Hydranencephaly is a rare neurological condition in which most of the cerebral hemispheres are absent and replaced with fluid.
Unlike in Anencephaly, which is a defect in brain development, in Hydranencephaly the baby’s brain develops normally until “something” happens to cut off the flow of blood to the baby’s brain or otherwise severely damage it. The affected part of the brain then starts to die and the tissue is resorbed by the body and replaced with cerebral spinal fluid (CSF). The “something” that starts this process can be quite brief. Some of the most common causes are a stroke in the baby, prenatal drug exposure, and the death of a twin in utero. In many of the children the cause is unknown. The damage to the brain usually occurs in the 2nd or 3rd trimester of pregnancy and can occur up to a year after birth as well.
While the damage to the hemispheres is typically extensive, the child’s brainstem is usually (but not always) intact. Since in our experience there does not seem to be any clear relationship between what remains of the hemispheres and the abilities of our children, it seems that they rely largely on their brainstems for relating to their surroundings, for expressing themselves and for their various emotional reactions. Given the highly sophisticated neural mechanisms housed in the brainstem, this is not as surprising as it might seem at first blush. Although it is often thought that someone has to have a cortex in order to be aware and interact with their environment children with Hydranencephaly prove otherwise.
A newborn with Hydranencephaly will look like any other newborn. Their heads may be somewhat enlarged due to Hydrocephalus (a buildup of fluid pressure in the skull) but Microcephaly (small head) may also occur. In some cases Hydranencephaly may not be diagnosed for several weeks or months. It can also be diagnosed fairly accurately in utero.
As time goes on, a child with Hydranencephaly may exhibit irritability, feeding difficulties such as gastro esophageal reflux, difficulty with swallowing or sucking, seizures and increased muscle tone. The first year is often very difficult for a child with Hydranencephaly and many die during this time, while others survive and stabilize. The oldest people we know of with Hydranencephaly are both in their 30s. Some children develop breathing difficulties and may need suctioning and in a few cases children have needed to have a tracheostomy and use a ventilator. Note, however that like other children, no two children with Hydranencephaly are exactly alike. They often differ in how their brain has been affected. Each child develops individually, with different abilities and difficulties which often change over time.
Most of the children we know of can hear and most do so very well, while many are visually impaired. Most of the children with Hydranencephaly know their family members and are very aware of their surroundings. Many can use their hands to play with toys or activate switches. . Most of them are communicatively responsive, and a few of the children can use several words. Children with Hydranencephaly often go to school, go for trips on planes, go swimming, to Disney World, etc. In other words they participate in life as does any other child.


The Brain stem In Hydranencephaly

Basically Hydranencephaly indicates that a child is missing much or most of their cerebral hemispheres, that is, the two masses of folded brain tissue (cortex) that surround the brain stem. Literally “anencephaly” means “without brain”, but this is technically incorrect as a term for the cases to which it is applied, which almost invariably have a brain stem. The brain stem is most definitely a part of the brain, and a very important part of the brain.. However, many children have some of their cerebral hemispheres so can use these and learn to do more than would be expected by this diagnosis. Just as all children are different, all children with Hydranencephaly are different as well. What may be a major difficulty for one child (like seizures) may not even be present in another.


In the figure we see the outline of the human brain in its place in the head. It is seen as if it were divided down the middle and viewed from the exposed side. If we did not open it up this way along the middle, but simply viewed the whole brain from the side, we would not see much of the brain-stem, because its upper parts would lie buried under the cortex which surrounds it on all sides except below.
The gray shading indicates the brain stem. It has several parts, each of which includes numerous neural systems with complicated connections with one another. At the top we see the “tweenbrain.” It is more often called the diencephalon, which means the same thing, namely that it is located “between” two other things. What it is sitting between is the brainstem and the cortex, because the whole cortex (the