Abstracts

Rationale: Hemimegalencephaly is a rare brain malformation that consists of unilateral hemispheric or lobar enlargement caused by atypical neural proliferation and dysfunction of cell migration. Clinical features include epilepsy, which is almost invariably refractory to multiple antiseizure medications (ASMs), epileptic encephalopathy, hemiparesis, significant developmental delays, and visual field deficits. Surgical intervention is required to achieve control of seizures and improve developmental outcomes. Functional or anatomic hemispherectomy has been standard of care, but this is often delayed by several months due to high surgical risks for neonates with early hemispherectomy. This delay typically leads to months of uncontrolled or under-controlled seizures with large numbers of ASMs in high doses, all of which can negatively impact neurodevelopment. Endovascular embolic hemispherectomy has previously been successfully used in younger patients to improve these outcomes (Pearl et al., J NeuroIntervent Surg 2024;16:81-87; Oluigbo et al., Childs Nerv Syst 2017;33:521-527). We describe the evolution of seizures throughout the stages of endovascular embolic hemispherectomy in the first case at our institution.

Methods: A neonate with hemimegalencephaly underwent staged endovascular embolic hemispherectomy, with EEGs performed pre-, intra-, and post-operatively for each of the three procedures.

Results: The preoperative EEG noted numerous EEG only and clinical seizures. The EEG evolved over the course of our serial EEG monitoring after the staged embolizations. After the first embolization of the PCA territory at 25 days of life (DOL), clinical seizures disappeared. There was an initial increase in electrographic only seizures, ~7-10/hr, within the first 5 hours, seen over the right centrotemporal and posterior regions. These decreased gradually over the first 3 days post-operatively and then sharply on POD 4 to 6 seizures total. The second procedure, embolization of the superior right MCA and anterior temporal artery, was performed on DOL 31. Seizures again increased to ~7-10/hr, seen over the right central region. The patient unfortunately developed a fever with concern for meningitis versus postoperative fever on POD 6, with concomitant increase in seizure frequency to 10-20/hr, but with rapid resolution with treatment. Seizures ceased on DOL 39. The final procedure, embolization of the residual right MCA and right ACA territories, was performed on DOL 46. Seizures increased to 2-8/hr over the right frontopolar region, but this was improved to 3 total on POD 3. Repeat recording at 58 days of life, POD 12, showed focal slowing and interictal discharges over the right frontopolar region, but no seizures.

Conclusions: EEG only seizure frequency increased transiently after each embolization in staged endovascular embolic hemispherectomy. While post-surgical EEG only seizure frequencies increased after the second and final procedures as well, the increase was most dramatic after the first embolization. Principal seizure onset location evolved over the course of the procedures related to the embolized territory.

Funding: N/A