Hydranencephaly

Hydranencephaly is a rare and severe congenital condition in which the cerebral hemispheres of the brain are absent and replaced by sacs filled with cerebrospinal fluid. The brainstem, cerebellum, and other subcortical structures are typically preserved, which allows basic life-sustaining functions such as breathing, heart rate regulation, and some reflexive responses to continue. The condition is thought to result primarily from bilateral internal carotid artery occlusion or other vascular insults during fetal development, leading to massive destruction of previously formed brain tissue. Other proposed causes include intrauterine infections (such as toxoplasmosis or cytomegalovirus), genetic factors, or other teratogenic exposures. Hydranencephaly is sometimes referred to as hydranencephaly syndrome. At birth, infants with hydranencephaly may initially appear normal, as the head size can be within normal range or only mildly enlarged. However, within weeks to months, affected infants typically develop signs of increased intracranial pressure, progressive macrocephaly (enlargement of the head), irritability, spasticity, seizures, and severe developmental delay. Vision is usually absent or severely impaired, and most infants fail to achieve developmental milestones. Feeding difficulties are common, and many affected children require gastrostomy tube placement for nutritional support. The condition primarily affects the central nervous system, but secondary complications can involve the musculoskeletal system (contractures), respiratory system, and gastrointestinal system. There is no cure for hydranencephaly, and treatment is supportive and symptomatic. Management may include placement of a ventriculoperitoneal shunt to relieve hydrocephalus and control head enlargement, anticonvulsant medications for seizure management, physical therapy, and nutritional support. The prognosis is generally poor, with many affected infants not surviving beyond the first year of life, although some individuals have survived into childhood or rarely beyond with intensive supportive care. Early diagnosis is typically made through prenatal ultrasound or postnatal neuroimaging such as cranial ultrasound, CT scan, or MRI, which reveals the characteristic absence of cerebral hemispheres.

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