Prostate gland & seminal vesicles

Nonneoplastic

Nephrogenic metaplasia / adenoma


Resident / Fellow Advisory Board: Alcino Pires Gama, M.D.
Deputy Editor-in-Chief: Maria Tretiakova, M.D., Ph.D.
Francesca Sanguedolce, M.D., Ph.D.

Last author update: 9 August 2023
Last staff update: 9 August 2023

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PubMed search: Prostatic nephrogenic adenoma

Francesca Sanguedolce, M.D., Ph.D.
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Cite this page: Sanguedolce F. Nephrogenic metaplasia / adenoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/prostatenephrogenichyper.html. Accessed May 19th, 2024.
Definition / general
  • Benign polypoid, papillary, fungating or velvety lesion found in the bladder or prostatic urethra after urothelial injury
  • Has multiple histologic patterns
Essential features
  • Evidence that it is derived from shed renal tubular cells (N Engl J Med 2002;347:653)
  • Alternatively, it is postulated that a subset of cases might be a metaplastic reaction (Int Sch Res Notices 2015;2015:704982)
  • Tubules lined by flattened, cuboidal or hobnail cells
  • Many morphologic variants: papillary, tubular, flat, cysts and microcysts, signet ring cell-like, fibromyxoid
  • Hyaline rim surrounds the tubules
  • No mitotic activity
  • Only occasional solid areas or rare clear cells present
  • May focally involve the prostatic parenchyma and mimic prostate adenocarcinoma
ICD coding
  • ICD-10: N32.9 - bladder disorder, unspecified
Epidemiology
Sites
  • Prostatic urethra
  • Described throughout the entire urothelium (see nephrogenic metaplasia in the bladder chapter)
Pathophysiology
Etiology
  • Prior injury to the urothelium
Clinical features
  • May present as a mass or with irritative lower urinary tract symptoms, hematuria, dysuria, obstruction
  • Usually small (< 1 cm) but may be up to 7 cm
Diagnosis
  • Biopsy, transurethral resection
Prognostic factors
  • May recur; risk factors not known
Case reports
  • 39 year old woman with nephrogenic adenoma arising in urethral diverticulum (Cureus 2023;15:e36578)
  • 62 year old man with giant prostatic hypertrophy and recurrent nephrogenic adenoma of the prostate (BMC Urol 2013;13:18)
  • 67 year old man with asymptomatic macroscopic hematuria and a history of laser photovaporization of the prostate for benign prostate hyperplasia (Urol Case Rep 2020;33:101382)
  • 72 year old man with nephrogenic adenoma presenting with irritative voiding symptoms as benign prostatic hyperplasia and mimicking prostatic and bladder carcinomas (Cureus 2023;15:e35998)
Treatment
  • Transurethral resection with regular follow ups
Gross description
  • Friable soft tissue fragments
Microscopic (histologic) description
  • Tubules lined by simple cuboidal, flattened or hobnail cells, forming an exophytic papillary or endophytic lesion (Urology 2016;95:29)
  • Associated acute and chronic inflammation and edema in the stroma; lack of desmoplastic reaction
  • Many morphologic variants (multiple patterns may occur in the same cases): papillary, tubular, tubulocystic, polypoid, flat, fibromyxoid, signet ring cell-like (Mod Pathol 2013;26:792)
  • Hyaline rim surrounds the tubules (PAS positive thickened basement membrane) (Adv Anat Pathol 2019;26:171)
  • No mitotic activity
  • Scant cytoplasm, finely granular uniform chromatin; usually inconspicuous nucleoli (Ann Diagn Pathol 2019;38:11)
  • Only occasionally solid areas, rare clear cells, blue mucin within the tubules present
  • Sometimes atrophic tubules filled with eosinophilic colloid-like material mimicking thyroid follicles and mesonephric hyperplasia
  • May be associated with radiotherapy
  • Rare fibromyxoid variant features, including compressed spindle shaped cells in a prominent fibromyxoid background; it can present as pure fibromyxoid or combined with classic (tubular) morphology (Am J Surg Pathol 2023;47:37)
Microscopic (histologic) images

Contributed by Francesca Sanguedolce, M.D., Ph.D.
Multiple morphologies

Multiple morphologies

Inflammation, thickened basement membrane

Inflammation, thickened basement membrane

Cytological features

Cytological features


Ki67

Ki67

AMACR

AMACR

PAX8

PAX8

CK7

CK7

Cytology description
  • Numerous vacuolated, polygonal and columnar shaped cells singly or in small groups
  • Papillary fragments resembling low grade papillary urothelial carcinoma (Am J Clin Pathol 2016;145:373)
Negative stains
Sample pathology report
  • Prostate, biopsy / transurethral resection:
    • Nephrogenic adenoma
Differential diagnosis
Board review style question #1

Which of the following statements is true about nephrogenic adenoma?

  1. Can have multiple morphological patterns
  2. Carcinoembryonic antigen (CEA) is often positive
  3. Has a high proliferative index
  4. Is a metaplastic lesion
Board review style answer #1
A. Can have multiple morphological patterns. Nephrogenic adenoma often features multiple different morphologies within the same lesion, the most common being tubular, cystic and papillary. Answer D is incorrect because it has been established that nephrogenic adenoma, which has been thought to be a metaplastic lesion, actually results from shed renal tubular cells. Answer C is incorrect because this entity has a very low proliferative index. Answer B is incorrect because this entity lacks CEA staining.

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Reference: Nephrogenic metaplasia / adenoma
Board review style question #2
Which of the following is a variant of nephrogenic adenoma?

  1. Fibromyxoid
  2. Glycogen rich
  3. Nested
  4. Plasmacytoid
Board review style answer #2
A. Fibromyxoid. The rare fibromyxoid variant features compressed, spindle shaped cells in a prominent fibromyxoid background; it can present as pure fibromyxoid or combined with classic (tubular) morphology. Answers B, C and D are incorrect because they all refer to subtypes of urothelial cancer.

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Reference: Nephrogenic metaplasia / adenoma
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