Kidney tumor
Benign adult tumors
Metanephric adenoma

Editor-in-Chief: Debra Zynger, M.D.
Tatjana Antic, M.D.

Topic Completed: 31 March 2020

Minor changes: 31 March 2020

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PubMed Search: Metanephric adenoma [title] pathology loattrfree full text[sb]

Tatjana Antic, M.D.
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Cite this page: Antic T. Metanephric adenoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormetanephric.html. Accessed August 8th, 2020.
Definition / general
  • Member of metanephric tumor family, including metanephric adenofibroma and metanephric stromal tumor
Essential features
  • Benign tumor composed of cytologically bland embryonic looking epithelium with frequent psammomatous calcifications
  • It can be seen in patients from pediatric to old adult age
Terminology
  • Metanephroid renal tumor, nephroblastoma-like adenoma, nephrogenic nephroma
ICD coding
  • ICD-O: 8325/0 - metanephric adenoma
Epidemiology
  • An uncommon, usually asymptomatic, incidentally discovered renal neoplasm
  • Rare, less than 0.5% of all renal neoplasm
  • Age range 5 - 84 years (mean about 54) (Oncotarget 2016;8:54096)
  • 60% are female
Sites
  • Renal cortex
Pathophysiology
Clinical features
  • Usually discovered incidentally with no presenting symptoms
  • If presenting with symptoms, can demonstrate hematuria, pyrexia, flank pain, abdominal mass and polycythemia (Oncol Lett 2016;11:352)
Diagnosis
  • Diagnosed by histopathologic examination of excised tissue
  • If diagnosis is questionable, immunohistochemistry can differentiate metanephric adenoma from its mimics
Laboratory
  • Routine laboratory within normal limits in incidental cases
  • Polycythemia might be suggestive of renal tumor
Radiology description
Radiology images

Images hosted on other servers:

CT scan

Prognostic factors
Case reports
Treatment
  • Surgical resection is a curative
Gross description
  • Most are 3 - 6 cm in diameter although 15 cm tumor has been reported (Urology 2017;101:147)
  • Mostly unilateral and unifocal
  • Rare cases with cystic change (Urology 2017;101:147)
  • Circumscribed, not encapsulated with pushing border
  • Cut surface is tan to grey and can be soft or firm and occasionally hemorrhage and necrosis can be present in larger tumors
  • Calcifications are often seen grossly
Gross images

Contributed by Debra L. Zynger, M.D.

Partial nephrectomy

Radical nephrectomy



Microscopic (histologic) description
  • Classic appearance is a cellular blue tumor composed of tightly packed tubules, long branching and angulated ducts and abortive glomeruli
  • Tumor cells have scant cytoplasm and nuclei are small with no nucleoli
  • Mitotic figures are very rare or absent
  • Stroma is scant and it can be edematous and occasionally look scar-like
  • Psammomatous calcifications can be abundant (Oncol Lett 2015;10:1816)
Microscopic (histologic) images

Contributed by Tatjana Antic, M.D.

Well circumscribed

Scar

Calcifications

Packed tubules

Loose stroma


Mitotic figure

Pseudopapillary

Pseudopapillary and glomeruloid

BRAF

WT1

Virtual slides

Images hosted on other servers:

Metanephric adenoma

Cytology description
Electron microscopy description
Molecular / cytogenetics description
Sample pathology report
  • Right kidney, partial nephrectomy:
    • Metanephric adenoma, 3.5 cm in greatest dimension (see comment)
    • Surgical margins, negative for tumor
    • Comment: The sections show well circumscribed tumor composed of tightly packed tubules. The nuclei are small and devoid of nucleoli. No mitotic activity or necrosis is present. The cytoplasm is scant. Numerous psammomatous calcifications are present. Immunohistochemical stains for WT1 and BRAF are positive.
Differential diagnosis
Board review style question #1

    A 66 year old woman with flank pain is found to have polycythemia. The computer tomography study shows a 3.8 cm solid, circumscribed and hypovascular renal cortical tumor. Which renal tumor is likely to be associated with the above clinical presentation, imaging study and histomorphology?

  1. Angiomyolipoma, triphasic
  2. Clear cell renal cell carcinoma
  3. Metanephric adenoma
  4. Nephroblastoma
  5. Urothelial carcinoma
Board review answer #1
C. Metanephric adenoma

Explanation: Metanephric adenoma is associated with polycythemia and a hypovascular renal mass on imaging study. The section shows a well circumscribed renal tumor composed of tightly packed tubules. Angiomyolipoma contain adipose tissue which is easily seen on CT scan. Patient age argues against diagnosis of nephroblastoma. Urothelial carcinoma is neither cortical tumor nor it is circumscribed. Clear cell renal cell carcinoma is hypervascular tumor although it can cause polycythemia and is not basophilic.

Reference: Metanephric adenoma

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Board review style question #2

    A renal mass from a 43 year old woman shows a tumor composed of tightly packed basophilic tubules. The cell nuclei are cytologically bland and cytoplasm is scant. Numerous psammomatous calcifications are present. No mitotic activity or necrosis is present. Which is the immunohistochemical profile that should be seen in this tumor?

  1. PAX8+, WT1+, CK7-, CD57+, BRAF+
  2. PAX8-, WT1+, CK7-, CD57+, BRAF-
  3. PAX8+, WT1+, CK7-, CD57+, BRAF-
  4. PAX8+, WT1-, CK7-, CD57+, BRAF+
  5. PAX8+,WT1-, CK7+, CD57+, BRAF+
Board review answer #2
A. PAX8+, WT1+, CK7-, CD57+, BRAF+

Explanation: This is a metanephric adenoma. The differential diagnoses include papillary renal cell carcinoma, type 1, solid variant and adult epithelial predominant nephroblastoma. Papillary renal cell carcinoma, type 1 is a PAX8+, vimentin+, CK7+, AMACR+, WT1-, CD57-, BRAF- tumor as opposed to metanephric adenoma that is positive for WT1, CD57 and BRAF and negative for CK7. Adult nephroblastoma is positive for WT1 but negative for CD57 and BRAF.

Reference: Metanephric adenoma

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