Flank pain with no stone: a wedge-shaped, non-enhancing cortical defect with the cortical rim sign, or global non-enhancement — then the cause (embolus from the heart, dissection, thrombosis).
Orient first
- Renal infarction is underdiagnosed because it mimics colic and pyelonephritis.
- The cortical rim sign — a thin enhancing subcapsular rim from capsular collaterals — separates infarct from pyelonephritis (after several hours).
- Causes: cardioembolism (atrial fibrillation), renal artery dissection, aortic dissection, vasculitis, thrombophilia.
Acquire the study
- CT with IV contrast: arterial and nephrographic phases; CT angiography when a renal artery or aortic cause is sought.
The manoeuvre
- Nephrographic phase: sharply demarcated wedge-shaped non-enhancing area with its base at the capsule.
- Cortical rim sign: a thin enhancing peripheral rim over the defect.
- Arterial phase: renal artery or branch occlusion, dissection flap, aortic source.
- Other organs: splenic infarcts, bowel ischaemia (embolic shower).
- Look for cardiac thrombus if the heart is in the field.
What confirms it
- A wedge-shaped non-enhancing renal defect with a rim sign or a demonstrated arterial occlusion.
What licenses you to exclude it
- Homogeneous nephrographic enhancement of both kidneys excludes established infarction.
The classic misread
- Calling a striated nephrogram of pyelonephritis an infarct — pyelonephritis is striated and has no rim sign.