on observing a chondroid or osseous are limited, reflecting the rarity of these tumors. matrix within a retroperitoneal soft-tissue mass at Regardless of the histopathologic subtype, rhab- CT (Figs 6, 7). Osteosarcomatous differentiation domyosarcomas of the perineal regions (vulva can also be seen in dedifferentiated liposarcoma in women and paratesticular soft tissues of men) and MPNST (41,42). are reported to be infiltrating masses with poorly defined borders (34,37,38). In the retroperito- Sarcomas of neum, these lesions are large masses at the time of Uncertain Differentiation clinical presentation, similar to other retroperito- The sarcomas of uncertain differentiation are neal sarcomas. On CT images, rhabdomyosarco- grouped together because they have unknown mas are predominantly isoattenuating to skeletal lineage. The WHO classification includes muscle. They may have areas of degeneration and synovial sarcoma (Fig 8), epithelioid sarcoma, intratumoral hemorrhage that create regions of hy- alveolar soft part sarcoma (Fig 9), clear cell poattenuation within the tumor. At MR imaging, sarcoma of soft tissue, extraskeletal myxoid the lesions are isointense to skeletal muscle on T1- chondrosarcoma, extraskeletal Ewing sarcoma, weighted MR images and demonstrate high signal desmoplastic small round cell tumor, extrarenal intensity on T2-weighted MR images (34). Calcifi- rhabdoid tumor, and malignant perivascular epi- cation is not a feature of rhabdomyosarcoma. thelioid cell tumor (also called “PEComa”) (Fig 10) (15). Each of these sarcomas has distinctive Recurrent and Metastatic Disease clinical and pathologic features and genetic al- Lymphadenopathy is an important feature of terations. These sarcomas represent less than 1% metastatic disease in rhabdomyosarcoma. In of all soft-tissue sarcomas. The imaging features those patients with abdominal and pelvic lesions, of these malignancies are nonspecific, and they the retroperitoneum is a common site for nodal may occur in the retroperitoneum and abdomi- disease, which may be present at the initial clini- nal wall and, very rarely, in the peritoneal cavity. cal presentation or may be discovered as a site of recurrence (34,37). The lung is the most com- Differential Diagnosis mon site for distant metastatic disease. In part 1 of this article, we discussed the dif- ferential diagnosis of soft-tissue masses of the Vascular Sarcomas abdomen and pelvis that contain fat, cystic com- Vascular sarcomas are only briefly mentioned ponents, myxoid material, and calcification (3). because of their exceedingly rare occurrence in These differential considerations are most helpful the soft tissues of the abdomen and pelvis. This with the most commonly occurring soft-tissue group of tumors includes epithelioid hemangioen- sarcomas. The uncommon soft-tissue sarcomas dothelioma, angiosarcoma, and Kaposi sarcoma. discussed in this article have less-specific features Epithelioid hemangioendothelioma is a low-grade and thus require a broader differential diagnosis malignancy that is usually seen in the extremi- and, in almost all cases, biopsy to establish the ties but can occur in any anatomic location. In diagnosis. the abdomen, the lesion is most often seen in the In general, in a patient with no known primary liver. Angiosarcomas of the soft tissues are more malignancy, a soft-tissue mass in the retroperito- common in the extremities. In the abdomen and neum that is not associated with a retroperitoneal pelvis, angiosarcomas of the soft tissues may rarely organ (adrenal gland, kidney, pancreas, or the arise in the soft tissues of the deep retroperito- retroperitoneal portions of the gastrointestinal neum, and some cases may involve the peritoneum tract) should be considered a sarcoma until diffusely, simulating mesothelioma (39). Visceral proven otherwise. If a patient has a known pri- angiosarcomas occur in the liver and spleen. mary malignancy, metastatic disease may be seen as single or multiple soft-tissue nodules or masses Chondro-osseous Sarcomas in the retroperitoneum or involving retroperito- Extraskeletal osteosarcoma is a soft-tissue sarcoma neal organs and the psoas muscle. Lymphoma composed of malignant cells that produce osteoid may manifest as a primary retroperitoneal mass. matrix. Extraskeletal osteosarcoma occurs predomi- Unlike many of the sarcomas, most lymphomas nantly in older patients and may be associated with demonstrate homogeneous CT attenuation and irradiation in at least 10% of cases (40). Extraskel- homogeneous MR signal intensity, because they etal osteosarcoma may be seen in the retroperito- lack degeneration and/or necrosis. The exception neum but is more common in the thigh and but- is high-grade lymphomas. Splenomegaly and re- tocks. Histologically, the tumors are usually high gional or distant adenopathy may also be present 806 May-June 2017 radiographics.rsna.org Figure 6. Soft-tissue osteosarcoma in a 59-year-old man with right flank pain. (a) Axial CT