Primary renal inflammatory malignant fibrous histiocytoma: a diagnostic challenge.

Renal inflammatory malignant fibrous histiocytoma (MFH) is an extremely rare lesion and is a great masquerader of common benign renal inflammatory lesions, especially xanthogranulomatous pyelonephritis (XGPN). The clinical presentation of mass with fever and peripheral leucocytosis (marked at times), and marked inflammatory, predominantly neutrophilic, infiltrate obscuring the malignant cells on histopathology, can lead to delay in the diagnosis of this poor prognostic malignant tumor. We present the case of a patient who underwent radical nephrectomy with a clinical diagnosis of renal malignancy, but histopathology showing XGPN. The patient showed an initial clinical response, only to recur two times, ultimately leading to a histological and immunohistochemical diagnosis of inflammatory MFH. The diagnosis, histology, therapeutic options and prognosis of this rare lesion are discussed.