Purpose: Hemimegalencephaly (HME) is a congential malformation of the brain, observed as hypertrophy of one hemisphere and epilepsy. However, knowledge on surgical outcomes is severely limited due to the rarity of HME. Thus, this work aims to provide a critical foundation surrounding surgical short-term and long-term outcomes as well as identify predictors for seizure recurrence in HME patients.

Methods: This observational study is a retrospective chart review of pediatric patients who were diagnosed with HME and received resective surgery, either functional or anatomic hemispherectomies at UCLA. This included 53 patients from 1990-2021, of which 50 had records available for analysis. Demographic information, seizure outcomes, complications and predictors of seizure outcomes were analyzed using R Studio.

Results: Due to a significantly faster time to seizure recurrence with less than hemispheric resections (HR 18.36; p=0.018), patients diagnosed with HME should be treated with either functional or anatomical hemispherectomies, however, there does not seem to be a significance in time to seizure recurrence between the two (p=0.869). Both techniques did not show an advantage in complication rate as well. If a patient fails after a FH, they can have either an anatomical hemispherectomy or residual connection revision operation as neither shows statistical significance (p=0.125), but there is a trend favoring better seizure freedom with residual connection revision surgeries. Significant predictors for a shorter time to seizure recurrence include a positive EPC status (HR 3.35; p=0.026) and > 6 months of age at time of first surgery (OR 7.91; p=0.021). ILAE FCD diagnosis of Type IIa showed favored better outcomes with respect to time to seizure recurrence (HR 0.12; p=0.040).

Conclusions: According to this work, for HME initial management, hemispheric resections should be performed over less than hemispheric resections. For failed hemispheric surgeries, residual connection revision surgeries should be performed over anatomical hemispherectomies.