Abstracts

Resection of hippocampus (HIP)has been the standard procedure for patients with drug resistant (DR) medial temporal lobe epilepsy (MTLE) (1), with a success rate of approximately 75%(1,2) . The reasons for the failure of almost 25% of the operated patients remain unknown. We aimed to investigate the influence of resection of medial temporal lobe (MTL) structures in addition to HIP in the surgical outcome(SO) of these patients., We studied 43 patients with DR, unilateral MTLE who underwent anteromedial temporal resection in the Epilepsy Service at UNICAMP, between 1998 and 2004. We selected patients according to our standard surgical investigation protocol (2) and included only patients with hippocampal atrophy supporting both clinical and electrophysiological findings. This study was approved by the ethics committee of our institution. All patients underwent a routine MRI scan at least six months after the surgery, with the following parameters: T1weighted with 1 mm isotropic voxels acquired on a 2 Tesla scanner. We used the Engel[apos]s postoperative outcome scale (1) and conducted a voxel lesion symptom mapping (VLSM) (3) of their post-operative MRI to discriminate the contribution of distinct segments of the MTL cortex to the SO (4).
We computed linear regressions and applied a cost function transformation of the resection maps for each patient to a common set of spatial coordinates., Patients underwent surgery with the mean age of 37 (range 17-56) years, and the mean follow up period was 40 (range 11-99) months. The SO classification was: 76% as Engel I,14% as Engel II,5% as Engel III and 5% as Engel IV. We observed that the extent of hippocampal removal was associated with better outcomes (t=2.371, p=0.023). However, when the resection of the HIP was associated with resection of the entorhinal cortex there was a greater likelihood of seizure control after surgery (t=3.286, p=0.002) (Fig.1).
Figure 1. VLSM maps are overlaid in a normal T1 template. Colors that are associated with low p-values (green, yellow and red) are the most significantly associated with a good SO and correspond to the entorhinal cortex and HIP.[figure1], Based upon this finding, the efficiency of the surgical treatment of MTLE can be improved by including the entorhinal cortex to the hippocampal resection.
Ref.:
1 N Engl J Med 2001;345:311-318
2 Seizure 2006;15:35-40.
3 Nat Neurosci 2003;6:448-450.
4 Hum Brain Mapp 2004;22:145-154., (Supported by FAPESP:05/59258.)