What is Chiari Malformation Type 2 (Arnold-Chiari malformation)?
In the late 1800s, doctors Julius Arnold and Hans Chiari described a complicated condition seen in children, which affected the formation of the lower part of the brain (the cerebellum and brainstem). This condition, now known as Chiari malformations, relates to a range of abnormalities that involve the cerebellum, brainstem, base of the skull, and the upper part of the spinal cord.
There are four different types of Chiari malformations, classified based on the specific part of the brain tissue that is displaced (herniated) into the spinal canal and the unique characteristics seen in the development of the brain or spine. Chiari malformations, along with another condition called basilar invaginations, are some of the most common disorders affecting the junction where the skull and spine meet, especially in adults.
Arnold-Chiari malformation, also known as Chiari malformation type 2, typically occurs with a condition called spina bifida and is identified by the lower displacement of the back part of the cerebellum, the brainstem, and a cavity in the brain known as the fourth ventricle. Even though the names of the conditions make it seem like Chiari 2 malformation is a more severe form of Chiari 1 malformation, the two conditions are actually distinct diseases with some similar findings when the brain is examined by imaging.
A number of additional features can be observed in Chiari 2 malformation, the most commonly seen are an accumulation of cerebrospinal fluid in the brain (hydrocephalus) and a disorder characterized by a fluid-filled cyst in the spinal cord (syringomyelia). The severity of these malformations varies. Chiari 1 malformation might not cause any symptoms, while Chiari 2, 3, and 4 malformations, which are present at birth, are clinically significant and might cause symptoms related to the spinal cord, hydrocephalus, brainstem, or lower cranial nerves.
Chiari malformations are classified into various types. For instance, Chiari 0 includes features like the presence of a syrinx, but it doesn’t respond to a specific type of surgery (posterior fossa decompression) and there is no descent of specific cerebellar structures called tonsils. Then, there is Chiari 0.5 where there is herniation (displacement) of the cerebellar tonsils in a particular direction. Chiari 1 can be identified by the downward displacement of cerebellar tonsils and is often associated with syringomyelia and potentially hydrocephalus.
Chari 1.5 includes similar aspects as Chiari 1 with the addition of downward displacement of the brainstem. Then, there’s Chiari 2 (Arnold-Chiari malformation) which is always seen with myelomeningocele (a form of spina bifida); Chiari 3 involving both downward movement of medulla (part of brainstem) and a condition called encephalocele, and finally Chiari 4 is primarily characterized by an underdeveloped cerebellum.
Each type has unique features and potential associations with other conditions. However, some classifications like type 0, 0.5, and type 1.5 Chiari malformations and complex Chiari aren’t universally accepted by all doctors and researchers.
What Causes Chiari Malformation Type 2 (Arnold-Chiari malformation)?
The exact cause of Chiari 2 malformation, a condition where brain tissue extends into the spinal canal, isn’t completely clear. Many theories have been proposed, with the most modern and accepted one being the “unified theory.” According to this theory, it is believed that problems with the neural tube, which is the structure in a developing fetus that becomes the brain and spinal cord, cause the traits associated with Chiari 2 malformation.
Earlier theories suggested that the condition was due to the spinal cord being pulled downward by a birth defect known as myelomeningocele, which is a type of spina bifida where the spinal cord and its protective covering protrude from an opening in the spine. However, these theories have become less popular over time.
Risk Factors and Frequency for Chiari Malformation Type 2 (Arnold-Chiari malformation)
Chiari 2 malformations are not very common and it’s difficult to pin down how often they occur because there hasn’t been a large-scale study. However, experts estimate that they affect approximately 0.44 out of every 1,000 births. They occur equally among boys and girls. A connection has been found between Chiari 2 malformations and a condition called myelomeningocele, and it appears that taking folate supplements during pregnancy could lower the chances of having a child with a Chiari 2 malformation.
Signs and Symptoms of Chiari Malformation Type 2 (Arnold-Chiari malformation)
Chiari 2 malformation is a medical condition with different possible symptoms. These could be linked to issues with the spinal cord, brain stem, and lower cranial nerve function. The symptoms can appear at any age but are uncommon in adults. The way symptoms appear can differ between newborns and older children. Newborns with this illness may experience quick and severe neurological worsening over a few days, with major brain stem difficulties. The symptoms in older children, however, often appear more slowly and are typically not severe.
The syndrome is associated with several clinical findings. These include:
- Facial weakness
- Weak or nonexistent crying
- Nystagmus, especially downward direction
- Opisthotonos state (severe muscle spasm bending the back backward with the head and heels touching the surface)
- Problems with swallowing and a reduced gag reflex leading to issues like difficulty feeding, long feedings, nasal regurgitation, bluish skin during feeding, and build-up of oral secretions.
- Breathing issues such as temporary stridor (high-pitched wheezing due to blocked airflow) that can escalate to respiratory arrest, and apnea spells due to impaired ventilatory drive.
- Arm weakness, which may develop into quadriparesis (weakness of all four limbs).
