If an MRI has shown that your child has a Chiari I malformation, or if a doctor has used that term in a clinic, this page explains what it means in plain language. The most important point upfront, many children with this finding have no symptoms at all and need no treatment. This page will help you understand when Chiari I matters, what to look out for, and what the surgery involves in the children who do need it. Your child's neurosurgeon will discuss what applies specifically to your child.
At the very base of the skull, there is a large opening called the foramen magnum, this is where the brain meets the spinal cord. Just above this opening sits the cerebellum, the part of the brain that handles balance and coordination. The lowest tips of the cerebellum are called the cerebellar tonsils.
In a Chiari I malformation, the cerebellar tonsils sit lower than they should, and they extend a short distance down through the foramen magnum, into the top of the spinal canal. One way to think about it is that the back of the skull is a little smaller than the brain that has to fit inside it.
Chiari I is very different from Chiari II, which is a more complex malformation that occurs with spina bifida (myelomeningocele) and is present from birth. This page covers only the Chiari I form, the more common and milder one, often found in otherwise healthy children.
Many children with Chiari I are diagnosed by chance, when an MRI is performed for something else entirely, for example a headache after a minor head bump, a routine evaluation, or another concern. In these children, the Chiari is often "incidental", meaning that it is real but is not actually causing any problems and may never cause any. Other children do have symptoms that come from the Chiari, and for them surgery can help.
In some children, Chiari I is found alongside a separate finding called syringomyelia, a small fluid-filled cavity inside the spinal cord. When a syrinx is present, it can affect the symptoms and the treatment decisions. Your child's neurosurgeon will look carefully for this on the MRI.
Most children with Chiari I have no symptoms at all. When symptoms do occur, they often follow a recognisable pattern, but many of these symptoms can also have completely unrelated causes. The classic Chiari headache is one of the most specific signs to look for.
Chiari I is diagnosed on an MRI of the brain. The MRI shows the position of the cerebellar tonsils very clearly. There is no single number that decides whether a Chiari is important, your child's neurosurgeon will assess how low the tonsils sit, the shape they take, and most importantly whether they are interfering with the flow of cerebrospinal fluid (CSF) around the brain.
If a Chiari is found, the team will usually also request an MRI of the spine to look for syringomyelia. A specific type of scan called a cine MRI may be performed, this is still an MRI but it produces short "movies" of the CSF as it flows around the foramen magnum. It helps the neurosurgeon to decide whether the Chiari is obstructing flow.
Other tests can be useful depending on the symptoms. A sleep study can check for sleep apnoea. A swallow study or an ENT (ear, nose, throat) examination can evaluate feeding and airway symptoms in babies. A neurological examination is always part of the assessment.
An important part of the assessment is deciding whether the symptoms your child has are genuinely being caused by the Chiari, or whether they could be from a separate problem, many children with Chiari I also have ordinary childhood headaches, for example. This is why the diagnosis is made by combining the MRI with a careful clinical assessment, and not by relying on the MRI alone.
Treatment depends entirely on whether your child has symptoms from the Chiari, whether there is a syrinx, and how the symptoms are affecting daily life. The two main pathways are careful observation and surgery, and one is not automatically better than the other. The right choice for your child is a decision that you and the neurosurgeon make together.
The decision to operate is not always straightforward. If your child has mild or vague symptoms and a small Chiari, the neurosurgeon may suggest a period of watching, or a second opinion. If symptoms are clear and life-affecting, surgery has good outcomes, particularly for the classic cough/strain headache. Ask the team to explain their thinking for your child's specific situation.
If your child is being observed without surgery, the rhythm is usually a clinic appointment once or twice a year, and a repeat MRI at intervals set by the neurosurgeon. Most observed children continue to do well and never need an operation.
If your child does have surgery, the operation itself usually takes two to three hours. Most children spend the first night in the paediatric intensive care unit (PICU) and another two to three nights on a regular ward. The total hospital stay is typically three to five days.
It is normal to have some neck stiffness and discomfort for one to two weeks after the operation. Pain control is straightforward with regular medications. Most children return to school in two to four weeks, and to full activity (including sport) in about six weeks, once the neurosurgeon confirms that healing is complete.
The headache caused by Chiari is the symptom that improves most reliably after a successful decompression, many children notice the difference within the first few weeks. Other symptoms such as numbness, balance problems, or syrinx-related findings tend to improve more slowly, over months. Symptoms that are not actually caused by the Chiari will not, of course, improve with the operation, this is why careful patient selection is so important.
Follow-up after surgery usually includes a clinic visit a few weeks later, and a repeat MRI several months later to confirm that the decompression has done its job, and, if a syrinx was present, that it has begun to shrink. In the long term, most children with Chiari I do very well, whether they have had surgery or not.
After surgery for Chiari I, most recovery is smooth, but some signs need to be checked right away. Do not wait, contact the neurosurgery team (or go straight to the emergency department) if you notice any of the following:
If your child is difficult to rouse, is having a seizure, or is having difficulty breathing, this is an emergency, go to the nearest emergency department or call the emergency services immediately.