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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.

General
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● 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)

Epidemiology
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● 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

Pathophysiology
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● 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
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● Typically benign
● Associated with polycythemia as a paraneoplastic syndrome in 12%

Case reports
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● 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
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● 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
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Encapsulated tan tumor in lower pole (arrow)


Well circumscribed tumor


Well-circumscribed, yellow-white or tan colored

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

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

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

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

Molecular images
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FISH shows 2 signals for #17 in most cells

Electron microscopy description
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● Cilia on luminal side rest on abundant basement membrane

Differential diagnosis
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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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