Abstracts

Rationale: Information on cognitive outcomes following stereotactic laser ablation (SLA) procedure for refractory temporal lobe epilepsy (TLE) remains sparse. This study examines change in neuropsychological test performance following SLA in relation to hippocampal volume loss. Methods: Neuropsychological evaluations were completed at 6-12 months pre and post-SLA. Volumetric analyses were completed by two independent experts using manual tracing with > 90% inter-rater reliability. Of 18 patients (left=10, right=8), 14 had MTS (left=7, right= 7) and 16 had fMRI/WADA documented left hemisphere language dominance (right=1, bilateral= 1). Mean duration of seizures was 29.1 years (SD=11.3) with mean age at time of surgery of 43 years (SD=13.4). 55% of the subjects were male, 78% White (78% Hispanic) and 22% African American, with an average education level of 12.4 years (SD=2.6). Results: Demographic variables did not differ based on side of ablation, with the exception of longer duration of seizure disorder in the right surgery group (p=.041). Differences in pre-surgical volumetric analyses including total temporal horn volume and pre-surgical hippocampal size were not statistically different. Patients received a total of 3-6 ablations (M=4.7, SD.75), resulting in a total volume loss ranging from 984-2312 mm3 (Left M=1731.3, SD 374.6; Right M=1455.2, SD= 422.7). Estimated percentage of hippocampus ablated ranged from 63-91% (M=81.59, SD=7.8), with no significant group differences. A one-way repeated measures analysis of variance (ANOVA) was conducted to evaluate for change in visual and verbal memory following ablation. Left ablation patients had significant time effects for delayed verbal recall (p < .05). However, no other memory measures differed significantly between time points for either the left or right ablation groups. In the right ablation group with pre and post-operative volumetric analysis (n=5), hippocampal volume loss was negatively correlated with delayed visual recall (p < .05). Percent ablated was negatively correlated with pre-post change in total visual learning score (p < .05). In the left ablation group with pre and post-operative volumetric analysis (n=8), total ablation size was significantly correlated with greater than a standard deviation change in delayed memory performance (p < .01). Correlations between all other volumetric analyses and memory measures were not statistically significant. Overall, the majority of patients experienced less than one standard deviation change in most memory measures, with only one patient experiencing greater than 1 SD decline in delayed verbal recall and one in delayed visual memory. For full neuropsychological profiles, see table 1 (attached). Conclusions: There is a wide range of hippocampal volume ablated during SLA. Our findings show concordance between side ablated and change in expected neuropsychological domains. While the majority of patients did not experience a clinically significant change in overall cognitive functioning, a few experienced greater than one standard deviation change in functions typically associated with both mesial temporal and cortical structures. Additional investigation of factors mediating post-surgical outcomes in SLA are needed in order to minimize cognitive morbidity following this procedure. Funding: none