Abstracts

Rationale: Epileptic seizures are considered a corticoreticular phenomenon, with motor expression mediated through the corticospinal tracts, yet patients with hydranencephaly commonly have seizures. The mechanisms mediating expression of seizures in hydranencephalic infants have not been well-studied, but they presumably reflect subcortical networks. Children with hydranencephaly thus provide a useful model for studying the clinical features of subcortical seizures. Methods: We studied two infants with hydranencephaly using V-EEG in order to determine if the seizures were of cortical origin, and to analyze features of seizures of subcortical origin. Results: Case 1: A term infant born after an uncomplicated pregnancy, labor, delivery. The child was small for gestational age but otherwise appeared normal. At 7 weeks, she presented with new onset seizures, involving tonic eye deviation to the L, L leg tonic extension, R arm flexion, occurring repeatedly in a spasm-like manner. A brain MRI revealed hydranencephaly (Fig. 1). The baseline EEG was abnormal with continuous arrhythmic spikes and sharp waves mainly in the right posterior quadrant (Fig. 2). Stereotypical clinical events were marked by eye deviation to the left, head turned to right, LLE extension, and tonic flexion posturing of the RUE. These events did not correlate with any EEG changes from baseline. Later, parents observed that stimuli, including noise and touch, could trigger an event. Response to antiepileptic medications (AEDs) has been poor. Case 2: Full-term AGA infant by SVD. Prenatal ultrasound at 34 wks revealed hydrocephalus vs. hydranencephaly, the latter confirmed at birth by MRI imaging (Fig.3). The child appeared normal at birth but for a head circumference (HC) >90th %. Seizures were first recognized at 7 weeks while in hospital in the post-operative period from a choroid plexectomy, done to address worsening hydrocephalus. The baseline EEG had continuous low voltage diffuse arrhythmic delta with some admixed faster frequencies but lacked state differentiation or normal background features. There were no epileptiform discharges present. Stereotypical clinical events were marked by eye deviation to the left with left nystagmus, rhythmic jaw clenching, facial twitching, lip smacking, and generalized stiffening. These clinical spells did not correlate with EEG changes (Fig. 4) Treatment with various AEDs has not been effective in controlling the seizures. Conclusions: Hydranencephaly provides a useful model for studying seizures of subcortical origin. The seizures are characterized by tonic posturing and automatisms, and they may be stimulus provoked. They overlap with the “brainstem release phenomena” often described in neonatal seizures, especially prevalent in the premature infant. The lack of an EEG correlate implicates a subcortical origin for the seizures. Response to treatment with standard antiepileptic medications is often poor. Further study of this group and other subcortical epilepsies is of great interest.