image (bone window) shows dense calcification (straight arrow) and an osteoid matrix (curved arrow) in a lobulated right pelvic mass. (b) Axial T2-weighted fat-sup- pressed MR image shows central areas of markedly T2-hyperin- tense necrosis (*). (c) Axial contrast-enhanced T1-weighted fat- suppressed MR image shows enhancement of the periphery (ar- row) of the mass. to support a diagnosis of lymphoma. Inflamma- adenocarcinomas of the colon, stomach, and small tory processes such as abscesses or phlegmons intestine, are mucosal in origin and will produce can simulate tumors. Clinical findings of infec- a luminal mass or mucosal irregularity. Gastro- tion are generally present to help distinguish intestinal adenocarcinomas tend to be infiltrative these inflammatory processes from malignancies. lesions that concentrically thicken the wall of the Retroperitoneal hemorrhage can also be mass- gastrointestinal tract and produce a serosal margin like. However, early hemorrhage will demonstrate that is poorly defined and spiculated. These pat- high attenuation typical of blood on CT images terns are not seen in GISTs or other soft-tissue obtained without administration of intravenous sarcomas. Furthermore, regional adenopathy is a contrast material. Also, retroperitoneal hemor- common feature in adenocarcinomas, whereas it rhage tends to spread along the fascial planes of is uncommon in sarcomas. Similar to gastrointes- the retroperitoneal compartments, rather than tinal adenocarcinomas, malignant neuroendocrine being round or oval in configuration. tumors and carcinoids of the gastrointestinal tract Intraperitoneal soft-tissue masses have a similar will have an abnormality in the involved segment differential diagnosis to that of retroperitoneal of bowel, either a focal mass or wall thickening. soft-tissue masses except that it may be more dif- Other intraperitoneal lesions that are consider- ficult to determine if the mass is arising from the ations in the differential diagnosis include meta- soft tissues or the gastrointestinal tract. GIST is static disease, lymphoma, desmoid tumor (also the most common intraperitoneal sarcoma, and called mesenteric fibromatosis), and sclerosing its diagnosis can be suggested when a well-defined mesenteritis. Rarely, benign soft-tissue and neural mass is arising from the bowel wall. GIST may tumors may be indistinguishable from sarcomas. also have an intraluminal component. Epithelial Special differential diagnostic considerations malignancies of the gastrointestinal tract, namely, are given to those lesions arising in the abdomi- RG Volume 37 Number 3 Levy et al 807 Figure 7. Chondrosarcoma in a 21-year-old woman with right lower quadrant pain. (a, b) Axial CT images ob- tained with soft-tissue window (a) and bone window (b) show a sharply marginated soft-tissue–attenuation mass closely approximating the right iliac wing (arrow on a), with chondroid-type calcifications in rings and arcs (arrows on b). (c, d) Axial T1-weighted (c) and T2-weighted (d) MR images better show the well-defined margins with scal- loping of the iliac wing, but without medullary infiltration (straight arrow). Note the hypointense foci of chondroid calcifications (curved arrow). nal wall. The differential diagnosis for skin le- benign lesions that do not metastasize but may sions such as dermatofibrosarcoma protuberans recur locally. On CT images, desmoid tumors are includes cutaneous and subcutaneous metastasis, classically well-defined homogeneous lesions that nerve sheath tumors, sebaceous cysts, heman- are isoattenuating to skeletal muscle, with little or giomas, and other primary skin or skin append- minimal enhancement after intravenous contrast age tumors of the trunk wall. In many cases, the material administration. On MR images, the signal clinical context and the appearance of the lesion intensity is often more heterogeneous, depending at clinical examination are diagnostic. on the amount of collagenous or myxoid stroma The differential diagnosis for deep lesions of the within the lesion (Fig 11). Those desmoid tumors abdominal wall includes desmoid tumor, endo- with abundant myxoid stroma demonstrate high metriosis, and metastatic disease. Other masses signal intensity on T2-weighted MR images (43). in the abdominal wall such as lipoma, hematoma, Most desmoid tumors characteristically show abscess, and hernia do not cause diagnostic dilem- avid enhancement on arterial phase MR im- mas because they are generally easily diagnosed ages obtained after administration of intravenous clinically and confirmed by the imaging find- gadolinium-based contrast material. Endome- ings. Desmoid tumors (also called fibromatosis) triosis in the abdominal wall is almost exclusively of the abdominal wall may be more difficult to associated with prior pelvic surgery and occurs in differentiate from sarcomas. Desmoid tumors are locations where surgical incisions were made, such 808 May-June 2017 radiographics.rsna.org Figure 8. Synovial