Syringomyelia - A Detailed Review

Definition and Terminology

• Syringomyelia - the cavity lies within cord parenchyma
• Hydromyelia - dilation of the central spinal canal itself
• Syringohydromyelia - overlapping term used when cerebellar ectopia/Chiari is the cause
• Syringobulbia - extension of the syrinx cranially into the medulla

• Harrison's Principles of Internal Medicine 22E, p. 3611
• Goldman-Cecil Medicine, p. 4047

Epidemiology

• Symptoms classically appear in late adolescence or early adulthood
• More than 50% of all cases are associated with Chiari type I malformation
• 90% of patients with syringomyelia have a Chiari I malformation (cerebellar tonsillar herniation)
• Scoliosis develops in 63-73% of children with syringomyelia and may be the first presenting sign
• Approximately 10-20% of cases are idiopathic (no identifiable cause)
• The spinal cord is enlarged in ~80% of cases, normal in size in 10%, and diffusely atrophic in 10%
• Rosen's Emergency Medicine, p. 2073
• Grainger & Allison's Diagnostic Radiology, p. 1309
• Campbell's Operative Orthopaedics 15th Ed 2026, p. 3363

Etiology and Classification

1. Communicating Syringomyelia (associated with CSF flow obstruction)

• Chiari I malformation - most common cause (~90%); cerebellar tonsils project below the foramen magnum (typically to C1-C2 level), intermittently obstructing fourth ventricular outflow and foramen magnum CSF flow
• Chiari II malformation - associated with myelomeningocele
• Basilar invagination, other craniocervical junction malformations

2. Non-communicating (Post-injury / Secondary) Syringomyelia

• Post-traumatic - develops months to years after spinal cord injury; one of the most important delayed complications
• Intramedullary tumors (ependymoma, astrocytoma) - cause local necrosis that organizes into cavities
• Spinal arachnoiditis - post-infectious (TB meningitis) or post-inflammatory causes
• Post-myelitis - transverse myelitis, multiple sclerosis
• Tethered cord syndrome

3. Idiopathic

• ~10-20% with no identifiable cause
• Rosen's Emergency Medicine, p. 2073
• Goldman-Cecil Medicine, p. 4047
• Harrison's Principles of Internal Medicine 22E, p. 3611

Pathophysiology

Gardner's Hydrodynamic Theory (Piston Theory)

Williams' Craniospinal Pressure Dissociation Theory

Oldfield's Propagating Wave Theory

• Harrison's Principles of Internal Medicine 22E, p. 3611
• Grainger & Allison's Diagnostic Radiology, p. 1309

Anatomy of the Syrinx

• Most commonly involves the cervical cord, though can extend to the thoracic cord
• Rarely extends cranial to C2 (only ~10% of cysts)
• Small cavities begin at the bases of the posterior columns, often communicating with the central canal
• Larger cavities cause extensive loss of cord substance
• Double cavities or multilocular cavities can occur
• The cord is enlarged in 80% of cases, correlating with internal pressure

• Grainger & Allison's Diagnostic Radiology, p. 1308-1309
• Bradley and Daroff's Neurology in Clinical Practice, p. 540

Clinical Features

Symptom Onset

Classic Presentation: Central Cord Syndrome

• Loss of pain and temperature in the upper extremities and shoulders ("cape-like" or "shawl-like" distribution), with preservation of light touch, vibration, and proprioception
• The anatomical basis: damage to the crossing fibers of the lateral spinothalamic tract at the anterior commissure, while the dorsal columns are spared
• Often begins asymmetrically - unilateral hand numbness that leads to burns and injuries unnoticed by the patient
• The sensory deficit is said to be "suspended" (not extending to the feet) in early stages
• Facial numbness can occur if the descending tract of the trigeminal nerve (at C2 or above) is damaged

• Segmental lower motor neuron signs in the arms/hands: muscle wasting, weakness, areflexia (from damage to anterior horn cells in the gray matter)
• Atrophy particularly of the intrinsic hand muscles

• Upper motor neuron signs in the legs: spasticity, hyperreflexia, weakness
• From compression/damage of the descending corticospinal tracts

• Horner's syndrome (ptosis, miosis, anhidrosis) - from damage to the ciliospinal center at C8-T1
• Bladder and bowel dysfunction (late)

