Mixed Epithelial Stromal Tumor of the Kidney with Polypoid Pattern A Case Report

BACKGROUND: Mixed epithelial stromal tumor of the kidney (MESTK) is a complex neoplasm of benign behavior that typically occurs in perimenopausal women. It presents as well-circumscribed, solid cystic masses that frequently protrude towards the renal pelvis. Histologically, they present a biphasic pattern composed of epithelial elements that form a glandular/cystic pattern in a fusocellular stroma of ovarian appearance that often contain receptors for estrogen and progesterone. CASE: A 63-year-old woman presented with hematuria and diffuse bilateral lumbar pain. The abdominal ultrasonography and the abdominopelvic CT scan showed an ectasia with occupation of the right renal excretory pathway. Macroscopically, in the medial third of the medullary level, a multiloculated cystic lesion with a diameter of 2 cm was observed, with a smooth wall and whitish coloration. Adjacent to this and towards the renal pelvis was a 1.5 cm, grayish polypoid lesion. The morphological and immunohistochemical findings set corresponds to a MEST. CONCLUSION: MEST is a rare entity that represents between 0.20-0.28% of all renal neoplasms. The interest of our case lies in the unusual form of presentation as a polypoid lesion in the renal pelvis, which after endoscopic resection had a recurrence associated with a cystic multiloculated lesion.