hemimegalencephaly
Pronunciation: HEM-ee-MEG-ah-len-SEF-ah-lee
A rare malformation of cortical development characterized by overgrowth of one cerebral hemisphere with abnormal neuronal organization.
Full Definition
Hemimegalencephaly is a rare congenital brain malformation characterized by unilateral cerebral hemisphere enlargement with dysplastic cortical development, abnormal neuronal migration, and white matter changes. The affected hemisphere shows increased volume, blurred gray-white matter differentiation, and often areas of polymicrogyria or pachygyria. Patients typically present with intractable epilepsy, developmental delay, and hemihemiplegia. MRI demonstrates the characteristic asymmetry with T2 hyperintensity in the affected white matter and cortical dysplasia. The condition may be isolated or associated with syndromes such as Proteus syndrome or epidermal nevus syndrome. Treatment often involves hemispherectomy for seizure control, particularly when seizures are medically refractory and function in the affected hemisphere is severely compromised.
Usage
Usage note: One word, not hyphenated. Specify affected side (left/right) in reports.
In Context
- "MRI reveals left hemimegalencephaly with associated cortical dysplasia and white matter signal abnormality." — Pediatric neuroradiology report
- "The patient with hemimegalencephaly underwent functional hemispherectomy for seizure control." — Epilepsy surgery documentation