Bear Paw Sign

 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. 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.

Evolving concepts in the diagnosis of xanthogranulomatous pyelonephritis. Parker MD, Clark RL  Urol Radiol 1989; 11:7-15. 

Classic Signs in Uroradiology. RB Dyer, MY Chen, and R. Zagoria,. RadioGraphics, October 2004, Volume 24, Issue suppl_1