[Renal angiomyolipoma with epithelial cysts: a clinicopathological analysis of four cases]

Objective: To investigate the clinicopathological features,diagnosis and differential diagnosis of renal angiomyolipoma with epithelial cysts(AMLEC). Methods: Four cases of renal AMLEC diagnosed between January 2014 and June 2019 at the Department of Pathology,Zhejiang Provincial People's Hospital were subjected to clinicopathological, histological and immunohistochemistry analyses along with a literature review. Results: All the four patients were females and aged from 19 to 52 years (mean 34.5 years). Three cases were accidentally discovered by physical examination, and the medical history was 1 to 6 years. The preoperative imaging Bosniak classification was grade Ⅲ in 3 and grade Ⅳ in 1 case. The maximum diameter of the tumor ranged from 2.5 to 9.0 cm (average 5.0 cm). Histologically, all of the 4 tumors showed three histological components: (1) simple epithelial cysts lined by a layer of cuboidal/low-columnar to occasionally, hobnailcells; (2) a thin, compact subepithelial "cambium-like" layer of cellular, mullerian-like short spindle cell stromas with prominent admixedchronic inflammation; (3) a outermost layer of thick, long-fascicles of smooth muscle-like stromas, often surrounded by dysplastic, tortuous thick-walled blood vessels. There was often a prominent lymphatic channel network in the smooth muscle component forming slit like branched and curvilinear spaces. None of the 4 tumors had fat content.Immunohistochemically, the epithelial cells lining the cysts strongly expressed PAX8 and CK7. The subepithelial "cambium-like" stromas strongly expressed melanocytic markers (HMB45, Melan A, Cathspin K, MiTF) and mullerian markers (ER,PR,CD10), and were negative for smooth-muscle markers(SMA,desmin,calponin). The outermost layer of smooth muscle-like stromas strongly expressed smooth-muscle markers, and were only focally positive for melanocytic and mullerian markers. Follow-up information was obtained in 3 cases, among which no evidence of tumor recurrence or metastasis was found at 3, 5, and 66 months of follow-up, respectively. Conclusions: Renal AMLEC is a rare histological subtype of angiomyolipoma with benign biological behavior, and has characteristic histological and immunophenotypic characteristics.Pathologists should be familiar with the clinicopathological appearances of AMLEC and include it in the differential diagnostic spectrums of renal tumors with biphasic epithelial and mesenchymal features.