Hydraencephaly is a rare condition that affects the development of the brain and the central nervous system. It usually occurs during the latter stages of pregnancy and is characterised by the absence of the cerebral hemispheres within the brain. In most cases babies with hydraencephaly are born with a larger than average head.

What exactly is hydraencephaly?

Hydraencephaly is rare neurological disorder that occurs when the cerebral hemispheres are missing. Instead, the cavities are filled with cerebral fluid. Other parts of the brain form normally and this enables the foetus to breathe and the heart to beat. However, development is delayed and in the most severe cases, babies die at birth. Typically, babies born with hydraencephaly tend to survive for just a few weeks, but some may survive for longer.

What causes hydraencephaly?

There is often no clear cause of hydraencephaly and there doesn’t seem to be evidence to mark out particular events during pregnancy that could result in the absence of key parts of the brain. Often, mothers are completely unaware of any issues until the baby is born and shows little sign of progress. A large head may also be indicative of hydraencephaly. Ultrasound scans may detect issues if they are carried out late in the pregnancy, but scans are usually only recommended when there is a risk of something going wrong in the third trimester or if abnormalities have already been highlighted on previous scans.

Possible causes include the death of a twin foetus, foetal bleeding and infections or illnesses and infections that affect the mother. However, this is believed to be uncommon.

There is some evidence to suggest that there may be an inheritance pattern. However, research is ongoing and the path of inheritance is not clear. Experts believe this is almost always an acquired condition.

What are the most common symptoms?

It is possible for babies born with hydraencephaly not to show obvious symptoms, but their behaviour and rate of growth and development may soon indicate problems. Sometimes, babies with hydraencephaly have a larger head at birth than normal and this may trigger further investigations.

Typically, babies with hydraencephaly suffer from delayed development, vision problems, rigid muscles and stiffness in the limbs, breathing difficulties, seizures, muscle spasms and exaggerated muscle responses.

A diagnosis is usually made based on the child’s symptoms and scans of the head, which show the structural deficits. Sometimes, prenatal scans may detect abnormalities. This enables a diagnosis to be made before birth.

How common is hydraencephaly?

Hydraencephaly is rare and the exact number of cases in the UK is unknown. It affects both boys and girls.

What are the treatment options?

There is no cure for hydraencephaly and the survival rate is low. Sometimes, a shunt may be recommended to remove fluid from the brain.

What is the prognosis for hydraencephaly?

The prognosis for children born with hydraencephaly is generally poor and in some cases, babies will survive just a few days after birth. Most tend to live up to 12 months, but it is very rare to live longer than this.

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