Alternatives to the Wada test: a critical view of functional magnetic resonance imaging in preoperative use

Abstract

The Wada or intracarotid amobarbital procedure is already in its fifties and, despite its invasive character, still routine for determining the lateralization of language and memory prior to epileptic surgery. Among the new techniques available, functional magnetic resonance imaging is one of the most promising alternatives. This non-invasive method has several advantages including the possibility of mapping relevant areas within the hemispheres and being able to prolong examination time in case of discordant results. Many functional magnetic resonance imaging studies have focused on correlations with the intracarotid amobarbital procedure as the gold standard and found an agreement of about 90%. More importantly, recent studies demonstrated a significant correlation between presurgical functional magnetic resonance imaging testing and postsurgical outcome for functional magnetic resonance imaging activations in frontal language areas. In some studies, prediction for outcome is already higher for functional magnetic resonance imaging than for the intracarotid amobarbital procedure. Current data support functional magnetic resonance imaging as a valid alternative to the intracarotid amobarbital procedure. Small sample sizes in outcome studies and restrictions to certain sites of operation, however, still call for caution. A standardized series of tasks to activate the whole language and memory system paired with good comparability between medical centres is needed.