Perinephric stranding refers to the appearance of edema within the fat of the perirenal space on CT or MRI. While a degree of symmetric bilateral perinephric stranding is common, particularly in the elderly, asymmetric or unilateral perinephric stranding is an important sign of renal inflammation or of acute obstruction. As such, it is seen in conditions such as acute pyelonephritis and with ureteric calculi. Care should be taken to differentiate perinephric stranding from normal perinephric bridging septa.
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