Purpose or Case Report: Hemimegalencephaly (HME) is a rare cortical brain malformation often resulting in medically refractory seizures which may be treated with staged transarterial embolization (TAE) as an alternative to hemispherectomy. We describe the baseline cranial ultrasound findings of 8 HME patients and present the timing of detection of ischemic changes, edema, and complications.
Methods & Materials: HME infants treated with serial TAE for refractory seizures with baseline ultrasound imaging were included. Serial ultrasound studies were performed on the day of each staged procedure then daily for 3 days. Ultrasound studies were retrospectively reviewed to define baseline findings and to detect ischemic change, progression of edema, and complications after each procedure.
Results: Eight HME infants (average age <2 months; 4 males, 4 females) with refractory seizures were treated with serial TAE from 2011-2024. Baseline ultrasound showed 5 right and 3 left enlarged hemispheres and 2 with cerebellar involvement. Abnormal echogenicity was detected in the white matter (75%) and thalamus (50%), in addition to cortical thickening (88%), unilateral ventricular enlargement (63%), midline shift (88%) and lenticulostriate vasculopathy (50%). One patient had a ventricular shunt placed prior to treatment. Over the course of staged TAE, ischemic changes were detected on average 3.1 days after stage 1, 2.7 days after stage 2, and 1.6 days after stage 3 (n=8). In patients whose treatment included a stage 4 (n=4), ischemic change appeared within 1 day; none were seen within 3 days after stage 5 (n=1). On average, peak edema was observed at 15.7 days and cystic changes at 37.3 days after the first embolization. Detected complications and adverse events included intraventricular hemorrhage (1), subarachnoid hemorrhage (3), non-target embolization (2), and ventriculomegaly requiring a shunt (1).
Conclusions: Most HME patients demonstrated baseline ultrasound findings of unilateral hemispheric enlargement without cerebellar involvement, abnormal white matter echogenicity, cortical thickening, unilateral ventricular enlargement and midline shift. Following stage 1 embolization, the average time to ischemic detection was 3 days which progressively decreased with later stages, likely due to compounding injury with fewer collaterals to maintain perfusion. Knowing the expected progression of ischemic change, edema, and potential complications visualized on ultrasound can help guide management of HME patients undergoing serial TAE.