American Urological Association - Urinary Bladder: Normal Urothelium


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Urinary Bladder: Normal Urothelium

Image A

Image B

  • Consists of several layers of polyhedral (transitional) cells.
    • 5-7 cells in contracted and 2-4 cells in dilated bladder.
  • Top to base, divided into umbrella, intermediate and basal cells (image A).
    • Basal cells are smaller cells next to basement membrane.
    • Basal and intermediate cells contain oval or elongated nuclei oriented perpendicularly to basement membrane ("normal polarity").
    • Nuclear groove is common in benign urothelium.
    • Superficial umbrella cells are larger with abundant cytoplasm and may exhibit nuclear pleomorphism* or multinucleation (image B).
  • Distinction of benign urothelium from carcinoma in situ (CIS).
    • Lack of marked atypia of basal and intermediate cells including oval nuclei (vs. round), absent mitosis and retention of polarity are features for benign urothelium vs. CIS.
    • Umbrella cell layer is generally lost in CIS, but can be retained in some uncommon "partial" CIS such as pagetoid CIS.
    • Umbrella cells are CK20+ and basal cells are CD44+. (In CIS, all cells are CK20+)

*Pleomorphism – marked atypia or variation in nuclear size and shape, an attribute almost always associated with malignant cells; rare exceptions in benign cells like umbrella cells.