Mixed epithelial and stromal tumor of the kidney with polypoid component extending into renal pelvis and ureter
A 61-year-old postmenopausal woman presented with gross hematuria for two weeks. The physical examination was unremarkable. She had no relevant family history or medical history other than mild obesity. Her routine blood investigation was normal with no elevated serum tumor marker. Ultrasonography revealed the presence of a left renal mass in the interpolar region extending into the renal pelvis. Exfoliative urine cytology was class 3. Excretory phase contrast-enhanced CT (Fig. ) showed a well-circumscribed multiseptate cystic mass of 44 × 40 × 45 mm in the interpolar region of the left kidney with a polypoid solid component protruding into the renal pelvis and proximal ureter. Calcification was identified within the solid component. Retrograde ureterography (Fig. ) showed mild hydronephrosis due to the polypoid part of the tumor in the ureter. Dynamic MRI study (Figs. and ) demonstrated delayed contrast enhancement of the solid polypoid component and multiple septa.\nSince the tumor was consistent with a Bosniak category IV cystic mass, we performed a laparoscopic left nephro-ureterectomy. Gross examination showed a well-marginated multilocular cystic mass with a polypoid solid component protruding into the renal pelvis and ureter (Fig. ). Histopathological analysis revealed an intermixture of epithelial elements consisting of varying sized glands and a proliferation of spindle cells resembling ovarian stroma. The polypoid lesion was superficially covered with normal urothelium. Complex glands with a single layer of flattened, cuboid or hobnail-appearing epithelium and a mild cellular atypia of swollen nuclei were marked in the cystic lesion. The tumor was well-marginated but no capsule was found histologically. No malignant cells were found. Immunohistochemically, spindle cells expressed vimentin and alpha smooth muscle actine, and were partially positive for progesterone receptor, bcl-2, CD99, and desmin. Epithelial cells were positive for cytokeratin and epithelial membrane antigen, partially positive for vimentin, bcl-2 and negative for CD99, alpha smooth muscle actine, desmin, or progesterone receptor. The estrogen receptor was negative in both. On the basis of the morphologic and immunohistochemical findings a pathologic diagnosis of MEST was achieved.\nThe postoperative course of the patient was uneventful. There was no local recurrence or metastasis during 10-month follow-up.