Renal angiomyolipoma with epithelial cysts: report of a rare cystic variant of angiomyolipoma and review of the literature

Angiomyolipoma with epithelial cysts (AMLEC), or cystic AML, is a recently characterized, distinctive cystic subtype of AML of the kidney. To date, less than two dozen of such case have been reported. Herein, we reported a prototypical case of AMLEC occurring in a 41-year-old female patient who presented with left low back pain for one month. Abdominal computed tomograph scan demonstrated a well-demarcated, 2.5-cm complex cystic mass in the mid-pole of left kidney which abutted renal capsule and protruded into perirenal fat. Laparoscopic tumorectomy was performed. Histologically, the tumor was composed of three components. The first component was multiple cysts lined by cuboidal to columnar epithelial cells. The second component was a compact layer of subepithelial “cambium-like” condensation composed of short-spindled to small round stromal cells. The third component was a thick exterior wall of plump smooth muscle cells that arranged in poorly formed fascicles, appearing to emanate from thick-walled, dysplastic blood vessels. Immunohistochemically, the subepithelial stromal cells showed strong and diffuse reactivity to antibodies against HMB45, melan A and CD10, and patchy reaction to antibodies against smooth muscle actin (SMA) and desmin. The exterior smooth muscle cells strongly and diffusely expressed SMA and desmin and occasionally expressed HMB45, melan-A and CD10. Both subepithelial stroma and exterior smooth muscle cells showed strong and diffuse nuclear labeling for ER and PR. The epithelium lining the cystic spaces labeled strongly with PAX8, AE1/AE3 and CK7, but not with melanocytic markers or hormone receptors. The patient has been alive with no evidence of disease for 8 months postoperatively. We summarize the clinicopathologic features of this usual variant of AML with an emphasis on differential diagnosis based on literature review.