Chiari malformation refers to deformity of the cerebellum, the lower part of the brain associated with controlling balance. It occurs when the cerebellum and brainstem (posterior part of the brain) are pushed downwards because of lack of space in the skull that is if the back of the skull is smaller than normal. This limits the flow of cerebrospinal fluid (fluid surrounding the brain and spinal cord) causing symptoms such as dizziness, muscle weakness, numbness, headache, difficulty with vision, and coordination problems.
Chiari malformation may be caused by abnormal brain formation during foetal development. This may be caused by exposure to harmful substances during foetal development or with genetic problems that may have a tendency to run in families.
Chiari malformations are categorized into four types depending on the severity of the disorder and the parts of the brain displaced into the spinal canal
Type I is the most common type, often remains non-symptomatic and is observed during examination for another condition. In this condition the bottom portion of the cerebellum extends through the opening at the base of the skull into the spinal canal.
Type II also called as Arnold-Chiari malformation accompanies a form of spina bifida, called myelomeningocele that occurs when the backbone and the spinal canal have not closed properly before birth. A portion of the lower back part of the brain (cerebellum) along with the brainstem extends into an opening at the base of the skull.
Type III is one of the severe forms of chiari malformation that causes neurological defects. In this condition the cerebellum, brain stem, and also part of the brain’s fourth ventricle (communicating cavities filled with cerebrospinal fluid) protrudes through the opening at the base of the skull into the spinal cord.
Type IV: In this condition the cerebellum fails to develop normally.
Many people with chiari malformations often do not have symptoms and may be observed when diagnosis is done for other conditions. Diagnosis includes combination of patient history, neurological examination, and imaging tests such as X-ray, CT scan, and an MRI of the brain and spine.
Surgery is the most preferred option to treat chiari malformation. The goal of the surgery is to stop the progression of changes in the central nervous system. The surgery can reduce pressure on the structures on the base of the skull and re-establish the normal flow of the fluid in the area.
Posterior fossa craniectomy or posterior fossa decompression is the most common operation for chiari malformation. During the procedure an incision is made at the back of the head and a small portion of the bone from the skull and occasionally portion of the first or second vertebrae of the back bone is removed (spinal laminectomy). This creates room for the brain and relieves the pressure exerted on the brain. The dura, covering of the brain is then opened and a patch is sutured into place to expand the space and restore normal cerebrospinal fluid flow. The patch may be a natural tissue harvested from your own leg or neck or may be an artificial patch.
Infection and problems with healing are the risks of the surgery. Regular follow up may be needed to know the outcome of the surgery and the flow of the cerebrospinal fluid.