Bladder, ureter & renal pelvis

Other nonneoplastic

Squamous metaplasia

Topic Completed: 1 February 2013

Minor changes: 23 November 2020

Copyright: 2002-2022,, Inc.

PubMed Search: Squamous metaplasia[title] "loattrfree full text"[sb]

Rugvedita Parakh, M.D.
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Cite this page: Parakh R. Squamous metaplasia. website. Accessed January 21st, 2022.
Definition / general
  • Replacement of urothelium by stratified squamous epithelium, both vaginal (nonkeratinized) and keratinized subtypes
  • Also called leukoplakia
  • Normal in women in trigonal area
    Urinary tract infections:
  • Escherichia coli, Proteus and Streptococcus faecalis infections
  • Schistosomiasis
  • Inflammatory trauma causes squamous metaplasia, which may cause defects in the glycosaminoglycan layer, which can cause more inflammation / infections (J Urol 1983;130:51)

    Urinary Tract Irritants:
  • Indwelling catheters, urinary calculi, urinary outflow obstruction, fistula, tumors, bladder extrophy, neurogenic bladder, previous bladder surgery and vitamin A deficiency
Clinical features
    Vaginal (nonkeratinized) subtype:
  • Common in trigone (also called pseudomembranous trigonitis); considered a normal finding by some
  • Only in females
  • Rarely occurs in children (Urol Int 2006;77:46)
  • Associated with inverted papilloma; not associated with chronic irritation
  • No risk for carcinoma
  • Treated with estrogen if symptomatic

Keratinizing subtype:
  • Also called leukoplakia
  • More common in males
  • Associated with chronic irritation (catheters, stones, parasite eggs), polypoid cystitis, cystitis glandularis
  • May have atypia
  • Risk factor for squamous cell carcinoma
Prognostic factors
  • Keratinizing squamous metaplasia may transform to squamous dysplasia/carcinoma
Case reports
  • Spontaneous resolution in some
  • Careful follow-up of keratinizing squamous metaplasia, particularly if atypia, to detect dysplasia or carcinoma (Urol Int 2008;81:247, Am J Surg Pathol 2006;30:883)
  • Transurethral resection and fulguration
  • Cystectomy may occasionally be recommended for extensive disease (Eur Urol 2002;42:469)
  • Possibly sodium pentosan polysulfate (used for painful bladder syndrome / interstitial cystitis, Drugs 2006;66:821)
Clinical images

Images hosted on other servers:

Bladder wall showing
flaky, white,
plaque-like lesions
during cystoscopy

Cystoscopy of trigone in 15 year old girl

Gross description
  • No striking gross changes to the epithelial lining of the bladder
  • The epithelial lining may appear paler and thicker than normal with irregular borders and a surrounding zone of erythema
Microscopic (histologic) description
    Nonkeratinized squamous metaplasia:
  • Epithelium has abundant intracytoplasmic glycogen, similar to vaginal or cervical squamous epithelium
  • Recommended that nonkeratinizing glycogenated squamous epithelium in trigone and bladder neck in women should not be reported as "squamous metaplasia" since this is a common finding with no significantly increased risk for squamous carcinoma

Keratinizing squamous metaplasia:
  • Hyperkeratotic squamous epithelium lining bladder lumen
  • Presence and extent of keratinizing squamous metaplasia should be reported
Microscopic (histologic) images

Images hosted on other servers:

Mixed nonkeratinizing and keratinizing squamous metaplasia

Cytology images

Images hosted on other servers:

Benign squamous cells

Positive stains
Negative stains
Differential diagnosis
Additional references
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