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Health condition · Clinically reviewed

Chiari malformation, the classic cough headache, MRI and when decompression helps.

Not every low-lying tonsil needs surgery. This guide explains the types, what the imaging shows, and how UK neurosurgical teams decide who benefits from posterior fossa decompression.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against UK neurosurgical practice, NICE and specialist Chiari centre standards.

  • 03

    Current for 2026

    Reflects modern MRI protocols, CSF flow imaging and posterior fossa decompression techniques.

Key facts

Chiari malformation at a glance.

The essentials, in plain English - what it is, the four types, and how UK teams decide who needs surgery.

  • What it is

    A structural abnormality where the cerebellar tonsils herniate below the foramen magnum into the upper cervical spinal canal.

  • Types

    Chiari I (commonest, tonsillar descent over 5 mm), Chiari II (with spina bifida), Chiari III (encephalocele) and Chiari IV (cerebellar hypoplasia).

  • Classic headache

    Occipital or subocciptal pain triggered by Valsalva - coughing, sneezing, straining, laughing or exercise - lasting seconds to minutes.

  • Syringomyelia link

    A fluid-filled cavity (syrinx) develops in the spinal cord in roughly 30 to 70 per cent of symptomatic Chiari I cases.

  • Imaging

    MRI of the brain and whole spine is the gold standard, with cine MRI to look at CSF flow across the foramen magnum.

  • Treatment

    Observation for many incidental cases; posterior fossa decompression surgery for symptomatic, progressive or syrinx-related disease.

Why this guide matters

Not every low tonsil is a Chiari that needs surgery.

The three points below are the ones that most often get lost in translation between the MRI report, the GP letter and the neurosurgery clinic.

  • The headache pattern matters more than the millimetres

    Tonsillar descent on MRI matters, but a Valsalva-triggered occipital headache is the feature that most often makes a Chiari symptomatic.

  • Secondary causes can be reversible

    A CSF leak or shunt overdrainage can pull the tonsils down. Treating the leak may resolve the imaging finding without any brain surgery.

  • Decompression is a specialist decision

    Timing, technique and whether to open the dura are judgement calls best made at a UK Chiari centre with a full neurosurgical MDT.

How the diagnosis is made

From cough headache to a clear MDT plan.

The steps a UK GP, neurologist and neurosurgical team will normally follow, in order - so you know what to expect and why each test is done.

  1. 01

    Assessing

    History and Valsalva headache pattern

    A careful history focused on cough-triggered occipital headache, neck pain, balance changes, swallowing and any sensory loss.

  2. 02

    Assessing

    Neurological examination

    Cerebellar signs, cranial nerves, power, sensation, reflexes and a look for dissociated sensory loss in a cape distribution.

  3. 03

    Assessing

    Consider secondary causes

    A low-lying tonsil can be secondary to a CSF leak or lumbar shunt overdrainage - and may resolve with treatment of the cause.

  4. 04

    Confirming

    MRI brain and whole spine

    Measure tonsillar descent, look for a syrinx, hydrocephalus and any associated pathology through the whole neuraxis.

  5. 05

    Confirming

    Cine MRI CSF flow study

    A dynamic sequence at the foramen magnum - obstructed flow supports a symptomatic Chiari and helps guide surgical decisions.

  6. 06

    Planning

    Selective upright MRI and sleep study

    Upright imaging can unmask craniocervical instability; a sleep study is useful when central or obstructive sleep apnoea is suspected.

  7. 07

    Planning

    Neurosurgery-led MDT review

    Neurology, neurosurgery, neuropsychology, speech and swallow input at a specialist Chiari centre before any operative decision.

Typical timeline: from GP visit to a settled neurosurgical plan in weeks, not months.

Symptoms

What Chiari actually feels like.

The classic mix of Valsalva headache, cerebellar and cranial nerve features - and the spinal cord symptoms that suggest a syrinx has formed.

