[A case of "verrucous hyperplasia"; a vesical leukoplakia showing unusual macroscopic and histological findings].

A patient who had vesical leukoplakia with unusual macroscopic and histological findings was studied. The mucous membrane of the urinary bladder in this patient showed a tumor-like proliferation similar to verrucous hyperplasia which is often found in the oral mucosa. We propose a new classification of vesical leukoplakia, dividing it into three groups, atrophic, hypertrophic and verrucous types. The atrophic type has a heavily keratinized, flat and thin type of epithelium with features resembling lichen sclerosis et atrophius. Histologically, it shows a variable degree of hyperkeratosis but no parakeratosis. The hypertrophic type has histological characteristics resembling features of leukoplakia in sites elsewhere in the body, which is marked by hyperkeratosis and irregular hyperplasia of the prickle cell layer with lengthening and abnormality in shape of rete pegs. The verrucous type has very rare features of coral shape, white color and verrucous proliferation. Histologically, this type shows severe hyperkeratosis, parakeratosis and elongation of the rete pegs, but no irregular invasion can be observed.