Syringomyelia and Chiari malformation !

In Chiari malformation the lower cerebellum sits in the spinal canal; this can block spinal fluid and form a cavity (syrinx) inside the cord.

Updated 2026-11-01

Structures involved

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Why it happens

What it is

Chiari malformation type I is a downward displacement of the cerebellar tonsils through the foramen magnum. Syringomyelia is a fluid-filled cavity (syrinx) inside the spinal cord, most often in the cervical cord, and Chiari I is its most common cause.

Who gets it

Chiari I is often found incidentally on MRI and many people never have symptoms. Syringomyelia usually becomes symptomatic between 25 and 40 years and is somewhat more frequent in men. Chiari II occurs almost always with myelomeningocele, which remains relevant in Latin America, where neural tube defects are prevented through folic acid fortification and supplementation.

Causes

Chiari I: small posterior fossa causing tonsillar descent, usually congenital
Chiari II: descent of the vermis and brainstem, associated with myelomeningocele and hydrocephalus
Syringomyelia secondary to Chiari malformation (most common)
Post-traumatic syringomyelia after spinal cord injury
Syringomyelia from spinal cord tumours or arachnoiditis after infection or haemorrhage

Risk factors

Neural tube defects (myelomeningocele) for Chiari II
Prior spinal cord injury or spinal infection
Connective tissue disorders and craniovertebral junction anomalies
Acquired tonsillar descent after repeated lumbar CSF drainage (rare)

Pathophysiology

The tonsils crowd the foramen magnum and obstruct the normal pulsatile flow of cerebrospinal fluid between the skull and the spinal canal. Pressure waves drive fluid into the cord, forming a syrinx that usually starts in the central cervical cord. The expanding cavity first interrupts the crossing spinothalamic fibres in the anterior commissure, causing loss of pain and temperature in a cape distribution with preserved touch and proprioception, then damages anterior horn cells and the long tracts.

Classification

Chiari type I: tonsils at least 5 mm below the foramen magnum
Chiari type II: vermis, brainstem and fourth ventricle displaced, with myelomeningocele
Chiari type III: herniation of hindbrain through an occipital or high cervical encephalocele (rare)
Syringomyelia: communicating, non-communicating (Chiari, trauma, tumour) or atrophic

Symptoms and signs

Occipital headache brought on by coughing, sneezing or straining (Chiari I)
Neck pain, dizziness, imbalance and unsteady walking
Loss of pain and temperature sensation over the shoulders and arms in a cape pattern, with painless burns or cuts
Weakness and wasting of the hand muscles with reduced arm reflexes
Spasticity and brisk reflexes in the legs
Scoliosis, especially in children
Trouble swallowing, hoarseness or sleep apnoea when the brainstem is involved

Diagnosis

Clinical: History of cough headache and examination showing dissociated sensory loss in a cape distribution, lower motor neuron signs in the arms and upper motor neuron signs in the legs, and cerebellar or lower cranial nerve signs.
Tests: No blood test is diagnostic. Nerve conduction studies and sleep studies may help in selected cases.
Imaging: MRI of the brain and whole spine is the key test: it shows tonsillar descent, a crowded foramen magnum and the syrinx; cine MRI assesses CSF flow. Contrast is used to exclude a tumour. CT myelography is an option when MRI is not possible.

Differential diagnosis

Cervical spondylotic myelopathy
Intramedullary spinal cord tumour
Multiple sclerosis or transverse myelitis
Amyotrophic lateral sclerosis
Carpal tunnel syndrome or cervical radiculopathy
Tonsillar descent secondary to low CSF pressure or raised intracranial pressure

Goal of treatment

Restore normal CSF flow at the foramen magnum, stop progression of the syrinx and preserve neurological function; observation is appropriate for people without symptoms.

Treatment

Follow-up: Clinical and MRI follow-up for asymptomatic Chiari I or small stable syrinxes.
Surgical: Posterior fossa decompression (suboccipital craniectomy with C1 laminectomy, often with duraplasty) is the main treatment for symptomatic Chiari I with or without syrinx. Shunting of the syrinx or treatment of a tumour or tethered cord in selected cases; hydrocephalus is treated first if present.
Medical: Analgesics and neuropathic pain agents for pain control.
Rehabilitation: Physiotherapy and occupational therapy; education on protecting insensate skin from burns and injuries.

Complications

Permanent weakness, wasting and sensory loss in the arms
Chronic neuropathic pain
Neuropathic (Charcot) joints in the shoulder or elbow
Progressive scoliosis
Brainstem dysfunction: dysphagia, sleep apnoea, vocal cord paralysis
Surgical complications: CSF leak, pseudomeningocele, meningitis, syrinx recurrence

Prognosis

Untreated symptomatic syringomyelia tends to progress slowly over years. Decompression usually halts progression and improves symptoms in most patients, although established sensory loss and wasting often persist.

Prevention

Folic acid supplementation before conception and in early pregnancy to prevent myelomeningocele and Chiari II
Prevention of spinal cord injury

Test yourself

Think of the answer, then tap the question to see it.

What is the classic sensory finding in cervical syringomyelia?

Loss of pain and temperature in a cape distribution with preserved touch and proprioception (dissociated sensory loss).

Why are pain and temperature lost first in syringomyelia?

The central syrinx first damages spinothalamic fibres crossing in the anterior white commissure.

Which headache pattern suggests Chiari I malformation?

Occipital headache triggered by coughing, sneezing or straining.

With which congenital defect is Chiari II almost always associated?

Lumbosacral myelomeningocele, usually with hydrocephalus.

What is the main surgical treatment for symptomatic Chiari I?

Posterior fossa (suboccipital) decompression, often with C1 laminectomy and duraplasty.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Syringomyelia: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2025); Chiari Malformation | National Institute of Neurological Disorders and Stroke (National Institute of Neurological Disorders and Stroke (NIH), 2025).

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Representative model, for educational purposes only.

Spinal cord highlighted on the Durgical 3D model