What is Heterotopia?
Heterotopia occurs when nerve cells (neurons) do not migrate properly during the early development of the fetal brain. Heterotopia means "out of place." In normal brain development, neurons form in the periventricular region, located around fluid-filled cavities (ventricles) near the center of the brain. The neurons then migrate outward to form the exterior of the brain (cerebral cortex) in six onion-like layers.
-Periventricular Heterotopia (PH)
- Periventricular Nodular Heterotopia (PNH)
- Anterior predominate and diffuse PNH
- Posterior predominant (temporal-trigonal) PNH
- Periventricular Laminar Heterotopia (PLH), not nodular (unilateral or bilateral)
- Ribbon-like heterotopia, bilateral undulating heterotopic band
-Subcortical Heterotopia (other than band heterotopia or cortical infolding)
Seizures and dyslexia are the most common presenting features associated with PH. Approximately 90% of patients with PH have focal epilepsy. When neuroimaging demonstrates PH in the absence of other brain malformations, patients generally have normal intelligence with their seizures beginning in the second decade of life. The EEG often shows only focal abnormalities, and the seizures usually do not become frequent and generally disappear. When the PH is associated with other cortical or cerebral malformations, patients may have intellectual disability, and the seizures generally begin during the first decade of life. The seizures generally increase in frequency and may become refractory. There is also a high incidence of dyslexia in this population. Several studies suggest that approximately 80% of individuals with PH have deficits in reading, processing speed and executive function.
Patients with subcortical heterotopia typically have congenital neurologic deficits and develop partial epilepsy during the second half of the first decade of life. The more extensive the subcortical heterotopia, the greater the deficit; bilateral heterotopia are almost invariably associated with severe developmental delay or mental retardation.
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3. Periventricular heterotopia. Genetics Home Reference (GHR). 2007; http://ghr.nlm.nih.gov/condition=periventricularheterotopia. Accessed 5/14/2014.