is a rare condition in which the brain's cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid (CSF). Affected infants may appear and act normal at birth, but irritability and hypertonia often develop within a few weeks. Other signs and symptoms may include seizures, hydrocephalus, visual impairment, lack of growth, deafness, blindness, paralysis, and intellectual disabilities. Prognosis is typically poor with many affected children dying before one year of age. In rare cases, children may survive for several years or more. It has been suspected to be an inherited condition, although some researchers believe it may be caused by prenatal blockage of the carotid artery where it enters the cranium. Treatment is generally symptomatic and supportive; hydrocephalus may be treated with a shunt. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.