Abstracts

Rationale: Right hemisphere language lateralization has been demonstrated to occur in a small subset of epilepsy surgical patients over the years using the intracarotid amobarbital (Wada) procedure. Many of these patients undergo surgical resections involving the left cerebral hemisphere to control their seizures, and usually do not undergo electrocorticography (ECOG) as their language is presumed not to be put at risk during surgery. We usually assume that these patients have experienced early reorganization of language function, and take the presence of seizure activity arising in the left hemisphere as confirmation that a pathological process has led to this change. In the current study, we present data from ECOG and Wada studies to demonstrate that right hemisphere language can occur as a normal but rare variant in some individuals and to “validate” the findings of the Wada. Methods: We examined the ECOG data of all right hemisphere surgical patients who had right hemisphere speech based upon the Wada. Out of 1255 surgical patients who underwent the Wada procedure at the University of Washington Regional Epilepsy Center between 1974 and 2006, there were 90 (7.2%) patients identified with right hemisphere speech only. Of these, only 22 (1.7% of the total sample) went on to undergo surgery involving the right hemisphere. Thirteen of these patients, all experiencing right temporal lobe epilepsy (10 idiopathic/3 secondary to tumors), had intraoperative mapping data available for review. The location of language sites in these individuals was ascertained by examining intraoperative photographs, and the distribution of sites was then compared to published data involving 117 left hemisphere language dominant patients performed by Ojemann et al. (1989). Results: Language cortex was identified in the right hemisphere during ECOG mapping for all thirteen patients. All sites could be classified within one of four regions (superior or middle temporal gyri, inferior parietal lobe, or inferior frontal gyrus), all of which were common sites where language was identified in the left hemisphere dominant comparison sample. Conclusions: Our results suggest that: 1) the Wada procedure is a valid measure for identifying right hemisphere language processing, and 2) the distribution of language sites in right hemisphere language dominant patients is consistent with that of left hemisphere language dominant patients, supporting the theory that right hemisphere language can occur as a normal variant of language lateralization.