Abstracts

Rationale: 18-?uorodeoxyglucose positron emission tomography (FDG-PET) is often used in pre-surgical workup to localize the seizure onset zone for patients with medically refractory focal epilepsy.  Its utility has been demonstrated by multiple studies, which have shown that the presence of FDG-PET glucose hypometabolism in the epileptogenic temporal lobe is predictive of seizure freedom after surgery.  However, FDG-PET hypometabolism is typically larger than the abnormality identified on structural imaging beyond the temporal lobe.  Previous studies have suggested that when extratemporal regions are involved, this typically portends a less favorable post-surgical outcome. However, involvement of specifically which extratemporal regions leading to negative outcomes has not been well defined. Methods: Thirty-eight patients were studied who underwent medial temporal lobectomies for medically refractory epilepsy due to histopathology-confirmed medial temporal sclerosis (MTS) with at least 5 years of post-operative follow up.  Preoperative FDG-PET was segmented and analyzed quantitatively for region-based Z-scores using MIM software.  Surgical outcomes were based on Engel scores, and divided into group 1A (complete seizure freedom) and not 1A (incomplete seizure freedom). Regions predictive of post-surgical outcome were determined by ridge regression using Z-scores for asymmetry, ipsilateral regions, and contralateral regions. Results: A total of 38 cases were identified, including 25 with class 1A outcome after 5 years and 13 with worse outcomes. The average time from FDG-PET to resection was 10.26 years.  Of those with a good outcome, 54.2% had a history of generalized tonic clonic seizures, as compared to 38.5% of those with a bad outcome.  The most evident differences between the good and poor outcome groups were in four regions: middle frontal gyrus (p=0.002), paracentral lobule (p=0.018), thalamus (0.020), and posterior cingulate (0.032). In the paracentral lobule, the asymmetry was due to higher contralateral than ipsilateral FDG uptake in the poor outcome group relative to good outcomes. In the middle frontal gyrus, thalamus, and posterior cingulate, there was no reliable directionality to the asymmetry. These four regions were also good predictors of outcome (p=0.010, p=0.019, p=0.021, p=0.025 respectively).  Additionally, some changes were good predictors of outcome despite being limited to small numbers, such that they did not affect the mean group scores. The most prominent of these changes were asymmetry in the middle occipital gyrus (p=0.005), superior temporal gyrus (p=0.007), and insula (p=0.025), as well as hypometabolism in the contralateral hippocampus (p=0.025).  Conclusions: Quantitative analysis of FDG-PET from patients with medial temporal sclerosis showed increased asymmetries in the  middle frontal gyrus, paracentral lobule,  thalamus, and posterior cingulate that were associated with worse post-surgical seizure. The findings in this study are significant when tailoring specific patient treatment options, stratifying which patients would be better surgical candidates, and prevent unwarranted harm to those who are not. Funding: No funding was received in support of this abstract.