Hydranencephaly is a condition that usually arises in mid or late pregnancy when a major reduction of blood supply to the brain results in loss of most of both cerebral hemispheres. The more primitive parts of the brain (brain stem, thalamus and cerebellum) are preserved so that, usually, the vital functions of breathing, heart function and temperature regulation are possible. The head mainly contains fluid-filled cavities with occasional small islands of the cerebral cortex remaining, particularly at the back of the head. A related condition of multiple cavities with more surviving brain is referred to as multicystic encephalomalacia.


Medical text written May 2003 by Professor B Neville. Last updated April 2008 by Professor Brian Neville, Emeritus Professor of Paediatric Neurology, UCL Institute of Child Health and Great Ormond Street Hospital, London, UK.

What are the symptoms?

The head may be abnormally small, of normal size, or large. Sometimes there may be an excessive rate of head growth and it may be appropriate to insert a shunt system for hydrocephalus to prevent the development of a very large head. Babies with hydranencephaly normally show no visual behaviour or other developmental progress. The life span is usually limited to weeks or months but is sometimes longer. Those who are most severely affected may die at birth.

The above description is of severe or true hydranencephaly. Some babies have more surviving brain tissue and may, therefore, have some developmental progress and a longer life span.

What are the causes?

Despite the severity of the damage, there is often no clear event in the pregnancy to account for it. There may be a reduction in fetal movements but the mother is often quite unaware of any problem. Recognised causes of this condition include intrauterine death of a twin, or blood loss from the baby by a number of possible mechanisms. A number of acute illnesses or injuries to the mother in pregnancy have been reported in the medical literature in a small number of instances but this is uncommon. Ultrasound late in pregnancy can show the abnormality but may only be performed in high-risk situations. Sometimes a similar situation may occur as a result of severe damage during or immediately after birth but the acute brain illness is then obvious.

Sometimes, where the birth was slow, it may be mistakenly thought that the damage occurred at birth.

Despite the severity of the brain defect, the baby may apparently behave normally at birth with spontaneous limb movements, crying and sucking. Others are unwell with spasticity and feeding and temperature regulation problems.

Epileptic seizures (see entry Epilepsy) are quite common and may not respond to treatment.

How is it diagnosed?

Diagnosis of the condition is made by ultrasound of the head. In severe cases, the EEG shows no activity.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
This is regarded as an acquired disorder and not genetic. A small number of families have had more than one baby with the disorder. It occurs equally in boys and girls. Counselling is therefore directed to looking for obstetric factors which might be identifiable and remediable. However, this is, in the main, a sporadic disorder with a low risk of recurrence.

Prenatal diagnosis
Late ultrasound in utero may find the abnormality.

Is there support?

There is no support group for hydranencephaly in the UK. Cross-referrals to other entries in Contact’s directory are intended to provide relevant support for these particular features of the disorder. Organisations identified in these entries do not provide support specifically for hydranencephaly.

A support group outside of the UK exists for hydranencephaly. Please ring our helpline for details.

Families can use Contact’s freephone helpline for advice, information and, where possible, links to other families. To meet other families with disabled children, join Contact’s closed (private) Facebook group.

Back to A-Z Conditions