• Palatal/vocal cord paralysis
• Dysarthria
• Horizontal or vertical nystagmus
• Episodic dizziness/vertigo
• Tongue weakness with atrophy (CN XII)
• Lower cranial nerve palsies (CN IX-XII)

• Scoliosis - very common, especially in children (63-73%); the curve is often left-sided with thoracic kyphosis (>40°) rather than hypokyphosis (unlike idiopathic scoliosis); lack of rotation through the apex; increased cervical lordosis
• Pes cavus deformity
• Occipital and upper cervical headaches
• Charcot (neuropathic) joints - from loss of pain sensation; classically shoulder and cervical joints
• Rosen's Emergency Medicine, p. 2073-2077
• Harrison's Principles of Internal Medicine 22E, p. 3611
• Campbell's Operative Orthopaedics 15th Ed 2026, p. 3363-3385

MRI Appearance

• Well-circumscribed central cord cavity with signal characteristics similar to CSF
• T1-weighted: hypointense (like CSF)
• T2-weighted: hyperintense (like CSF) - a key diagnostic sequence
• Pulsatile cysts may show flow-related signal changes on standard sequences
• Cord may appear enlarged (80% of cases) or atrophic (10%)
• Must image from brain to lumbar spine to assess: full syrinx extent, Chiari malformation, hydrocephalus

• Harrison's Principles of Internal Medicine 22E, p. 3611
• Grainger & Allison's Diagnostic Radiology, p. 1309

Differential Diagnosis

• Rosen's Emergency Medicine, p. 2079
• Miller's Review of Orthopaedics, p. 8111

Investigations

1. MRI spine + brain - investigation of choice; must include craniocervical junction to identify Chiari
2. Phase-contrast MRI - CSF flow dynamics at foramen magnum
3. CT myelography - reserved for when MRI is contraindicated; C1-C2 puncture preferred (a subarachnoid web at a lower level acts as a one-way valve that may not be seen with lumbar contrast)
4. EMG/NCS - to assess extent of anterior horn cell damage
5. Somatosensory evoked potentials - baseline and monitoring

Treatment

Indications for Surgery

• Progressive neurological deficit
• Large symptomatic syrinx
• Acute neurological deterioration (~5% of Chiari-associated cases require urgent decompression)

Asymptomatic/Stable Cases

• Serial clinical and MRI monitoring without surgery

Surgical Options

• Suboccipital craniectomy + upper cervical laminectomy (C1 ± C2) + duraplasty (dural graft)
• Restores fourth ventricular outflow and normal CSF circulation
• Most effective approach: 70-80% of cases achieve syrinx collapse
• If the curve/syrinx continues to progress, further intervention may be needed
• Note: direct syrinx drainage in addition to decompression has NOT been shown to add benefit and carries more complications

• For large syrinx not associated with Chiari, or residual/recurrent syrinx after decompression
• Types: syringosubarachnoid, syringopleural, or syringoperitoneal shunting
• The three approaches (foramen magnum decompression, syringo-subarachnoid shunting, lumboperitoneal shunting) are reported to be equally effective in achieving syrinx collapse in 70-80% of cases
• Important caveat: clinical outcome and syrinx extension on interval imaging bear NO reliable relationship to whether the cavity remains collapsed on MRI

• When syrinx is secondary to intramedullary tumor (ependymoma, astrocytoma), resection of the tumor is the primary treatment

• Shunting of hydrocephalus, when present, generally precedes correction of the syrinx

• Drainage of the cyst followed by observation is recommended initially; 70% reduction in syrinx size can lead to curve stabilization
• If curve continues to progress after posterior fossa decompression, scoliosis surgery may be indicated
• Caution: instrumentation/fusion in a patient with untreated syringomyelia carries risk of paraplegia and cyst rupture; neurosurgical consultation before orthopedic surgery is mandatory
• Harrison's Principles of Internal Medicine 22E, p. 3611-3612
• Grainger & Allison's Diagnostic Radiology, p. 1309
• Campbell's Operative Orthopaedics 15th Ed 2026, p. 3387-3393
• Rosen's Emergency Medicine, p. 2083

Prognosis

• Natural history is variable; many patients have prolonged periods of stability with sporadic progression
• Surgery can stabilize the deficit; some patients improve
• Neurological improvement is more likely with early intervention before significant cord damage
• Clinical severity does not correlate reliably with syrinx size on MRI
• Even with successful syrinx collapse post-operatively, clinical improvement may not occur

Summary Table