Summary

Chiari malformations are structural defects in the base of the skull and cerebellum, characterised by herniation of cerebellar tissue through the foramen magnum into the spinal canal. Type I (most common in adults) involves descent of the cerebellar tonsils >5mm below the foramen magnum and is often associated with syringomyelia. Type II (Arnold-Chiari) is more severe, almost always associated with myelomeningocele (spina bifida), and presents in infancy. Types III and IV are rare and severe. Symptoms of Type I include occipital headache worsened by Valsalva (coughing, straining), neck pain, and symptoms related to syringomyelia or brainstem compression. Treatment is surgical decompression for symptomatic patients.

Key Facts

• Type I: Adult presentation, tonsils >5mm descent, associated with syringomyelia
• Type II: Paediatric, associated with myelomeningocele (spina bifida)
• Type III/IV: Rare, severe, often fatal
• Key Symptom (Type I): Headache worse with Valsalva (coughing, sneezing)
• Association: Syringomyelia (60% of Type I)
• Treatment: Foramen magnum decompression (symptomatic cases)

Clinical Pearls

"Cough Headache = Think Chiari": An occipital headache that worsens with coughing, straining, or laughing is classic for Chiari I. Always get an MRI.

"5mm is the Threshold": Cerebellar tonsils descending >5mm below the foramen magnum on MRI defines Chiari I.

"Syrinx = Consequence": Syringomyelia (CSF-filled cavity in spinal cord) often results from Chiari I and causes sensory and motor symptoms.

"Type II = Spina Bifida": Chiari II is almost always associated with myelomeningocele and is diagnosed in infancy.

Neurological Examination

• Cranial nerves (especially lower: IX, X, XII)
• Upper limb: Weakness, wasting (syrinx)
• Sensory: Cape-like loss (pain/temperature; syrinx)
• Reflexes: May be brisk (myelopathy)
• Gait: Ataxia
• Nystagmus (especially downbeat)

Signs of Syringomyelia

• Dissociated sensory loss (loss of pain/temperature, preserved vibration/proprioception)
• Hand weakness and wasting
• Scoliosis (especially in children)

With Surgery (Type I)

• Headache improves in 70-80%
• Syrinx stabilises or improves in most
• Neurological deficits may not fully reverse

Without Surgery (Asymptomatic)

• Many remain stable
• Risk of progression uncertain

Type II

• Prognosis depends on severity of spina bifida and hydrocephalus
• Lifelong multidisciplinary care needed

Key Guidelines

1. American Association of Neurological Surgeons: Chiari Guidance
2. NICE: Referral Guidelines for Neurological Conditions

Key Evidence

Surgery

• FMD effective for symptomatic relief
• Duraplasty may improve outcomes but increases complication risk

What is a Chiari Malformation?

A Chiari malformation is a condition where part of the brain (the cerebellum) pushes down through the opening at the base of the skull into the spinal canal. This can block the flow of spinal fluid and put pressure on the brain and spinal cord.

What Are the Types?

• Type I: The most common; usually found in adults. Part of the cerebellum slips down slightly.
• Type II: More severe; almost always occurs with spina bifida in babies.

What Are the Symptoms?

• Headaches (especially when coughing, sneezing, or straining)
• Neck pain
• Dizziness, balance problems
• Weakness or numbness in hands
• Swallowing difficulties (if severe)

How is it Diagnosed?

An MRI scan shows how far the brain tissue has dropped and whether there's a fluid-filled cavity in the spinal cord (syrinx).

How is it Treated?

• If you have no symptoms, you may just need monitoring with regular MRIs
• If symptomatic, surgery (foramen magnum decompression) creates more space at the base of the skull to relieve pressure