General Considerations The appearance of the kidney on CT, usually associated with xanthogranulomatous pyelonephritis Features calcifications in a non-functioning kidney that has multiple collections of hyperattenuating masses which resemble a pattern of hydronephrosis There may be enhancement of the margins of these masses after contrast administration. This appearance on CT scans has been described as the bear paw sign It has also been described in congenital uretero-pelvic junction obstruction Bear Paw Sign Bear Paw Sign. Axial, enhanced CT of the right kidney displays a pattern of large "hydronephrotic" collections in the regions of the calyces in the shape of a bear's paw. The renal pelvis is not dilated. The sign is associated with xanthogranulomatous pyelonephritis.