Pseudosarcomatous fibromyxoid tumor of the urinary bladder.

The light-microscopic, immunohistochemical, and ultrastructural features of two examples of a pseudosarcomatous fibromyxoid tumor of the urinary bladder are reported. Both patients were women, 56 and 52 years old. Gross hematuria was the chief complaint and occurred for two days and two weeks, respectively, before presentation. Cystoscopy revealed a 2 X 1 X 1 cm mass located at the dome in case 1 and a 4 X 3 X 3 cm mass at the left posterior lateral wall in case 2. Microscopically, the lesions were composed of spindle, plump, or stellated fibroblast-like cells embedded in myxoid stroma with little collagen; mitotic figures were about 2 per 10 high-power fields, and both cases showed encroachment of the superficial muscle bundles. Because of bizarre spindle cell proliferation, occasional mitoses, and invasion to the underlying muscle, these lesions were initially diagnosed as embryonal rhabdomyosarcoma. However, follow-up examination disclosed the benign nature of these lesions. There was no previous instrumentation or surgery on the genitourinary tract. Immunohistochemical and ultrastructural studies revealed the fibroblastic-myofibroblastic nature of these lesions. These cases illustrate that clinicopathologic correlation is essential to define certain pseudosarcomatous lesions.