Inflammatory malignant fibrous histiocytoma of kidney: a case report

Among the renal sarcomas, inflammatory malignant fibrous histiocytoma (MFH) is an extremely rare presentation. A 45-year-old woman presented with acute retention urine following an episode of gross hematuria. Computerized tomography showed a solid mass at the lower pole of the left kidney. The patient underwent left nephrectomy. Histologically and immunohistochemically, the tumor was diagnosed as an inflammatory subtype of MFH. Histological appearances of inflammatory MFH vary widely and frequently overlap with benign reactive conditions such as Xanthogranulomatous pyelonephritis (XGPN) and malignant lesions, e.g. malignant lymphoma and, less frequently, a sarcomatoid variant of renal cell carcinoma. It is important, though difficult, to differentiate inflammatory MFH from these lesions. Careful morphological examination and immunohistochemical findings of the lesion are of great value, in particular in excluding it from its mimics. We discuss the pathological features and challenges involved in differentiating inflammatory MFH from its masquerader.