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About Hydranencephaly

This page is going to be more technical than most of the other pages on this site. There is information from a radiologist on the diagnosis of Hydranencephaly. And, then there is an overview of the brain and brainstem.

Radiological Diagnosis of Hydranencephaly
Jim Barkovich, MD is one of the best-known pediatric neuroradiologists in the country. His book, Pediatric Neuroimaging, is one of the most used references on the subject. He defines Hydranencephaly as "...a condition in which most of the brain mantle (cortical plate and hemispheric white matter) has been damaged, liquefied, and resorbed." This condition may be the end result of more than one causative event. Infection and massive vascular occlusion involving the carotid arteries are the two most often cited. Because Hydranencephaly may be a result of different processes the imaging can be somewhat variable. The "classic" appearance is complete replacement of the cerebral hemispheres with fluid. No cortical mantle is visible on MRI. The thalami and cerebellum are usually spared. Some sparing of the inferior frontal and inferior temporal lobes may be present. Roger Harned

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.  

A brief orientation about the brainstem by Dr Bjorn Merker

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 outer, folded part of the brain) is attached to the brainstem only at the tweenbrain. This means that the tweenbrain is well connected with the cortex, and the part of it, which is particularly, so is called the thalamus, which is the upper part, bulging upwards. The remaining, lower part of the tweenbrain is called the hypothalamus ("below the thalamus"). It is a vital integrating center for hormonal, visceral and motivational regulation. You can see its glandular appendage, the pituitary gland (also called the hypophysis), extending down from it to the right.

The next part of the brainstem is the midbrain, technically known as the mesencephalon. On the left you can see two small bumps. These are the colliculi, or "little hills," where vision, hearing and the sense of touch are integrated. Below them is a region of neural tissue surrounding a canal called "the aqueduct." If you look closely the aqueduct is indicated by dotted lines. It carries a fluid - cerebrospinal fluid - which bathes the brain. When the flow of this fluid is obstructed the fluid builds up in the brain, causing hydrocephalus. This must be corrected by a shunt, which allows the fluid to drain. The neural tissue surrounding the aqueduct is called the periaqueductal grey matter, which plays an important role in emotional expression.

Then we come to the large part of the brainstem called the hindbrain. It has several major parts. On the left is the cerebellum, the "little brain." It got its name because like the cortex it has a folded surface, and looks like a small brain in its own right. It has a role in the adjustment of movement patterns based on learning, and is well connected with both brainstem and cortex. The bulge that you see extending to the right, opposite the cerebellum, is called the pons, the "bridge." It contains a mass of nerve fibers connecting the cerebellum with itself and the rest of the brain. The border region between the pons and the midbrain houses important systems for regulating cycles of sleep, wakefulness and alertness.

Finally, the lower part of the hindbrain, called the medulla, or "bulb," extends on into the spinal cord. It contains in a sense the basic wiring of the brain. It houses numerous system - both sensory and motor - which maintain vital functions such a breathing, heart rate and balance and organized reflexes such as swallowing and coughing at an automatic level of functioning.

The above is only a thumb-nail sketch of the most essential parts of the brainstem. With regard to Hydranencephaly it is important to remember that function is determined not only by which parts of the brain are missing and which are present, but also by how the parts that are present are affected by the loss of connections from the parts that are missing. Here there is much that we do not yet know, and some of this we might learn from children with Hydranencephaly.
Dr B. Merker is a neuroscientist in Sweden who is a friend of the families of children with Hydranencephaly.

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August 16, 2001- January 12, 2005

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