Hemimegalencephaly with accelerated myelination in the affected hemisphere

Hemimegalencephaly is an uncommon malformation of cortical development characterized by congenital enlargement and dysplasia of part or all of one cerebral hemisphere. It usually presents in early life with developmental delay, hemiparesis, and drug-resistant seizures. We report the case of a 7-month-old boy with recurrent seizures beginning in the neonatal period. Electroencephalography demonstrated slow spike-and-wave discharges arising from the left frontotemporal region and propagating to the ipsilateral centroparietal region. Brain MRI showed enlargement of the left cerebral hemisphere, thickened and dysmorphic gyri predominantly in the frontal lobe, ventricular asymmetry, and an aberrant left midsagittal fiber tract located beneath the corpus callosum. The involved white matter showed visually advanced myelination for age, manifested by relatively increased T1-weighted signal and decreased T2-weighted signal compared with the expected myelination pattern at 7 months. These findings are consistent with left hemimegalencephaly with accelerated myelination. This case illustrates a recognizable MRI pattern that may support early diagnosis in infants with epilepsy, while emphasizing that the relationship between epileptic activity and accelerated myelination remains associative rather than causal in a single-patient report.