Objective: To determine outcome after epilepsy surgery in patients with normal preoperative magnetic resonance imaging (MRI). Methods: 24 adult and paediatric patients with normal preoperative MRIs were studied. They underwent epilepsy surgery between 1994 and 2001 and had at least one year of follow up. Results: At the most recent follow up, nine patients (37%) were seizure-free and 18 (75%) had at least a 90% reduction in seizure frequency with weekly or monthly seizures. Seizure freedom was not significantly different after resections in frontal (5/9) or temporal regions (4/13) (p = 0.24, Fisher's exact test), or among patients with or without localising features on EEG, PET, or ictal SPECT. Subdural grids, used in 15 of 24 patients, helped tailor resections but were not associated with differences in outcome. Histopathology showed cortical dysplasia in 10 patients (42%), non-specific findings in 13 (54%), and hippocampal sclerosis in one (4%). Cortical dysplasia was seen in seven patients with frontal resection (78%) and non-specific findings in nine (69%) with temporal resection. Seizure outcome did not differ on the basis of location of resection or histopathology. Conclusions: While these results were less favourable than expected for patients with focal epileptogenic lesions seen on MRI, they represented worthwhile improvement for this patient population with high preoperative seizure burden. In this highly selected group, no single test or combination of tests further predicted postoperative seizure outcome. M agnetic resonance imaging (MRI) has become indispensable in the presurgical evaluation of patients with intractable epilepsy. Identification of a focal epileptogenic lesion on preoperative MRI may affect postoperative seizure outcome favourably in both adult and paediatric patients, depending on location and pathology. [1][2][3][4][5][6][7][8][9] Similarly, other studies have shown a worse postoperative seizure outcome when no lesion has been found on MRI.
10-17As MRI technology improves, smaller and more subtle lesions are being imaged and identified. For example, the advent of FLAIR (fluid attenuation recovery) imaging has improved the detection of mesial temporal sclerosis and malformations of cortical development.7 18-22 However, some patients continue to have no detectable lesions on MRI, despite the suggestion of a focal lesion on seizure semiology and neurophysiology. The purpose of this retrospective study was to review the outcome of epilepsy surgery in patients with drug resistant focal epilepsy and normal preoperative MRI.
METHODSAdult and paediatric patients were identified from the Cleveland Clinic epilepsy surgery database if they had epilepsy surgery from August 1994 to 2001, normal preoperative MRI as interpreted by staff neuroradiologists, and at least one year of postoperative follow up. Only cases operated on after August 1994 were selected, because since 1994 all presurgical cases have had MRI investigation, which included the modern imaging techniques outlined below.All MRI st...