The muscularis mucosae of the human urinary bladder. Implications for tumor staging on biopsies.

The human urinary bladder wall is traditionally described as being without a muscularis mucosae. A consecutive one year material of 772 bladder biopsies from 171 patients were examined for the proposed presence of lamina muscularis mucosae (MM). MM was observed in 15% of the biopsies and in 35% of the patients and graded into three patterns according to its continuity. Biopsies with transitional cell carcinomas were reviewed in order to find out whether MM-positive biopsies had been staged correctly. The data are discussed in relation to earlier studies on the subject.