  • Valsalva-induced occipital headache

    Brief seconds-to-minutes occipital or subocciptal pain triggered by coughing, sneezing, straining, laughing or exercise - the classic feature.

  • Neck and suboccipital pain

    Persistent ache at the base of the skull and upper neck, often worse with head position and exertion.

  • Cerebellar signs

    Ataxia, dysmetria, nystagmus and diplopia reflecting cerebellar and brainstem crowding at the foramen magnum.

  • Cranial nerve symptoms

    Dysphagia, dysarthria, hoarseness, tinnitus, hearing change or vertigo from lower cranial nerve compression.

  • Spinal cord and syrinx features

    Weakness, numbness and a suspended dissociated sensory loss in a cape distribution when a syringomyelia has formed.

  • Autonomic and sleep symptoms

    Syncope, palpitations and central or obstructive sleep apnoea can accompany brainstem involvement.

  • Incidental MRI finding

    Low-lying tonsils are often picked up on MRI performed for another reason and never cause symptoms.

  • Red flag - rapid neurological change

    New brainstem signs, swallow failure, rapidly progressive weakness or sleep-disordered breathing need urgent neurosurgical review.

Treatment

How Chiari is treated in the UK.

From watchful observation to posterior fossa decompression - matched to symptoms, the imaging, any syrinx and any secondary cause.

  • Observation and serial MRI

    For asymptomatic incidental Chiari I - most do not progress. Yearly to three-yearly MRI, patient education and clear red flags.

  • Symptomatic medication

    Analgesia, amitriptyline or gabapentin for neuropathic pain, antiemetics, migraine treatment and management of any sleep apnoea.

  • Posterior fossa decompression

    The standard operation - subocciptal craniectomy and C1 laminectomy to create more space at the craniocervical junction. See our treatment guide.

  • Decompression with duroplasty

    Adds opening of the dura with a pericranial or synthetic patch (Dura-Gen, Alloderm) and selective tonsil shrinkage where flow remains obstructed.

  • Syringomyelia management

    Decompression usually collapses the syrinx over months; a syringosubarachnoid shunt is reserved for persistent, symptomatic cavities.

  • Hydrocephalus treatment

    Endoscopic third ventriculostomy (ETV) or a ventriculoperitoneal (VP) shunt when hydrocephalus is driving symptoms - often before decompression.

  • Treat the underlying cause

    Secondary Chiari from a CSF leak is treated with an epidural blood patch; overdrainage needs shunt revision - decompression is not always required.

  • Concurrent tethered cord release

    When a tethered cord or craniocervical instability co-exists, a combined neurosurgical plan is safer than treating one problem in isolation.

For the surgical detail see our guide to Chiari decompression surgery.

What this guide is based on

The sources behind every claim on this page.

UK neurosurgical practice, specialist society standards and patient charity information, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP, neurologist or neurosurgeon knows your imaging and history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE. Clinical Knowledge Summaries and interventional procedure guidance relevant to Chiari malformation and syringomyelia.

  • Society of British Neurological Surgeons (SBNS). Standards for craniocervical junction surgery.

  • Ann Conroy Trust. Patient information and clinician standards for Chiari and syringomyelia care in the UK.

  • International guidance on posterior fossa decompression, cine CSF flow imaging and management of Chiari-related syringomyelia.

Red flags

When Chiari needs urgent attention.

Many people with Chiari live well with observation. These are the features that change the plan and warrant urgent neurosurgical input.

  • Rapidly progressive weakness

    New or worsening limb weakness, numbness or gait disturbance needs urgent neurosurgical assessment - not a routine outpatient wait.

  • Swallowing failure or aspiration

    Loss of safe swallow, choking on food or recurrent chest infections points to brainstem involvement and demands urgent review.

  • Sleep-disordered breathing

    Central sleep apnoea or worsening obstructive apnoea in Chiari can be life-threatening and needs prompt sleep and neurosurgical input.

  • Sudden severe headache

    Thunderclap or unusually severe headache is never a Chiari headache until other causes such as subarachnoid haemorrhage are excluded.

