Kidney tumor
Benign (usually) adult tumors
Metanephric adenoma

Author: Mandolin Ziadie, M.D.

Revised: 19 April 2018, last major update February 2012

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Metanephric adenoma [title] kidney

Cite this page: Ziadie, M.S. Metanephric adenoma. website. Accessed June 21st, 2018.
Definition / general
  • Member of metanephric tumor family, including metanephric adenofibroma (mixed epithelial-stroma) and metanephric stromal tumor (purely stromal)
  • Pure epithelial tumor composed of embryonal type epithelium with bland features
  • Also called metanephroid renal tumor, nephroblastoma-like adenoma of kidney and nephrogenic nephroma
  • First described in 1995 (Am J Surg Pathol 1995;19:1101)
  • Rare, 0.2% of adult renal epithelial neoplasms; < 100 cases described
  • Mean age 41 years but range is 5 - 83 years
  • 40 - 50% are incidental
  • 2/3 female
  • May arise from distal nephron / collecting duct (resembles developing metanephric tubular epithelium)
  • May represent mature Wilms tumor due to its resemblance to nephrogenic rests / maturing Wilms tumor by histology and immunohistochemistry (Am J Surg Pathol 2001;25:1290), but 56% have changes at 2p13 not found in Wilms tumor (Hum Pathol 2001;32:101)
Clinical features
  • Typically benign
  • Associated with polycythemia as a paraneoplastic syndrome in 12%
Case reports
Gross description
  • Single, well circumscribed, non encapsulated, tan / gray / white / yellow, solid / lobulated, mean 5 cm (range 0.3 to 15 cm)
  • Large tumors may have secondary cystic or hemorrhagic changes
Gross images

Images hosted on other servers:

Encapsulated tan tumor in lower pole (arrow)

Well circumscribed tumor

Well circumscribed, yellowish white or tan colored

Microscopic (histologic) description
  • Small, uniform, closely packed tubules or papillae in loose stroma, composed of small cells with minimal cytoplasm, bland nuclei that may overlap, uniform chromatin, glomeruloid bodies and rare mitoses
  • May see hemorrhage, necrosis, calcifications (psammoma bodies) or cysts
  • No atypia, no blastema, no / rare mitotic figures, no infiltrative growth and no vascular invasion
Microscopic (histologic) images
Scroll to see all images:

Images hosted on PathOut server:

Images contributed by Dr. Mercury Y. Lin, Naval Medical Center San Diego (USA):

Various images

Images hosted on other servers:

Well circumscribed tumor

Small tubules composed of bland cells with uniform nuclei

Solid appearance due to tight packing of acini / tubules

Left: glomeruloid bodies; right: psammoma bodies

Various images

Case report - 36 year old woman:

Fig 1: large, tan and fleshy tumor;
Fig 2: nests and tubules of small blue cells

Case report - 44 year old woman:

Fig 1: well circumscribed, tan and firm nodule;
Fig 2: unencapsulated, hypercellular and basophilic staining tumor with pushing margin against normal kidney;
Fig 3: tumor composed of small tightly packed tubules with scant stroma and occasional calcifications;
Fig 4: tumor cells have scant cytoplasm, uniform nuclei, delicate chromatin and indistinct nucleoli

Comparison with other tumors:

Compared to papillary carcinoma solid variant and metastatic thyroid insular carcinoma

Metanephric adenoma,
papillary renal cell
carcinoma and Wilms tumor

Stains left to right: CD57+, WT1+, AMACR-, CK7-

Cytology description
Positive stains
Negative stains
Molecular / cytogenetics description
Molecular / cytogenetics images

Images hosted on other servers:

FISH shows 2 signals for #17 in most cells

Electron microscopy description
  • Cilia on luminal side rest on abundant basement membrane
Differential diagnosis