What is Chiari Malformation Type 1?
Chiari malformations are a range of abnormalities at the back of your brain, which involve the cerebellum, brainstem, base of the skull, and upper part of the spinal cord. These malformations are categorized into four types, depending on the nature of the brain tissue that’s moved out of place, into the spinal canal, and the specific anomalies in the brain or spine’s growth.
Chiari malformations, including a condition called basilar invagination, are the most common abnormalities seen in adults’ craniovertebral joints – the area where your skull and your spine meet. These conditions were first described in detail by pathologists Julius Arnold and Hans Chiari at the end of the 19th century.
Among the Chiari malformations, type 1 Chiari malformation (or Chiari 1) is the most common. This condition happens when a part of the cerebellum, known as cerebellar tonsils, descends into the space called the foramen magnum – the hole at the base of your skull where the spinal cord begins. These patients may not have any symptoms or may exhibit symptoms like unique headaches triggered by coughing and specific neurological symptoms. However, the exact definition of Chiari 1 is not universally agreed upon by all doctors due to differences in clinical and imaging findings.
Chiari 2, 3, and 4 malformations are present at birth and impact the patient significantly. Meanwhile, the classification of other forms, like Chiari 0, 0.5, 1.5, and complex Chiari, are still debated among experts. Each of these classifications has specific features insightful, which can be visualized through medical imaging techniques, and would be explained by your doctor based on your individual case.
What Causes Chiari Malformation Type 1?
Chiari 1 malformation can be linked to genetic factors, or it can develop as a result of various conditions that alter the base of the skull. These conditions include early closing of the bones in the skull, cause undersized skull, flattened base of the skull, abnormal development of the spinal cord, and disorders that affect bone metabolism. Furthermore, this malformation can also occur due to excessive pressure in the brain caused by conditions like fluid buildup (also known as hydrocephalus) or a brain tumor.
In some instances, Chiari malformation is secondary to conditions like excess fluid buildup, increased pressure within the skull of unknown origin – sometimes manifested in conditions such as pseudotumor cerebri, or the presence of a mass within the skull. This is known as secondary Chiari malformation type 1. Chiari 1 malformation has also been reportedly caused by procedures such as a lumboperitoneal shunt performed for treating increased pressure within the skull. An injury can also result in this type of malformation, though it’s quite rare.
In certain cases, the cause of the malformation might be a pulling force from below. For example, the descent of tissue at the base of the brain (tonsils) in Chiari 1 malformation might be triggered by the pull exerted by the filum terminal (a threadlike structure connecting the base of the spinal cord to the tailbone), which tugs at the bone marrow and structures of the brainstem, causing the brain tissue to descend.
Potential genetic reasons have been associated with specific chromosomes 2, 9, 14, and 15. For example, a mutation identified in the gene NKX2-1 (found on chromosome 14), which is vital to forming certain body structures during early development, has been linked to a girl suffering from Chiari 1 malformation. Other potential mutations could involve the gene EPAS1 (found on chromosome 2) which is responsible for a key protein in the regulation of red blood cell production and bone formation.
These genetic disorders might hinder the development of certain tissues near the spinal cord, leading to herniation (protrusion) of brain tissue, resulting in a small space at the back of the skull and a condition where this space is excessively crowded. This is similar to what’s seen with certain disorders of the connective tissues, like Ehlers-Danlos syndrome. Still, the exact link between the two conditions remains unclear. Even so, recent studies have shed more light on various pathways that might be affected in Chiari 1 malformation.
Despite these findings, the genetic factors of the Chiari 1 malformation still need further corroboration. Recent research identified certain genes associated with Chiari 1 malformation, such as chromodomain genes CHD3 and CHD8, which carry several variations that could be linked to this condition. Lastly, it’s critical to note that different causes are likely, and Chiari 1 malformation can indeed be passed down from one generation to the next.
Risk Factors and Frequency for Chiari Malformation Type 1
Chiari 1 malformation is the most common type of Chiari malformation. It’s estimated to occur in about 1 out of every 1000 babies born. It’s a bit more common in females than in males, with a ratio of about 1.3 females for every male. However, these numbers might not be fully accurate because many people with this condition have few symptoms and only start to experience problems when they reach adulthood. In fact, based on brain imaging data, we think this condition might actually be more common in children than we previously thought, possibly affecting as many as 1% of children.
Signs and Symptoms of Chiari Malformation Type 1
Chiari 1 malformation is a medical condition that often shows no symptoms. When symptoms do appear, they’re commonly experienced as headaches or neck pain. However, very young children might show symptoms differently, such as excessive crying, irritability, or not gaining weight and growing as expected.
