Bladder

Bladder biopsy specimens are usually submitted to rule out a urothelial neoplasm. The procedure may be indicated because of hematuria, an abnormal urine cytology, a history of urothelial neoplasm, or a lesion seen on cystoscopy. The cystoscopic impression is important, and you usually do not diagnose a papillary lesion if none was seen by the urologist. The bladder biopsy specimen is typically a tiny tissue fragment, so you should look at each level carefully.

The normal urothelium consists of a stratified nonsquamous epithelium, also called transitional cell epithelium. It consists of a five- to seven-cell thick layer of uniform cells that do not significantly mature as they reach the surface (unlike squamous epithelium) and that tend to have oblong nuclei oriented perpendicular to the surface (Figure 12.1). The nuclei are about two to three times the size of lymphocytes. Mitoses are usually seen only at the basal layer, but in the presence of inflammation and reactive changes they may be seen throughout. At the surface is a specialized cell layer called the umbrella cells, large pillowy cells that appear wider than the underlying urothelial cells. Umbrella cells may have atypical nuclei and should be ignored when assessing the urothelium for neoplasia.

Underneath the urothelium lies the lamina propria, a connective tissue layer that has vessels, lymphatics, occasional smooth muscle fibers, and even occasional fat. Deep to this is the thick muscularis propria, also known as the detrusor muscle. Beyond the muscular wall is either adventitia or, where the bladder lies against the peritoneum, peritonealized serosa.