Anyone who experiences migraine knows that these headaches can be debilitating. Many triggers can lead to migraine episodes, with the most common being exposure to smells, light, noise, and stress.

Sometimes, underlying health conditions can be a cause, too. But currently, no evidence suggests that low-lying cerebellar tonsils are related to migraine.

Cerebellar tonsils are a part of the brain that sits at the base — just above the brainstem. Usually, they sit completely inside the skull.

But for some people, instead of sitting inside the skull, the two cerebellar tonsils descend or protrude through the skull and into the upper spinal canal. This is referred to as low-lying cerebellar tonsils or a Chiari malformation (CM). Other names for this condition are cerebellar tonsillar ectopia or herniated cerebellar tonsils.

There are four types of Chiari malformations. If the brain has no structural irregularities other than low-lying cerebellar tonsils, this is known as CM type 1. All other forms are accompanied by some type of structural irregularity with the brain.

People with any type of CM may have a skull that isn’t properly developed, according to the National Organization for Rare Disorders (NORD). The area closest to the base of the skull may be atypically small compared with the size of the cerebellum, or the back portion of the brain.

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Illustration by Joules Garcia.

So far, there’s no scientific evidence that there’s a direct link between low-lying cerebellar tonsils and migraine.

More importantly, migraine episodes can occur because of a wide array of triggers. So, even if low-lying cerebellar tonsils might create pressure that causes a headache, it can be hard to verify that the condition is the sole cause.

Headaches can be a symptom of this condition, however.

The type of headache attributed to CM is typically an occipital headache or suboccipital headache. That means the headache happens near the portion of the brain lobe at the lower back of the skull. Sneezing or coughing can make the headache worse. It typically lasts about 5 minutes, according to the International Classification of Headache Disorders.

The cerebellum controls key behaviors that affect motor functions, such as coordination, balance, vision, and speech. So if you’re living with cerebellar tonsillar ectopia or another form of CM, you might experience symptoms that affect your ability to coordinate movements or manage basic motor or sensory functions.

Depending on how much your cerebellar tonsils shift down, or are herniated, your symptoms can range from mild to severe. Common symptoms associated with this condition can include:

  • neck pain
  • dizziness
  • upper body weakness
  • hearing loss
  • difficulty swallowing
  • tingling or numbness in your hands or feet
  • inability to feel pain or temperature in the upper body
  • difficulty maintaining balance or walking

Low-lying cerebellar tonsils can occur during fetal development as well as later in life.

Low-lying cerebellar tonsils from birth

If the condition is present at birth, it means that the malformation began during fetal development. This is known as primary CM. The primary form is the more common type, according to the National Institute of Neurological Disorders and Stroke.

Low-lying cerebellar tonsils that develop later in life

If CM appears later in life, it’s usually the result of treatment for a traumatic injury, infection, or disease. Often, in these cases, CM is caused by excessively draining spinal fluid from either the lumbar or thoracic portions of the spine. This type of CM is referred to as acquired or secondary CM.

According to NORD, secondary CM may also be caused by tumors, arachnoid cysts, or hematomas. A 2021 case study shows that these are extremely rare. The overwhelming majority of cases are the primary form.

If you have CM type 1 — low-lying cerebellar tonsils without any other structural irregularities in the brain — the condition is not considered life threatening. Although symptoms can be uncomfortable, there are treatment options. Recommended solutions vary depending on how much symptoms affect your quality of life and ability to function.

But if CM is present with other irregularities, the outlook can vary widely. Again, it depends on the severity of the condition and how much it affects quality of life.

Additionally, treatments will depend on your age, overall health, type of CM, and other underlying conditions.

The impact of this condition depends on the severity of the herniated cerebellar tonsils. Because of this, complications can range from minimal discomfort to intrusive symptoms that make everyday tasks difficult to complete.

Some people with CM type 1 find that the condition causes only discomfort, like frequent headaches. Others may find that the complications greatly affect their quality of life.

More serious complications are present when other brain irregularities are confirmed with CM. Many people with CM also have other neurological or orthopedic issues, such as:

Even though migraine isn’t specifically linked to low-lying cerebellar tonsils, the headaches that this condition may cause can be debilitating.

Depending on the severity, different treatment methods may be recommended.

The first line of treatments for headaches usually involves conservative treatments. These include preventive medications and headache treatment medications, which can be over the counter or prescription. Options include:

When CM type 1 occurs without other neurological or orthopedic irregularities, it can cause severe headaches that do not respond to conservative treatments. For this type of CM, doctors may recommend surgery to address the root cause.

The two most common surgeries are:

  • Posterior fossa decompression. This is the removal of the lower back portion of the skull. According to a small 2019 study, it may relieve pressure and allow spinal fluid to flow freely.
  • Cerebellar tonsillar reduction. Microsurgery shrinks the lower portion of the tonsils that are not needed for essential brain or bodily functions. According to the American Association of Neurological Surgeons, this allows spinal fluid to move freely.

It’s important to note that surgery often does not ease headache symptoms. It’s better suited for treating the other symptoms that affect motor and sensory function. And in many cases, people will need consistent follow-up treatment to manage symptoms and any associated pain or discomfort.

Headaches are frustrating. But people with low-lying cerebellar tonsils may experience other symptoms that can affect basic bodily functions. Beyond the headaches, you may have trouble with:

  • maintaining balance
  • seeing
  • breathing
  • controlling movements

It’s important to get medical help to determine what’s causing these issues. Even if you don’t have a form of CM, if you do have frequent headaches or migraine, it’s important to get help. Migraine is equally imposing and can decrease your quality of life.

CMs, including low-lying cerebellar tonsils, are not common conditions. While headaches can be an associated symptom, usually other more serious issues may be present. You could have trouble with breathing, swallowing, dizziness, maintaining balance, or controlling muscle movements.

If you have migraine, it’s unlikely that low-lying cerebellar tonsils are the cause. But it’s still important to get medical help to manage your pain symptoms.