THE RELATION BETWEEN QUANTITATIVE MRI MEASURES OF HIPPOCAMPAL STRUCTURE AND THE INTRACAROTID AMOBARBITAL TEST

Purpose: The increasing sophistication of quantitative magnetic resona nce imaging (MRI) techniques has generated hopes that they may eventua lly supersede the intracarotid amobarbital procedure (IAP) in the pres urgical screening for bilateral abnormalities in prospective candidate s for temporal lobe epilepsy surgery. As the first step toward this ai m, the purpose of this study was to examine the relationship between t hese measures of structural and functional integrity. Methods: We exam ined the relation between memory performance and pass/fail rates on th e IAP and two MRI measures of hippocampal integrity: hippocampal volum es, adjusted for intracranial volume (HCvol) and hippocampal T-2 relax ometry (HCT2), in 48 patients with medically intractable temporal lobe epilepsy, who underwent the IAP as part of their presurgical evaluati on for temporal lobectomy. Results: The unilateral memory scores from the IAP were not significantly correlated with the corresponding HCvol or HCT2 measures in the right- and left-temporal-lobe groups. However , the MRI measures of hippocampal asymmetry (right minus left HCvol, r ight minus left HCT2) were significantly correlated with our measure o f functional asymmetry, the right minus left hemisphere memory score f rom the IAP, supporting the role of the IAP in lateralising temporal l obe dysfunction. Forty-six patients with unilateral hippocampal sclero sis and concordant EEG studies passed the IAP. Two patients failed the memory component of the IAP. In both cases, other presurgical investi gations suggested bilateral abnormalities. Conclusions: We conclude th at patients with unilateral hippocampal sclerosis, established by a ri gorous quantitative MRI protocol, and concordant ictal and interictal EEG findings may not be at risk for postoperative amnesia, despite bas eline neuropsychological deficits suggestive of bilateral disturbance.