Blurring the lines between lesional and nonlesional MRI.

Commentary Important developments in the MRI evaluation of patients with medically resistant focal epilepsy are frequently reviewed in this journal. In the current review, we again turn to MRI and highlight a recent article examining the pathological substrate of MRI " white matter blurring " in the temporal pole of patients with mesial temporal sclerosis (MTS). The MRI abnormalities in patients with MTS, an early epilepsy imaging success story, extend well beyond the hippocampus. In addition to hippo-campal atrophy and increased T 2-weighted signal, subsequent studies showed differential atrophy with the hippocampal head most affected, along with entorhinal, perirhinal, and amygdala atrophy (1). Not only the hippocampal and cortical gray matter are abnormal in patients with MTS (2, 3), but there are also MRI abnormalities in the temporal pole white matter (4) and even outside the temporal lobe, with subcortical and extratemporal atrophy (5). The diffuse MRI abnormalities are consistent with the spectrum of neuropathological findings affecting neocorticies, including widespread, laminar-specific neocortical abnormalities (6) and white matter pathology (4, 6, 7). White-matter " blurring " refers to the increased signal on T 2-weighted images in white matter and the gray/white-matter junction. Garbelli et al. point out that while the underlying pathology for the increased T 2-weighted signal and poor distinction of gray/white matter has been variably attributed to diffuse gliosis, heterotopic gray matter in the white matter, myelin alterations, nonspecific increase in temporal lobe water content, and metabolic/perfusion alterations (4, 7, 8, 9), there is no consensus regarding the underlying functional or histo-logic abnormalities. Diffuse gliosis was not found in a previous Magnetic resonance imaging-positive temporal lobe atrophy with temporo-polar grey/white matter abnormalities (usually called 'blurring') has been frequently reported in patients with temporal lobe epilepsy associated with hip-pocampal sclerosis. The poor distinction of grey and white matter has been attributed to various causes, including developmental cortical abnormalities, gliosis, myelin alterations, a non-specific increase in temporal lobe water content and metabolic/perfusion alterations. However, there is still no consensus regarding the genesis of these abnormalities and no histopathological proof for a structural nature of magnetic resonance imaging changes. The aim of this study was to investigate the pathological substrate of temporo-polar blurring using different methodological approaches and evaluate the possible clinical significance of the abnormalities. The study involved 32 consecutive patients with medically intractable temporal lobe epilepsy and hippocampal sclerosis who underwent surgery after a comprehensive electroclinical and imaging evaluation. They …