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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors

Metanephric adenoma

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 13 August 2014, last major update February 2012
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.


● 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

● 7 year old girl with lung metastasis (Am J Surg Pathol 2000;24:570)
● 9 year old boy with multifocal tumor (Pathol Int 2009;59:49)
● 24 year old pregnant woman (Hum Pathol 2006;37:1227)
● 35 year old woman with passive seeding of hilar node (Arch Pathol Lab Med 2005;129:1317)
● 36 year old woman (Arch Pathol Lab Med 1999;123:1285)
● 44 year old woman (Arch Pathol Lab Med 2004;128:926)
● 54 year old woman (Mod Pathol 1996;9:329)

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

Encapsulated tan tumor in lower pole (arrow)

Well circumscribed tumor

Well-circumscribed, yellow-white or tan colored

Micro 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

Micro images

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

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

Various images

Case report - 36 year old woman:

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

Case report - 44 year old woman:

Figure 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

● Small, well-differentiated epithelial tubules with bland nuclei, psammoma bodies (Cytopathology 2008;19:80, Acta Cytol 2007;51:468)

Positive stains

● WT1 (strong / diffuse), CD57 (strong / diffuse), CK7 (focal), AE1 (focal) and vimentin (solid areas)

Negative stains

● AMACR (Mod Pathol 2006;19:218)
● Also glycogen, CD56, desmin, NCAM and EMA

Molecular description

● No consistent abnormalities (Mod Pathol 2003;16:1060)

Molecular images

FISH shows 2 signals for #17 in most cells

Electron microscopy description

● Cilia on luminal side rest on abundant basement membrane

Differential diagnosis

Metastatic insular thyroid carcinoma: Arch Pathol Lab Med 1999;123:415)
Papillary renal cell carcinoma: particularly solid variant; red-brown with thick capsule, cells have more cytoplasm, nuclear grooves and prominent nucleoli; also foamy histiocytes, delicate vasculature; strong CK7, strong AE1, strong AMACR, EMA+, CD57-, WT1-, +7 and +17
Wilms’ tumor: younger age, grossly tan-gray with hemorrhage or cysts, triphasic, WT1+, CD57- and vimentin-

End of Kidney tumor - cysts, children, adult benign > Benign (usually) adult tumors > Metanephric adenoma

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