Hydranencephaly is a condition where the brain cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid. Hydranencephaly (or hydroanencephaly) is a type of cephalic disorder. These disorders are congenital conditions that derive from either damage to, or abnormal development of, the fetal nervous system in the earliest stages of development in utero. These conditions do not have any definitive identifiable cause factor; instead generally attributed to a variety of hereditary or genetic conditions, but also by environmental factors such as maternal infection, pharmaceutical intake, or even exposure to high levels of radiation. This is a rare condition in which the cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid. This should not be confused with hydrocephalus, which is an accumulation of cerebrospinal fluid in the ventricles. In hemi-hydranencephaly, only half of the brain is filled with fluid.
Usually the cerebellum and brainstem are formed normally, although in some cases the cerebellum may also be absent. An infant with hydranencephaly may appear normal at birth or may have some distortion of the skull and upper facial features due to fluid pressure inside the skull. The infant's head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal, depending on the severity of the condition. However, after a few weeks the infant sometimes 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. Some infants may have additional abnormalities at birth including seizures, myoclonus (involuntary sudden, rapid jerks), and respiratory problems. Still other infants display no obvious symptoms at birth, going many months without a confirmed diagnosis of hydranencephaly. In some cases a severe hydrocephalus, or other cephalic conditions, diagnosis is misdiagnosed.
Although the exact cause of hydranencephaly remains undetermined in most cases, the most likely general cause is by vascular insult such as stroke or injury, intrauterine infections, or traumatic disorders after the first trimester of pregnancy. In a number of cases where intrauterine infection was determined the causing factor, most involved toxoplasmosis and viral infections such as enterovirus, adenovirus, parvovirus, cytomegalic, herpes simplex, Epstein-Barr, and syncytial viruses. Another cause factor is determined to be monochorionic twin pregnancies, involving the death of one twin in the second trimester, which in turn causes vascular exchange to the living twin through placental circulation through twin-to-twin transfusion, causing hydranencephaly in the surviving fetus. One medical journal reports hydranencephaly as an autosomal inherited disorder with an unknown mode of transmission, where an unknown blockage of the carotid artery where it enters the cranium causes obstruction and damage to the cerebral cortex. As a recessive genetic condition, both parents must carry the asymptomatic gene and pass it along to their child, a chance of roughly 25 percent. Despite determination of cause, hydranencephaly inflicts both males and females in equal numbers. Though hydranencephaly is typically a congenital disorder, it can occur as a postnatal diagnosis in the aftermath of meningitis, intracerebral infarction, and ischemia (stroke), or other traumatic brain injury.
There is no standard treatment for hydranencephaly. Treatment is symptomatic and supportive. Hydrocephalus may be treated with a shunt.The prognosis for children with hydranencephaly is generally quite poor. Death usually occurs in the first year of life. Medical text identifies that hydranencephalic children simply have only their brain stem function remaining, thus leaving formal treatment options as symptomatic and supportive. Severe hydrocephalus causing macrocephaly, a larger than average head circumference, can easily be managed by placement of a shunt and often displays a misdiagnosis of another lesser variation of cephalic condition due to the blanketing nature of hydrocephalus. Plagiocephaly, the asymmetrical distortion of the skull, is another typical associated condition that is easily managed through positioning and strengthening exercises to prevent torticollis, a constant spasm or extreme tightening of the neck muscles.