Abstracts

RATIONALE: The availability of newer magnetic resonance imaging techniques in children with intractable epilepsy may enable visualization of structural abnormalities not easily seen by conventional techniques. During the past 12-month period we have performed surgery on 8 children in whom use of MRI-guided frameless stereotactic techniques enabled intraoperative localization of lesions associated with medically intractable epilepsy which would have been otherwise difficult to localize. We report our results using these techniques.
METHODS: Patients ranged in age from 1 to 10 years with a mean of 6 years. All patients underwent detailed MRI including MPRAGE, T1, T2, FLAIR, MT, and diffusion-weighted sequences. All 8 patients had focal abnormalities, but in most cases these were visible only on one or two sequences, most often FLAIR, MT, or T2. Preoperative localization of the epileptogenic zone was accomplished by video EEG monitoring with scalp or subdural electrodes and confirmed by intraoperative corticography. In cases in which seizures appeared to project to a relatively wide area of cortex overlying a subcortical lesion, resection was guided by removal of the anatomically abnormal tissue using MRI-guided stereotaxy, coupled with intraoperative corticography after lesion removal.
RESULTS: Pathology included tubers in three patients with known tuberous sclerosis, tuber-like dysplasias in two patients, more widespread cortical dyplasia in one, dyplasia and ganglioglioma in one, and fibrillary astrocytoma in one. In 6 patients the entire area of anatomic abnormality seen on MRI could be removed; all of these patients are seizure-free with a mean of 9 months followup. In two patients tubers or dyplasia involved eloquent cortex. Resection in these patients was coupled with multiple subpial transection; these patients are improved but not seizure-free. No patient has had a new permanent focal neurologic deficit.
CONCLUSIONS: Use of MRI frameless stereotaxy may increase the number of children who may be considered as candidates for possible resective surgery for intractable epilepsy. Because these focal lesions may only be seen on specific MRI sequences, may have complex three-dimensional shapes, may project to wide areas of overlying cortex, and are usually not readily apparent on visual inspection of the tissue, steroetaxy has proven invaluable in this group of patients in intraoperative localization of the anatomic abnormality. Coupled with preoperative and intraoperative corticography, these techniques may enhance effective resective therapy for focal or multifocal epilepsies in children with subtle MRI abnormalities.