Primary carcinoid tumor of the urinary bladder with prominent subnuclear eosinophilic granules.

Primary carcinoid tumor of the urinary bladder is a very rare neoplasm. We report here a case of primary carcinoid tumor of the urinary bladder with an unusual cytological feature in a 72-year-old Japanese man. A bladder polypoid mass was incidentally found by ultrasonography during the follow-up of a benign prostate hyperplasia. Histological examination of the transurethrally resected tissue revealed that the upper part of the mass was a tumor showing tubuloglandular anastomosing structures. Most of the tumor cells had peculiar subnuclear eosinophilic granules. The features of the granules were reminiscent of those observed in neuroendocrine cells of the intestine. The tumor cells were immunohistochemically positive for chromogranin A and synaptophysin. The tumor was diagnosed as carcinoid tumor of pure form of the urinary bladder. The lower part of the mass showed the findings of glandular cystitis, as its coexistence with carcinoid tumors of the bladder has often been described in previous reports.