Cortical rim sign (kidneys)
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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. In addition to CT and MRI, this enhancement pattern can also be visualised using CEUS 4.
See also
-<p>The <strong>cortical rim sign</strong> is useful in distinguishing <a href="/articles/acute-pyelonephritis-1">acute pyelonephritis</a> from a segmental <a href="/articles/renal-infarct">renal infarct</a> and is seen on contrast-enhanced CT or MRI.</p><p>In the setting of <a href="/articles/acute-pyelonephritis-1">acute pyelonephritis</a>, 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.</p><p>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 <a href="/articles/renal-capsular-artery">renal capsular artery</a> which is an early branch of the <a href="/articles/renal-artery">renal artery</a>. As such, when a branch of the renal artery is occluded (by thromboembolism, <a href="/articles/arterial-dissection">dissection</a> etc) perfusion may be preserved to a thin rim (2-4 mm) of cortex which enhances normally.</p><p>Unfortunately, the cortical rim sign is only seen in approximately half of renal infarcts.</p><p>A "<em>reverse </em>cortical rim sign", with relative hypoenhancement of the renal cortex and normal enhancement of the renal medulla, is a finding of<a href="/articles/renal-cortical-necrosis"> renal cortical necrosis</a>. It may occur in the setting of renal transplant rejection, intravascular haemolysis, shock, and as an obstetric complication <sup>3</sup>. In addition to CT and MRI, this enhancement pattern can also be visualised using CEUS <sup>4</sup>. </p><h4>See also</h4><ul><li><a href="/articles/rim-sign-renal-vascular-compromise">rim sign in renal vascular compromise</a></li></ul>- +<p>The <strong>cortical rim sign</strong> is useful in distinguishing <a href="/articles/acute-pyelonephritis-1">acute pyelonephritis</a> from a segmental <a href="/articles/renal-infarct">renal infarct</a> and is seen on contrast-enhanced CT or MRI.</p><p>In the setting of <a href="/articles/acute-pyelonephritis-1">acute pyelonephritis</a>, 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.</p><p>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 <a href="/articles/renal-capsular-artery">renal capsular artery</a> which is an early branch of the <a href="/articles/renal-artery">renal artery</a>. As such, when a branch of the renal artery is occluded (by thromboembolism, <a href="/articles/arterial-dissection">dissection</a> etc) perfusion may be preserved to a thin rim (2-4 mm) of cortex which enhances normally.</p><p>Unfortunately, the cortical rim sign is only seen in approximately half of renal infarcts.</p><h4>See also</h4><ul><li><a href="/articles/rim-sign-renal-vascular-compromise">rim sign in renal vascular compromise</a></li></ul>
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