Bear paw sign (kidney)

Last revised by Dr Mostafa El-Feky on 22 Oct 2021

The bear paw sign refers to the cross-sectional appearance of the kidney affected by xanthogranulomatous pyelonephritis. There is a radial arrangement of multiple, low attenuation rounded spaces representing dilated calyces, surrounded by thin renal parenchyma that has higher attenuation or contrast enhancement, mimicking the appearance of the dark toe pads on a polar bear's paw.

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Cases and figures

  • Figure 1: polar bear (photo)
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  • Case 1: bear paw sign
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  • Case 2: even seen on non-contrast CT
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  • Case 3
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  • Case 4
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