Abstracts

Rationale: To determine whether the posterior background rhythm on scalp EEG shows improvement following anatomical hemispherectomy in children with medically-uncontrolled epilepsy and whether interictal epileptiform discharges involving the presumed healthy hemisphere is abolished by anatomical hemispherectomy. Methods: The inclusion criteria of the present study included: (i) children who underwent anatomical hemispherectomy in Children’s Hospital of Michigan between 2004 and 2008; (ii) scalp EEG performed both before and after surgery. The exclusion criteria included: no awake-EEG segment (with the eyes closed) available for review. Fourteen out of 20 children who underwent anatomical hemispherectomy satisfied both inclusion and exclusion criteria and were analyzed in the present study. The age at surgery ranged from 3-months to 15-years (mean: 4.2-years-old). Seven children had a right-sided hemispherectomy. The posterior background rhythm in the presumed healthy side during wakefulness as well as the extent of interictal epileptiform discharges were compared between pre- and post-operative EEG studies. Pre-operative EEG was performed 8.4 weeks (on average) prior to surgery, whereas post-operative EEG was performed 6.4 weeks (on average) after surgery. Results: In 13 children, the mean frequency of posterior background rhythm in the healthy side during wakefulness was 5.4 Hz (standard deviation [SD]: 2.0 Hz) before surgery and 6.2 Hz (SD: 1.1 Hz) after surgery. Paired t-test failed to demonstrate that the mean frequency of background rhythm was greater after surgery compared to before surgery (p-value = 0.19). The remaining 11-month-old child showed no posterior dominant background rhythm but a burst-suppression pattern prior to surgery, and showed a posterior dominant theta activity at 5.0 Hz following surgery. Prior to surgery, interictal spike-wave discharges involved the epileptogenic hemisphere in all 14 children and the presumed healthy hemisphere in 8 children. Following surgery, no interictal epileptiform discharge but consistent background attenuation was noted in the resected hemisphere in all 14 children; interictal spike-wave discharges were noted in the presumed healthy hemisphere in one child. Conclusions: The present study failed to demonstrate significant improvement of background rhythm in the presumed healthy hemisphere following anatomical hemispherectomy. However, resection of the affected hemisphere resulted in cessation of interictal epileptiform discharges involving the presumed healthy hemisphere in the majority of children with hemispheric catastrophic epilepsy. Supported by NIH Grant 47550 (to E. Asano)