Localized cystic disease of the kidney: distinction from cystic neoplasms and hereditary polycystic diseases.

Cystic changes are common in both neoplastic and non-neoplastic kidney diseases. The most important diagnostic consideration is to rule out cystic neoplasms and hereditary polycystic kidney disease for patient management. Localized cystic disease of the kidney is a rare, nongenetic and nonprogressive cystic disease that may mimic cystic neoplasms or hereditary polycystic disease. However, reports in the literature on its pathologic characteristics are scarce, and most surgical pathologists are unfamiliar with this entity. We report the clinicopathologic characteristics of 9 such cases that mimicked renal neoplasms and were treated surgically. Nine patients, including 5 men and 4 women, had a mean age of 33.3 years (range, 18 to 56 y) at diagnosis. Two patients presented with gross hematuria. In the remaining 7 patients, localized cystic disease was discovered incidentally. None had a personal history of cystic disease of the kidney or other organs or a family history of cystic renal disease. On imaging studies, solitary multilocular cystic lesions were identified in all patients with a mean size of 2.9 cm (range, 0.8 to 6 cm). Of 7 patients with documented Bosniak classification, 4 lesions were class III, and 3 lesions were class II. Follow-up was available in 5 patients, with a mean follow-up time of 14.6 months (range, 5 to 31 mo). No cysts were observed in the ipsilateral and contralateral kidneys during follow-up. Partial and total nephrectomy was performed in 8 and 1 patient, respectively. Grossly, the cystic lesions were not discrete and merged imperceptibly with the adjacent renal parenchyma without a discrete margin or capsule. Microscopically, cystic lesions involved renal papillae in all cases, and the cystic space was continuous with dilated collecting ducts. Cysts were lined with cuboidal or flat epithelial cells identical to those lining the collecting ducts. Significant inflammation was absent. The surrounding renal parenchyma was normal. With this study, we hope to raise awareness among surgical pathologists of this rare cystic lesion in order to avoid potential misdiagnosis of this lesion as a cystic neoplasm or hereditary polycystic disease. We also presented a diagnostic algorithm for working up the renal cystic lesions.