By Coryn Hoffman

Have you ever heard of a Chiari malformation (CM)? CM is a condition caused by a developmental abnormality in the structure of the brain. Normally, the lower part of the brain (the cerebellum) sits above the opening in the skull where the spinal cord connects to the brain. A CM causes the cerebellum to bulge into this opening and into the upper spinal canal (Figure 1), putting pressure on the cerebellum, brain stem, and spinal cord, often blocking the flow of cerebrospinal fluid (CSF), the clear fluid that surrounds the brain. Putting pressure on the cerebellum and disrupting this flow of CSF can cause a variety of symptoms that range from mild (with minor symptoms like headaches), to severe (with life-threatening complications like nerve damage or paralysis). Other than surgery, there aren’t many good treatment options, so more research is needed to develop alternative treatments or diagnostic imaging methods to improve early detection strategies.

Chiari Malformations: Types, Prevalence, Causes, and Symptoms

Type I

CM type I is the most common form, affecting just under 1/1000 people, with a slight female predominance. The majority of these patients are asymptomatic and are not diagnosed until teenage years or young adulthood. Most “asymptomatic” patients – which can exhibit symptoms, just not ones easily attributable to CM – may not recognize their symptoms as anything serious, or may attribute them to typical things like stress or dehydration, and therefore never investigate their symptoms any further. This can unfortunately delay diagnosis for many. In fact, CM is most often detected by coincidence, when patients undergo diagnostic imaging for unrelated purposes.

CM type I can either be congenital (present at birth) or acquired. In congenital CM, the malformation occurs during development and is likely caused by either exposure to harmful substances during pregnancy or by genetic anomalies that can be inherited. Acquired CM can develop later in life due to injury, infection, or exposure to a harmful substance.

The cerebellum is the part of the brain that controls balance and coordination, and is usually composed of two hemispheres. Below the surface of these hemispheres are two small protrusions called the tonsils (not the ones in your throat). CM type I occurs when these tonsils are misshapen and descend further than normal (at least 4 mm) into the upper spinal canal, where they block the normal flow of CSF (Figure 2). This blockage can often lead to syringomyelia, the development of a syrinx, which is a fluid-filled cavity in the spinal canal. As a syrinx fills with fluid, it expands and puts pressure on the spinal cord, affecting neuromuscular function. The presence of a syrinx during development can also lead to the development of scoliosis, an abnormal curvature of the spine.

In addition to the symptoms associated with a syrinx, the most common symptoms of CM type I include: bad headaches/neck pain, lack of balance and coordination, numbness or tingling of the hands and feet, and muscle weakness or spasms, among other symptoms. Less often, patients with CM type I can also experience ringing or buzzing in the ears, slow heart rhythm, or trouble breathing/sleep apnea. Patients may experience varying degrees of these symptoms, and those who experience the more severe symptoms are more likely to be diagnosed earlier in life.

Type II

CM type II is always congenital because it occurs almost exclusively in infants with neural tube defects such as myelomeningocele, a form of spina bifida that affects 1/4000 infants. In spina bifida, the neural tube does not close properly during fetal development. In CM type II, a greater amount of brain tissue (from both the cerebellum and the brain stem) extends into the spinal canal (Figure 2). Medical experts still do not know what causes this malformation to occur during development, and researchers continue to search for genetic causes.

The most common problem with CM type II is hydrocephalus – too much spinal fluid in the brain, which increases pressure on the brain and can damage brain tissues. Since the brain stem controls important functions like breathing, heartbeat, and swallowing, infants with CM type II may experience: brief periods of apnea where they stop breathing, trouble swallowing/vomiting, and problems inhaling food or fluid into the lungs. Older babies or children may also experience: progressive hydrocephalus, or loss of vision, hearing, or fine motor skills. These children may also develop a syrinx, causing pain in the arms or legs and making it difficult for them to walk.

While not discussed at length in this article, CM types III and IV are very rare and have much higher rates of fatality and life-threatening complications. The children that do survive CM type III or IV have severe neurological defects such as seizures as well as mental and physical delays.

Can patients with Chiari malformation live a normal life?

The most serious complications that can occur with either type of CM include syringomyelia, hydrocephalous, or tethered cord syndrome, where the spinal cord attaches to the spine, causing it to stretch and causing serious nerve and muscle damage in the lower body. Once these issues are resolved with surgery, most patients can live a relatively normal life using only pain relievers to treat, or exercises to prevent headaches and neck pain. Patients may require regular check-ups to make sure their symptoms do not progress. The more serious cases can involve permanent damage to muscles or nerves, paralysis or respiratory failure from not enough oxygen reaching a child’s lungs. In the more severe cases, patients may need speech therapy for swallowing problems, nutrition therapy, or physical, occupational or rehabilitation therapy. Most cases, however, are not this severe and can be managed without major medical treatments or procedures.

How are Chiari malformations diagnosed?

The most common way to diagnose CM is by imaging to look for evidence of structural malformations or the presence of a syrinx. This is done most commonly using magnetic resonance imaging (MRI), which can provide an accurate view of the brain, cerebellum and spinal cord so the physician can identify the presence and the extent of the malformation (Figure 3). Imaging techniques such as computed tomography (CT) scan or ultrasound can also be used to diagnose CM.

Beyond diagnostic imaging, physicians may also perform a sleep study to look for evidence of sleep apnea, or a swallowing study to determine whether there is an abnormality in the internal swallowing process that is suggestive of lower brainstem dysfunction. Additional neurological tests include a brainstem auditory evoked response (BAER) test to examine hearing and brainstem connections, or a somatosensory evoked potentials (SSEP) test to measure nerve sensation. This variety of tests can help physicians determine the extent of a patient’s symptoms and what interventions may be necessary.

How are Chiari malformations treated?

The treatment options for CM depend on the exact type of malformation, as well as what symptoms are experienced. CM type I that is asymptomatic should be left alone or simply treated with pain relievers or physical therapy. If the malformation is considered symptomatic (causes hydrocephalous, syringomyelia or tethered cord syndrome), treatment is recommended to relieve symptoms and prevent the progression of these complications. In these cases, decompression surgery is typically performed, where a small portion of bone is removed from the bottom of the skull to create more space for the cerebellum, relieving pressure on the spinal cord and restoring the normal flow of CSF.

CM type II is usually symptomatic and requires surgery. The decompression surgery for CM type II is similar but is often restricted to decompressing the tissues in the spinal canal rather than disrupting the back of the skull. Some patients may also require a shunt in the brain to drain excess fluid in the case of hydrocephalus, or a shunt in the spinal cord to drain fluid from a syrinx. When deciding on treatment options for CM, the benefits of surgery should always outweigh the risks. Some patients benefit immensely from surgery while others may not, as prior nerve damage cannot usually be reversed.

The state of CM research:

The cause of CM remains unknown. Many cases are thought to be the result of part of the skull not being large enough for the brain, causing the malformation of the cerebellar tonsils during development. There is evidence that CM runs in some families, where patients may have inherited a faulty gene that caused problems with skull development. However, the specific genes that may be involved have not yet been identified. Chiari malformations can sometimes be debilitating, so researchers are working hard to learn more about the genetics and brain mechanisms behind CM, and develop better neuroimaging tools and surgical methods to help improve the lives of patients, like me, who suffer from CM (yes, I am the CM patient in figure 3). 

TL:DR

• Chiari malformation (CM) is a structural defect in the brain that causes severe headaches and other neurological symptoms.
• Treatment for CM depends on the type, but most often involves surgery.