Relevance of temporal lobe white matter changes in hippocampal sclerosis -Magnetic resonance imaging and histology

RATIONALE AND OBJECTIVES. TO evaluate the diagnostic relevance of ipsilater al atrophy of the collateral white matter in the parahippocampal gyrus (ACW Mp) and temporal lobe gray/white matter demarcation loss (GWDL) on magnetic resonance imaging in patients with histologically confirmed hippocampal sc lerosis, In the second part of this investigation, histologic specimens wer e analyzed to find an explanation for GWDL. METHODS. Retrospective visual assessment of hippocampal signal intensity an d size and of ACWMp and GWDL was performed using 4- to 5-mm coronal T2-weig hted spin-echo magnetic resonance images of 80 patients with histologically proven hippocampal sclerosis and of 30 age matched controls without epilep sy. Frequency of occurrence and likelihood ratios of ACWMp and GWDL were ca lculated and their contribution to the diagnosis of hippocampal sclerosis w as assessed, particularly in patients with no or restricted hippocampal abn ormalities (either high signal or smaller size) on magnetic resonance imagi ng. The second part of the study involved the morphologic histologic assess ment of neocortical temporal lobe specimens of all patients. Myelin density was evaluated in specimens of a subgroup of six patients with hippocampal sclerosis and GWDL on MRI and six patients with hippocampal sclerosis witho ut GWDL. RESULTS. ACWMp was found in 68% and GWDL in 65% of patients with hippocampa l sclerosis on magnetic resonance imaging, Both features had an infinite po sitive likelihood ratio. Sixty-two patients (77.5%) had concomitant hippoca mpal signal increase and smaller size. Eighteen patients (22.5 %) had no or restricted hippocampal abnormalities on magnetic resonance imaging. When u sing ACWMp and GWDL as additional diagnostic parameters, 13 of these 18 pat ients were more unambiguously diagnosed as having hippocampal sclerosis. No significant morphologic differences were found between GWDL-positive and G WDL-negative specimens, A significantly lower average myelin stain was foun d in the white matter of the GWDL-positive group compared to the GWDL-negat ive group. CONCLUSIONS. ACWMp and GWDL can improve the visual diagnosis of hippocampal sclerosis, particularly in patients with no or restricted hippocampal abno rmalities. These results suggest that loss of myelin may be the underlying cause of GWDL in association with hippocampal sclerosis.