Adult Cystic Nephroma and Mixed Epithelial and Stromal Tumor of the Kidney: Clinical, Radiographic, and Pathologic Characteristics

Objectives: Adult cystic nephroma (CN) and mixed epithelial and stromal tumor (MEST) are benign renal tumors readily distinguished from cystic renal cell carcinoma and other malignant variants based on histopathology. Clinical and radiographic data regarding these lesions are sparse, especially with respect to factors providing clinical suspicion for CN or MEST. Methods: Pathology of 22 CN (21 patients) and 10 MEST (9 patients) treated between 1987 and 2005 was re-reviewed according to 2004 WHO classification. Results: Nineteen CN patients (90%) and 9 MEST patients (100%) were female and median ages were 55 (range: 39 to 79) and 52 (range: 39 to 67) years, respectively. Twenty-two patients (73%) presented symptomatically. CN were commonly Bosniak III lesions (77%), whereas 70% of MEST had solid enhancing components. An intrapelvic component was present in 5 CN (23%) and no MEST. Preoperative radiologic suspicion was documented in 36% of CN, but in only 1 patient with MEST. Nephron-sparing surgery was performed for 16 tumors (50%), including 5 suspected preoperatively and 3 that were 7 cm or greater. There was 1 case each of bilateral CN and MEST. Two patients with CN had concomitant renal cell carcinoma. One patient with MEST had sarcomatous component. At mean follow-up of 4.5 years (range: 1 to 18), no patient had novel or recurrent tumors develop. Conclusions: CN and MEST typically present symptomatically in perimenopausal women. Pedunculation of a multiloculated cystic lesion may allow for preoperative suspicion of these lesions in the proper clinical setting. Nephron-sparing surgery is the preferred treatment even for large and/or central lesions, if amenable.