Cortical rim sign

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

In the setting of acute pyelonephritis, the areas of abnormally reduced enhancement typically involve a complete wedge of renal parenchyma, extending from medulla peripherally to the capsule. The imaging appearance is thought to correspond to a combination of oedema and ischaemia.

By contrast, segmental renal infarcts may result in wedge shaped areas of abnormal renal parenchymal hypoenhancement with relative sparing of the cortex.  This occurs because the blood supply to the 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 thromboembolism, dissection etc) perfusion may be preserved to a thin rim (2-4 mm) of cortex which enhances normally.

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

A "reverse cortical rim sign", with relative hypoenhancement of the renal cortex and normal enhancement of the renal medulla, is a finding of renal cortical necrosis. It may occur in the setting of renal transplant rejection, intravascular haemolysis, shock, and as an obstetric complication 3.

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Article information

rID: 9958
System: Urogenital
Section: Signs
Synonyms or Alternate Spellings:
  • Rim sign (of renal infarction)
  • Renal cortical rim sign

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Cases and figures

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    Absent cortical r...
    Case 1: acute pyelonephritis
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    Cortical rim sign
    Case 2: renal infarction
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    Case 3
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    Case 4
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