Nephrogenic Adenoma of the Prostatic Urethra

Nephrogenic Adenoma of the Prostatic Urethra
Gladell P. Paner, MD
Rugvedita Parakh, MD
Bonnie L. Balzer, MD, PhD
Key Facts
Terminology
  • Tubulo-papillary proliferations along urothelial mucosa that resemble immature renal tubules
Etiology/Pathogenesis
  • Renal tubular cell seeding hypothesis
  • Nephrogenic metaplasia hypothesis
Microscopic Pathology
  • Most common as small round to oval tubules
  • Thickened peritubular basement membrane
  • May contain intraluminal basophilic or eosinophilic secretions
  • Other architectural patterns include cystic, papillary-polypoid, solid growth, and rare fibromyxoid subtype
  • Monolayer of cuboidal, flattened, or “hobnailed” cells
  • Scanty to modest eosinophilic to clear cytoplasm
  • Nuclei with minimal atypia, inconspicuous nucleoli, and absent to rare mitosis
  • Tubules may be very small simulating signet ring cells
  • Admixture of these different patterns is common
  • Polypoid-papillary growth when present is always seen with underlying tubular proliferation
  • Extension of tubules into subjacent prostate fibromuscular stroma is common
Ancillary Tests
  • Key immunohistochemical panel: PAN-CK(AE1/AE3) (+), pax-2(+), PSA/PAP(-) in majority of cases
Top Differential Diagnoses
  • Prostatic acinar adenocarcinoma
  • Urethral papillary neoplasms
Low-power magnification of NA of the prostatic urethra shows polypoid growth with subjacent tubular and cystic proliferations in the lamina propria.
High-power magnification of NA shows variably sized round hollow tubules with characteristic thickened basement membrane image. Some of the tubules contain intraluminal eosinophilic secretions.
TERMINOLOGY
Abbreviations
  • Nephrogenic adenoma (NA)
Synonyms
  • Nephrogenic metaplasia
Definitions
  • Benign epithelial lesion of urethra characterized by tubular, glandular, &/or papillary growth pattern that is morphologic and immunohistochemical mimic of prostatic adenocarcinoma
ETIOLOGY/PATHOGENESIS
Renal Tubular Cell Seeding Hypothesis
  • In renal transplant patients, NA cells shown to have same sex chromosome status with allografted kidneys and not with surrounding bladder tissue in opposite gender recipients
  • May represent seeding implantation and growth of renal tubular cells in injured urothelial mucosa
Nephrogenic Metaplasia Hypothesis
  • Metaplastic alteration of urothelium in response to insult or injury
CLINICAL ISSUES
Epidemiology
  • Age
    • Mean: 66 years; range: 21-77 years
Site
  • Vast majority of NA encountered in urinary bladder
  • Prostatic urethra is involved in approximately 15% of cases and may extend into subjacent prostate stroma
Presentation
  • Most are incidental findings
    • Mainly seen in transurethral resection of prostate (TURP) specimens for benign prostatic hyperplasia
Natural History
  • Majority of cases with preceding genitourinary surgery, instrumentation, urinary tract infection, or calculi
Treatment
  • None required
Prognosis
  • Benign, but with high “recurrence” rate (37%) if inciting etiology persists
MACROSCOPIC FEATURES
General Features
  • Only about 1/3 may assume macroscopic proportions, which may be seen at cystourethroscopically as exophytic papillary or polypoid lesions
Size
  • Generally < 1 cm, average 0.3 cm
MICROSCOPIC PATHOLOGY
Histologic Features
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Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Nephrogenic Adenoma of the Prostatic Urethra

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