pediatrics
Porencephaly
Hydranencephaly
Hydranencephaly is an extreme form of porencephaly in which the cerebral hemispheres are almost totally absent. Usually, the cerebellum and brain stem are formed normally, and the basal ganglia are intact. The meninges, bones, and skin over the cranial vault are normal. In hydranencephaly, cyst formation usually is caused by massive interruption of the blood supply to the developing hemispheres after the 12th week of pregnancy. The blood supply is interrupted by bilateral large-vessel strokes in utero. The skull of an affected infant does not have a defect in this case, and externally the infant may appear normal. The infant may be capable of normal infantile reflex movements, such as sucking and grasp, but does not progress further developmentally. Neurologic examination is usually abnormal; children often have seizures and profound intellectual disability. At best, people with true hydranencephaly are able to sustain vital functions, such as respiration, and are able to react to painful stimulation, but their ability to interact with others or tend to personal needs is severely limited. Although the head may appear normal, when transilluminated, light shines completely through. Often hydranencephaly is diagnosed by prenatal ultrasonography. CT or ultrasonography confirms the diagnosis. Treatment of hydranencephaly is supportive, with shunting if head growth is excessive. 