Aggressive angiomyxoma of the thigh.

Aggressive angiomyxoma is a rare tumour that typically occurs in the perineum in women of reproductive age. A small number of cases occurring in men have been reported, all of which were located in the low pelvis, perineum or scrotum. While benign, the tumour is locally infiltrative and consequently has a high rate of local recurrence following surgery; therefore, accurate pre-operative diagnosis is important. The characteristic location of these tumours in the low pelvis or perineum has led to speculation that aggressive angiomyxomas arise from a mesenchymal cell that is unique to the perineum. We describe a case of aggressive angiomyxoma arising in the thigh of a 54-year-old man, which we believe is the first reported instance of this rare neoplasm occurring remote from the pelvis or perineum in a male patient. Cross-sectional imaging demonstrated a well-defined mass that had low density on CT and high intensity on fluid-sensitive MR sequences. Biopsy was non-diagnostic and excision was performed. At histological analysis, the tumour exhibited the characteristic features of aggressive angiomyxoma, with bland spindle cells and large, hyalinised blood vessels in a hypocellular myxoid matrix. Extensive immunohistochemical staining further supported the diagnosis. While the imaging features of these tumours are non-specific and suggestive of myxoid neoplasms, the diagnosis should be considered whenever biopsy of a myxoid-appearing mass yields hypocellular, non-diagnostic material, despite adequate sampling.