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Chiari Malformation

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Ismail Munir

Overview

Chiari malformation is a congenital defect characterized by the brain tissue extending into the spinal canal. 
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The first cases of Chiari malformation were described in 1883. However, it wasn&rsquo;t until 1891 that Professor Hans Chiari, a German pathologist, classified it into types I to III. Later, Chiari&rsquo;s colleague, Julius Arnold further modified the definition of Chiari type II malformation and it became known as Arnold-Chiari malformation. Researchers later added type IV malformation to the group.

Chiari malformations are believed to have a congenital nature, but may not show symptoms until later in life. Acquired versions of the disorder have also been identified.

Structural defects in the brain and spinal cord are to blame for the development of Chiari malformations. As a result, the brain tissue is displaced into the spinal canal, putting pressure on the brain stem and spinal cord. Moreover, the flow of the cerebrospinal fluid may also be blocked. Although most people show no symptoms, some may present with headaches, dizziness, tinnitus, neck pain, and hearing or balance problems.<a href="#accordion">[1]</a> <a href="#accordion">[4]</a>

Most cases of Chiari malformation are discovered coincidentally while the patient is undergoing imaging for an unrelated reason. Type 1 is the most common and occurs in approximately 1 in 1000 births. Females are more commonly affected than males, with a ratio of 1.3-1. 
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Chiari malformations are classified based on the severity and part of the brain structure that extends into the spinal canal.<a href="#accordion">[1]</a> <a href="#accordion">[2]</a> <a href="#accordion">[3]</a> 
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Type I Chiari Malformation 

This is the most common and least severe form. It is characterized by the lower half of the cerebellum, and not the brain stem, extending through a hole at the base of the skull, called the foramen magnum.&nbsp;Type 1 Chiari malformation is the only form of the disorder that can also be acquired. While most children remain asymptomatic, some develop symptoms as adolescents or adults. 

Severe headaches, that worsen with sneezing or coughing, are characteristic of Chiari malformation. Other symptoms result from the formation of a fluid-filled cavity in the spinal cord (syrinx). These include loss of muscle strength, pain, and temperature sensation in the hands and arms. Moreover, children and infants may present with motor delays, loss of muscle tone, difficulty swallowing, and failure to thrive. Approximately 30-50% of patients also experience anomalies of the base of the skull and spine, such as <a href="https://merisehat.pk/disease/scoliosis">scoliosis</a>, cervical spina bifida occulta, and Klippel-Feil deformity.

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Type II Chiari Malformation 

Previously referred to as the Arnold-Chiari malformation, type II is characterized by the herniation of both the cerebellum and brain stem through the foramen magnum. It only affects children born with a severe form of spina bifida, myelomeningocele. 

Since type II is more severe than type I Chiari malformation, symptoms usually appear during childhood. These include loss of arm strength, altered breathing patterns with periods of apnea, depressed gag reflex, and involuntary, rapid, downward eye movements. Life-threatening complications are common and require surgical treatment.

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Type III Chiari Malformation 

This is the most serious form. It includes the protrusion of the cerebellum and brain stem through the foramen magnum and into the spinal cord. In some instances, the membranes that cover the brain or spinal cord also extend through the hole, resulting in an encephalocele. 

Children present with serious neurological abnormalities, <a href="https://merisehat.pk/disease/absence-seizures">seizures</a>, and learning delays. Moreover, life-threatening complications cause high early mortality rates for the disorder.&nbsp; 

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Type IV Chiari Malformation 

This rare form is the most severe type of Chiari malformation. An underdeveloped or incomplete cerebellum (cerebellar hypoplasia) is the cause of type IV Chiari malformation. It may present with exposed spinal cord and skull tissue. Most infants do not live beyond infancy.

