Papillary Adenomas and Other Small Epithelial Tumors in the Kidney: An Autopsy Study

The aim of this work was to study small neoplasms of the epithelium of the renal tubules; kidneys from 402 unselected autopsies were sectioned at 1 to 2 mm intervals. All lesions were examined histologically. A total of 232 papillary adenomas were found in 76 patients (19%), ranging from 1 to 35 adenomas/patient (mean: 3, median: 2). Patients with papillary adenomas were older (range: 27 to 90 y) (P<0.0001), more commonly smokers (P=0.01), and more frequently had glomerulosclerosis (P=0.0001) than those without. Papillary adenomas ranged in size from 0.5 to 5 mm (mean: 1.4, median: 1) and were morphologically classified in 4 subtypes. Type A adenomas consisting of papillae and/or tubules covered by cells with scant cytoplasm, often with psammoma bodies, were the most common (149 adenomas). In 30, the papillae were broad with lymphocytes in the cores (type B). Thirty were more cystic lined by columnar cells and contained macrophages and psammoma bodies (type C). Sixteen were composed of large eosinophilic cells with pseudostratified nuclei, occasionally near the apical membrane (type D). Four were unclassified. Mixtures of types were observed only once (3 adenomas in one patient, each composed of a mixture of types B and D). Other epithelial lesions included 31 adrenal rests, 5 oncocytomas, 2 clear cell papillary renal cell carcinomas, 2 tubulocystic renal cell carcinomas, and 2 acquired cystic disease-associated renal cell carcinomas. In conclusion, papillary adenoma was the most common small epithelial neoplasm. The first type of papillary adenoma (type A) closely resembles papillary renal cell carcinoma, type 1, and the fourth (type D) resembles type 2. No other type of renal cell neoplasm was found (including clear cell renal cell carcinoma and chromophobe renal cell carcinoma). No nephrogenic rest was found. Angiomyolipomas and renomedullary interstitial cell tumors were found, and these findings have been reported in earlier papers.