New Imaging Techniques Enhance Selection of Candidates for Epilepsy Surgery

November 1, 2005

epilespy, focal epilepsy, temporal lobe epilepsy, 3 Tesla phased array MRI, surgical intervention for epilepsy

Advances in imaging techniques are proving useful in the selection of patients with epilepsy who would be helped by surgery. One study1 by an international team of investigators found that additional diagnostic information that was not revealed with 1.5 Tesla (1.5T) MRI was obtained for 19 (48%) of 40 patients with focal epilepsy syndromes by using 3 Tesla phased array (3T PA) MRI. In the other study,2 researchers showed that analysis of hippocampal volume differences using 3-dimensional surface meshes of MRI scans can predict which patients with temporal lobe epilepsy (TLE) will respond to surgical intervention.

In his commentary3 about the 2 studies that appear in the October 11 issue of Neurology, Fernando Cendes, MD, PhD, associate professor of neurology in the Department of Neurology at Brazil's University of Campinas, cited a study4 suggesting that surgery should be considered in patients in whom 2 different courses of antiepileptic drugs (AEDs) have failed. Although Cendes conceded that additional research must be launched to validate the findings and clinical feasibility of the 2 studies, he said that their advent highlighted the relevancy of imaging techniques and the ongoing need for more options and refinements in such technology.

ENHANCED SENSITIVITY OF 3T PA MRI

About 15% of patients with focal epilepsy are not adequately managed with AEDs and may be candidates for surgical intervention. MRI has been used to detect lesions in the epileptogenic area of the brain. Patients in whom MRI and electroencephalographic (EEG) findings are concordant are more likely to be seizure-free after surgery (72% vs 41% of patients whose MRI-EEG findings are not concordant), explained a consortium from Massachusetts General Hospital and its A. A. Martinos Center for Biomedical Engineering, Philipps-University in Marburg, Germany, and the National Center for Epilepsy in Sandvika, Norway.1 The group compared standard 1.5T MRI scans with 3T PA MRI scans in 40 patients with medically intractable focal epilepsy.

Not only were more diagnostically relevant data acquired with 3T PA MRI, this more sensitive MRI modality identified lesions in 15 (65%) of 23 patients whose 1.5T MRI scans were normal. Eight (73%) of these patients had focal cortical dysplasias--lesions that are typically difficult to detect with MRI. Those patients (4) who underwent complete surgical resection, to date, are seizure-free and also avoided invasive monitoring, according to the research team.

HIPPOCAMPAL MAPPING FOR TLE

The second study,2 conducted by a multidisciplinary team from the University of California at Los Angeles, looked at a different kind of MRI-dependent technology to predict which patients with TLE would be seizure-free after surgical intervention. The team explained in their research brief that patients with mesial TLE (MTLE) and hippocampal sclerosis are more likely to be helped by surgical intervention than AEDs; however, some patients continue to experience seizures postsurgery. Predictors of which patients will or will not be seizure-free have been elusive.

To tackle the problem, the team developed a surface modeling technique that is applied to MRI scans, whereby the scan is converted into a 3-dimensional parametric surface "in which the radial size of the hippocampus is measured from a centerline and plotted in color on the surface to index radial atrophy." They examined the hippocampi of 40 patients who had undergone surgery for MTLE and compared the data on patients who were seizure-free postsurgery with that of patients who experienced seizures postsurgery.

The research team found that non-seizure-free patients had more diffuse atrophy in the area of the hippocampus ipsilateral to seizure activity, compared with seizure-free patients. They hypothesized that the greater atrophy was attributed to disease progression.

REFERENCES

1. Knake S, Triantafyllou C, Wald LL, et al. 3T phased array MRI improves the presurgical evaluation in focal epilepsies: a prospective review. Neurology. 2005;65:1026-1031.

2. Lin JJ, Salamon N, Dutton RA, et al. Three-dimensional preoperative maps of hippocampal atrophy predict surgical outcomes in temporal lobe epilepsy. Neurology. 2005;65:1094-1097.

3. Cendes F. Higher resolution MRI and image modeling for predicting surgical outcome in partial epilepsy. Neurology. 2005;65:975.

4. Trevathan E, Gilliam F. Lost years: delayed referral for surgically treatable epilepsy. Neurology. 2003;61:432-433.