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Type 0 Chiari Malformation

This is an extremely rare form. Although there is little to no expansion of the cerebellum into the foramen magnum, significant crowding of the brain tissue occurs at that level. Symptoms result from an irregular flow of cerebrospinal fluid (CSF) at the base of the skull. 
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Signs and Symptoms

The cerebellum is located at the base of the skull and is responsible for the coordination of movement. It is composed of two lateral hemispheres and a central vermis, with two small tonsils on the undersurface. The fourth ventricle, filled with cerebrospinal fluid, is located in front of the cerebellum and behind the brainstem. A large opening in the base of the skull, called the foramen magnum connects the spinal cord to the brainstem. Herniation of the brain tissues through the foramen magnum results in Chiari malformation.

Some people have symptoms from birth. Others experience symptoms in their late teens or early 20s. Additionally, symptoms may improve or worsen with time.<a href="#accordion">[1]</a>

Some common symptoms include: 
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<ul>
	<li>Problems With Balance Or Movement - Coordination issues, muscle weakness, and numbness in the limbs may lead to issues with fine motor skills. Dizziness, balance problems, and vertigo can also occur. 
	&nbsp;</li>
	<li>Headache - This is the most common symptom of Chiari malformation. It typically worsens after coughing, straining, or sneezing. The pain is sharp, throbbing, or of a stabbing nature It begins at the back of the head and can spread to the shoulders and neck. 
	&nbsp;</li>
	<li>Vision And Hearing Problems - Tinnitus is a buzzing or ringing noise that some people experience occasionally along with dysfunction. Additionally, possible symptoms include&nbsp;sensitivity to light (photophobia), abnormal eye movements (nystagmus), and double vision (diplopia). 
	&nbsp;</li>
	<li>Speaking, Drinking, And Eating Problems - Dysphagia, or difficulty swallowing, can affect children with Chiari malformation. These infants may also frequently drool, gag, or vomit. As a result of the difficulty eating, failure to thrive is common in children. 
	&nbsp;</li>
	<li>Sleeping Difficulty- The pain from migraines can occasionally cause insomnia. Additionally, some people have sleep apnea. 
	&nbsp;</li>
	<li>Bowel And Bladder Issue - Chiari malformation can result in the loss of bowel and bladder function. 
	&nbsp;</li>
	<li>Other Symptoms - Other signs and symptoms include tingling or burning in the fingers, toes, or lips, palpitations, fainting spells, and persistent weariness. 
	&nbsp;</li>
</ul>

Causes

Structural defects in the brain and spinal cord are mostly to blame for the development of Chiari malformation. These defects develop during fetal development within the womb.

Genetic mutations or a nutrient-deficient maternal diet have been linked to an abnormally small bony space at the base of the skull. This causes overcrowding and places pressure on the cerebellum. Thus, causing herniation of brain tissue through the foramen magnum.

Some cases of Chiari malformation seem to occur in more than one family member, signifying that the disorder might also be inherited.

Although the disorder is almost always present at birth, in rare instances, tumors, abnormalities in the spine, or hematomas may cause the skull or spinal cord to shift shape and result in Chiari malformations in people not born with the disorder.<a href="#accordion">[3]</a> 
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Prenatal ultrasounds can help detect some types of Chiari malformations. Moreover, associated conditions like spina bifida and hydrocephalus can also be detected on prenatal ultrasounds.

Screening is not typically recommended in adolescents and adults. However, if an individual shows symptoms and has a family member with Chiari malformation, the doctor may suggest an MRI or CT scan for the detection of the disease. 
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Diagnosis

