Purpose: To demonstrate magnetic resonance imaging (MRI) findings of the focal sparing of iron and fat in liver tissue in patients with hepatic iron overload.
Materials and methods: We retrospectively reviewed 48 liver MRIs performed in patients with hemosiderosis from 2007-2009. We selected five (10%) of these patients based on the observation of focal signal abnormalities in the posterior aspect of segment 4, anterior to the portal vein, on in- and out-of-phase T1-weighted gradient-echo images. To further characterize this signal abnormality in segment 4, we calculated the simultaneous proton density fat fraction and R2* relaxometry using the investigational version of a quantitative chemical shift-based water-fat separation method known as IDEAL-IQ with a multiecho gradient echo sequence. Visual assessment and objective measurements were performed for the focal sparing of iron and fat.
Results: The diagnoses of the five patients included thalassemia (n=3), aplastic anemia (n=1), and myelodosysplastic syndrome (n=1). The focal sparing of iron was hypointense on R2* relaxometry compared to the rest of the liver. Fat fraction images failed to demonstrate a heterogeneous fat distribution. The focal sparing of fat in the liver with iron overload appeared as a reduced fat-containing area (fat fraction, 4%) in segment 4 compared to the remainder of the left lobe (fat fraction, 12%). The R2* map revealed no difference between the focal fat-sparing area and the rest of the liver. Areas in which focal fat and iron sparing occurred were not visible on post-contrast and diffusion-weighted images.
Conclusion: Focal fat and iron sparing in patients with liver siderosis can mimic a lesion. Quantitative MRI techniques can help to characterize abnormal signal changes in segment 4 of the liver in patients with hepatic iron overload and can eliminate the need for biopsy of pseudolesions.