These conditions are caused by a malformation in the lower rear of the brain that causes the cerebellum and in some cases the brain stem to be pushed downward into the cervical spine. Although the vast majority are asymptomatic and do not require treatment, others may result in a variety of symptoms, including headache, pain, numbness, vocal cord dysfunction, swallowing difficulty and others.
Type I Chiari malformations are defined by downward herniation of the cerebellum, causing it to protrude below the normal opening at the base of the skull where the brain connects with the spinal cord (foramen magnum). Chiari I malformations are common congenital malformations occurring in up to 1% of the general population and are usually asymptomatic throughout life. Chiari I malformations may also occur as a result of increased pressure in the brain from a tumor or hydrocephalus.
Congenital Chiari malformations may occasionally cause a wide range of symptoms, resulting from either the blockage of normal movement of the cerebrospinal fluid (the fluid that circulates around the brain and spinal cord) or direct compression of the brain against the bone. These symptoms can be divided into three categories:
Headaches. These are usually occipital (occurring in the back of the head) and may occur with or without neck pain. Chiari-related headaches typically occur suddenly after an episode of coughing, sneezing, laughing, or straining to have a bowel movement. They are usually brief in duration. The intensity of the headache may vary from relatively mild to severe and disabling. They are called “tussive” headaches from the Latin word “to cough.” Frontal headaches are less consistently associated with Chiari I malformation. Surgical treatment may be indicated when such headaches negatively impact activities of daily living or affect quality of life. It is essential that these Chiari-related headaches are differentiated from other, far more common headache disorders such as migraines before surgical therapy is considered.
Spinal cord dysfunction. This results from the development of a fluid-filled cavity or syrinx (syringomelia) within the center of the spinal cord. Early symptoms include loss of feeling over the shoulders, arms and hands. Scoliosis, particularly with a left curve, may be secondary to the syrinx. Left untreated, there can be progressiveweakness/paralysis, atrophy, incontinence, and in rare instances difficulty with breathing and swallowing.
Local brain or cranial nerve compression. This is the least common presentation of a Chiari I malformation. Symptoms of brain compression include unsteady walking and lack of coordination in fine motor skills. Symptoms of nerve compression include difficulty swallowing, hoarseness, facial numbness or pain, and sleep apnea. After many years of symptoms, respiratory failure may occur.
Chiari I malformations are diagnosed with MRI scans. Imaging of the brain and entire spine is usually suggested in order to rule out any additional factors, such as hydrocephalus syringomelia. If the Chiari I malformation is clearly symptomatic, causing one of the three syndromes described above, surgical treatment will reliably halt its progression and often affords durable relief of symptoms. A variety of procedures can be performed; all of these operations involve decompression of the bone, usually with opening the dura and an expansion of the dura (duraplasty). Infrequently, there are associated bony abnormalities of the craniospinal junction or instability of the spine that could require additional surgery on the front of the spine and spinal fusion (this is not indicated in the vast majority of patients).
If the Chiari is secondary to a tumor or hydrocephalus, the primary treatment is directed to those conditions. Regardless of the specific procedure, the goal of surgery is to relieve compression at the foramen magnum and normalize cerebrospinal fluid flow while minimizing surgical risk.
Chiari II malformations are usually associated with spina bifida (myelomeningocele). In Chiari II malformations, there is always displacement of both the cerebellum and brainstem out of the skull and into the cervical spine as well as abnormalities of the cerebellum and upper brainstem. The vast majority of these children have associated hydrocephalus from aqueduct stenosis and may have other congenital malformations of the brain as well, including agenesis of the corpus callosum and maldevelopment of the cerebral hemispheres. Most children with spina bifida and a Chiari II malformation do not require direct treatment of the Chiari; treatment of the associated hydrocephalus usually avoids Chiari symptoms.
Infants with spina bifida may demonstrate symptoms of aspiration, weak crying or apnea. Once it has been determined that the infant’s hydrocephalus is well controlled and there is no evidence of shunt malfunction, urgent decompression is indicated. If these infants progress to paralysis of the vocal cords, there is a high risk of death within one year.
Older children and young adults may develop symptoms similar to those of the Chiari I malformation, particularly syringomyelia and tussive headaches.