Abstracts

Rationale: -Methods: We retrospectively reviewed ictal and interictal EEG findings, MRI and PET scan data in 27 patients (21 males and 6 females) with HH.Results: EEG was abnormal in 21/27 (78%) patients and normal in 6/27 (22%) patients. Interictal EEG was abnormal in 18/27 (67%) patients. Out of the 18 patients who had abnormal interictal EEG, 10/18 (56%) had abnormalities lateralized to the right hemisphere, 5/18 (28%) lateralized to the left hemisphere, and 3/18 EEGs were abnormal but no lateralizing findings were found. Ictal EEG was abnormal in 13/27 (48%) patients. Out of the 13 patients who had abnormal ictal EEG, 6/13 (46%) had abnormalities lateralized to the right hemisphere, 4/13 (31%) to the left hemisphere, 2/13 (15%) had abnormalities in the midline central region, and 1/13 (8%) had multiple dialeptic seizures with bifrontal generalized spike and wave discharges. 8/27 patients had gelastic seizures with no changes on the EEG. In 6/27 patients, either no seizures were recorded or no data was available. All the patients had gelastic seizures and ten patients also had complex partial seizures. MRI - HH had right sided attachment in 9/27 patients (in 5/9, EEG lateralized to right and 4/9 there was no lateralization), left sided attachment in 3/27 (1/3 EEG lateralized to the left and 2/3 there was no lateralization), bilateral attachment in 1/27 ( no EEG lateralization), bilateral attachment with L>R in 1/27 (EEG lateralized to the left) and R>L in 4/27 (2/4 lateralized to the right and 2/4 had no lateralization), no lateralization was found on MRI in 6/27 (2/6 had EEG lateralization to the right, 2/6 to the left and 2/6 had no lateralization). 3/27 patients had prior surgery at an outside hospital. PET scan was normal in 7/27 (26%) patients, 9/27 (33%) did not have a PET scan, and 7/27 (26%) had non lateralizing findings. 2/27 (7%) lateralized to the left (MRI had R attachment in one and bilateral attachment with R>L in second). 2/27 (7%) lateralized to the right temporal lobe (one attached to the right and another R>L on the MRI).Conclusions: EEG was abnormal in 78% of patients. Interictal EEG was abnormal in 67% of the patients, and out of these 84% of interictal abnormalities lateralized to one hemisphere. Ictal EEG was abnormal in 48% of the patients, and out of these 77% of ictal abnormalities lateralized to one hemisphere. In 67% of the patients HH attachment on MRI lateralized to either right, left or bilateral. EEG was lateralized to the same side as the MRI in 50% of the patients. Of the patients who had the PET scan done, 78% were either normal or non-lateralizing. We conclude that there is a high percentage of interictal and ictal abnormalities on EEG in patients with HH, which often lateralize to one hemisphere. In 50% of the patients abnormalities on EEG lateralized to the same side as the HH attachment on MRI. EEG can have a good lateralizing value in presurgical evaluation of HH patients in preperation for laser ablation surgery. Whereas, PET scan does not appear to have a good lateralizing value.