Seizure outcome after epilepsy surgery in patients with normal preoperative MRI

Abstract

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...

Optimizing MR Imaging Detection of Type 2 Focal Cortical Dysplasia: Best Criteria for Clinical Practice

“…This suggests that frontal drug-resistant partial epilepsy with normal MR imaging findings should raise the suspicion of type 2 FCD, and this is supported by surgical series of cryptogenic partial epilepsy, in which up to 40% of the resected cortical specimens (especially in the frontal lobe) corresponded to type 2 FCD at histology. 9,31,32 Moreover, a recent report of the International League against Epilepsy noted that none of the children with epilepsy diagnosed with tumor or ischemia had normal MR imaging findings. 11 Our study has some limitations.…”

Temporal lobe epilepsy in patients with nonlesional MRI and normal memory: an SEEG study

“…10,13,14,25 A number of studies have analyzed clinical characteristics and seizure outcome after temporal lobectomy in patients with MRI-negative TLE, although most of these have included patients with heterogeneous semiology, EEG, and memory scores. [6][7][8]11,15,21,23,32,35 In general, these investigations have documented inferior results after temporal lobectomy compared with mesial temporal sclerosis. Studies using intracranial recordings have demonstrated that the epileptogenic zone can lie exclusively within the mesial temporal lobe even when MRI results are completely normal.…”

“…[6][7][8]11,15,21,23,32,35 In addition, memory loss is often present in TLE, and material-specific memory deficits are highly specific to indicate laterality of TLE. 4,9 Therefore, it might be expected that the absence of MRI abnormalities and memory deficits would suggest an extramesial or extratemporal source of the seizures, even when the ictal semiology and the video electroencephalography (EEG) results are typical of TLE.…”

Focal cortical dysplasia: a review of pathological features, genetics, and surgical outcome

“…Chapman, et al, 9 have described outcomes for 24 patients who had intractable seizures and normal MR imaging findings. In 42% of these patients, FCD was found.…”