To diagnose one with Chiari malformation, doctors will first take a medical history and conduct a complete physical exam. During the physical examination, the individual&rsquo;s movements, balance, sensations, and hearing are tested. Moreover, children may also be assessed for developmental delays, learning issues, cognitive delays, hypotonia, and failure to thrive. The doctors may also order the following tests:<a href="#accordion">[1]</a> 
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<ul>
	<li>Magnetic Resonance Imaging (MRI) - An MRI scan provides a detailed image of the brain and spinal cord. Moreover, it can detect associated abnormalities, such as hydrocephalus and syringomyelia. CSF flow studies can help assess the degree of fluid obstruction and neuronal movement at the foramen magnum. 
	&nbsp;</li>
	<li>Computed Tomography Scan (CT&nbsp; scan) - A CT scan is helpful in people who cannot undergo MRI scans. It allows for visualization of the cerebral ventricles and any obvious obstruction. Moreover,&nbsp; bone abnormalities near the cervical canal and the base of the skull can also be detected. It performs less well when used to examine the spinal cord or the contents of the posterior fossa. 
	&nbsp;</li>
	<li>Sleep Study - Snoring, breathing, oxygenation, and seizures are all monitored while the patient is asleep in a room so that any sign of sleep apnea can be accounted for. 
	&nbsp;</li>
	<li>Swallowing Study - Fluoroscopy (X-rays) is a technique used to observe the internal swallowing process in order to spot any anomalies that might point to lower brainstem dysfunction. 
	&nbsp;</li>
	<li>Brainstem Auditory Evoked Potential (BAER) - This is an electrical test that examines the connection between the brainstem and the hearing apparatus. It is used to assess the brainstem&#39;s functionality. 
	&nbsp;</li>
	<li>Myelogram - Following the injection of contrast material into the CSF space, an X-ray of the spinal canal may reveal pressure on the spinal cord or nerves as a result of abnormalities. This exam is now conducted less frequently. 
	&nbsp;</li>
	<li>Somatosensory Evoked Potentials (SSEP) - This is an electrical test of the sensory nerves and can give insight into the function of the brain, spinal cord, and peripheral nerves. 
	&nbsp;</li>
	<li>X-ray - It is used to visualize any bone abnormalities in the skull and neck. 
	&nbsp;</li>
</ul>

Treatment

The treatment plan relies on the severity of the symptoms. If the symptoms are mild, the doctor will monitor the patient&rsquo;s health with regular MRIs. In more severe instances, surgery will be recommended. The aim of surgery is to decompress the nerve tissue and reconstruct normal CSF flow around and behind the cerebellum.&nbsp;

Doctors recommend the following surgical procedures: 
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<ul>
	<li>Posterior Fossa Decompression - This is the most common method used to treat Chiari malformation. Surgeons remove a portion of the bone in the back of the skull (posterior fossa) to relieve the pressure on the brain.</li>
	<li>Laminectomy - To improve the flow of cerebrospinal fluid and create more space for the spinal cord, the surgeon might also need to remove a small section of the bones that encase the spinal column, depending on how severe the Chiari malformation is.</li>
	<li>Duraplasty - The surgeon opens the dura during the decompression procedure. Then a patch is sewn in to enlarge the membranes and give the brain extra space. The region is enlarged, which releases pressure on the brain.</li>
	<li>Electrocautery - Surgeons may use a tiny amount of electricity to shrink a small portion of the brain, known as the cerebellar tonsils. This helps make more space and enables the cerebrospinal fluid (CSF) to drain. The tonsils in the cerebellum retract without harming the nervous system. 
	&nbsp;</li>
</ul>

Additional surgical interventions that may be required are<a href="#accordion">[5]</a>:

<ul>
	<li>Endoscopic Third Ventriculostomy (ETV) - Trapped fluid is released via a hole made in the wall of one of the cavities of the brain.</li>
	<li>Ventriculoperitoneal Shunting - A catheter is passed into the brain via a small hole drilled into the skull to drain the CSF and relieve pressure.</li>
	<li>Untethering - A tethered spinal cord, or improperly attached spinal cord, is present in certain children with type 1 Chiari malformations. Untethering entails releasing tension in the spine and detaching the spinal cord.</li>
	<li>Spinal Fixation - As a result of hypermobility syndrome, such as Ehlers-Danlos syndrome, some Chiari I patients may need surgery to stabilize their spine.<a href="#accordion">[3]</a> 
	&nbsp;</li>
</ul>

The following complications can result from Chiari malformation: 
&nbsp;

