Abstracts

Rationale: 1-2% of patients being evaluated for epilepsy surgery have an auditory aura, presumably arising in primary or association auditory cortex. Patients with auditory auras are often studied with intracranial EEG to define the epileptogenic zone and for functional mapping in the dominant hemisphere; however, whether invasive monitoring helps is not known. Methods: All patients (n=24) who presented with an auditory aura and underwent epilepsy surgery between 1988 and 2007 were included in this retrospective analysis. Patients were implanted using hippocampal depths and subdural strips or grids to cover the lateral temporal neocortex. In 9 patients, lateralization was clear and the reason for implantation was for localization or speech mapping. In 3 patients, lateralization was not clear. Surgical outcome 1 year after surgery in the patients who underwent invasive monitoring was compared to the outcome in the patients who did not undergo invasive monitoring. The yield of the intracranial EEG (IEEG) was determined using the presence of a well localized ictal onset, location of onset, subdural strips versus grids, and whether the resection was limited by language cortex. Results: All 24 patients (mean age 32.9 years at time of surgery, range 16-57 years, 9 men, 15 women, mean duration of epilepsy 18.8 years, range 1-49 years) who presented with an auditory aura were right handed and had temporal lobe resections (13 left and 11 right). Nine of 11 right temporal resection patients were seizure free, whereas only 5 of 13 left temporal resection patients were seizure free (p = .05). Twelve patients had invasive monitoring prior to surgery (6 left, 6 right). Of the 12 patients without IEEG, 7 or 56% were seizure free at 1 year; 4/5 had right temporal resection and 3/7 had left temporal resection. Of the 12 patients who had IEEG, 7 or 56% were seizure free at 1 year. Only 2/6 patients with left temporal resection were seizure free. Both seizure free patients had hippocampal seizure onset, whereas the others all had temporal neocortical seizure onset. 5/6 right temporal resection patients were seizure free; the patient with persistent seizures had orbitofrontal, hippocampus and temporal neocortical ictal onset. Conclusions: IEEG monitoring did not appear to improve seizure outcome in patients with auditory auras, although the sample size is small. Surgical outcome was better in patients who underwent a non-dominant temporal resection whether IEEG was used or not, and suboptimal in patients who underwent a dominant temporal resection. We suggest that IEEG as conventionally practiced with superficial subdural electrodes is superfluous in patients with auditory auras and non-dominant temporal foci. In patients with auditory auras and dominant temporal lobe epilepsy, different methods are needed to identify the boundaries of the epileptogenic zone and define eloquent cortex.