Imaging features of low-grade fibromyxoid sarcoma (Evans tumor)

To determine common imaging features of low-grade fibromyxoid sarcoma (LGFMS), a rare subtype of fibrosarcoma with a benign histological appearance but with a propensity for local recurrence and metastasis.

By review of medical records, 29 patients (14 males, 15 females) with mean age of 41 years (range, 11-64 years) with diagnosis of LGFMS and imaging available in PACS were identified. The study included radiography (9/29), ultrasound (1/29), CT (14/29), and MRI (22/29). Imaging features evaluated included anatomic site, and lesion size, number, location, US echogenicity, CT attenuation, calcifications, MR signal intensity pattern, and contrast enhancement.

Twenty-two patients had imaging at initial diagnosis, and seven had imaging only at local recurrence. The majority of tumors (27/29) were deep in tissue, with mean size of 6.2 cm (range, 1.4-19.0 cm). Tumor was single at initial diagnosis and multiple at local recurrence; lower extremity was the most common site. On radiographs, tumor was visible in four of nine without bone erosion or calcification. Areas of CT attenuation hypodense to muscle were seen in 13/14 patients. Calcification was uncommon (3/14). On fluid-sensitive MRI sequences, the predominant signal intensity was hyperintense to muscle in 11/21 patients. In 13/21 patients, tumor displayed either a brain gyriform pattern of alternating hypointense and hyperintense signal intensity (9/13) or intralesional nodules (3/13); 1 case had both patterns. On US tumor was solid with heterogeneous echogenicity.

LGFMS is commonly single at initial diagnosis and multiple at local recurrence. LGFMS frequently shows areas of CT attenuation hypodense to muscle and gyriform patterns of signal intensity and contrast enhancement at MRI.