What is Chiari Malformation?
A Chiari malformation is a structural defect in the brain where the cerebellum and medulla are displaced slightly downwards. This occurs due to the shortened growth of the posterior fossa, which is the area near the base of the skull. The residual pressure that this causes can push cerebellar tonsils, the lowest part of the cerebellum, toward the spinal column. The result is that a segment of the cerebellum is located below the foramen magnum, which is the opening of the spinal canal.
This placement of the cerebellum produces pressure that may affect the functions for which this part of the brain is responsible, including motor control and balance. In addition, it can impede the flow of the cerebrospinal fluid that surrounds the brain as it travels between the brain and spinal cord. This condition may be congenital or may occur as the patient grows.
Symptoms of Chiari Malformation
There are several types of Chiari malformations, categorized by the severity of the condition and what areas of the brain are entering the spinal canal. The most common of these, Type I, does not involve the brain stem and may be totally asymptomatic. In fact, this form of Chiari malformation may not be noticed until adulthood and is frequently discovered during imaging tests for an unrelated issue.
Depending upon the extent of the disorder, the symptoms will vary. The most common symptoms of a Chiari malformation include severe headaches, muscle weakness, nausea, fatigue, inability to balance, pain in the upper neck and hearing problems. The symptoms may also change in nature or in significance based on the amount of pressure the cerebrospinal fluid is placing on nearby nerves. Some forms of Chiari malformation result in serious neurological problems, but these are related to the rarer variations of the condition.
A number of disorders relating to the brain or spinal cord may develop along with a Chiari malformation. Some of the conditions it is frequently associated with include:
- Hydrocephalus, which is an accumulation of cerebrospinal fluid in the brain
- Paralysis, due to extensive damage to the spinal cord
- Spina bifida, an incomplete formation of the spinal cord
- Syringomyelia, a cyst filled with cerebrospinal fluid that develops on the spinal cord
- Tethered cord syndrome, which is an attachment of the spinal cord to the bones of the spine
- Spinal curvature, in the form of scoliosis or kyphosis, results in abnormal bending of the spine
Diagnosis of a Chiari Malformation
A Chiari malformation is typically made after a medical history is taken and a physical examination is completed. The testing will likely include an assessment of balance, memory, cognition, reflexes and motor skills. In addition, diagnostic imaging such as X-rays and CT or MRI scans may be useful in providing a detailed view of the area to identify abnormalities.
Treatment and Surgery Options for a Chiari Malformation
Patients who are not experiencing any symptoms of Chiari malformation may simply be medically monitored. If the displacement is not progressing, the symptoms are extremely mild or the patient is not healthy enough for surgery, the doctor may opt for a conservative approach consisting of pain management and life evaluation to reduce the likelihood of future complications.
In many cases, a Chiari malformation may be treated surgically to relieve symptoms and halt the progression of the condition. Typically, this is achieved with a foramen magnum decompression procedure. This involves making an incision at the back of the head to access the bottom of the skull and upper spinal column and correcting the abnormal structure. It is intended to create more space for the brain within the skull, usually by removing a small piece of posterior bone in the area of the foramen magnum. In some cases, the lamina of the first cervical vertebrae as well as excess tissue may also be removed to relieve pressure on the brain and spinal cord. In addition, the dura tissue is usually expanded, using either the patient’s own tissue or a synthetic material, in order to promote the flow of cerebrospinal fluid.