They can be a small single node or a large number of nodes, can exist on either or both sides of the brain at any point along the higher ventricle margins, can be small or large, single or multiple, and can form a small node or a large wavy or curved mass. Symptomatic women with subependymal heterotopia typically present with partial epilepsy during the second decade of life; development and neurologic examinations up to that point are typically normal. Symptoms in men with subependymal heterotopia vary, depending on whether their disease is linked to their X-chromosome. Men with the X-linked form more commonly have associated anomalies, which can be neurological or more widespread, and they usually suffer from developmental problems. Otherwise (i.e., in non-X-linked cases) the symptomology is similar in both sexes. Focal subcortical
Subcortical heterotopia form as distinct nodes in the white matter, "focal" indicating specific area. In general, patients present fixed neurologic deficits and develop partial epilepsy between the ages of 6 and 10. The more extensive the subcortical heterotopia, the greater the deficit; bilateral heterotopia are almost invariably associated with severe developmental delay or intellectual disability. The cortex itself often has an absence of gray matter and may be unusually thin or lack deep sulci. Subependymal heterotopia are frequently accompanied by other structural abnormalities, including an overall decrease in cortical mass. Patients with focal subcortical heterotopia have a variable motor and intellectual disturbance depending on the size and site of the heterotopion.
The DCX protein is thought to direct neuronal migration by regulating the organization and stability of microtubules, necessary for neuronal motility. The malformation is seen only in females, as the gene is found on the X-chromosome. Since there are two X chromosomes in females, after X-inactivation, only some neurons lose doublecortin function. These neurons with the mutant DCX gene fail to migrate into the cortex and thus form the underlying heterotopic band, while neurons which express the normal gene successfully migrate out to the cortical plate. Males with DCX mutations develop classical lissencephaly. Diagnosis
Detection of heterotopia generally occurs when a patient receives brain imaging—usually an MRI or CT scan—to diagnose seizures that are resistant to medication. Correct diagnosis requires a high degree of radiological skill, due to the heterotopias resemblance to other masses in the brain. Treatment
When seizures are present in any forms of cortical dysplasia, they are resistant to medication. Frontal lobe resection provides significant relief from seizures to a minority of patients with periventricular lesions. Prognosis
In general, gray matter heterotopia is fixed in both its occurrence and symptoms;  that is, once symptoms occur, it does not tend to progress. Varying results from surgical resection of the affected area have been reported. Although such surgery cannot reverse developmental disabilities, it may provide full or partial relief from seizures. Heterotopia are most commonly isolated anomalies, but may be part of a number of syndromes, including chromosomal abnormalities and fetal exposure to toxins (including alcohol).