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Chiari Malformation: Symptoms, Scans and Treatment

Spinemathema picture card for Chiari Malformation

By Mr Ahmed-Ramadan Sadek, Neurosurgeon · 8 min read

🎧 Listen to this guideAudio version coming soon. Narrated in Mr Sadek’s voice using AI voice technology, from a script he has reviewed.

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Key points

  • Chiari malformation type 1 means the lowest part of the back of the brain, the cerebellar tonsils, sits lower than usual and reaches into the top of the spinal canal.
  • It is often found by chance on an MRI scan done for another reason, and many people never get symptoms from it.
  • The typical symptom is a headache at the back of the head that comes on with coughing, sneezing or straining.
  • Some people develop a fluid-filled cavity in the spinal cord, called a syrinx, which needs specialist review.
  • Surgery is considered for troublesome symptoms or problems from pressure on the spinal cord, not for an MRI finding on its own.

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This guide is about adults. Children are looked after by children’s specialist teams.

If you have a Chiari malformation:

  • Contact your GP or specialist team for advice if you develop any new symptoms or your symptoms get worse.[1]
  • If you cannot contact your GP, or you are not sure what to do, use NHS 111 online or call 111.[2][3]
  • Call 999 for a life-threatening emergency, such as signs of a stroke.[3]

Symptoms worth reporting include new numbness or weakness, problems using your hands, difficulty walking, swallowing problems, and changes in bladder or bowel control.[1]

What is a Chiari malformation?

At the back of your head, below the main part of the brain, sits the cerebellum. It helps with balance and coordination. Its lowest parts are two small rounded lobes called the cerebellar tonsils. Normally they sit inside the skull, just above a large opening in its base called the foramen magnum, where the brainstem becomes the spinal cord.

In Chiari malformation type 1 (often written Chiari I or CM1), the tonsils extend down through this opening into the top of the spinal canal. This can press on the brainstem and spinal cord and slow the flow of cerebrospinal fluid (CSF), the clear fluid that cushions them. The NHS describes four main types of Chiari malformation. Type 1 is by far the most common and is the subject of this guide. It used to be called an Arnold-Chiari malformation.[1]

In adults, tonsils more than 5 mm below the opening are generally taken as the sign of Chiari 1 on a scan.[4][5] But the amount of descent does not always match how many symptoms a person has.[5]

The exact cause of Chiari 1 is not known. It is usually present from birth but is often only found in adulthood. In many people, part of the skull is thought to be slightly too small for the brain. It can run in families, but the risk of passing it on is very small.[1]

How often is it found by chance?

Because so many people now have MRI scans, Chiari 1 is found more and more often by chance. A US hospital review of more than 22,000 people having MRI of the head or neck found tonsils more than 5 mm below the opening in 0.77%. Of these, 14% had no symptoms at all.[4] A 2021 review of adult Chiari quotes figures of 0.56% to 0.77% on MRI.[6]

So roughly 1 in 180 to 1 in 130 scans show this finding, and many people who have it are well. A report mentioning “low-lying tonsils” does not on its own mean you need treatment.

Symptoms

Many people with Chiari 1 have no symptoms. When symptoms do occur, the most typical one is a headache at the back of the head, brought on or made worse by coughing, sneezing, straining or bending over. Other possible symptoms include:[1]

  • neck pain;
  • dizziness and problems with balance;
  • weakness, numbness or tingling in the arms or legs;
  • blurred or double vision, or sensitivity to light;
  • difficulty swallowing;
  • hearing loss or ringing in the ears (tinnitus);
  • feeling or being sick;
  • poor sleep and low mood.

These symptoms are common and have many other causes, so your specialist will look carefully at how well your symptoms fit with what the scan shows.

Syringomyelia

In some people, fluid collects inside the spinal cord and forms a long, thin cavity called a syrinx. This is called syringomyelia. The NHS notes that a syrinx can damage the spinal cord if it is not treated promptly, and can lead to problems using the hands, difficulty walking, pain, or bladder and bowel problems.[1]

Tests

MRI is the main test. In adults, the position of the tonsils can be measured reliably on either a head MRI or a neck MRI.[7] Imaging of the spine also shows whether a syrinx is present. Special MRI sequences, sometimes called cine or phase-contrast CSF flow studies, can show whether fluid flow around the base of the skull is disturbed, which can help link the scan to your symptoms.[5] Your specialist will also ask about your symptoms and examine your nervous system.

The international consensus on Chiari 1 in adults

In November 2019, experts met at the Chiari and Syringomyelia Consensus Conference in Milan. Using a structured voting process called a Delphi method, a jury of 31 people (19 neurosurgeons, 6 neurologists, 4 neuroradiologists and 2 patient representatives) worked on 63 statements about adult care. These covered four areas: definition and classification, planning, surgery, and syringomyelia without Chiari. All 63 statements were finally approved.[8] The document was published in the journal Neurological Sciences (online in 2021, in print in 2022).[8]

A 2023 commentary by members of the same group explains why this matters to patients. There are still no randomised trials to base firm guidelines on, opinions on surgery differ, and some operations or reasons for surgery that most experts disapprove of are still in use.[9] If you are offered surgery, it is reasonable to ask how the plan fits with this consensus.

