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22 July 2015 - Case of the Week #359

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Case of the Week #359

Clinical History:
A 26 year old woman presented with a 4.0 cm renal mass.

Micro images:

H&E images

What is your diagnosis?

Angiomyolipoma with epithelial cysts (AMLEC)

Immunostains were obtained:





Angiomyolipoma/AML with epithelial cysts (AMLEC) (Am J Surg Pathol 2006;30:593, Mod Pathol 2006;19:669), is a rare variant of fat poor angiomyolipoma mimicking a malignant cystic mass on MR imaging (Diagn Interv Imaging 2015 Apr 23 [Epub ahead of print], Clin Radiol 2015;70:206). It is associated with tuberous sclerosis (Am J Surg Pathol 2009;33:289) and tuberous sclerosis-related renal cell carcinoma (Am J Surg Pathol 2014;38:1457). The diffuse labeling of the epithelial cysts with PAX2/PAX8, coupled with their consistent negativity for estrogen receptor and HMB45 suggests that this epithelium represents entrapped cystically dilated renal tubules that herniate beyond the renal capsule (Am J Surg Pathol 2011;35:1264, Pathol Int 2008;58:664).

Histology shows three components: (a) epithelial cysts lined by cuboidal to hobnail cells; (b) compact subepithelial Müllerian-like AML stroma with admixed chronic inflammation and (c) muscle predominant AML with dysmorphic blood vessels exterior to the subepithelial stroma (Diagn Pathol 2007;2:11). Immunostains show that the subepithelial stroma stains most intensely with HMB45 and MelanA, as well as ER, PR and CD10. The muscle predominant AML areas stain most intensely with smooth muscle actin and desmin. The cyst lining stains for pancytokeratin, but is negative for HMB45, MelanA, ER, PR and CD10. The differential diagnosis includes mixed epithelial stromal tumor / MEST. However, MEST occurs almost exclusively occurs in perimenopausal women with obesity or receiving exogenous hormones, or men treated with lupron or DES. It lacks the distinctive dysplastic blood vessels and disorganized exterior muscular layer of AML, and has a different immunohistochemical profile.

AMLEC typically has benign behavior.

Nat Pernick, M.D., President
and Shivani Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
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Email: NatPernick@gmail.com