A condition in which the cerebral hemispheres of the brain are absent and replaced by sacs filled with cerebrospinal fluid. Usually the cerebellum and brainstem are formed normally. An infant with hydranencephaly may appear normal at birth. The infant's head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal. However, after a few weeks the infant usually becomes irritable and has increased muscle tone (hypertonia). After several months of life, seizures and hydrocephalus may develop. Other symptoms may include visual impairment, lack of growth, deafness, blindness, spastic quadriparesis (paralysis), and intellectual deficits. Hydranencephaly is an extreme form of porencephaly (a disorder characterized by a cyst or cavity in the cerebral hemispheres) and may be caused by a vascular insult or injuries, infections, or traumatic disorders after the 12th week of pregnancy. Diagnosis may be delayed for several months because the infant's early behavior appears to be relatively normal. Transillumination of the head (in which a strong light shines through the head) usually confirms the diagnosis. Some infants may have additional abnormalities at birth including seizures, myoclonus (involuntary sudden, rapid jerks), and respiratory problems. There is no standard treatment for hydranencephaly. Treatment is symptomatic and supportive. Hydrocephalus may be treated with a shunt. The outlook for children with hydranencephaly is poor. Death generally occurs before age 1.
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Absence of cereberal hemispheres, which have been replaced by fluid-filled sacs, lined by leptomeninges. The skull and its brain cavities are normal. [hydr- + G. an- priv. + enkephalos, brain]

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hy·dran·en·ceph·a·ly .hī-.dran-en-'sef-ə-lē n, pl -lies a congenital defect of the brain in which fluid-filled cavities take the place of the cerebral hemispheres

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hy·dran·en·ceph·a·ly (hi″dran-ən-sefґə-le) complete or almost complete absence of the cerebral hemispheres, the space they normally occupy being filled with cerebrospinal fluid.

Medical dictionary. 2011.

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