Microscopic description and IHC:

Sections show smooth muscle bundles and dysmorphic blood vessels without an obvious adipose tissue component. Scattered throughout the lesion are epithelial cysts lined by cuboidal to hobnailed cells.

There is a compact subepithelial “cambium-like” layer of müllerian stroma. The lesional cells are negative for AE1/3 and positive for HMB45, smooth muscle actin, with ER (not shown) and PR positivity in the subepithelial stroma.

Discussion:

Angiomyolipomas (AMLs) are benign triphasic neoplasms from the perivascular epithelioid cell family of tumors. They are comprised of varying amounts of blood vessels, smooth muscle, and adipose. The cells show characteristic co-expression of melanocytic and smooth muscle markers. They occur sporadically, but are associated with tuberous sclerosis complex. They are more common in women than men.

Grossly, AMLs are usually solid lesions and lack an epithelial component. However, there is a distinct variant which appears as a cystic mass; it is known as angiomyolipoma with epithelial cysts (AMLEC). The vascular and smooth muscle elements common in typical AMLs are maintained, and a significant adipose component is uncommon. The subepithelial component is comprised of müllerian-like stroma. These lesions express the characteristic melanocytic and smooth muscle markers of AMLs, along with müllerian markers.

Mixed epithelial and stromal tumors (MEST) and cystic nephromas are part of the spectrum of renal epithelial and stromal tumors. Grossly, both are cystic lesions. MEST is associated with women and men with a long term history of estrogen exposure. The cysts are within ovarian type stroma. Cystic nephromas also contain multiple cysts within mesenchymal stroma. Both lesions can show increased vessels, however, these are well formed in contrast to the dysplastic vessels in AMLEC.

Multilocular cystic renal neoplasm of low malignant potential is composed of variably sized cysts separated by thin fibrous septa. They are lined by a single layer of tumor cells with abundant clear cytoplasm. Within the septa usually exist clusters of tumor cells similar to cells lining the cysts. This is in contrast to AMLEC in which the cysts are lined by cuboidal and hobnailed epithelium and do not have fibrous septa.

Metastatic endometrial cancer would be unlikely in a male.

References:

Fine SW, Reuter VE, Epstein JI, Argani P. Angiomyolipoma with epithelial cysts (AMLEC): a distinct cystic variant of angiomyolipoma. Am J Surg Pathol. 2006 May;30(5):593-9.

Tajima S, Yamada Y. Cysts in angiomyolipoma with epithelial cysts may be consisted of entrapped and dilated renal tubules: report of a case with additional immunohistochemical evidence to the pre-existing literature. Int J Clin Exp Pathol. 2015 Sep 1;8(9):11729-34. eCollection 2015.

Davis CJ, Barton JH, Sesterhenn IA. Cystic angiomyolipoma of the kidney: a clinicopathologic description of 11 cases. Mod Pathol. 2006 May;19(5):669-74.

Montironi R, Cheng L, Lopez-Beltran A, Michal M, Moch H. “Multilocular cystic renal neoplasm of low malignant potential.” WHO Classification of Tumors of the Urinary System and Male Genital Organs. Ed. Holger Moch, Ed. Peter A . Humphrey, Ed. Thomas M Ulbright, and Ed. Victor E. Reuter. Lyon, 2016. 22. Print.

CASE IMAGES