sarcoma in two different patients. (a) Sy- novial sarcoma in a 59-year-old woman who presented with rapid enlargement of a palpable painless mass: Axial contrast- enhanced CT image shows a well-circumscribed heteroge- neously enhancing mass within the right anterior abdominal wall (arrows), with cystic components (*). (b, c) Synovial sar- coma in a previously healthy 36-year-old man with new onset of intractable vomiting: Axial contrast-enhanced CT images (c obtained at a lower level than b) show a large heterogeneous mass (straight arrow) infiltrating along the gastrohepatic liga- ment and circumferentially invading the gastric antrum and lesser curvature (curved arrows on b), with mass effect on the liver, gallbladder, duodenum, and pancreas. Areas of nonen- hancing hyperattenuation are consistent with intratumoral (*) and intraperitoneal (arrowheads on c) hemorrhage. Figure 9. Alveolar soft part sarcoma in a 45-year-old woman with back pain. Axial (a) and sagittal (b) contrast- enhanced CT images show a well-circumscribed enhancing soft-tissue mass (arrow) that is inseparable from the posterior abdominal wall, with mass effect on the posterior right kidney. RG Volume 37 Number 3 Levy et al 809 Figure 10. Malignant perivascular epithelioid cell tumor in a 56-year-old man with crampy left lower quadrant pain. (a, b) Axial (a) and sagittal (b) contrast-enhanced CT images show a heterogeneously enhancing soft-tis- sue mass inseparable from the anterior abdominal wall musculature (straight arrow), with central low-attenuation areas of necrosis (* on a) and punctate calcifications (curved arrow). (c, d) Axial T2-weighted fat-suppressed (c) and contrast-enhanced T1-weighted (d) MR images show heterogeneous T2 hyperintensity and avid enhance- ment within the cellular portions (straight arrow), with more focal hyperintensity and lack of enhancement of the necrotic portions (*). Abdominal wall invasion (curved arrows) is more apparent on the MR images. (e) Photograph of the cut surface of the resected specimen shows corresponding areas of necrosis and hemor- rhage (*) within the predominantly solid lobulated mass. Mass is inseparable from the abdominal wall (arrow). 810 May-June 2017 radiographics.rsna.org Figure 11. Desmoid tumor incidentally identified in the anterior abdominal wall of a 43-year-old man. (a) Axial contrast-enhanced CT image shows heterogeneous expansion of the left rectus muscle, with a suspected mass in the medial aspect of the muscle (arrows). (b, c) Axial T2-weighted fat-suppressed (b) and contrast-enhanced T1-weighted (c) MR images obtained to better characterize the lesion show a heteroge- neous predominantly hyperintense solid mass (arrows on b) with heterogeneous enhancement (arrows on c). as cesarean section scars or laparoscopic port sites. commonly, undifferentiated pleomorphic sar- On CT images, abdominal wall endometriosis is coma, solitary fibrous tumor, and MPNST may a solid enhancing mass. At MR imaging, abdomi- be found in the retroperitoneum and pelvis. nal wall endometriosis is heterogeneous in signal intensity on T1- and T2-weighted MR images and References may enhance after administration of intravenous 1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin 2016;66(1):7–30. gadolinium-based contrast material (Fig 12) (44). 2. Cormier JN, Pollock RE. Soft tissue sarcomas. CA Cancer Abdominal wall endometriosis may contain cystic J Clin 2004;54(2):94–109. areas, areas of T1 hyperintensity caused by blood 3. Levy AD, Manning MA, Al-Refaie WB, Miettinen MM. Soft-tissue sarcomas of the abdomen and pelvis: radiologic- products, or areas of T1 and T2 hypointensity pathologic features, part 1—common sarcomas. RadioGraph- caused by hemosiderin. ics 2017;37(2):462–483. 4. Goldblum JR, Folpe AL, Weiss SW. Undifferentiated Conclusion pleomorphic sarcoma. In: Goldblum JR, Folpe AL, Weiss SW, eds. Enzinger and Weiss’s soft tissue tumors. 6th ed. 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Endometriosis in the abdominal wall of a 43-year-old woman with worsening pain in the right lower quad- rant that had begun 4 months after laparoscopic hysterectomy for menorrhagia. (a) Axial contrast-enhanced CT image shows a heterogeneously enhancing mass (arrow) in the right lateral abdominal wall musculature, adjacent to the anterior iliac wing. (b, c) T1-weighted (b) and T2-weighted (c) MR images show heterogeneous signal intensity within the multiloculated mass, with increased T1 and T2 signal intensity in a lateral loculated component (arrow). (d, e) T1- weighted fat-suppressed MR images obtained before (d) and after (e) the administration of gadolinium-based contrast material better show the intrinsic T1 hyperintensity (arrow on d) and heterogeneous enhancement (arrow on e). 812 May-June 2017 radiographics.rsna.org 8. Atmatzidis KS, Pavlidis TE, Galanis IN, Papaziogas BT, 26. Shanbhogue AK, Prasad SR, Takahashi N, Vikram R, Zaheer Papaziogas TB. 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