Nephrogenic adenoma

Nephrogenic adenoma, also known as mesonephric adenoma, and nephrogenic metaplasia, is a rare lesion that is classically in the urinary bladder and can mimic adenocarcinoma.

Nephrogenic adenoma
Diagnosis in short
Nephrogenic adenoma. H&E stain.
Synonyms	mesonephric adenoma, nephrogenic metaplasia
LM	classically tubular structures with a microcystic appearance lined by hobnailed cells +/-thick eosinophilic basement membrane; may have tubulocystic, polypoid, papillary or fibromyxoid architecture; usually associated with chronic inflammation
LM DDx	urothelial carcinoma microcystic and nested variants, prostatic adenocarcinoma, clear cell adenocarcinoma (clear cell adenocarcinoma of the urethra, clear cell carcinoma of the urinary bladder, metastatic clear cell adenocarcinoma)
IHC	CK7 +ve, PAX8 +ve, p53 -ve, CEA -ve, Ki-67 low (<5%)
Site	urothelium - usu. urinary bladder
Prevalence	uncommon
Endoscopy	occasionally a papillary-like mass or flat velvety lesion
Prognosis	benign
Clin. DDx	no treatment necessary (?)

It should not be confused with metanephric adenoma.

General

Features:

• Benign.
  • May mimic adenocarcinoma!
• Classic location is the urinary bladder.
  • Also reported in ureter and prostatic urethra.
• It is thought to result from displacement of renal tubular cells, as this entity in renal transplant recipients is graft derived.

Gross

Features:

• Usually an incidental finding only seen on microscopy.
• May manifest as:
  • A papillary-like mass.
  • A flat velvety lesion with an irregular border.

Microscopic

Features:

• Tubular structures - the classic morphology. †
  • Lined by a single cell layer - classically hobnailed. ‡
  • +/-Thick eosinophilic basement membrane.
  • Typically microcystic appearance.
• Usually associated with chronic inflammation.

Notes:

• May mimic vascular/lymphatic channels - can be sorted-out with IHC.
• † May be tubulocystic, polypoid, papillary or fibromyxoid.
• ‡ May be flat.
• Should not have necrosis or mitoses.

DDx:

• Urothelial carcinoma, microcystic and nested variants.
• Clear cell adenocarcinoma.
  • Clear cell adenocarcinoma of the urethra.
  • Mesonephroid adenocarcinoma (also known as clear cell carcinoma) - may be deceptively bland.
• Prostatic adenocarcinoma.

• Metastatic tumours.
  • Clear cell renal cell carcinoma.
  • Other clear cell tumours.

Images

• 

  Nephrogenic adenoma - low mag. (WC/Nephron)

• 

  Nephrogenic adenoma - intermed. mag. (WC/Nephron)

• 

  Nephrogenic adenoma - high mag. (WC/Nephron)

• 

  Nephrogenic adenoma - very high mag. (WC/Nephron)

www:

• NA (archivesofpathology.org).

IHC

Features:

• CK7 +ve.
• PAX2 +ve.
• PAX8 +ve.
• AMACR +ve/-ve.

Others:

• p53 -ve.
• CEA -ve.
• Ki-67 low (<5%).
• MUC1 +ve.
  • Marks distal renal tubule.
• PSA -ve.
• PSAP -ve.
• CD34 -ve. (???)
• p63 -ve (0/32 cases ).
• CK20 -ve usually (6 +ve of 32 cases).
• CK34betaE12 -ve usually (8+ve of 32 cases).

Sign out

PROSTATE TISSUE, TRANSURETHRAL RESECTION OF THE PROSTATE (TURP):
- BENIGN PROSTATE TISSUE WITH GLANDULAR AND STROMAL PROLIFERATION.
- UROTHELIAL MUCOSA WITH A MILD LYMPHOCYTIC INFILTRATE AND CHANGES CONSISTENT
  WITH CYSTITIS CYSTICA.
- BENIGN CALCIFICATIONS.
- NEPHROGENIC METAPLASIA (MESONEPHRIC ADENOMA), SEE COMMENT.
- NEGATIVE FOR MALIGNANCY.

COMMENT:
Nephrogenic metaplasia is a benign finding.  It is confirmed with immunostaining 
(POSITIVE for CK7, PAX8; NEGATIVE for AMACR, CK34betaE12 (very focal staining)).

See also

• Urothelium.
• Metanephric adenoma.
• Mesonephric remnant of the prostate gland.