MR imaging of hemorrhage and iron deposition in the kidney.

Hemoglobin and its degradation products result in signal intensity changes at T1- and T2-weighted magnetic resonance imaging that can either facilitate or obstruct diagnosis of renal lesions. These substances are deposited in the kidney by means of hemorrhage or systemic intravascular hemolysis. Hemorrhage commonly occurs into a renal cyst, resulting in an appearance that cannot be reliably distinguished from that of renal cell carcinoma without use of contrast material. Hemorrhage may also occur diffusely in the renal medulla, and the resulting low signal intensity on T1- and T2-weighted images is characteristic of the rare disease hemorrhagic fever with renal syndrome. Systemic intravascular hemolysis results in low signal intensity in the renal cortex on T2-weighted images, owing to hemosiderin deposition; this occurs in severe hemolytic anemias. Familiarity with the spectrum of findings in the kidney resulting from hemorrhage or iron deposition is necessary for accurate diagnosis of renal disease.