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Bladder

Metaplasia

Squamous metaplasia


Reviewer: Rugvedita Parakh, M.D. (see Reviewers page)
Revised: 9 February 2013, last major update July 2010
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Definition
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● Replacement of urothelium by stratified squamous epithelium, both vaginal (non-keratinized) and keratinized subtypes

Terminology
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● Also called leukoplakia

Epidemiology
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● Normal in women in trigonal area

Etiology
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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
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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
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● Keratinizing squamous metaplasia may transform to squamous dysplasia/carcinoma

Case reports
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● 54 year old man with tetraplegia, keratinizing squamous metaplasia and prophylactic cystectomy (J Spinal Cord Med 2007;30:389)
● Three women in one family with no bladder pathology (J Urol 1987;137:979)

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


Cystoscopy of trigone in 15 year old girl

Gross description
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● 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
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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
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Non-keratinizing squamous metaplasia


Keratinizing squamous metaplasia


Mixed non-keratinizing and keratinizing squamous metaplasia


CK20 stains only umbrella cells

Cytology images
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Benign squamous cells and inflammatory cells

Positive stains
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● CK14 (Spinal Cord 2003;41:432)
● L1 antigen detected by monoclonal antibody Mac387 has been used as marker of squamous differentiation; absent in normal urothelium and transitional cell carcinoma (Histopathology 1991;19:245)

Negative stains
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● CK20 (BMC Urol 2002;2:7)

Differential diagnosis
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Radiation atypia: degenerative type epithelial changes
Squamous dysplasia: atypia is present
Squamous cell carcinoma (renal pelvis, ureter and bladder): marked atypia, hemorrhage, necrosis
Urothelial carcinoma in situ: marked atypia, but may not be full thickness
Verrucous carcinoma: well differentiated tumor with broad based invasive front

Additional references
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eMedicine (trigonitis)

End of Bladder > Metaplasia > Squamous metaplasia


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