Localized focal cortical dysplasia type II: seizure freedom with lesionectomy guided by MRI and FDG-PET

OBJECTIVE The authors perform thorough, noninvasive presurgical evaluations for intractable epilepsy at their center and avoid unnecessary intracranial EEG when possible. The purpose of this study was to clarify the appropriateness of their lesion-oriented surgical strategy for localized focal cortical dysplasia (FCD) type II. METHODS Fifty-one patients with pathologically proven localized FCD type II who were followed for at least 1 year after surgery were included. Patients with FCD type II with lobar or multilobar distribution were excluded. The results of presurgical evaluations, including thin-slice 3-T MRI, FDG-PET, and ictal SPECT, as well as surgical procedures and postoperative seizure and functional outcomes, were examined retrospectively. RESULTS MRI was positive in 46 (90%) of 51 patients, and FDG-PET revealed localized hypo- or hypermetabolism in 47 (92%) of 51 patients. Ictal SPECT revealed concordant hyperperfusion in 37 of 42 patients examined. Intracranial EEG was used in only 13 patients (25%), including 5 with negative MRI results and 4 with subtle MRI findings. Of the 15 patients with FCD in the vicinity of eloquent (sensorimotor and language) areas, intracranial EEG was used in 4. Lesionectomy was performed in all 51 patients. Intraoperative electrocorticography (ECoG) was performed in 8 patients, but the findings were not used to tailor the extent of resection. Postoperative seizure outcomes were Engel class I in 47 patients (92%) and Ia in 45 (88%). In the 15 patients with FCD in the vicinity of eloquent areas, 13 (87%) achieved a class I outcome. Predictive factors for favorable seizure outcome were complete resection of the MRI lesion (p = 0.006) and frontal lobe surgery (p = 0.012). Postoperative neurological deficits were noted in only 4 (27%) of 15 patients with FCD in the vicinity of eloquent areas. All 5 MRI-negative patients achieved an Engel class I outcome. CONCLUSIONS In most of the patients with localized FCD type II, MRI and/or FDG-PET detected the localized abnormality. Lesionectomy without intracranial EEG led to seizure freedom in most cases. Even when lesions were in the vicinity of eloquent areas, seizure and functional outcomes were favorable. Intraoperative ECoG may thus be unnecessary. Complete resection of the lesion is essential for favorable seizure outcome in MRI-positive patients. In MRI-negative patients, surgery with intracranial EEG guided by FDG-PET provided seizure-free outcomes.