Morphological keys in the differential diagnosis of bladder inverted papilloma. Study of two types, trabecular and glandular.

OBJECTIVE

Inverted papilloma of the urinary bladder is an uncommon urothelial neoplasm that may be specially difficult to distinguish from urothelial carcinoma.

METHODS

Two patients with obstructive symptoms and hematuria have been studied. In the transurethral resection, accidentally, one showed a papillary lesion in the context of nodular hyperplasia of the prostate, where as the other showed a polypoid tumor of the urinary bladder

RESULTS

Histologically, in both cases, a bladder inverted papilloma was demonstrated, originating from the surface transitional epithelium. Basal cells exhibited peripheral palisading pattern in the trabecular form. In the glandular type, Dogiel or umbrella cells into the gland-like structures, were recognized. Immunohistochemical stains for p53 and Ki-67 were negative. Umbrella cells were positive for cytokeratin 20.

CONCLUSIONS

Two cases of bladder inverted papilloma with relevant morphological aspects are presented, which we consider useful for the differential diagnosis with urothelial carcinoma.