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The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

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Synonyms of Hydranencephaly

Disorder Subdivisions

General Discussion

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.

Affected Populations

Hydranencephaly is a rare disorder that affects males and females in equal numbers.

Related Disorders

Porencephaly is a disorder of the central nervous system involving cerebral cysts or cavities in cortical brain tissue. The disorder can occur before or after birth. Fluid which can accumulate in the head can be drained through a surgical shunt procedure. The prognosis is variable. Some patients with this disorder may develop only minor neurological problems and have normal intelligence, while others may be severely disabled.

Hydrocephalus is a term describing an accumulation of fluid in the brain cavity which usually causes increased pressure inside the skull. It is characterized by enlargement of the head and prominence of the forehead. This disorder may begin suddenly and can be congenital or acquired; it can be a symptom of another disorder or a primary condition. Treatment with a surgical shunt procedure is generally successful in relieving pressure on the brain by draining the fluid out of the head. (For more information on this disorder, choose "hydrocephalus" as your search term in the Rare Disease Database.)

Standard Therapies

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.

Investigational Therapies

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.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:

Hydranencephaly Resources

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at solivo@rarediseases.org.)

Other Organizations:


Birth Defects Encyclopedia: Mary Louise Buyse, Editor-In-Chief; Blackwell Scientific Publications, 1990. Pp. 885-86.

Textbook of Child Neurology, 5th Ed.: John H. Menkes, M.D., Author; Jonathan W. Pine, Jr. et al., Editors; Williams & Wilkins, 1995. Pp. 307-08.

Principles of Neurology, 6th Ed.: Raymond D. Adams, Maurice Victor, and Allan A. Ropper, Editors; McGraw-Hill, Inc., 1997. P. 995.

Nelson Textbook of Pediatrics, 15th Ed.: Richard E. Behrman, Editor; W.B. Saunders Company, 1996. P. 1684.

Hydroanencephaly. S. Gabrovski et al.; Ah Vopr Reirokhir (Sept-Oct 1984; 5). Pp. 32-38.

Hydranencephaly: Prenatal and Neonatal Ultrasonographic Appearance. D. J. Coady et al.; Am J Perinatol (Jul 1985; 2(3)). Pp. 228-30.

Ultrasonographic Prenatal Diagnosis of Hydranencephaly. A Case Report. H. A. Hadi et al.; J Reprod Med (Apr 1986; 31(4)). Pp. 254-56.

Development of Visual Function in Hemihydranencephaly. G. Porro et al.; Dev Med Child Neurol (Aug 1998; 40(8)). Pp. 563-67.

Brain Functions of an Infant with Hydranencephaly Revealed by Auditory Evoked Potentials. T. Yuge et al.; Int J Pediatr Otorhinolaryngol (Sept 15 1998; 45(1)). Pp. 91-95.

Report last updated: 2007/08/07 00:00:00 GMT+0