Type I Chiari malformations are characterised by downward displacement of the tonsils of the cerebellum through the foramen magnum into the upper portions of the spinal canal. This form of Chiari malformation is associated with hydromyelia and usually presents in adolescents or adults. In adolescents, the main symptoms are due to this hydromyelia - a flexed paralysis of the arms, loss of pain and temperature sensation of the upper torso and arms, as well as loss of muscle strength in the hands and arms. Adults typically complain of an occipital headache felt at the base of the skull that is made worse by coughing. They also experience neck and arm pain, sometimes in a cape-like distribution.
Type II Chiari malformations: are characterised by the displacement of the cerebellar vermis, tonsils, the fourth ventricle, and the medulla, which is a section of the brainstem, through the foramen magnum.
Type II, also known as Arnold-Chiari malformation, is more highly associated with hydromyelia than
Type I Chiari malformations and is almost always associated with myelomeningocele. A meningomyelocele is a congenital failure of the closure of the spinal cord and column in the lumbar region during foetal developement. Other associated abnormalities include hydrocephalus (increased fluid pressure within the skull), cardiovascular abnormalities, imperforate anus as well as other gastrointestinal abnormalities, and genitourinary abnormalities. Symptoms of this malformation are usually obvious and present shortly after birth and may include brief periods of cessation of breathing; depressed gag reflex; involuntary, rapid, downward eye movements; and a loss of arm strength.
Type III Chiari malformations: consist of displacement of the cerebellum and portions of the brainstem into a meningocele. In this case, the meningomyelocele involves the occiput or cervical spine. The tissue surrounding the brain and spinal cord protrude into the meningocele.
Type IV Chiari malformations: are associated with an underdeveloped cerebellum. Both Type III and IV Chiari malformations are rare.
While the cause of Chiari malformation is not exactly known, several potential explanations exist. Most theories indicate that an increase in pressure above the cerebellum is forced downward into the foramen magnum not unlike a cork into the neck of a bottle. Magnetic Resonance Imaging (MRI) allows physicians to accurately view the cerebellum and the associated structures and determine what form and to what extent the malformation has progressed.
There are many ways to treat Chiari malformations, but all require surgery. Surgical therapy for Chiari malformation consists of either local decompression or diversion of CSF pressure. Decompression is performed under general anaesthesia and consists of removing the very base of the back of the skull as well as the back of the first few vertebrae to the point where the cerebellum descends. This effectively widens the opening of the foramen magnum to provide more space for the brainstem, spinal cord, and descended cerebellar components. The dura mater, a thick membrane surrounding the brain and spinal cord, is also opened. A tissue graft is often spliced into this opening to provide even more room for the unimpeded passage of CSF. Occasionally, the cavity within the spinal cord resulting from hydromyelia can be drained with a diverting shunt tube. This tube can be directed from the spinal cord cavity to either the chest wall or the abdominal wall. These procedures can be done together or at separate sittings.
Please be aware: The information above is copyright and is not intended to replace consultation with a qualified neurosurgical professional.
If you have recently been diagnosed with any of the above conditions or are already a sufferer and would just like to chat, please contact me. Marysia