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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.

General
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● 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

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

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

Treatment
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● Benign
● Excision is curative
● Chemotherapy not required

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

Micro description
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● 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
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Spindle and myxoid stroma with adenomatous foci are characteristic


Foci resembling collecting duct carcinoma are seen in some lesions

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

Negative stains
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Epithelium: EMA
Stroma: actin, desmin

Differential diagnosis
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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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