Abstracts

RATIONALE: This study[ssquote]s goal was to examine the ability of Wada results to predict surgical outcome following left or right anterior temporal lobectomy. We expected our Wada lateralization index to be a better predictor of seizure control than more general measures of cortical integrity. As the left and right hemisphere may have different capacities for altering cognitive processes and compensating for surgery, we assessed prediction of outcome separately for left and right temporal lobectomy patients.
METHODS: Wada scores from a 176 left and 181 right temporal lobectomy patients were used with separate analysis for the left and right side surgery groups. Discriminant function analyses were used to determine the relative power of the variables to predict post-surgical seizure control using a 6-level scheme for classifying outcome: the isolated ipsilateral and contralateral Wada scores, the Wada lateralization ratio, measures of general cortical integrity (verbal and performance IQ), and handedness. We examined the predictive power of isolated ipsilateral (operated) and contralateral (nonoperated) hemisphere Wada performance, the ratio between them (difference in the Wada scores, divided by the total score), and measures of general cortical integrity (VIQ and PIQ scores) to predict seizure control, because IQ has been found to be related to seizure outcome with higher IQ indicating a better prognosis. We viewed the Wada ratio as an index of memory lateralization, more reflective of the consequences that ensue following temporal lobe surgery due to shifts in the neurocognitive demand placed on each hemisphere.
RESULTS: The discriminant function analysis in left temporal lobectomy patients was significant and contained three factors (Wilks[ssquote][lambda] .822, [chi]2=32.2, df=18, p [lt].05). The largest canonical function explained 67.4% of the variance in surgical outcome with the loading for the Wada ratio highest (standardized coef.=.91, 27.6% higher than others) and Verbal IQ second in strength (stand. coef.=-66). Performance IQ and handedness also loaded significantly on this factor. The second canonical function explained 23.3% of the variance in surgical outcome with handedness (stand. coef.=-.54) and contralateral Wada scores (stand. coef.=.55) the significant loadings. The discriminant function analysis with the right temporal lobectomy patients was not statistically significant.
CONCLUSIONS: Measures of memory lateralization and general measures of cortical integrity have predictive power in terms of post-surgery seizure control. The best predictor was the asymmetry between Wada scores for the two hemispheres. This Wada ratio data suggested that when the contralateral side possessed a larger advantage in memory the surgical outcome was worse; conversely, when ipsilateral memory was superior the surgical outcome was better. The results suggest: (1)Wada memory variables that take into account the context of overall Wada performance provide better predictive power than the Wada memory scores from the isolated hemispheres, (2) Wada memory asymmetry predicts surgical outcome more strongly than measures of general cerebral integrity or gross indices of cerebral dominance, (3) if the asymmetry in Wada scores reflects good functional reserve for memory in the hemisphere undergoing surgery than the prognosis for outcome is improved.