INTRODUCTION TO CONGENITAL DISORDERS OF THE BRAIN & SKULL

As a general rule, it is apparent that the more complex the formation of a structure, the more opportunities for malformation. Some of the most serious neurological abnormalities (e.g., anencephaly [no Brain], encephalocele [part of the Brain is exterior to the Skull) develop in the first two months of gestation and represent defects in neural tube (the embryonic precursor of the entire central nervous system) formation. The medical term for this is "dysraphia". Other defects (e.g., hydranencephaly, porencephaly [conditions where the Brain is severely malformed]) occur later and appear to be secondary to destructive processes after the Brain has formed.

Modern investigative methods, such as amniocentesis and ultrasonography may provide an accurate in utero detection of many malformations. Genetic counseling for parents of a child with a major neurological abnormality is important, since the risk of a subsequent child's having such a defect is high. These parents frequently also need psychological help and support. Women who have had a pregnancy resulting in an infant or fetus with a neural tube defect should be advised that folic acid supplementation (4 mg/day) before conception and during early pregnancy may substantially reduce the risk of neural tube defects in subsequent pregnancies.

BRAIN ABNORMALITIES

Terminology

Brainstem auditory evoked potential (BAER): An electrical test to examine the hearing abilities of the Brainstem.

Brainstem: The base of the Brain which controls many basic functions such as breathing, swallowing, eye movement and other basic functions.

CT (Computed Tomography) scan: A special type of radiograph ("x-ray") which is especially useful to look at bone structure. It also shows the Brain and Spinal Cord, but not in the detail that can be obtained with MRI.

Central Canal: A tubular cavity in the center of the Spinal Cord which is normally not dilated.

Cerebellum: The portion of the Brain which is in the Posterior Cranial Fossa. It is involved in coordination of all our movements.

Dura Mater: The leather-like covering over the surface of the Brain and Spinal Cord.

Electroencephalogram (EEG): A test to evaluate the patterns of the Brain's "electrical waves".

Electromyography (EMG): An electrical test used to evaluate the function of different muscles, nerves, and groups of nerves. It is often combined with a measurement of the Nerve Conduction Velocity (NCV).

Foramen Magnum: The opening at the Base of the Skull through which the Spinal Cord passes.

Hydrocephalus: Often called "water on the Brain". In this condition, the fluid spaces of the Brain (Ventricles) are larger than normal because of an abnormal accumulation of the Cerebrospinal Fluid (CSF).

Hydromyelia: See Syrinx.

MRI (Magnetic Resonance Imaging): A study which uses sophisticated technology and a magnetic field to produce high quality images of the Brain, Spinal Cord or other body parts.

Myelogram: A test which involves a spinal puncture to inject dye into the Cerebrospinal Fluid space around the Spinal Cord. This dye can be moved into the Cervical Spine and Base of the Skull. Both plain x-rays and CT scans can be used to help define problems in the spine.

Shunt: A tube system which drains Cerebrospinal Fluid (CSF) from one space to another body structure.

A Ventriculo-peritoneal Shunt is created by placing a special catheter into one of the Brain's Lateral Ventricles, connecting it to a "one-way" pressure valve (a concept similar to the valve that controls a "pressure cooker" used in food preparation) and then passing beneath the skin towards the abdominal cavity where the "distal" portion of the shunt catheter "floats" within the peritoneal space from which the shunted CSF can be absorbed back into the circulatory system.

A Ventriculo-atrial Shunt is created by placing the "distal" catheter through the Jugular Vein (in the neck) into the Right Atrium of the Heart.

A Lumbar Subarachnoid-Peritoneal Shunt is used in some unusual circumstances by placing the first ("Proximal") portion of the Shunt into the subarachnoid space in the lower lumbar region and passing it beneath the skin and inserting it into the Peritoneal Cavity.

A Cyst-Peritoneal Shunt is used in conditions such as Dandy-Walker Cyst by placing the "Proximal" catheter into the cyst and draining that CSF into the Peritoneal Cavity.

Spasticity: Increased tightness or tone in the arms and/or legs, making the patient less flexible; the arms and/or legs seem stiff.

Syrinx (syringomyelia; hydromyelia): These terms all refer to an abnormally dilated fluid filled cavity in the Spinal Cord.

Tonsils: The lower portion of the Cerebellum which can be pushed down into the Cervical Spinal Canal in the Arnold Chiari Malformation.

Ventricles: Fluid filled cavities within the Brain. The Cerebrospinal Fluid (CSF) is made by a "gland-like" apparatus (the "Choroid Plexus") lying within the Ventricle (about 2 pints each day) and circulates through the Ventricles, over the surface of the Brain and Spinal Cord and to then be reabsorbed into the Arachnoid Granulations (special structures that drain into the Brain's veins.) If there is a blockage to either the flow or reabsorbtion within the system, the fluid can build up and cause Hydrocephalus.

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This page last edited on 2/22