Squamous metaplasia

Author: Rugvedita Parakh, M.D. (see Authors page)

Revised: 8 June 2016, last major update February 2013

Copyright: (c) 2003-2016,, Inc.

PubMed Search: Squamous metaplasia[title]
Cite this page: Squamous metaplasia. website. Accessed March 28th, 2017.
Definition / General
  • Replacement of urothelium by stratified squamous epithelium, both vaginal (non-keratinized) 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 (non-keratinized) 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
Micro Description
    Non-keratinized squamous metaplasia:
  • Epithelium has abundant intracytoplasmic glycogen, similar to vaginal or cervical squamous epithelium
  • Recommended that non-keratinizing 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
Micro Images

Images hosted on other servers:

Non-keratinizing squamous metaplasia

Keratinizing squamous metaplasia

Mixed non-keratinizing and keratinizing squamous metaplasia

CK20 stains only umbrella cells

Cytology Images

Images hosted on other servers:

Benign squamous cells

Positive Stains
Negative Stains
Differential Diagnosis
Additional References