Guideline advises on fMRI use for mapping brain function prior to epilepsy surgery
medwireNews: The American Academy of Neurology has recommended the use of functional magnetic resonance imaging (fMRI) as an alternative to the intracarotid amobarbital procedure (IAP; Wada test) for presurgical mapping of language and memory function in patients with epilepsy.
“Because fMRI is becoming more widely available, we wanted to see how it compares to the Wada test,” lead author Jerzy Szaflarski (University of Alabama at Birmingham, USA) told the press. “While the risks associated with the Wada test are rare, they can be serious, including stroke and injury to the carotid artery.”
Other inherent advantages of fMRI over the IAP include greater potential for localization of function and lower cost, the team notes in Neurology. While evidence supports the use of fMRI over the IAP, the researchers caution that it is weak due to many of the studies being small, conducted at one institution, and involving patients with similar lesion size and location and types of epilepsy, thereby limiting the generalizability of the results, notably to children and adolescents.
The practice guideline is based on data from 37 articles (excluding studies involving fewer than 15 patients, meta-analyses, and editorials), which was evaluated by a panel of 11 experts.
The guideline says that the language lateralization information provided by fMRI is concordant with that of the IAP in 87% of medial temporal cases and 81% of extratemporal cases, according to several Class I–III studies and is therefore a suitable alternative. But there are insufficient data to support its use for temporal tumors or temporal neocortical epilepsy.
In terms of predicting postsurgical language outcomes, there was evidence for considering it for patients with temporal lobe epilepsy undergoing anterior temporal lobe resection, although the quality of evidence was low.
The researchers say that if fMRI is used, clinicians need to consider task design, data analysis methods, and epilepsy type.
“Compliance with the activation tasks is a prerequisite for eliciting the modulation of brain activity on which fMRI depends,” they explain.
“Clinicians need to have a thorough understanding of the cognitive processes (language and nonlanguage) elicited by the tasks and be mindful of the advantages and disadvantages of particular language and baseline or contrast tasks.”
There was modest concordance between fMRI and IAP for lateralizing memory function. It is recommended for this purpose in place of the IAP in patients with medial temporal lobe epilepsy, with moderate evidence suggesting that fMRI leftward activation asymmetry during encoding of verbal material could predict verbal memory decline in such patients.
The evidence for nonverbal memory tasks was less convincing, however; fMRI activation asymmetry was possibly predictive of visuospatial memory decline in medial temporal lobe epilepsy patients and could be considered in place of the IAP. But the ability of fMRI to predict global amnesia was not assessed and is not yet established as an alternative to the IAP for this.
By Lucy Piper
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