Urogenital Imaging

Renal adenoma

benign renal cortical tumour that is usually only a few mm in diameter and most often an incidental autopsy finding. Frequently there are multiple nodules in the kidney, commonly in the cortex close to the renal capsule. These tumours grow slowly, being completely surrounded by a thick connective tissue capsule containing numerous thin-walled veins. Histologically, they can be divided into papillary, tubular, alveolar and sometimes mixed types. Most adenomas show a papillary structure on histological examination with the fronds often within cystic areas and occasionally with foci of calcification. Some adenomas exhibit a tubular structure of elongated, irregular tubules, commonly with basophilic cells. In other adenomas, the alveolar type, the predominant cells have abundant clear cytoplasm and small hyperchromatic nuclei often indistinguishable from clear cell adenocarcinoma of low malignancy or precursors of adenocarcinoma. Although a size of less than 3 cm in diameter was originally used as a criterion for benign adenoma, renal adenomas are currently considered benign if they are less than 2 cm in diameter and show no pathological, histological or imaging features to suggest malignant or aggressive behaviour. The distinction is, however, often academic, since with increased use of cross-sectional imaging, small renal cell carcinomas are also detected. Renal adenomas even when large are usually asymptomatic, due to their peripheral location in the kidney and absence of destruction of the pelvicalyceal system. Oncocytoma is a rare type of adenoma with characteristic histological features. Also, see oncocytoma renal.

On urography the features are alteration of the renal contour; however, small adenomas may cause no bulge. Occasionally the adenoma may be very vascular resembling a renal cell carcinoma. CT also shows an enhancing mass that may be difficult to differentiate from a renal cell carcinoma.

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