Abstracts

RATIONALE: The postoperative outcome of the refractory epilepsy associated with focal cortical dysplasia (FCD) is very unsatisfactorily[prime]. The morphological demarcation of FCD remains problematic despite of the advances in the sensitivity of imaging studies. ¹⁸FDG-PET shows hypometabolic zones with high sensitivity, which are often not restricted on the epileptogenic lesion or on the zone of the seizures peacemaker. Furthermore, operative electrocorticography studies have found epileptic activity in areas shown to be hypometabolic on ¹⁸FDG-PET scans. In the present study, we evaluated, if the extension of the hypometabolic zone beyond or further of the resection area has an influence on the postoperative seizures outcome.
METHODS: Preoperative ¹⁸FDG-PET of 14 patients with refractory epilepsy and MRI and/or histologically confirmed focal cortical dysplasia were evaluated by means of SPM99 regarding statistical significant hypometabolic zones. Hypometabolic zones were merged with postoperative 3D-MRI (MPRAGE) data. The distribution of hypometabolic zones was classified as (1) absent, (2) restricted to the lobe of the dysplasia, (3) involving otther lobes of the ipsilateral hemisphere, (3) involving also the contralateral hemisphere. We have correlated these findings with the postoperative seizure outcome (seizures free vs. not seizures free) and the extension of the resection with a follow-up period of 6-21 months (mean: 9 months).
RESULTS: From 14 patients, 9 had a hypometabolic zone on the area of the dysplastic lesion detected with high-resolution MRI. In 1 of 9 patients, the hypometabolic area was restricted to the MRI lesion, in 8 patients the hypometabolism were restricted to the same lobe but was more extended than the morphological lesion. 4 patients had an additional ipsilateral hypometabolism involving other lobes, and 7 patients had hypometabolic zones in the contralateral hemisphere. 1 patient had no statistically significant hypometabolic zones. The presence of hypometabolism in the same lobe of the lesion showed a tendency better postoperative seizure outcome (p=0.07). In 5/9 patients, the hypometabolic zone within the lobe of dysplasia was resected completely. They all became seizure free irrespective of additional hypometabolic zones in other ipsilateral or contralateral lobes. In 6 patients, the hypometabolic zone within the lobe of dysplasia was resected incompletely. Only 2 of these 6 patients became seizure free. This difference was statistically significant (p=0.04).
CONCLUSIONS: A significant hypometabolic zone in the same lobe of the focal dysplasia can influence the postoperative seizure outcome negatively if it is not resected. The ¹⁸FDG-PET should be consequently taken into consideration when planning the extension of the resection. Additional hypometabolic areas outside the lobe of the lesion seem to have no relevance for the postoperative seizure outcome.
[Supported by: DAAD]