Primary Osseous Low-grade Myxofibrosarcoma of Metatarsal Masquerading as Enchondroma: A Case Report

INTRODUCTION: Low-grade myxofibrosarcoma (LGMFS) is a neoplasm of soft tissues. According to the World Health Organization, LGMFS is a malignant myofibroblastic tumor arising from deep soft tissues with potential for recurrence and late metastatic spread. The incidence estimates are 0.18/million, accounting for 0.6% of all soft-tissue sarcomas. It can directly invade the bone and metastasize to bone; however, primary osseous low-grade myxofibrosarcoma is a rare entity. Thus, recognizing atypical presentations of uncommon neoplasms are a pertinent skill for the radiologist due to significant implications for management. CASE REPORT: A 40-year-old male with complaints of midfoot pain was referred to radiology department for imaging. Radiographs of the foot showed a lytic mildly expansile lesion in the first metacarpal with wide zone of transition and no sclerotic margin or matrix calcification. Magnetic resource imaging (MRI) and computed tomography (CT) examination demonstrated well defined lobulated lesion which appeared heterogeneously hyperintense on T2W images with cortical breach, extraosseous soft-tissue component, and early rapid progressive enhancement. The radiological diagnosis of enchondroma with pathological fracture was considered. Atypical findings of early progressive enhancement and extraosseous soft-tissue component were, however, incongruous with enchondroma and possibility of an aggressive/malignant etiology was also considered. Hence, the lesion was biopsied and diagnosis of LGMFS was made and subsequently confirmed on excised specimen. Follow-up CT scan post 6 months of surgical resection demonstrated no recurrence. CONCLUSION: Primary osseous LGMFS is a rare entity and radiologically mimics enchondromas. Both LGMFS and enchondromas show T2W hyperintensity. MRI features that distinguish LGMFS from enchondroma include low apparent diffusion coefficient values and slow progressive enhancement in dynamic contrast-enhanced MRI.