Hemimegalencephaly: what happens when children get older?

Functional cognitive and language outcomes after cerebral hemispherectomy for hemimegalencephaly

OBJECTIVE

Hemispheric surgeries are an effective treatment option to control seizures for children with hemimegalencephaly (HME); however, not enough is known about their cognitive outcomes. This study aimed to delineate the cognitive and language outcomes after hemispherectomy for HME and identify the clinical characteristics associated with cognition and language.

METHODS

Data came from the Global Pediatric Epilepsy Surgery Registry, a patient-driven web-based registry for epilepsy surgery. We focused on children's functional status, assessed through parent-reports of cognitive and language skills. Parents also reported on their satisfaction with surgery, their child's quality of life, and various demographic, clinical, and surgery characteristics.

RESULTS

Parents of 45 children (40% female) participated. Children were aged 2.6 (SD 6.5) months at seizure onset, 10.8 (SD 12.7) months at hemispherectomy, and 8.7 (SD 4.8) years at follow-up, at which point 68% were seizure-free. We found that at follow-up, 43% had average or mildly impaired cognition, 26% could speak age appropriately, and 21% had satisfactory reading skills. A total of 55%, 43%, and 17% of children first babbled, spoke their first words, and started speaking in sentences at an age-appropriate period, respectively. Children who had undergone a right hemisphere resection and those who were older at epilepsy onset were more likely to have better cognitive and language outcomes.

SIGNIFICANCE

Children with HME have delayed language milestones and continue to require significant language and literacy support long-term after cerebral hemispherectomy.

Hemimegalencephaly and intractable seizures associated with the NPRL3 gene variant in a newborn: A case report

Hemimegalencephaly (HME) is a rare hamartomatous congenital malformation of the brain characterized by dysplastic overgrowth of either one of the cerebral hemispheres. HME is associated with early onset seizures, abnormal neurological findings, and with subsequent cognitive and behavioral disabilities. Seizures associated with HME are often refractory to antiepileptic medications. Hemispherectomy is usually necessary to provide effective seizure control. The exact etiology of HME is not fully understood, but involves a disturbance in early brain development and likely involves genes responsible for patterning and symmetry of the brain. We present a female newborn who had refractory seizures due to HME. Whole genome sequencing revealed a novel, likely pathogenic, maternally inherited, 3Kb deletion encompassing exon 5 of the NPRL3 gene (chr16:161898-164745x1). The NPRL3 gene encodes for a nitrogen permease regulator 3-like protein, a subunit of the GATOR complex, which regulates the mTOR signaling pathway. A trial of mTOR inhibitor drug, Sirolimus, did not improve her seizure control. Functional hemispherectomy at 3 months of age resulted in total abatement of clinical seizures.

Neurite Outgrowth Inhibitor (NogoA) Is Upregulated in White Matter Lesions of Complex Cortical Malformations

Complex cortical malformations (CCMs), such as hemimegalencephaly and polymicrogyria, are associated with drug-resistant epilepsy and developmental impairment. They share certain neuropathological characteristics including mammalian target of rapamycin (mTOR) activation and an atypical number of white matter neurons. To get a better understanding of the pathobiology of the lesion architecture, we investigated the role of neurite outgrowth inhibitor A (NogoA), a known regulator of neuronal migration. Epilepsy surgery specimens from 16 CCM patients were analyzed and compared with sections of focal cortical dysplasia IIB (FCD IIB, n = 22), tuberous sclerosis complex (TSC, n = 8) as well as healthy controls (n = 15). Immunohistochemistry was used to characterize NogoA, myelination, and mTOR signaling. Digital slides were evaluated automatically with ImageJ. NogoA staining showed a significantly higher expression within the white matter of CCM and FCD IIB, whereas cortical tubers presented levels similar to controls. Further analysis of possible associations of NogoA with other factors revealed a positive correlation with mTOR and seizure frequency. To identify the main expressing NogoA cell type, double staining revealed dysmorphic neuronal white matter cells. Increased NogoA expression is associated with profound inhibition of neuritic sprouting and therefore contributes to a decrease in neuronal network complexity in CCM patients.

Evolution of epilepsy in hemimegalencephaly from infancy to adulthood: Case report and review of the literature

Hemimegalencephaly (HME) is a rare disorder of cortical development with overgrowth of one cerebral hemisphere. Patients have intellectual delay, hemiparesis and severe epilepsy. Drug-resistant epilepsy is often treated with a hemispherectomy. We review the literature on HME natural history and report a 26-year-old man with HME who did not undergo hemispherectomy in childhood with recurrent focal convulsive or non-convulsive status epilepticus.

Few patients with HME have been followed into adulthood. Reported adult cases have milder epilepsy or underwent hemispherectomy in childhood. Patients surviving to adulthood have poor outcomes, regardless of treatment method, although seizure burden is improved with hemispherectomy.

•

Hemimegalencephaly is a rare disorder of neuronal migration characterized by epilepsy, developmental delay and hemiparesis.

•

Outcomes of hemimegalencephaly are generally poor; however, this is typically reported in pediatric populations, not adults.

•

Hemispherectomy is beneficial in reducing seizure burden; however, most do not obtain seizure-freedom.

•

Seizures are typically focal onset; however, the epileptogenic area may increase with poor seizure control.