MR imaging findings of superficial acral fibromyxoma: a report of two cases with histopathological correlation.

Superficial acral fibromyxoma (SAFM) is a rare benign, slow-growing soft-tissue neoplasm with a predilection for the periungual or subungual regions of the fingers and toes. Although the histopathological and clinical features of SAFM have been extensively described, reports detailing its MRI characteristics remain limited. We present two cases of SAFM with differing MRI features and comparative histopathology. Case 1 was a 38-year-old man with a 2-year history of a painful slow-growing tumor arising on his left second finger. The tumor was hypointense on T1-weighted images (T1WI) and heterogeneously hypointense on T2-weighted images (T2WI), with faint, gradual peripheral enhancement on dynamic contrast-enhanced (DCE) MRI. The neoplasm consisted of fibroblast-type fusiform cells in a matrix of myxoid material and collagen. Case 2 was a 47-year-old man with a 10-year history of a slow-growing tumor on his right second toe. A radiograph revealed a non-calcified soft-tissue tumor with cortical erosion of the underlying distal phalanx. The tumor was hypointense on T1WI and a heterogeneous mixture of slight hyperintensity and hypointensity on T2WI, with heterogeneous enhancement on contrast-enhanced T1WI. The tumor consisted of spindle and stellate cells in an abundant myxoid matrix. Although rare, radiologists should be aware that the MRI features of SAFM are non-specific as they depend on the variable proportions of fibrous and myxoid stroma and consider them in the differential diagnosis of any slow-growing firm tumor located in the periungual or subungual regions of the fingers and toes in adult patients.