Urogenital ImagingAcute renal cortical necrosis
a distinct and very rare form of acute
renal failure. It is characterized pathologically by
ischaemic necrosis of the
renal cortex with relative sparing of the medulla. The precise pathogenesis is unclear, but most cases occur in pregnancy complicated by placental abruption, septic abortion or placenta previa. Acute cortical necrosis may also occur with burns, sepsis, incompatible blood transfusion, dehydration or
peritonitis.
In the early phase of acute cortical necrosis, ultrasound (US), CT or MRI demonstrates bilateral renal enlargement. Urography may show a feeble or absent nephrogram with faint opacification of the collecting systems. However, urography is now rarely performed in acute renal failure. Later, the kidneys shrink with preservation of a smooth renal outline. Characteristic tramline calcification may develop in the renal cortex. Tramline calcification develops at what are believed to be the boundaries of the ischaemic cortex. Externally the boundary is with a thin rim of subcapsular cortex, and internally the boundary is with a thin rim of juxtamedullary cortex. The spared subcapsular and juxtamedullary cortex are presumed to have a different arterial supply to the ischaemic cortex. These delayed changes may be associated with reduced echogenicity in the outer cortex on US, and hypoattenuation in the outer cortex at CT (Fig.1). The extent of cortical necrosis determines whether renal failure supervenes, in which case renal replacement therapy is required.
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Axial contrast-enhanced CT section through the kidneys demonstrates a peripheral rim of nonenhancement (arrows) in the cortex of both kidneys, due to acute cortical necrosis.
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Acute renal cortical necrosis, Fig.1 | |