Frequently, patients with Chiari 1 malformation will experience worsening of their headaches during the Valsalva maneuver, a medical test where you try to breathe out while blocking your mouth and nose. This is due to the reduced space available in the spinal canal. It’s important to distinguish this from chronic headaches that do not change with the Valsalva maneuver, which could indicate other conditions.
People with Chiari 1 malformation are just as likely to experience migraines as the general population. However, they usually have an earlier age of onset and stronger symptoms. Additional symptoms, besides headaches, can vary widely. These are often due to the pressure that the malformed part of the brain places on the brainstem, leading to autonomic dysfunction, or problems with reflexive body functions like heartbeat and sweating.
In addition to these symptoms, Chiari 1 malformation can also present with the following:
- Fainting and slow heartbeat due to autonomic dysfunction
- Changes in swallowing and vomiting
- Problems with balance and walking
- Difficulty with hand coordination
- Sensations of numbness and tingling in the limbs
- Dizziness
- Ringing in the ears
- Weak and stiff muscles, especially in the back, shoulders, arms, or legs
- Bladder and bowel problems due to a condition called syrinx compression
- Scoliosis, especially in children, which can be caused by syringomyelia, another associated condition
- Involuntary eye movements
Adults and children can show different presentations of Chiari 1 malformation. For instance, children are more likely to have brainstem dysfunction, sleep apnea, or feeding difficulty, typically caused by an impaired gag reflex and hoarseness. Since the cerebellum, the part of the brain affected by Chiari 1 malformation, is involved in advanced cognitive functions, deficits in executive functioning, verbal fluency, spatial cognition, language, and memory processing have also been reported.
Testing for Chiari Malformation Type 1
Magnetic resonance imaging (MRI) is the main tool used to diagnose Chiari 1 malformation. This condition affects the area where the skull and spine meet and can sometimes lead to further complications such as fluid build-up in the brain (hydrocephalus) or a fluid-filled cyst in the spinal cord (syringomyelia). If for some reason an MRI scan cannot be done, other types of imaging like CT scans, x-rays of the head and neck, or a special type of CT scan using a contrasting agent (myelography) may be used.
On an MRI scan, the part of the brain at the base of the skull (cerebellar tonsils) may look like they are descending or ‘peg-like’. Sometimes there’s a ‘kink’ in the area where the brain and spinal cord (cervicomedullary) meet, which is seen in most of the symptomatic cases. The more the cerebellar tonsils descend, the greater the chance that the person has symptoms.
For people who do not have symptoms but show some signs of the condition on an MRI scan (referred to as tonsillar ectopia), additional MRI studies looking at the flow of cerebrospinal fluid (the fluid that cushions the brain and spinal cord) might be useful. These studies can show things like whether the cerebellar tonsils move in a pulsatile manner along with the heartbeat and whether there’s a blockage in the flow of fluid at the opening at the base of the skull (foramen magnum). This extra information can help doctors decide if surgery might be beneficial.
An exciting discovery is that Chiari 1 malformation and syringomyelia could sometimes be identified even before birth on routine ultrasound scans during pregnancy.
While laboratory tests cannot diagnose Chiari 1 malformation, certain tests like a full blood count and tests to check the function of your liver and kidneys, may be needed prior to any surgical intervention. Other tests, such as a chest x-ray and an electrocardiogram (to check heart function), may also be performed as part of the pre-surgery evaluation.
Other studies which may be considered include:
- Sleep studies: In this procedure, your sleep is monitored in a specialized room to check for issues like disturbed breathing or snoring, a drop in oxygen levels, or seizure activity during sleep, which could indicate sleep apnea.
- Swallow studies: This procedure involves the use of a tool called fluoroscopy, which allows doctors to visualize your internal swallowing process to see if there are any abnormalities that suggest a dysfunction in the lower part of the brainstem.
- Brainstem auditory evoked potential: This electrical test checks the function of your hearing mechanism and its connections within the brainstem to ensure they’re functioning correctly.
- Somatosensory evoked potentials: This is another type of electrical test that checks the nerves responsible for sensation. This test provides information about the function of your peripheral nerves, spinal cord, and brain.
Treatment Options for Chiari Malformation Type 1
Chiari 1 malformation is a complex condition that doesn’t have a universally agreed upon treatment plan. Treatment typically includes a mix of conservative methods and surgery depending on the patient’s symptoms.
Conservative approaches mainly help manage symptoms like headaches or neck pain. These include non-steroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, and neck-supporting braces. However, these options might not be as effective for less common symptoms such as trouble walking. Therapies like meditation, yoga, or mindfulness have also been suggested to help manage pain.
