Inflammatory pseudotumor of the urinary bladder. A clinicopathological, immunohistochemical, ultrastructural, and flow cytometric study of 13 cases.

We report 13 cases of inflammatory pseudotumor of the urinary bladder in patients having no history of recent local trauma. The average age of the patients (eight females, five males) was 35.4 years (range, 19 to 60 years). Gross hematuria (nine of 13 cases) and recurrent cystitis (three of 13 cases) were the most common presentations. Cystoscopy and gross examination revealed either a polypoid intraluminal mass or a submucosal mural mass, ranging in size from 2 to 7 cm. The lesions were commonly gelatinous. Histological examination showed that the lesions consisted of spindle cells with tapering eosinophilic cytoplasm, typically widely separated in a vascular myxoid matrix with acute and chronic inflammatory cells. In four cases the lesions had more compact cellularity with areas of fibrosis and less myxoid change. The muscularis propria was involved in 10 cases, the perivesical fat in two cases. The spindle cells were immunoreactive for vimentin (10 of 10) and muscle-specific actin (10 of 10). A few cases exhibited immunoreactivity for smooth-muscle-specific actin (three of eight), cytokeratin (two of 10), desmin (two of nine), and epithelial membrane antigen (two of eight). Ultrastructural examination of four cases revealed myofibroblasts, fibroblasts, or a mixture of the two cell types. DNA content analysis by flow cytometry yielded diploid histograms (six of six). Clinical follow-up in all cases demonstrated no evidence of recurrence (mean follow-up, 25.8 months). The findings indicate that this lesion is a benign, likely inflammatory or reparative, mesenchymal lesion that can be recognized by its distinctive pathological features.