A case report of inflammatory pseudosarcoma of the urinary bladder.

A case of inflammatory pseudosarcoma of the urinary bladder in a 35-year-old Japanese male is presented. This benign lesion can easily be mistaken for spindle cell sarcoma since it consists of rhabdomyoblast-like elongated strap cells showing infiltrative growth, and whether it is benign or malignant is difficult to determine by microscopic examination. In this case, spindle cell proliferation extended among bundles of the superficial muscle layer. However, no abnormal mitoses, severe nuclear atypia or cellular pleomorphism could be seen, thus indicating inflammatory pseudosarcoma. Although the lesion was not completely resected, no recurrent disease has been clinically observed for two years following transurethral resection. Urologists and surgical pathologists must be able to detect this lesion in order to avoid unnecessary surgical procedures.