Abstracts

Rationale: The reason for nonlateralized Wada memory in patients with intractable temporal lobe epilepsy (TLE) remains unclear. Since quantitative morphometric MRI studies in such patients have shown bilateral regional atrophy in temporal and extratemporal structures, we hypothesized that volume loss in contralateral temporal structures could contribute to nonlateralized Wada memory results. Methods: We investigated patients with TLE who underwent standard presurgical evaluation during 2005-10. Patients with focal lesions other than mesial temporal sclerosis (MTS) were excluded. Seizure onset was determined by video-EEG monitoring. Wada test was done with a fixed dose of 120 mg of sodium amytal. Memory was assessed with 17 or 18 verbal and nonverbal items. Memory was considered nonlateralized if the difference in % correct recall scores between ipsilateral and contralateral injections was ≤ 11% (i.e., 2 items). Volumetric data obtained from 3T MRI using FreeSurfer software were compared against a pre-existing database of 22 age/gender-matched controls to determine the extent of abnormalities. Between-group differences in volume/cortical thickness of temporal structures was assessed by t-test. Relationship between volume and Wada memory scores was evaluated by Spearman's rank correlation coefficient. Statistical significance was declared for p value < 0.05. Results: Thirty-six patients (34 right-handed, 2 left-handed) met the inclusion/exclusion criteria. Of these, 22 had left TLE (14 MTS, 8 nonlesional) and 14 with right TLE (7 MTS, 7 nonlesional). All patients had higher Wada memory scores with injections ipsilateral to the surgical hemisphere. Ipsilateral scores were lower in patients with left TLE than right TLE (55±21 vs 67±26%, p=0.06). Wada memory was lateralized in 27 (75%) and nonlateralized in 9 patients (25%). All nonlateralized scores were seen in left TLE. In left TLE, the ipsilateral scores were significantly lower in the nonlateralized than the lateralized group (33±16 vs 55±21%, p= 0.007) but the contralateral scores were similar in the two groups (30±22 vs 37±19, p=0.7). Among all patients, right injection scores were significantly correlated with volume/cortical thickness of left hippocampus (r= 0.49), amygdala (r=0.36), parahippocampal gyrus (r=0.38), fusiform gyrus (r= 0.45) and entorhinal cortex (r=0.32). Left injection scores were significantly correlated with the volume of right hippocampus (r= 0.39) and left transverse temporal gyrus (r= 0.45). Regardless of the side of seizure onset, the volumes of temporal lobe structures were reduced bilaterally although more pronounced ipsilaterally. The contralateral temporal lobe volume loss was significant in patients with nonlateralized than lateralized Wada test (p< 0.05). Conclusions: Patients with TLE have significant volume loss in bilateral temporal structures. The observed volume loss in the nonsurgical temporal structures may contribute to the nonlateralized Wada memory in these patients.