Chiari Malformation

Chiari malformation is a group of hindbrain anomalies with descent of the cerebellar tonsils or other posterior fossa structures through the foramen magnum. Type I (tonsillar descent of 5 mm or more through the foramen magnum) is the commonest.

Type I is found in about 0.5 to 1% of MRI studies, most of which are asymptomatic. Symptomatic disease is commoner in women and presents in adults aged 20 to 40 years.

Classification. Type 0 (syrinx without tonsillar descent), type I, type 1.5 (tonsillar and brainstem descent), type II (with myelomeningocele and hydrocephalus), type III (occipital encephalocele) and type IV (cerebellar hypoplasia).

Associations. Syringomyelia (30 to 70% of type I), scoliosis, hydrocephalus, basilar invagination, connective tissue disorders and craniosynostosis.

Pathophysiology. A small posterior fossa volume crowds the hindbrain, obstructs CSF flow at the foramen magnum and creates pressure gradients that can cause syrinx formation.

Presentation is occipital or suboccipital headache provoked by cough, strain or Valsalva, neck pain, vertigo, tinnitus, dysphagia, hoarseness, sleep apnoea, limb numbness, weakness and gait ataxia. Examination may show downbeat nystagmus, cape like dissociated sensory loss, hand weakness, spasticity and scoliosis in children. Type II presents in infancy with hydrocephalus and myelomeningocele.

Red flags.

• Progressive weakness, sphincter dysfunction or new sensory deficit.
• Dysphagia with aspiration, apnoea or stridor.
• Rapidly enlarging syrinx or hydrocephalus.

MRI of the brain and whole spine (tonsillar position, crowding, syrinx, hydrocephalus, basilar invagination). Phase contrast cine MRI assesses CSF flow at the foramen magnum. CT of the craniocervical junction for bone anomalies. Sleep study if apnoea is suspected. Swallow assessment for dysphagia.

Differential diagnosis.

• Intracranial hypotension with acquired tonsillar descent, and idiopathic intracranial hypertension.
• Primary cough headache, tension and migraine headache, and cervical spondylosis.
• Posterior fossa mass and hydrocephalus.

Management depends on symptoms and the syrinx.

Asymptomatic and incidental. Observation without surgery, with advice to return if symptoms appear.

Symptomatic. Analgesia for headache (paracetamol 1 g every 6 hours, maximum 4 g daily, and low dose amitriptyline or gabapentin), and treat sleep apnoea and swallowing problems.

Surgery. Posterior fossa decompression with or without duraplasty (and sometimes tonsillar reduction) for progressive neurological deficit, syringomyelia, brainstem dysfunction, or disabling cough induced headache with typical findings. Complications include CSF leak, pseudomeningocele, meningitis and hydrocephalus. Shunting for hydrocephalus and treatment of basilar invagination with fusion when present.

Spinal deformity. Monitor and treat scoliosis.

Pregnancy and delivery. Vaginal delivery and epidural analgesia are acceptable in most with stable disease, with neurology and anaesthetic planning.

Monitoring. Symptoms and neurological examination yearly, with MRI at 6 to 12 months after surgery and then as needed.

Referral and escalation. Refer to neurosurgery. Refer urgently for progressive deficit or bulbar failure.

Special groups. In children, treat hydrocephalus and monitor for scoliosis. Avoid neck manipulation.