Mixed Epithelial and Stromal Tumor of the Kidney: a Case Report

Abstract

Introduction : Mixed epithelial and stromal tumor (MEST) of the renal pelvis, also known in the past as cystic hamartoma is a rare benign tumor, recently recognized as a distinct clinical and pathological entity. This complex neoplasm is composed of a mixture of stromal and epithelial elements. Women are more often involved (ratio of women to men 6:1), especially perimenopausal women. It was originally described in 1973 by Block as a congenital mesoblastic nephroma. The term MEST was credited to Michal and Syrucek in 1998. Methods and Materials : A 54-year-old woman underwent laparotomy because of pheochromocytoma. In addition, another tumor was found in the left kidney - a partly cystic and partly solid mass in the renal pelvis, so left-sided nephrectomy was carried out. Results : Macroscopically, the lesion in the renal pelvis had an oval form, measuring 15/8 cm, well circumscribed from the surrounding parenchyma, and with fatty tissue at the periphery; the cut surface revealed multiple cysts of varying size, showing papillary projections on the inner side. On histological examination, a well-delineated tumor was seen, composed of cysts of varying size lined by columnar and cuboidal epithelium. Surrounding stroma showed a mixture of an ovarian type of stroma and eosinophilic loci resembling white bodies and a lot of calcifications. Conclusion : Only about 200 cases of MEST have been described in the literature. Mixed epithelial and stromal tumor of the kidney usually presents in perimenopausal women as a partially cystic mass, and its growth may be influenced by hormones. In the literature, there is no other description of coexisting MEST and pheochromocytoma.