INFLAMMATORY PSEUDOTUMOR OF THE URINARY-BLADDER WITH AN ABERRANT EXPRESSION OF CYTOKERATIN

A case of inflammatory pseudotumor of the urinary bladder in a 47 year old Japanese male patient is presented. Inflammatory pseudotumor of t he urinary bladder is a benign but rare proliferative lesion of the su bmucosal stroma, easily mistaken for a malignant neoplasm. Based on th e clinical diagnosis of bladder cancer by cystoscopy and magnetic reso nance imaging (MRI), urologists started chemotherapy before results of the histological report were available which described inflammatory p seudotumor on the biopsy. Biopsied materials showed marked proliferati on of irregularly bundled spindle cells, varied in size and shape and separated in severe loose myxoid stroma with moderate infiltration of the inflammatory cells and capillary proliferations. At a glance, thes e findings resemble the sarcomatous pattern. However neither severe nu clear atypism nor atypical mitoses were present. Immunohistochemically , these spindle cells, which were positive for vimentin and alpha-smoo th muscle actin, showed a diffuse aberrant expression of cytokeratin. Some of them were positive for phosphotungstic acid hematoxylin. Elect ron microscopy revealed only the fibroblasts. No recurrence has been o bserved for 10 months. These findings indicate that inflammatory pseud otumor is a benign mesenchymal lesion that must be discriminated from true sarcoma to avoid subjecting the patient to unnecessary therapy. O nly careful histological examination can enable a successful diagnosis .