<ul>
	<li>Hydrocephalus - This is characterized by a buildup of excessive CSF in the brain. It results from the Chiari malformation blocking the flow of CSF and applying pressure within the head. These children will have characteristically enlarged skulls and/or mental dysfunction. If left untreated, it can turn fatal. Type II Chiari malformation is most commonly associated with hydrocephalus. 
	&nbsp;</li>
	<li>Spina Bifida - This is the incomplete closure of the bone and membranes surrounding the spinal cord. As a result, the spinal cord is partially exposed, which can lead to serious diseases including paralysis. Myelomeningocele is a kind of spina bifida that is typically seen in people with Chiari malformation type II. 
	&nbsp;</li>
	<li>Syringomyelia And Hydromyelia - CSF can accumulate in a cavity or cyst (syrinx) within the spine and cause damage to the spinal cord. The CSF-filled cyst presses on the nerves and destroys the center of the spinal cord. Thus, results in loss of bladder and bowel control, discomfort, muscle weakness, muscle spasms, and loss of sensation in the area innervated by the affected nerves. 
	&nbsp;</li>
	<li>Tethering Cord Syndrome - Spina bifida is a spinal disorder that can affect people with Chiari malformations. In some types, the spinal cord&#39;s incorrect attachment to the spine may put pressure on the nerves due to growth and movement. Additionally, tethered cord syndrome is more likely to manifest itself in&nbsp;children born with myelomeningocele, a severe form of spina bifida. This happens when scarring from the initial closure surgery causes the spinal cord to attach to the spine. Tethered cord syndrome can cause gradual, progressive nerve loss that impairs the ability of the lower body, legs, bowel, and bladder muscles to operate normally. 
	&nbsp;</li>
	<li>Spinal Curvature - Scoliosis and kyphosis are the two common spinal curvatures common in Chiari malformation. Kyphosis is described as the forward bend of the spine, while scoliosis is the bending of the spine to the left or right. 
	&nbsp;</li>
</ul>

Although research suggests that Chiari malformation runs in families, no potential hereditary components have been identified. <a href="#accordion">[6]</a> 
&nbsp;

Chiari malformation normally develops while the baby is still in the womb. A genetic mutation is responsible for its development. Therefore, it cannot be prevented.

Since type II Chiari malformation is typically associated with spina bifida, pregnant women can prevent neural tube defects by taking folic acid supplements. However, all supplements should only be taken on the doctor&rsquo;s advice.<a href="#accordion">[3]</a> 
&nbsp;

Key Points

<ul>
	<li>Chiari malformation is a congenital defect characterized by the brain tissue extending into the spinal canal.</li>
	<li>Chiari 1 malformation is by far the type that is seen the most frequently in kids. The lower half of the cerebellum, but not the brain stem, extends into a hole at the base of the skull called the foreman magnum.</li>
	<li>Typically, only children who are born with spina bifida exhibit Chiari malformation type II. </li>
	<li>Some people have symptoms from birth. Others experience symptoms in their late teens or early 20s. Additionally, symptoms may improve or worsen with time.</li>
	<li>MRI scans are most commonly used to diagnose Chiari malformation.</li>
	<li>The treatment plan relies on the severity of the symptoms. </li>
	<li>Surgical procedures such as posterior fossa decompression, laminectomy, duraplasty, and electrocautery are often used to treat Chiari malformation. 
	&nbsp;</li>
</ul>
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[1] Chiari malformation. AANS.

[2] Arnold Chiari malformation: Symptoms, types, and treatment. WebMD.

[3] Chiari malformation. Cleveland Clinic.

[4] Peyman Pakzaban MD. Chiari malformation treatment & management. Medical Therapy, Surgical Therapy, Preoperative Details.

[5] NHS choices.

[6] Chiari malformation. Mayo Clinic.

[7] Sadler B, Kuensting T, Strahle J, et al. Prevalence and impact of underlying diagnosis and comorbidities on Chiari 1 malformation. Pediatric Neurology.

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