Low-Signal-Intensity Renal Cortex

The normal renal cortex is more intense than the medulla on T1-weighted images. Low-signal intensity in the renal cortex on T2-weighted images can be seen with intravascular hemolysis and renal cortical necrosis. Diseases that can give this appearance include:

• Paroxysmal nocturnal hemoglobinuria:Proteinuria, hematuria, hemosiderinuria.
• Sickle cell disease: The T2-weighted, fat-saturated image above is from a patient with sickle cell disease (SSD). In SSD, most of the hemolysis is extravascular, which does not lead to low signal intensity in the cortex. Intravascular hemolysis occurs during crises and can be due to multiple transfusions. Other findings in SSD include low signal intensity in the spleen due to extravascular hemolysis and low signal intensity in the liver or pancreas in patients who have received multiple blood transfusions.
• Mechanical hemolysis (e.g, from heart valves).
• Renal cortical necrosis: The inner cortex is involved. Can be due to third-trimester obstetric hemorrhage, severe traumatic shock, septic shock, transfusion reaction, severe dehydration, venom toxin, hemolytic uremic syndrome, and renal transplantation.

References

• Hricak H, Crooks L, Sheldon P, Kaufman L. Nuclear magnetic resonance imaging of the kidney. Radiology 1983; 146:425-432.
• Jeong JY, Kim SH, Lee HJ, Sim JS. Atypical Low-Signal-Intensity Renal Parenchyma: Causes and Patterns. RadioGraphics 2002; 22:833-846.