Urinary cytology in inverted papilloma of the lower urinary tract.

Urinary cytology is reported in six cases of inverted papilloma of the bladder. Abnormal features were found in five of the six cases. These were essentially an increase in the number of single or small clusters of degenerate transitional cells. As their cytologic features fell within the range of normal but degenerate transitional epithelium, a diagnosis of transitional cell tumor was not possible in these cases. Histologic features suggest that the desquamating cells may be derived from the surface epithelium of the papilloma, the underlying cords and trabeculae, or from the adjacent transitional epithelium.