Watchful waiting

If you have no symptoms, or only mild ones, the usual approach is to monitor. A systematic review found that 93% of people without symptoms stayed symptom-free, even some who had a syrinx. Among people with symptoms who did not have surgery, between 27% and 47% improved over about 15 months. Headache and nausea often settled, but balance problems and altered feeling tended not to improve on their own.[10]

The review concluded that mild or symptom-free Chiari 1 in adults usually behaves in a benign way, and that it is reasonable to watch people with mild or no symptoms, even when the tonsils sit low or there is a syrinx.[10] Painkillers can help with headaches and neck pain.[1] Follow-up usually means clinic reviews and, when needed, repeat MRI. Let your team know if anything changes.

When is surgery considered?

According to the NHS, surgery may be recommended if headaches are severe or if pressure on the spinal cord is causing problems such as difficulty with movement.[1] The decision should rest on how severe and long-lasting your symptoms are, not on the scan alone.[10]

What the operation involves

The main operation is a posterior fossa decompression, sometimes called a foramen magnum decompression. Under general anaesthetic, a cut is made at the back of the head. The surgeon removes a small piece of bone from the base of the skull, and may also remove a small piece from the top of the spine, to reduce pressure and help fluid flow normally.[1]

The surgeon may also open the tough membrane that covers the brain (the dura) and stitch in a patch to widen the space. This is called a duraplasty. Reviews of adult studies have found that bone-only decompression has fewer complications but a higher chance of needing a second operation, while duraplasty carries more risk of problems such as CSF leaks. Neither approach has clearly given better symptom relief in adults.[11][12] All of this evidence comes from observational studies rather than randomised trials.[11]

A few people need a different procedure, for example to treat a build-up of fluid in the brain (hydrocephalus) or to stabilise the spine.[1]

Outcomes and risks

Surgery mainly aims to stop symptoms getting worse. Many people also improve, especially their headaches, but some do not, and a few get worse.[1] The figures below come from reviews of adult studies and are averages, not predictions for any one person.

After surgery in adultsWhat studies report
HeadacheResolved in 79% on average (adult studies 2000 to 2019)
Nerve symptomsImproved in 77% on average
SyrinxResolved or improved in 74% on average
Complications after duraplasty9% to 20%, depending on technique
CSF-related complications after duraplasty5% to 15%, depending on technique
Repeat surgery after duraplastyFrom under 1% to about 8%, depending on technique

The headache, nerve and syrinx figures are averages from published adult series, gathered in a 2021 review.[6] The complication and repeat surgery figures come from an adult meta-analysis, which found fewer problems when the thin inner layer around the brain (the arachnoid) was left intact.[13] The NHS also notes a small risk of serious complications such as paralysis or stroke.[1]

Living with Chiari

The NHS does not consider Chiari 1 to be life-threatening, and many people have no symptoms at all.[1] There is little research on exercise and sport in adults with Chiari, so advice is practical and individual:

  • Keep active: walking, swimming and general fitness are good for you.
  • Coughing, straining and bending can bring on Chiari headaches.[1] If certain activities do the same, pace or adapt them.
  • Ask your specialist before taking up contact sports or very heavy lifting.
  • Keep your follow-up appointments, and report new numbness, weakness, swallowing problems or a change in your headaches.[1]

Frequently asked questions

Is Chiari malformation serious?

For most people, no. The NHS does not consider Chiari 1 to be life-threatening, and many people with it never have symptoms.[1] Some people do get troublesome headaches or other symptoms, and a fluid-filled cavity in the spinal cord (a syrinx) can damage the cord if it is not treated promptly.[1] A systematic review found that 93% of people without symptoms stayed symptom-free over time.[10] Your specialist can explain what your own scan means.

Can a Chiari malformation get worse over time?

It can, but in most adults it does not. A systematic review described mild or symptom-free Chiari 1 in adults as relatively benign and not usually progressive.[10] Among people with symptoms who did not have surgery, 27% to 47% improved over about 15 months, although balance problems and altered feeling tended not to improve on their own.[10] This is why follow-up is advised, and why you should report any new or worsening symptoms.[1]

Do I need surgery if my Chiari was found by chance?

Usually not. In a large MRI review, 14% of people with a Chiari 1 finding had no symptoms at all.[4] A systematic review concluded that it is reasonable to watch people with mild or no symptoms, even when the tonsils sit low or there is a syrinx, and that surgery should depend on how severe and long-lasting symptoms are.[10] The amount of tonsil descent on a scan does not always match symptoms.[5]

Can I exercise and play sport with a Chiari malformation?

