Clinical and magnetic resonance imaging features of soft tissue extraskeletal myxoid chondrosarcoma: A retrospective observational cohort study.

Objectives: To review the MRI, histological, and clinical features of extraskeletal myxoid chondrosarcoma (EMC).

Methods: Retrospective review of pre-treatment MRIs in 44 patients with pathologically proven EMC. Patient demographics, tumor MR-imaging features, histology and gene rearrangements, clinical management, and follow-up were reviewed. MRI features assessed included lesion size, location, morphology, signal characteristics, and relation to adjacent structures. Correlative analysis was performed to assess associations between demographic, clinical, molecular, and MRI variables with metastatic disease.

Results: EMCs were predominantly located in the lower extremity (38/44, 86%) and deep-to-fascia (36/44, 82%). All lesions (44/44) demonstrated well-circumscribed margins. Mean maximal dimension was 8.8 cm (range 1.7-36 cm); 93% (41/44) of lesions were hyperintense on fat-suppressed T2-weighted/ STIR imaging. Post-contrast enhancement was "solid" (> 80% enhancement) in 18%, "mixed" (20-80% enhancement) in 53%, and "sparse" (< 20% enhancement) in 29%. Nodal metastases were detected on preoperative imaging in four patients (9%), and pulmonary metastases in three cases preoperatively, and five cases postoperatively (range 14-128 months). EWSR1::NR4A3 fusion rearrangements were documented in 25 tumors (57%), and non-EWSR1 NR4A3 fusions in six cases (14%). The only variable demonstrating a significant correlation with metastatic disease was "solid" pattern of lesional enhancement (p = 0.035).

Conclusions: EMC is most commonly a deep lesion of the extremities demonstrating hyperintense T2-weighted signal, internal septations, and variable patterns of enhancement on MRI. Nodal disease is relatively frequent, and prolonged surveillance is recommended as metastases may develop years after diagnosis. Although analysis is limited by small case numbers, a "solid" (> 80%) pattern of enhancement was significantly associated with metastatic disease.