[A case of mixed epithelial and stromal tumor (MEST) of the kidney monitored as angiomyolipoma (AML) : a case report].

A 32-year-old woman presented with left abdominal pain. Intratumoral hemorrhage within a renal angiomyolipoma (AML) was suspected and embolization was performed. However, the patient declined surgery and was thus kept under observation. During the next 5 years, the tumor increased in size, and upper left abdominal pain appeared. Therefore, left radical nephrectomy was performed. The histopathological diagnosis was mixed epithelial and stromal tumor (MEST) of the kidney. A retrospective examination of imaging findings indicated that the fat which had been regarded as evidence of AML was actually either perinephric fat displaced by either the tumor or the renal sinus. In fact, the tumor consisted mainly of a cystic component containing a solid component. The possibility of MEST must be kept in mind when distinguishing renal tumors consisting mainly of cystic components in young to middle-aged women.