Atypical spindle cell lipomatous tumor of the perineum

A 61-year-old male with no significant personal or family medical history presented to the urology department with a perineal mass that had been present for 1-2 years but had shown rapid growth over the last 2-3 months, with no associated symptoms. Laboratory tests were mostly unremarkable, except for slightly elevated blood glucose (109 mg/dL). Perineal ultrasound revealed a large, well-defined, solid, heterogeneous, isoechoic lesion with internal vascularity on color Doppler. Magnetic resonance imaging with intravenous contrast demonstrated a voluminous mass located beneath the right corpus cavernosum. The lesion showed heterogeneous signal intensity, with a characteristic swirling appearance, predominantly hyperintense on T2-weighted sequences, suggesting the possibility of a spindle cell tumor such as an aggressive angiomyxoma. Surgical resection with curative intent was performed. Histopathological examination revealed a spindle cell neoplasm with patchy positivity for CD34, SOX10, and desmin, and no immunoreactivity for estrogen or progesterone receptors, MUC4, or STAT6. Fluorescence in situ hybridization analysis for MDM2 gene amplification was negative, supporting the diagnosis of atypical spindle cell lipomatous tumor (ASCLT). ASCLT is a rare, benign adipocytic neoplasm typically affecting middle-aged adults, with a slight male predilection. It most occurs in the extremities (eg, hands, feet, and thighs) and usually presents as a slow-growing, painless mass. Perineal involvement has not been previously reported. Complete surgical resection with clear margins is essential to prevent local recurrence.