  • New bladder or bowel dysfunction

    Suggests cord or conus involvement, particularly in Chiari II or when a tethered cord or syrinx is progressing - needs urgent MRI.

  • Neonatal Chiari II features

    Stridor, apnoea, feeding failure or new hydrocephalus in a baby with spina bifida is a paediatric neurosurgical emergency.

  • Signs of raised pressure

    Morning vomiting, papilloedema or reduced consciousness suggests hydrocephalus and needs same-day imaging.

  • Suspected CSF leak

    Postural (orthostatic) headache that eases on lying flat points to intracranial hypotension - the tonsils may look low but the cause is different.

  • Connective tissue clues

    Hypermobility, easy bruising and joint dislocations - consider Ehlers-Danlos and craniocervical instability, which change the surgical plan.

Living with it

A structural condition, with a clear ladder.

Four things that make the biggest difference day to day - managing Valsalva triggers, keeping to an MRI schedule, using the specialist charities and planning recovery well if you do have surgery.

A quiet reminder

Stable does not mean ignored.

Incidental Chiari deserves a plan of its own - agreed scan intervals, an agreed symptom list and a named team you can contact if anything changes.

  1. 01 Pacing

    Manage Valsalva triggers

    Treat coughs, hay fever and constipation early - anything that repeatedly raises intracranial pressure worsens the classic headache.

  2. 02 Monitor

    Keep to your MRI schedule

    Stable incidental Chiari still deserves a plan - agreed intervals for MRI and a clear list of symptoms that mean an earlier scan.

  3. 03 Support

    Use the specialist charities

    The Ann Conroy Trust and Chiari Malformation Support UK offer patient information, peer support and lists of UK specialist centres.

  4. 04 Recovery

    Plan for post-surgical rehabilitation

    After decompression, expect weeks of neck stiffness and gradual return to activity - physiotherapy and pacing help most people.

Frequently asked

Everything we get asked about Chiari.

Quick answers on the headache pattern, imaging, syringomyelia and posterior fossa decompression.

  • What is a Chiari malformation?

    A structural abnormality where the cerebellar tonsils sit below the foramen magnum and crowd the upper cervical spinal canal. It ranges from an incidental MRI finding to a symptomatic condition with headache, cranial nerve and spinal cord features - and is sometimes associated with a syrinx in the spinal cord.

  • What causes it?

    Most Chiari I malformations are thought to reflect a congenitally small posterior fossa. Some are secondary to intracranial hypotension from a CSF leak or lumbar shunt overdrainage, and may resolve when the underlying cause is treated. Tethered cord, craniocervical instability and connective tissue disorders such as Ehlers-Danlos are recognised associations.

  • What does the classic headache feel like?

    A brief, seconds-to-minutes occipital or subocciptal headache triggered by Valsalva - coughing, sneezing, straining, laughing or exercise. It is different from migraine and usually eases quickly when the trigger stops. Postural headache that eases on lying flat suggests a CSF leak instead.

  • How is it diagnosed?

    MRI of the brain and the whole spine is the gold standard - it measures tonsillar descent, looks for a syrinx and any associated pathology. A cine MRI CSF flow study at the foramen magnum helps show whether flow is obstructed. Upright MRI, sleep studies and neurology or neurosurgery review are added where needed.

  • Do I always need surgery?

    No. Many people with an incidental Chiari I never need an operation and are managed with observation, serial MRI and clear red flags. Posterior fossa decompression is reserved for symptomatic disease, progressive neurological change, a significant syrinx or hydrocephalus - and always after specialist assessment.

  • What does decompression surgery involve?

    A subocciptal craniectomy and C1 laminectomy to create more room at the craniocervical junction. Many centres also open the dura and place a patch (duroplasty) to further improve CSF flow, with selective shrinkage of the tonsils if flow remains obstructed. Our treatment guide covers approach, recovery and risks in detail.

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