Most adults can stay active, but there is little research to guide sport choices, so advice is individual. The NHS notes that Chiari headaches can be brought on by coughing, straining, sneezing or bending over.[1] If an activity does the same, pace or adapt it. Walking, swimming and general fitness are usually fine. Ask your specialist before taking up contact sports or very heavy lifting, especially if you have a syrinx or have had surgery.

Can I have a normal birth or an epidural if I have Chiari?

Often yes, but plan ahead with your maternity team. A US case series looked at 95 deliveries in 63 women with Chiari 1 who had not had surgery. No one’s nerve symptoms got worse, whether they had a vaginal birth or a caesarean, and 62 deliveries with an epidural or spinal anaesthetic had no nerve complications.[14] The authors concluded that, without signs of raised pressure in the head, the way the baby is delivered can be based on usual pregnancy reasons.[14] This was a small study, so tell your midwife and anaesthetist about your diagnosis early.

Is Chiari malformation hereditary?

Sometimes, but the risk is small. The NHS explains that Chiari malformations can run in families, possibly through genes that affect how the skull develops, but the risk of passing one on is very small.[1] Someone who does inherit it may never have symptoms.[1]

How successful is surgery for Chiari malformation?

Most adults improve, but not everyone. Averaging adult studies published between 2000 and 2019, headaches resolved in 79%, nerve symptoms improved in 77%, and a syrinx resolved or improved in 74%.[6] The main aim is to stop symptoms getting worse, and some people notice no improvement.[1] In an adult meta-analysis, complications after duraplasty ranged from 9% to 20%, depending on technique.[13] Your surgeon can explain what to expect in your case.

When should I get urgent help with a Chiari malformation?

If you have been diagnosed with Chiari, the NHS advises contacting your doctor for advice if you develop any new symptoms or your symptoms get worse.[1] Symptoms worth reporting include new numbness or weakness, problems using your hands, difficulty walking, swallowing problems, and changes in bladder or bowel control.[1] If you cannot reach your GP, or you are not sure whether you need emergency help, use NHS 111 online or call 111.[2][3] Call 999 for a life-threatening emergency, such as signs of a stroke.[3]

Further reading

References

  1. NHS. Chiari malformation. NHS website, page last reviewed 9 November 2022. Link
  2. NHS. When to use NHS 111 online or call 111. NHS website. Link
  3. NHS. When to call 999. NHS website, page last reviewed 3 February 2023. Link
  4. Meadows J, et al. Asymptomatic Chiari Type I malformations identified on magnetic resonance imaging. J Neurosurg. 2000;92(6):920-6. Link
  5. Fakhri A, et al. Advanced Imaging of Chiari 1 Malformations. Neurosurg Clin N Am. 2015;26(4):519-26. Link
  6. Arnautovic KI, et al. The 270° Circumferential Microsurgical Decompression of the Foramen Magnum in Adult Chiari Malformation Type I: Single Surgeon Series of 130 Patients with Syringomyelia, Neurologic, and Headache Outcomes. World Neurosurg. 2021;146:e1103-17. Link
  7. Eisenberg L, et al. Cranial Versus Cervical Spine Magnetic Resonance Imaging in Adult Chiari Malformation Type I Diagnostics: Is There a Difference in Tonsil Ectopia Length? World Neurosurg. 2023;175:e243-6. Link
  8. Ciaramitaro P, et al. Diagnosis and treatment of Chiari malformation and syringomyelia in adults: international consensus document. Neurol Sci. 2022;43(2):1327-42. Link
  9. Massimi L, et al. Chiari Malformation Type 1 and Syringomyelia: Why Do Patients Claim for International Guidelines? Commentary on the 2021 Chiari and Syringomyelia Consensus Document. Acta Neurochir Suppl. 2023;135:139-45. Link
  10. Langridge B, et al. Chiari Malformation Type 1: A Systematic Review of Natural History and Conservative Management. World Neurosurg. 2017;104:213-9. Link
  11. Förander P, et al. The case for duraplasty in adults undergoing posterior fossa decompression for Chiari I malformation: a systematic review and meta-analysis of observational studies. Clin Neurol Neurosurg. 2014;125:58-64. Link
  12. Yuan C, et al. Comparison of Foramen Magnum Decompression with and without Duraplasty in the Treatment of Adult Chiari Malformation Type I: A Meta-Analysis and Systematic Review. Turk Neurosurg. 2022;32(6):893-902. Link
  13. Osborne-Grinter M, et al. Posterior Fossa Decompression and Duraplasty with and without Arachnoid Preservation for the Treatment of Adult Chiari Malformation Type 1: A Systematic Review and Meta-Analysis. World Neurosurg. 2021;151:e579-98. Link
  14. Waters JFR, et al. Management of Anesthesia and Delivery in Women With Chiari I Malformations. Obstet Gynecol. 2018;132(5):1180-4. Link

This article is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist before making any change to your treatment.

Last checked: October 2026