El signo de la "pata de oso" En TC

the "bear paw sign" is an unusual radiologic finding indicating xantogranulomatous pyelonephritis (xgp). it refers to the replacement of the renal parenchyma by necrotic areas or xanthomatous collections with a pattern mimicking hydronephrotic calyx dilatation, associated with peripheral enhancing of the renal cortex after intravenous contrast administration. this sign can be observed on computed tomography (ct) scannings, where the cross-sectional appearance of the kidney resembles the paw of a bear and necrotic areas mimic the toe-pads of the paw. depending on the presentation of the disease (i.e., focal or diffuse), a differential diagnosis considering tumor-like renal cell carcinomas or fibrolipomatous replacement of the kidney has to be performed. a proper recognition of the "bear paw sign" on ct scans enables the radiologist to establish the diagnosis of xgp.