Abstracts

RATIONALE: Malformations of cortical development (MCD) are frequently associated with severe partial epilepsy. Unfavorable outcome after surgical resection has been reported in patients with Taylor type focal cortical dysplasia (FCD). In other types of MCD, surgical results are difficult to analyse because of unresolved classification issues.
METHODS: Over a 5-year period, a MCD was found in 20 out of 130 patients (15.4 %) operated for intractable partial epilepsy : Taylor type FCD in 9, other type of FCD in 6, heterotopia in 4 and schizencephaly in 1. Hippocampal sclerosis was associated with the MCD in 3 cases. Mean age at surgery was 28 years (range: 17-40). Taylor type FCD was extratemporal in 8 cases out of 9 (frontal in 7, parietal in 1, temporal in 1), while other types of MCD involved the temporal lobe in 8 cases out of 11 (pure temporal in 6, frontal in 2, occipital in 1 and occipito-temporal in 2). MRI was considered as normal in 6 cases (30 %), however PET-scan imaging demonstrated a focal hypometabolic area in 18 cases (90 %). All patients underwent invasive monitoring using depth electrodes : in all patients with Taylor type FCD interictal rhythmic spiking activity was recorded from electrodes implanted within the dysplastic tissue. Less typical patterns were observed in other types of MCD.
RESULTS: Surgical resection of the dysplastic cortex was based on both imaging and invasive monitoring data. Follow-up data of one year or more was available in 15 patients: all six Taylor type FCD patients were in Engel[ssquote]s Class IA, while only 3 of the 9 patients with other types of MCD were in Class I (2 were in Class IA). Other patients had less favorable outcome: 3 in Class II, 1 in Class III and 2 in Class IV. Favorable seizure outcome in Taylor type FCD was observed in all extratemporal cases with limited resections including the whole dysplastic cortex. In the temporal Taylor type FCD a large lobectomy was considered as necessary. Less favorable or poor outcome in other types of MCD could be related to limited resection in functional cortex in 3 patients with occipital or occipito-temporal MCD. In addition, large epileptogenic networks as demonstrated by intracranial recordings could explain surgical failures.
CONCLUSIONS: Taylor type FCD represent a specific group among the MCD with particular electrophysiological patterns that help in planning surgical resection. In this group a complete seizure relief may be expected. Less favorable results on seizure outcome are observed in other types of MCD.
[Supported by: Public hospital global funding (no specific funding)]