Invasive carcinomas of the urinary bladder. Evaluation of tunica muscularis mucosae involvement.

Awareness of the existence of a tunica muscularis mucosae in the urinary bladder complicates the assessment of muscle invasive carcinomas on bladder biopsy. Sixty cystectomy specimens and select bladder biopsies were reviewed to analyze this problem. The patterns of development of the tunica muscularis mucosae were categorized as continuous, interrupted, scattered, or absent. Most bladders demonstrated several patterns of development rather than a uniform appearance. The most frequently observed pattern was that of scattered smooth muscle fibers seen in 33 of 40 (82.5%) cases. The rarity of carcinomatous invasion limited to the tunica muscularis mucosae is emphasized. The authors conclude that the potential for overstaging bladder carcinomas because of misinterpretation of this structure is small.