Bladder
Metaplasia
Nephrogenic metaplasia

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

Revised: 7 June 2016, last major update February 2013

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

PubMed Search: Nephrogenic metaplasia
Definition / General
  • Metaplastic change with papillary or cystic structures composed of small hollow tubules similar to mesonephric tubules, usually lined by a single layer of bland cuboidal or hobnail cells, surrounding eosinophilic or basophilic secretions
Terminology
  • Also called mesonephric adenoma / metaplasia, nephrogenic adenoma; also adenomatoid tumor (but a different entity), adenomatoid metaplasia
Epidemiology
Sites
  • Affects bladder, urethra, ureter and renal pelvis in decreasing frequency
  • More common at bladder neck and adjacent urethra
Etiology
  • Increased incidence after organ transplantation and immunosuppression
  • In renal transplant recipients, derived from exfoliated and implanted renal tubular cells in the urinary tract (N Engl J Med 2002;347:653)
  • In other patients, appears to be metaplastic and not a neoplasm
  • Associated with inflammation (Urology 1976;8:283), bcg, calculi, chronic catheterization, exstrophy, interstitial cystitis, intravesical thiotepa, malakoplakia, Mullerian lesions, surgery (adults: prostatic lesions, children: congenital lesions); note that these conditions also cause cystitis glandularis and cystitis cystica
Clinical Features
  • Irritative bladder symptoms, occasionally hematuria
  • Velvety appearance on cystoscopy; often mistaken for papillary urothelial carcinoma
  • Benign behavior; no malignant transformation even if significant cytologic atypia ( Cancer 2000;88:853, but see Hum Pathol 2006;37:117)
Case Reports
Treatment
  • Resection, but often recurs; requires long term follow-up
  • Case report of 12 year old boy treated with sodium hyaluronate (J Pediatr Urol 2007;3:156)
  • May regress if underlying cause is removed
Gross Description
  • Polypoid, sessile or papillary, 20% are multiple
Micro Description
  • Small hollow tubules similar to mesonephric tubules, usually lined by single layer of bland cuboidal or hobnail cells, surrounding eosinophilic or basophilic secretions (Mod Pathol 1995;8:722)
  • Cells have clear or eosinophilic cytoplasm, small nuclei, no prominent nucleoli
  • May have thickened basement membrane
  • Usually inflammatory infiltrate (plasma cells and lymphocytes) and stromal edema
  • Involves lamina propria but spares muscularis propria
  • Most cases also have a cystic pattern; occasionally are pseudoinfiltrative, may contain <10% clear cells, may have small slender papillary structures on mucosal surface
  • Occasionally luminal blue mucin compresses the nuclei giving a signet ring-like appearance
  • Minimal atypia, minimal mitotic figures
  • No necrosis, no desmoplasia

  • Fibromyxoid subtype: compressed spindled cells within a fibromyxoid background with only rare tubular and cordlike structures, mimics mucinous carcinoma (Am J Surg Pathol 2007;31:1231)
  • Prostatic urethra: lesions closely resemble prostatic adenocarcinoma and are AMACR+
Micro Images

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Papillary and cystic structures lined by cuboidal epithelium

Cells have hobnail appearance

Papillary mucosal surface epithelium


Invasive adenocarcinoma

Tubulopapillary lesion

Small grouped ducts

Papillary lesion

Various stains

Cytology Description
  • Benign features and PAX2+ (Diagn Cytopathol 2008;36:47)
  • Small clusters and single scattered cells with central nuclei and vacuolated cytoplasm
  • Nuclei show evenly distributed chromatin with small nucleoli and regular nuclear membranes
  • Occasional small pseudopapillary clusters of cells with slightly irregular nuclear membranes and prominent nucleoli
  • Background of reactive urothelial cells and squamous cells (Diagn Cytopathol 2009;37:468)
Positive Stains
Negative Stains
Electron Microscopy Description
Molecular / Cytogenetics Description
Differential Diagnosis