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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors

Metanephric adenofibroma

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 28 March 2012, last major update February 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Biphasic, circumscribed tumor with focal embryonal epithelium identical to a combination of metanephric adenoma and bland spindled stroma
● Part of a family of metanephric tumors including metanephric adenoma and metanephric stromal tumor
● Morphology may merge with that of Wilms’ tumor, supporting the hypothesis that these are related lesions (Am J Surg Pathol 2001;25:433, Pediatr Dev Pathol 2011 Jun 28 [Epub ahead of print])
● Previously known as nephrogenic adenofibroma


● Rare (< 50 reported cases)
● Mean age 14 years; range 2–35 years old

Clinical features

● Associated with papillary renal cell carcinoma, polycythemia and hypertension, which resolve after nephrectomy (Am J Surg Pathol 1992;16:325)


● Benign
● Excision is curative
● Chemotherapy not required

Gross description

● Solitary, non-encapsulated, vaguely circumscribed, irregular or spherical firm mass with tan-gray-white-yellow cut surface
● Variable cysts

Micro description

● Well-circumscribed biphasic tumor with focal embryonal epithelium identical to metanephric adenoma and bland spindle cell stroma
● Areas of intratumoral angiodysplasia, concentric cuffing of entrapped tubules ("onion skinning") and heterologous differentiation
● Spans morphologic spectrum between benign pure stromal and pure epithelial lesions
● Epithelial cells are bland with no mitotic figures
● Entrapped tubules may have papillary hyperplasia
● Numerous psammoma bodies

Micro images

Spindle and myxoid stroma with adenomatous foci are characteristic

Foci resembling collecting duct carcinoma are seen in some lesions

Positive stains

Epithelium (stains like metanephric adenoma): keratin
Stroma: vimentin, fibronectin and CD34 (often)

Negative stains

Epithelium: EMA
Stroma: actin, desmin

Differential diagnosis

Mesoblastic nephroma: congenital myofibroblastic tumor with collagen; irregular infiltrating edges
Wilms’ tumor: epithelial predominant - triphasic tumor with undifferentiated blastema

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

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