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Cortical rim sign

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

The cortical rim sign is useful in distinguishing lobar nephronia from a segmental renal infarct and is seen on contrast enhanced CT or MRI.

The wedges of reduced enhancement seen in the setting of acute pyelonephritis represent oedema and ischaemia which involves the whole wedge or renal parenchyma, from medulla to the capsule.

In segmental infarcts, the later blood supply to the very outer aspect of the cortex is derived from perforating branches of the renal capsular artery which is an early branch of the renal artery. As such, when a branch of the renal artery is occluded (by thromboembolim, dissection etc..) perfusion is preserved to a thin rim (2 - 4mm) of cortex which enhances normally.

Unfortunately the cortical rim sign is only seen in approximately half of renal infarcts.

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