Hydranencephaly is a central nervous system disorder characterized by an enlarged head and neurological deficits. The exact cause of Hydranencephaly is not known. This extremely rare form of Hydrocephalus involves the absence of portions of the brain. Results of neurologic examination in newborns may be normal or abnormal. The head usually appears enlarged at birth. Vision impairment, lack of growth and intellectual deficits are symptomatic of this disorder.
Hydranencephaly can usually be detected at birth due to an enlarged head. Some infants may appear healthy at birth but may later fail to grow at a normal rate. Irritability, poor feeding, infantile spasms or seizures, and spasticity or rigidity of arms and legs are symptomatic of this disorder. Some affected individuals may experience an exaggeration of muscular reflexes (hyperreflexia) and/or increased muscle tone (hypertonia). Poor body temperature regulation, vision impairment and mental retardation may also occur.
Hydranencephaly is suspected to be an inherited disorder although the mode of transmission remains unknown. Some researchers believe that prenatal blockage of the carotid artery where it enters the cranium may be a cause of this disorder. However, the reason for the blockage is not known.
An autosomal recessive inheritance has been described in some cases. Human traits, including the classic genetic diseases, are the product of the interaction of two genes, one received from the father and one from the mother. In recessive disorders, the condition does not occur unless an individual inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.
Hydranencephaly is a rare disorder that affects males and females in equal numbers.
The diagnosis of Hydranencephaly may be confirmed based upon a thorough clinical evaluation, the identification of characteristic physical findings, a detailed patient history, and advanced imaging techniques, such as transillumination, an x-ray of the blood vessels using dye (angiogram), or computerized tomography (CT scan). During CT scanning, a computer and x-rays are used to create a file showing cross-sectional images of internal structures such as the brain.
In some cases, the disorder may be diagnosed before birth (prenatally) using fetal ultrasonography to identify characteristic physical abnormalities. In fetal ultrasonography, an image of the developing fetus is created using sound waves.
There is no treatment for Hydranencephaly. A shunt may be recommended to facilitate the drainage of fluid from the brain.
Research into Hydranencephaly and other central nervous system birth defects is ongoing. Understanding the role of genetics in fetal development is a major goal of scientists studying congenital neurological disorders.
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