Porencephaly: A disorder of the central nervous system involving a cyst or cavity in a cerebral hemisphere of the brain. The cysts or cavities are usually the remnants of destructive lesions, but are sometimes the result of abnormal development. The disorder can occur before or after birth.
Porencephaly has a number of different causes including absence of brain development and destruction of brain tissue. The presence of porencephalic cysts can sometimes be detected by transillumination of the skull in infancy (when a strong light is shined through the head). The diagnosis may be confirmed by CT, MRI, or ultrasonography.
More severely affected infants show symptoms of the disorder shortly after birth, and the diagnosis is usually made before age 1. Signs may include delayed growth and development, spastic paresis (slight or incomplete paralysis), hypotonia (decreased muscle tone), seizures (often infantile spasms), and macrocephaly or microcephaly. Individuals with porencephaly may have poor or absent speech development, epilepsy, hydrocephalus, spastic contractures (shrinkage or shortening of muscles), and mental retardation. An extreme form of porencephaly is called hydranencephaly.
The prognosis for individuals with porencephaly varies according to the location and extent of the lesion. Some patients with this disorder may develop only minor neurological problems and have normal intelligence, while others may be severely disabled. Others may die before the second decade of life.