The American Academy of Neurology has issued an evidence-based guideline that says physicians may consider using functional magnetic resonance imaging (fMRI) to map the memory and language functions of patients’ brains prior to epilepsy surgery, rather than using the more invasive amobarbital procedure known at the Wada test.
An article titled “Practice guideline summary: Use of fMRI in the presurgical evaluation of patients with epilepsy,” and published in the journal Neurology, summarizes the American Academy of Neurology (AAN) guideline.
However, according to the authors, the evidence used to form the guideline is weak, as many of the studies they reviewed have small sample sizes, epilepsy patients with similar types of the condition, and were conducted at only one clinical site.
Epilepsy surgery is considered when anti-epileptic drugs are not effective in controlling seizures. The surgery involves removing the area of the brain where seizures begin, or using other surgical techniques that can limit the spread of seizure activity. Before surgery, doctors need to properly scan a patient’s brain to prevent damage to language and memory abilities.
To assess the diagnostic accuracy and prognostic value of functional MRI in determining lateralization and predicting postsurgical language and memory outcome, a panel of 11 researchers evaluated and rated available evidence according to the 2004 American Academy of Neurology process. At least two panelists fully reviewed 172 articles and selected 37 for data extraction. Case reports, reports with less than 15 cases, meta-analyses, and editorials were excluded.
They looked for evidence comparing fMRI and intracarotid amobarbital procedure (IAP), a highly invasive procedure in which doctors inject a medication into the carotid artery and one side of the patient’s brain is put to sleep.
But the fMRI brain activity detects changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.
“Because fMRI is becoming more widely available, we wanted to see how it compares to the Wada test,” Jerzy Szaflarski, MD, PhD, lead author said in a press release. “While the risks associated with the Wada test are rare, they can be serious, including stroke and injury to the carotid artery,” said Szaflarski, of the University of Alabama at Birmingham and Fellow of the American Academy of Neurology.
The researchers found that the use of fMRI may be considered an option for lateralizing language functions (determining the hemispheres of the brain responsible for specific functions) in place of IAP in patients with medial temporal lobe epilepsy (MTLE), temporal epilepsy in general, or extra temporal epilepsy. However, the evidence was weak.
For patients with temporal neocortical epilepsy or temporal tumors, the evidence is insufficient, therefore, the authors could not to make a recommendation for people with temporal neocortical epilepsy or temporal tumors.
The use of fMRI may be considered for lateralizing memory functions in place of IAP in patients with MTLE, but is of unclear utility in other epilepsy types, the authors found.
The authors also found that fMRI of verbal memory or language encoding should be considered for predicting verbal memory outcome, and that fMRI using nonverbal memory encoding may be considered for predicting visuospatial memory outcomes.
“Larger studies need to be conducted to increase the quality of available evidence,” Szaflarski said. “Plus, neither fMRI nor the Wada test have standardized procedures. Doctors should carefully advise patients of the risks and benefits of fMRI versus the Wada test,” he said.