Abstracts

The intracarotid amobarbital procedure (IAP) is considered the gold standard for assessment of hemispheric dominance for language functions despite the recent development of functional imaging studies for this purpose. These methods are highly reliable when language is clearly unilateral. However, the presence of even subtle language ability in the nondominant hemisphere may place a patient at risk for postoperative aphasia. This study reports on patients who appeared primarily right hemisphere language dominant on IAP but nonetheless clearly demonstrated left hemisphere language areas during electrical stimulation studies. Two male and two female patients, ages 11-18 years, underwent IAP and electrical stimulation studies prior to focal resection for intractable seizures involving the left frontal or temporal area. Three of four were left-handed. IQ was mildly impaired (74-81) in all patients. All four evidenced left hemisphere structural abnormalities, and three evidenced left mesial temporal sclerosis. During cortical mapping, language was tested in five modalities (rote speech, naming, repetition, comprehension and reading). These mapping data were contrasted with the IAP. All patients displayed primarily right hemispheric language dominance on IAP; however, minor language production (rote or automatic speech) was noted following right hemisphere injection in three patients, and paraphasic errors, which were sometimes subtle, were noted following left hemisphere injection in three patients. On cortical stimulation, clear frontal and temporal language areas were identified in all patients, with the exception of one patient whose subdural electrode array did not extend anterior to the motor area, precluding identification of a frontal language area. Right hemisphere language dominant epilepsy surgery candidates with even subtle evidence of left hemisphere language on IAP should be considered for cortical mapping prior to resection.