Comparison of lesion morphology of “iron dot” lesions in Susac syndrome and multiple sclerosis

Comparison of lesion morphology of “iron dot” lesions in Susac syndrome (bottom) and multiple sclerosis (top). The figure illustrates differences in morphology on 7T T2*w images between “iron dots” in Susac syndrome (red arrows) and the central vein sign (white and black arrow) as well as T2*w hypointense core lesions (blue arrows with zoom) in multiple sclerosis. T2*-weighted imaging is an MRI sequence to quantify observable or effective T2 (T2* or "T2-star"); in this sequence, hemorrhages and hemosiderin deposits become hypointense (Chavhan GB, Babyn PS, Thomas B, Shroff MM, Haacke EM. Principles, techniques, and applications of T2*-based MR imaging and its special applications. Radiographics 2009;29[5]:1433-49). All exemplary T2*w images in the bottom are from different patients with Susac syndrome. Note that the “iron dots” in Susac syndrome (red arrows) appear punctate and sharply delineated on T2*w. In contrast, the T2*w hypointense core lesions (blue arrows with zoom) in multiple sclerosis often appear just slightly less hyperintense on T2*w in comparison to other multiple sclerosis lesions. Only when the lesion is viewed on strongly susceptibility-weighted sequences (right) does a rather diffuse signal loss become apparent. The central vein sign in multiple sclerosis also appears as a point-like, pronounced hypointensity on T2*w images when the slice plane is perpendicular to the long axis of the multiple sclerosis lesion (white arrow). However, if the slice plane is parallel to the long axis of the lesion, the central vein sign can be recognized as a straight line running through the center of multiple sclerosis lesions (black arrow). (Source: Strunk D, Sinnecker T, Kleffner I, et al. Central intra-lesional iron deposits as a possible novel imaging marker at 7 Tesla MRI in Susac Syndrome: an exploratory study. BMC Med Imaging 2024;24[1]:4. Creative Commons Attribution 4.0 International [CC BY 4.0] license, creativecommons.org/licenses/by/4.0.)