Multilocular renal cysts in adults. Possible relationship to renal adenocarcinoma.

Three grossly typical multilocular renal cysts are described. In one case, results from cytologic examination of a cyst aspirate were suggestive of malignancy. In this and the second case, histologic examination revealed cysts lined by attenuated to pump epithelium, with mild cytologic atypia and clear cytoplasm. The third case, arising in the clinical setting of chronic renal insufficiency, had the above histologic features as well as papillary proliferations and septal invasion by clear cells, interpreted as a renal adenocarcinoma. Although the preoperative evaluations in each case were suggestive of a multilocular cyst, a cystic or partially necrotic adenocarcinoma could not be ruled out. The concept of renal adenocarcinoma arising in a multilocular cyst is controversial. Because the natural evolution of multilocular cysts is indolent, these papillary and clear cell changes may represent a malignant neoplasm or a peculiar atypical hyperplasia.