The American Academy of Neurology (AAN) has issued guidelines on the use of functional MRI (fMRI) for presurgical mapping in epilepsy. The guidelines have been endorsed by the American College of Radiology (ACR) and the American Epilepsy Society (AES).
The practice guidelines, published in the January issue of Neurology, provide physicians with evidence-based recommendations for presurgical evaluation and postsurgical outcome predictions. These recommendations are based on the number of Class I, II, and III studies of the 37 relevant articles evaluated by members of the AAN Guideline Development, Dissemination and Implementation Subcommittee.
There currently are no established standards for performing either an intracarotid amobarbital procedure (IAP) or fMRI for presurgical language and mapping assessment. The IAP is used to assess risk to language and memory functions before brain surgery. Multiple factors need to be taken into account when selecting the most appropriate study, according to lead author Jerzy P Szaflarski, MD, PhD, professor of neurology and director of the Division of Epilepsy at the University of Alabama at Birmingham, and co-authors. Six clinical topics are addressed in the article, with summaries of key studies, conclusions derived from them and subcommittee recommendations.
Measuring language lateralization
fMRI seems to provide language lateralization information that is concordant with that of IAP for nearly 90% of medial temporal cases, but there is insufficient data to make a similar conclusion with respect to temporal tumors or lateral temporal cases. Patients with medial temporal lobe epilepsy Level C, extratemporal epilepsy Level C and temporal epilepsy in general Level C may be appropriate candidates for fMRI.
Measuring memory lateralization
fMRI may be considered as an option to lateralize memory functions in patients with medial temporal lobe epilepsy based on one Class II study. This study of 67 patients employed an FMRI contrast between novel visual scenes and meaningless visual patterns to show a significant correlation between a hippocampal fMRI LI and IAP memory LI.
Predicting postsurgical language outcomes after temporal lobectomy
Two studies (one a Class II and the other a Class III) studies suggest that fMRI is possibly effective in aiding the prediction of postsurgical language deficits. It may be considered for patients after anterior temporal lobe resection performed to control Level C temporal lobe epilepsy.
Predicting postsurgical verbal memory outcomes after temporal lobectomy
Nine class II studies suggest that verbal memory decline after left medial temporal lobectomy (MTL) surgery can probably be predicted with fMRI leftward activation asymmetry during encoding of verbal material. Presurgical fMRI of verbal memory or of language could be considered as an option for epileptic patients undergoing evaluation for left MTL surgery Level B.
Predicting postsurgical nonverbal (visuospatial) memory outcomes after medial temporal lobectomy
A single Class II study of 72 patients found that asymmetry of face recognition-related activation was the best predictor of visual-spatial decline after surgery. It suggested that fMRI activation asymmetry during scene and facial recognition memory tasks is possibly predictive of nonverbal memory decline after MTL surgery. Presurgical fMRI using nonverbal memory encoding may be considered for patients undergoing evaluation for temporal lobe surgery Level C.
fMRI as a replacement for the IAP (Wada test) in presurgical evaluation for epilepsy surgery
The subcommittee states that fMRI has some inherent advantages over the IAP. These include lower risk, lower cost, and greater potential for localization of function. “Whether fMRI is a suitable replacement for the IAP, however, depends on whether it produces results that are concordant with those from the IAP and whether it can predict cognitive outcomes as accurately as the IAP,” the authors wrote.
The evidence for language lateralization is high between the two types of exams. Data on the ability to predict language outcomes are limited for both IAP and fMRI. The subcommitee recommends that if fMRI is to be used, the task design, data analysis methods and epilepsy type need to be considered. The authors caution that only small numbers of patients with lesional epilepsy were included the Class II and Class III studies they referenced.
The objectives of the memory portion of the IAP are to assess the risk of global amnesia after anterior temporal lobe (ATL) resection. Because concordance is low between IAP memory asymmetry and fMRI MTL activation asymmetry, the question needs to be asked if fMRI can predict memory outcome better than the IAP. The authors advise that fMRI may possibly be more accurate in predicting material-specific verbal memory change and outcome. However, they caution that it has not been established for prediction of global amnesia.
The authors conclude that available evidence leaves many critical matters unresolved, and leaves open the question of which test is more accurate in discordant cases. The authors also emphasize the importance of following published standards and that clinicians performing fMRI have advanced technical expertise and a thorough understanding of the cognitive processes of the tests. They also specifically identify seven areas where research needs to be performed.
Guidelines for fMRI in presurgical evaluation of patients with epilepsy. Appl Radiol.