If there are signs linked to syringomyelia (a disorder in which a cyst forms within the spinal cord), these often correspond to the involved spinal cord level, the size, and the location of the cyst. Some of these associated symptoms might be:
- Differentiated sensory loss (like keeping the sense of light touch and position but loss of pain and temperature sense)
- Varying involvement with pain
- Autonomic symptoms like heartbeat abnormalities
- Sensorimotor dysfunction (problems with muscle control or coordination)
- Lhermitte phenomenon (an electric shock-like sensation that runs down the body when the neck is bent forward)
- Problems with joints and bones
- Scoliosis, especially if it is caused by lateralized anterior horn compression (muscular problems on one side of the spine) that can happen in syringomyelia. This condition often results in uneven muscle strength along the backbone. Children with this kind of scoliosis often record symptoms like rapid curve development, an unusual curve and back pain symptoms at a young age.
Testing for Chiari Malformation Type 2 (Arnold-Chiari malformation)
When a doctor suspects a patient has Chiari 2 malformation, which is a condition where the brain tissue grows into the spinal canal, they rely heavily on imaging studies to make a diagnosis. These studies provide a detailed view of the brain’s structure. The most effective way to explore these changes in the brain is through a brain scan technique called Magnetic Resonance Imaging (MRI). MRI gives the clearest image, which makes it easier for doctors to evaluate the patient’s condition.
If for some reason a patient can’t handle an MRI (like feeling claustrophobic in the scanner, for example), a Computed Tomography (CT) scan might be an alternative. Although a CT scan gives useful information on the bone structure of the skull, it’s not as clear as an MRI. Also, CT scans use a bit of radiation, which isn’t ideal, especially for children.
In some cases, if there’s an enlargement of the ventricles (fluid-filled structures) in the unborn baby’s brain, doctors might detect Chiari 2 malformation with a prenatal ultrasound. This makes sense as ultrasound uses sound waves to create pictures of the inside of the body and is safe for both the mother and the baby.
Apart from the usual evidence of the displacement of certain parts of the brain (like the cerebellar vermis and brainstem) towards the spinal canal, doctors look for certain characteristics that are often present in Chiari 2 malformation. These include but are not limited to:
- “Lemon sign”: This is when the frontal bone of the skull has an indentation that reminds doctors of a lemon.
- “Banana cerebellum sign”: This is when the cerebellum (a part of the brain) wraps around the brain stem, similar to how a banana wraps around its center while peeling.
- Beaking of tectum: A pointy appearance of the tectum, part of the brain.
- Absence of the septum pellucidum: When part of the brain called the septum pellucidum, is missing or maldeveloped.
- Hydrocephalus: A condition where there is an accumulation of excessive cerebrospinal fluid in the brain. It might make an individual’s head grow large.
- Syringomyelia: A disorder where a cyst or cavity forms within the spinal cord.
- Tethered cord syndrome: A condition where the spinal cord is attached or “tethered” at the base of the spine, causing it to stretch abnormally.
Understanding Chiari 2 malformation properly is crucial, especially for patients with spinal myelomeningocele where the spinal cord doesn’t close completely during development. In these people, an MRI can help diagnose Chiari 2 malformation by showing a downward displacement of the brain’s medulla and cerebellum vermis, among other findings.
In addition to these diagnostic imaging methods, doctors can also do sleep, swallow studies, and laryngoscopy. Sleep studies monitor patients overnight while they sleep, this may be used to check for sleep apnea. Swallow studies use a special X-ray machine, called a fluoroscope, to show problems related to swallowing. Laryngoscopy allows doctors to see the throat and check the movement and function of the vocal cords.
Treatment Options for Chiari Malformation Type 2 (Arnold-Chiari malformation)
Chiari 2 malformation is a severe condition that often requires a medical procedure to manage the effects it has on the brain and spine. It manifests differently in various patients, and the exact strategies employed often depend on the specific symptoms and associated neurological impairments. Unfortunately, the condition often has serious complications, and related symptoms can result in severe health issues and even fatality.
It’s quite common for patients with Chiari 2 malformation to need surgery. This can be necessary to fix open defects in the neural tube (the structure that develops into the brain and spinal cord during fetal development) and to help drain excess cerebrospinal fluid (a condition called hydrocephalus), usually by inserting a shunt, which is a tube that carries the fluid away from the brain.
In terms of timing, it is generally accepted that decompression surgery, a procedure to relieve pressure on the brain, should be carried out early in infants and children whose symptoms are directly associated with Chiari 2 malformation. However, there is still some debate about this among medical professionals, in part because there are not many studies exploring the topic.
There are some professionals who argue against early surgery. They suggest that many neurological symptoms could be due to inherent abnormalities that surgery can’t improve. On the other hand, advocates for immediate decompression argue that some damages to the brain are due to ongoing compression and lack of blood flow. They suggest that if there are heart or respiratory issues like stridor (a high-pitched wheezing sound), episodes of stopped breathing, or difficulty swallowing due to a neurological issue, surgery should be carried out immediately.
