Renal duplication with a diminutive lower pole: the Nubbin sign

Eight patients with a duplex kidney demonstrated severe attenuation of parenchyma in the lower pole. The radiographic appearance of a diminutive lower collecting system indicated the proper diagnosis when there was sufficient parenchyma for visualization. Parenchymal attenuation may represent either hypoplasia or inflammatory atrophy. Whichever the cause, it is important that the diminutive lower pole not be mistaken for a renal mass, extrinsic tumor, renal infarction, or a postoperative change.