The Ewing sarcoma family of tumors includes osseous Ewing sarcoma, extraskeletal Ewing sarcoma, primitive neuroectodermal tumor, and Askin tumor. They share a karyotype abnormality with translocation involving chromosomes 11 and 22. Histologically, these lesions demonstrate crowded sheets of small round blue cells. Imaging features of osseous Ewing sarcoma often suggest the diagnosis, with aggressive long-bone destruction in the metadiaphysis of an adolescent or young adult and an associated soft-tissue mass. Focal areas of cortical destruction are frequent, allowing continuity between the intraosseous and extraosseous components. This continuity is also commonly seen as subtle channels extending through the cortex at computed tomography or magnetic resonance (MR) imaging, a finding that reflects the underlying pathologic appearance. Extraskeletal Ewing sarcoma commonly demonstrates a nonspecific radiologic appearance of a large soft-tissue mass affecting the paraspinal region or lower extremity. Askin tumor represents extraskeletal Ewing sarcoma involving the chest wall. Imaging typically reveals a large pleural-based mass and associated pleural effusion. Treatment of these tumors is usually a combination of neoadjuvant chemotherapy followed by surgical resection, which may be supplemented with radiation therapy. Imaging, particularly MR, is also vital to evaluate response to neoadjuvant therapy, direct surgical resection, and detect local recurrence or metastatic disease.

The fibromatoses are a group of benign fibroblastic proliferations that vary from benign to intermediate in biological behavior. This article will discuss imaging characteristics and patient demographics of the adult type superficial (fascial) and deep (musculoaponeurotic) fibromatoses. The imaging appearance of these lesions can be characteristic (particularly when using magnetic resonance imaging). Palmar fibromatosis demonstrates multiple nodular or band-like soft tissue masses arising from the proximal palmar aponeurosis and extending along the subcutaneous tissues of the finger in parallel to the flexor tendons. T1 and T2-weighted signal intensity can vary from low (higher collagen) to intermediate (higher cellularity), similar to the other fibromatoses. Plantar fibromatosis manifests as superficial lesions along the deep plantar aponeurosis, which typically blend with the adjacent plantar musculature. Linear tails of extension (“fascial tail sign”) along the aponeurosis are frequent. Extraabdominal and abdominal wall fibromatosis often appear as a heterogeneous lesion with low signal intensity bands on all pulse sequences and linear fascial extensions (“fascial tail” sign) with MR imaging. Mesenteric fibromatosis usually demonstrates a soft tissue density on CT with radiating strands projecting into the adjacent mesenteric fat. When imaging is combined with patient demographics, a diagnosis can frequently be obtained.

Myxoid soft-tissue lesions are a heterogeneous group of benign and malignant mesenchymal tumors with an abundance of extracellular mucoid material. These lesions may mimic cysts on radiologic evaluation because of the high water content, and histopathologic features also overlap. Benign myxoid lesions include intramuscular myxoma, synovial cyst, bursa, ganglion, and benign peripheral nerve sheath tumor, including neurofibroma and schwannoma. Malignant entities include myxoid liposarcoma, myxoid leiomyosarcoma, myxoid chondrosarcoma, ossifying fibromyxoid tumor, and myxofibrosarcoma. Some syndromes are associated with myxoid soft-tissue lesions, such as Mazabraud syndrome in patients with soft-tissue myxomas and fibrous dysplasia. Certain discriminating features, such as intralesional fat in a myxoid liposarcoma, perilesional edema and a rim of fat in soft-tissue myxoma, and the swirled T2-weighted signal intensity and enhancement pattern of aggressive angiomyxoma, assist the radiologist in differentiating these lesions. The presence of an internal chondroid matrix or incomplete peripheral ossification may suggest myxoid chondrosarcoma or ossifying fibromyxoid tumor, respectively. The entering-and-exiting-nerve sign is suggestive of a peripheral nerve sheath tumor. Communication with a joint or tendon sheath and peripheral enhancement may indicate a ganglion or synovial cyst. This article (a) reviews the magnetic resonance, computed tomographic, and ultrasonographic imaging characteristics of soft-tissue myxomatous lesions, emphasizing imaging findings that can help differentiate benign and malignant lesions; (b) presents differential diagnoses; and (c) provides pathologic correlation.

Chondrosarcoma is the third most common primary malignant bone tumor. Currently, outcomes are based largely on a histologic grading scale described by the World Health Organization (WHO) Classification of Bone Tumors (2002). This classification scheme possesses evident utility in the evaluation and management of higher grade tumors, but it is often unable to distinguish enchondromas from low-grade chondrosarcomas. This is problematic when low-grade lesions that are histologically similar to enchondromas demonstrate aggressive imaging features. Because histologic classification alone often belies the clinical significance of chondroid lesions, it is also important to consider radiologic staging as part of the clinical decision making process. This article focuses on medical decision support considerations relevant when confronted with this challenging subset of chondroid tumors, particularly differentiating the benign enchondroma from its notorious relative, the low-grade chondrosarcoma. In doing so, we present a review of the salient imaging features and discuss key differentiating characteristics.