It’s worth noting that other medical problems, like feeding difficulties in newborns, abnormal pauses in breathing, breathing failure, and a neurological issue affecting bowel function, may need medical or surgical intervention. Before making any decision, it is always necessary to rule out other possible causes of these symptoms, like viral infections.
Surgery to repair myelomeningocele, a severe birth defect where the spinal cord doesn’t develop properly, is also often required for patients with Chiari 2 malformation. Some suggest that performing this type of surgery on the fetus while still in the womb could be helpful. After birth, it’s important to administer antibiotics as a preventative measure and to wrap the lesion. The open neural tube defect should ideally be surgically repaired within the first three days after birth. Following the surgery, the patient should be closely monitored for hydrocephalus development (accumulation of fluid in the brain). Also, evaluations for abnormal neurological functions are needed throughout the patient’s lifespan.
Almost all patients with myelomeningocele will have a bladder that doesn’t function normally due to a neurological problem. This typically requires using a catheter intermittently to protect the kidneys from disease. Be aware that a change in this function could indicate a serious neurological complication.
In patients with Chiari 2 malformation, hydrocephalus, or water on the brain, is another common issue. The need and timing for surgical intervention are mainly determined by the findings from neuroimaging studies (like MRI or CT scans) and the severity of symptoms. Some of these symptoms may include vomiting, developmental delays, headaches, focal neurological deficits (specific, localized neurological problems), and swelling of the optic disc (the area where the optic nerve enters the eyeball). Surgery is urgently necessary for patients with rapidly worsening hydrocephalus. A common surgical intervention is shunt placement, which helps in preventing further complications by diverting the cerebrospinal fluid, reducing the pressure on the brain.
What else can Chiari Malformation Type 2 (Arnold-Chiari malformation) be?
Your doctor should understand that certain signs and symptoms could be linked with medical conditions such as myelomeningocele, syringomyelia, scoliosis, and hydrocephalus or failure of a medical device called a shunt. These symptoms may also suggest a condition known as Chiari 2 malformation.
When diagnosing Chiari 2 malformation, other conditions that may present with similar symptoms include:
- Fourth ventricle ependymoma (a type of brain tumor)
- Lhermitte-Duclos disease (a rare, slow-growing brain tumor)
- Rhombencephalosynapsis (a rare congenital brain malformation)
- Other types of Chiari malformation (a condition where brain tissue extends into the spinal canal)
What to expect with Chiari Malformation Type 2 (Arnold-Chiari malformation)
The outlook for people with a condition known as Chiari 2 malformation can vary quite a bit. It largely depends on how severe the malformations are and the symptoms the patient is experiencing. In infants who have symptoms like vocal cord paralysis, weakened arm muscles, or heart and lung failure within two weeks of first showing signs of the condition, the death rate is pretty high at 71%. On the other hand, if the patient’s condition worsens more gradually, the death rate is lower at 23%.
Having paralysis in both vocal cords is a sign that the patient might not respond well to a type of surgery called suboccipital decompression. This surgery is used to relieve pressure on the lower part of the brain. Intelligence Quotient scores may increase or remain stable post surgery.
For those who do have the surgery, around 68% of patients experience total or near-total relief from their symptoms. However, 20% see no improvement, and about 12% continue to have mild to moderate symptoms after the operation.
Possible Complications When Diagnosed with Chiari Malformation Type 2 (Arnold-Chiari malformation)
A study on patients with Chiari 2 malformation, who had undergone a type of brain surgery known as suboccipital hindbrain decompression, identified the main causes of death. Out of 17 patients who died, the most common cause was respiratory arrest (experienced by 8 patients). Other causes of death included meningitis or ventriculitis (in 6 patients), aspiration (in 2 patients), and biliary atresia (in 1 patient). Furthermore, the study reported a 37.8% death rate among patients who had this surgery and were monitored for up to six years.
Main Causes of Death:
- Respiratory arrest (8 patients)
- Meningitis or ventriculitis (6 patients)
- Aspiration (2 patients)
- Biliary atresia (1 patient)
Preventing Chiari Malformation Type 2 (Arnold-Chiari malformation)
Chiari 2 malformation, also known as Arnold-Chiari malformation, is a condition that’s often found in individuals with spina bifida. Spina Bifida is a birth defect where the spine and spinal cord don’t form properly. In Chiari 2 malformation, parts of the brain, including a section called the cerebellar vermis, the brainstem, and the fourth ventricle, are positioned lower in the skull than they should be. Most people with a condition called myelomeningocele, a severe type of spina bifida, also have Chiari 2 along with a condition called hydrocephalus, which involves a buildup of fluid in the brain.
Chiari 2 malformation is usually diagnosed using a type of scan called an MRI. Treatment often involves surgery, but it can be complicated due to how differently the condition presents itself in each patient. The outlook for individuals with Chiari 2 depends on the degree of abnormality in their brain and spine.
Unfortunately, there is no known way to prevent Chiari 2 malformation as it is a birth defect. However, educating patients and their families about the signs and symptoms of the condition is very important. This can help in managing their expectations and also in making informed decisions about treatment options. This education also includes discussing non-surgical and surgical treatments, which can help patients and their families make joint decisions about care.