![]() Spindle cell lipomas are lipomas made up of lipocytes and spindle cells. 33 Because SS can occur intra-articularly and because SS may have fluid-fluid levels, they may be confused with synovial hemangiomas. 32 Synovial hemangiomas present with the above features, and may also present with low intensity linear structures, likely due to fibrous septa or vascular channels (Figure 3), as well as fluid-fluid levels. ![]() 30,31 They exhibit variable enhancement on T1-weighted images with contrast, depending on flow dynamics and timing of injected contrast bolus. 28 On MRI, hemangiomas demonstrate low to intermediate signal intensity on the T1-weighted images however, they appear hyperintense on T2-weighted images. 29 The majority of hemangiomas occur superficially, and in the head and neck region. 28 Hemangiomas affect females three times more often than males. 27 They are one of the most common soft-tissue tumors in children. Hemangiomas are an abnormal proliferation of blood vessels and are perhaps better termed venous malformations. 24,25 While most neurofibromas show avid enhancement on T1 postcontrast imaging, the enhancement pattern can be variable. 22,23 MR imaging features that help identify neurofibromas include (1) arising along a major nerve, (2) visualization of the nerve entering and exiting the tumor, (3) the target sign (round hypointense lesion with hyperintense rim) on T2-weighted imaging (Figure 2), (4) the fascicular sign (multiple small hypointense foci scattered within a hyperintense region on T2-weighted or proton-density weighted MR images), and (5) the split-fat sign-a rim of fat surrounding the lesion (best appreciated on T1-weighted images). Neurofibromas usually occur superficially anywhere on the body. Neurofibromas are benign nerve sheath tumors 21 and may be associated with type 1 neurofibrosis (NF1). 15 MRI: Benign mimickers of synovial sarcomas Neurofibromas The biopsied tissue is often tested for the t(X 18)(p11 q11) translocation using fluorescence in situ hybridization (FISH), for which about 90% of SS are positive. 14 Definitive SS diagnosis is based on biopsy. 14 Confirmation of the presence of a mass by radiography and MRI is usually performed prior to biopsy. Synovial sarcomas are usually first detected as painless growing masses. 13 The poor survival rate of SS is likely related to local recurrence and lung metastases. 13 Five-year and 10-year survival rates of SS are estimated to be about 70%, and 60% respectively. 12įactors that result in a worse prognosis include large tumor size, metastases at diagnosis, trunk disease, and positive margins after surgical resection. 12 Finally, the undifferentiated type is made up of cells resembling those of small round blue cell tumors. 12 The biphasic type consists of spindle cells and epithelial cells. 12 The monophasic type is most common and made up of only of spindle cells. 11 There are three common histologic types. 10 Synovial sarcomas are high-grade (II/III). 6 Ninety percent of SS occur in the lower extremities often near joints, and in the trunk wall, but the disease can be found anywhere in the body 9 with rare reports of intra-articular SS. 5 Males and females seem to be equally affected. In one study, 84% of synovial sarcoma patients were between 10 and 50 years old. The aim of this article is to describe the key magnetic resonance imaging (MRI) features of SS, as well as to describe those of benign and malignant tumors that are often confused with SS (Table 1). Conversely, mistaking a benign lesion for an SS may result in increased patient anxiety and costs due to unnecessary procedures and imaging tests. Incorrectly assuming that an SS is a benign lesion will lead to delays in diagnosis and possibly prognosis. For these tumors to be biopsied, it is essential that interpreting radiologists or orthopedic oncologists not deem them benign. Since synovial sarcomas are so rare, many clinicians and radiologists are not familiar with their presentation and imaging appearance. 4 However, they are the second-most prevalent soft-tissue tumors after rhabdomyosar coma in children, adolescents, and young adults. 1-3 Synovial sarcomas are rare, with an estimated incidence of 2.75 in 100,000 people. Synovial sarcomas (SS) are malignant soft tissue tumors thought to account for 5-10% of soft tissue sarcomas.
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