Transient Focal Lesions in the Splenium of the Corpus Callosum with Restricted Diffusion: An Enigma

Small transient lesions in the central part of the splenium of the corpus callosum (SCC) have been reported in MR examinations, particularly in patients with encephalitis or encephalopathy, and in patients with or without epilepsy who are receiving antiepileptic drugs. The MR findings are characteristic: an ovoid T2-high signal lesion in the SCC, no enhancement after contrast agent, restricted diffusion shown by diffusion MR imaging, and complete disappearance on follow-up MR examinations. Most noteworthy is that these lesions have restricted diffusion but are reversible, which is distinct from infarction lesions seen in energy failure. The exact mechanism of these transient lesions remains uncertain and enigmatic. We review previously reported patients to show these unique MR findings and describe possible pathogenesis of particular SCC lesions.