Malignant mesenchymal renal tumor: a rare case of primary renal fibrosarcoma.

Malignant mesenchymal neoplasms of kidney constitute a rare group of tumors. Primary fibrosarcoma of kidney is an extremely rare subtype of primary malignant mesenchymal renal neoplasms. An elderly female presented with a gradually increasing abdominal lump and mild abdominal discomfort. On cross-sectional imaging, the lesion showed features suggestive of an atypical renal mass not conforming to either ball or bean type growth pattern. The mass was surgically removed and on histopathological and immunohistological investigations diagnosed to be primary renal fibrosarcoma.