Inflammatory Pseudotumor Containing Necrotizing Granulomatous Lesions of Kidney: A Hitherto Undescribed Entity

Herein reported is a case of inflammatory pseudotumor (IPT) of kidney. It is not described in WHO, AFIP, and other books. A review of the literature revealed about 35 cases. A 76-year-old man underwent nephrectomy under clinical diagnosis of renal pelvic carcinoma. Grossly, a solid tumor was seen in renal parenchyma. Microscopically, it was composed of spindle cell tissue with inflammation and many necrotizing granulomas. Epithelioid histiocytes were abundant but giant cells were few. Lymphocytes and plasma cells were also seen. The features suggested tuberculosis (TB), but Ziehl-Neelsen stains and PCR revealed no TB bacillus. Immunohistochemistry showed that the tumor spindle cells were positive for vimentin, CD68, CD45, and Ki-67 (labeling = 18%), α-smooth muscle antigen, and NSE. Focal staining of KIT (mast cells), S100 protein (Langerhans cells), and CD10 (spindle cells) was present. IgG4 was negative. The tumor spindle cells were negative for other antigens examined.