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. 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 heterotopia's 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). Footnotes Further reading GeneReviews/NCBI/NIH/UW entry on X-Linked Periventricular Heterotopia Central nervous system disorders