Surgical treatment is usually reserved for patients who have severe or worsening symptoms, have an imaging confirmation of their cerebellum descending lower than normal, and have an MRI confirmation of a Chiari malformation that’s blocking the flow of cerebrospinal fluid, or CSF, which surrounds and cushions the brain and spinal cord. The goal of surgery is to relieve pressure at the junction between your brainstem and spinal cord and restore normal CSF flow. The most common surgical approach is to remove a portion of the skull near the top of the spinal column and possibly replace a portion of the tough membrane that encloses the brain and spinal cord. This surgery is frequently used and can help restore normal CSF flow.
A less invasive procedure involving the removal of the lower part of the cerebellum (also known as cerebellar tonsillar herniation) has been proposed as an alternative treatment. Patients with severe fluid-filled cysts (syringomyelia) may also have these cysts drained. Other non-invasive methods for alleviating the cysts have also been suggested. A specialized MRI has been proposed to help guide the surgeon’s decision to replace the membrane during the surgery.
A particular surgical procedure, posterior fossa decompression with duraplasty, may provide better long-term relief of symptoms, more significant reduction in fluid-filled cysts, and less need for further decompression surgeries than decompression without duraplasty. However, it might also increase the risk of postoperative headache and nausea.
Occasionally, Chiari 1 malformation can cause the front part of the brainstem to be compressed due to abnormal bone growth in the head or spine. In these cases, an initial procedure can be performed to reduce the compression, followed by further surgical intervention to keep the abnormality in check. Insertion of a stent in the fourth ventricle, a part of the brain, has been shown to be a safe and effective treatment method.
What else can Chiari Malformation Type 1 be?
When looking into the medical condition known as Chiari 1 malformation, doctors often consider whether other conditions might be responsible for the patient’s symptoms. These other conditions include:
- Just a little bit of tonsillar ectopia (less than 5 mm)
- Other types of Chiari malformation (types 2 to 4)
- A condition where the brain acts like there’s a tumor, but there isn’t one (Idiopathic intracranial hypertension due to pseudotumor cerebri)
- A decreased amount of fluid around the brain and spine (Craniospinal hypotension)
- A condition where the base of the skull pushes into the spinal canal (Basilar invagination)
What to expect with Chiari Malformation Type 1
The results of surgeries are generally positive, with 73% of patients experiencing improvements less than a year after surgery and 79% showing progress 1 to 3 years later. PFD, a surgical procedure, has been found to alleviate symptoms in about two-thirds of people, particularly those who don’t suffer from syringomyelia, a disease where a fluid-filled cyst forms within the spinal cord.
Possible Complications When Diagnosed with Chiari Malformation Type 1
The most frequent complications after surgery can include leakage of the cerebrospinal fluid (fluid around the brain and spine), and the development of a pseudomeningocele (an abnormal collection of cerebrospinal fluid). This condition can sometimes require additional surgery or the insertion of a shunt- a device to help drain fluid.
Other potential problems can involve sterile and bacterial inflammation of the membranes covering the brain (meningitis), injury to the arteries of the spine, neurological issues, and formation of epidural hematoma (a blood clot near the spine).
Regarding different surgical approaches, one study found that inflammation of the membranes covering the brain or spinal cord (meningitis), particularly came about when using animal tissue (bovine pericardial xenograft) for decompression and dura enhancement surgery compared with using human graft tissue.
Common Side Effects:
- Cerebrospinal fluid leakage
- Formation of a pseudomeningocele
- Undesirable inflammation of the membranes covering the brain (aseptic and bacterial meningitis)
- Injury to vertebral arteries
- Neurological issues
- Epidural hematoma formation
- Complications from different surgical procedures
- Possible inflammation of the membranes covering the brain or spinal cord due to the type of surgical approach used
Recovery from Chiari Malformation Type 1
After surgery, some patients might have headaches and neck pain. This is due to the operation and is generally managed by doing neck exercises designed to help regain complete mobility as quickly as possible. Patients can usually go back to work in about 4 to 6 weeks. As part of the recovery monitoring, they will also receive an MRI around 6 months to 1 year after the surgery.
Fully recovering from the surgery to fix Chiari 1 malformation, a type of genetic problem affecting the brain’s construction, can take several months or even longer. The patients will be guided to carefully start increasing their physical activity in stages. However, they should avoid heavy lifting in the early stages of recovery.
Preventing Chiari Malformation Type 1
Although you can’t prevent a condition called congenital Chiari 1 malformation because it’s present from birth, learning about it is very important. This includes understanding its signs and symptoms. Sharing this knowledge with close family, friends, and those who take care of the patient is also crucial so they are aware of the condition. Learning about how this condition can be managed, both through lifestyle changes (conservative management) and surgery, is key in helping you and your doctor make decisions together about your treatment plan.