Syringomyelia

Syrinx Formation Mechanisms

• Abnormal CSF Dynamics and Pressure Dissociation: In post-traumatic and tethered cord syringomyelia, disruption of normal CSF flow dynamics creates abnormal pressure gradients within the spinal cord. The "pulsatile pumping theory" proposes that transmitted CSF pressure waves during cardiac systole expand the syrinx, while viscous drag forces during diastole fail to fully collapse it. This pressure-time mismatch generates a net expansile force. Additionally, loss of normal arachnoid-dural compliance due to scar tissue or adhesions prevents cushioning of pressure oscillations, amplifying syrinx expansion.

• Spinal Cord Ischemia and Metabolic Dysfunction: Chronic hypoxia within the expanding syrinx triggers glutamate excitotoxicity, oxidative stress, and mitochondrial dysfunction. Disruption of the blood-spinal cord barrier increases inflammatory cell infiltration and cytokine release. Progressive demyelination and neuronal apoptosis occur, with loss of axonal function preceding actual tissue loss. Astrogliosis and microglial activation contribute to chronic neuroinflammation.

• Cord Tethering and Mechanical Tension: In tethered spinal cord, abnormal traction on spinal roots and cord parenchyma creates chronic mechanical stress. This stretching damages oligodendrocytes and axons directly, impairs axonal transport, and triggers ischemic changes through microvascular compromise. The resulting tissue damage and gliosis create local compliance changes that perpetuate syrinx formation.

Post-Traumatic Syringomyelia (most common, 50-80% of cases)

• Occurs at any time after spinal cord injury, from months to decades later
• Risk increases with severity of initial injury, complete spinal cord lesions, and incomplete recovery
• Mechanism involves CSF flow obstruction by post-traumatic scar tissue and tethering

Chiari Malformation Type I (15-20% of cases)

• Tonsillar herniation through foramen magnum creates flow obstruction
• More symptomatic with larger tonsillar descent (>5-10 mm) or associated syrinx
• Syrinx typically located rostral to the malformation

Tethered Spinal Cord

• Filum terminale tightness, lipoma, or scar adhesions prevent normal cord excursion
• Progressive stretching during growth or aging creates mechanical disruption

Spinal Cord Tumors (10-15% of cases)

• Both intramedullary (ependymoma, hemangioblastoma, astrocytoma) and extramedullary tumors cause syrinx
• Mechanisms include cord expansion, CSF obstruction, and peritumoral edema

Arachnoiditis

• Post-infectious (tuberculosis, syphilis), post-traumatic, or idiopathic
• Adhesions and scarring impair CSF flow

Spinal Cord Tethering Syndromes

• Lipomyelomeningocele, dermal sinus tract, spina bifida
• Dural insufficiency, Ehlers-Danlos syndrome

Other Causes

• Spinal stenosis with myelopathy
• Syrinx associated with Klippel-Feil syndrome
• Idiopathic (10-20% of cases) with unclear etiology

Risk Factors for Progression

• Large syrinx diameter (>5 mm)
• Rostral location
• Young age at onset
• Presence of cord tethering
• Incomplete spinal cord injury

Cardinal Symptoms

• Neuropathic pain (>70% of patients): burning, aching pain in neck, shoulders, or extremities; often precedes motor deficits by months or years
• Progressive myelopathy: weakness, numbness, and loss of fine motor control
• Weakness: typically begins distally and progresses proximally; often asymmetric in traumatic syringomyelia
• Sensory loss: pain and temperature sensation affected before proprioception due to spinothalamic tract involvement

Characteristic Physical Examination Findings

• Suspended sensory level: loss of pain and temperature sensation in a Cape-like distribution across shoulders, arms, and upper back (classic for intramedullary pathology affecting crossing spinothalamic fibers before they decussate)
• Dissociated sensory loss: selective loss of pain and temperature with preserved light touch and proprioception (indicating central cord gray matter involvement)
• Lower motor neuron findings at syrinx level: atrophy and fasciculations in affected myotomes
• Upper motor neuron findings below the syrinx: hyperreflexia, spasticity, Babinski sign
• Horner syndrome: if syrinx involves C8-T1 segments
• Nystagmus and ataxia: if syrinx extends into brainstem (syringobulbia)

Additional Features

• Charcot arthropathy of joints distal to sensory loss (painless joint destruction)
• Trophic changes: nail dystrophy, ulceration in denervated areas
• Postural changes and scoliosis (from asymmetric weakness)
• Neurogenic pain that may be severe and treatment-refractory

Imaging (Gold Standard)

Spinal MRI with and without Gadolinium

• T1-weighted: syrinx appears as isointense to hypointense cavity within spinal cord
• T2-weighted: syrinx appears as hyperintense (CSF signal intensity), best for visualization and measurement
• Syrinx diameter measured on axial images; >5 mm generally considered significant
• Identify underlying etiology: Chiari malformation, cord tethering, tumor, cord compression, arachnoiditis
• Gadolinium may enhance cord parenchyma surrounding syrinx or show enhancement of underlying tumor
• Serial imaging determines progression: increase in syrinx length or diameter indicates need for intervention

Additional Imaging

• Brain MRI: evaluate for Chiari malformation, posterior fossa pathology
• Flexion/extension cervical spine MRI: assess for instability, tethering dynamics
• CT myelography: useful when MRI contraindicated; can show adhesions, cord tethering
• X-ray spine: assess for traumatic changes, deformity, instability

Laboratory Studies

• Cerebrospinal fluid analysis: elevated protein, pleocytosis if infectious/inflammatory cause
• Serology: RPR/VDRL (syphilis), ACE level, TB testing if arachnoiditis suspected
• Genetic testing: if syndromic features (e.g., Ehlers-Danlos, connective tissue disorder)

Electrodiagnostic Testing

• EMG/NCS: documents motor unit changes; lower motor neuron pattern with denervation in affected myotomes; may show conduction slowing if cord compression coexists
• Somatosensory evoked potentials (SSEPs): may show slowed or absent response below syrinx; reduced amplitude
• Motor evoked potentials (MEPs): helps assess functional integrity of corticospinal tract

Diagnostic Criteria

• Radiographic evidence of intramedullary cavity on MRI
• Clinical symptoms and signs consistent with cord dysfunction
• Exclusion of mimics: cord edema without cavitation alone does not constitute syringomyelia

Treatment Strategy Depends on Etiology and Progression

First-Line Management: Treat Underlying Cause

• Chiari malformation: Suboccipital decompression with possible duraplasty; indicated if symptomatic syrinx or progressive neurological deficit; goal is to restore normal CSF flow
• Tethered spinal cord: Surgical untethering (division of filum terminale, removal of lipoma, or lysis of adhesions); prevents progressive traction and syrinx expansion
• Spinal cord tumor: Gross total resection when feasible; may lead to syrinx regression
• Spinal cord compression/stenosis: Decompressive laminectomy with fusion if unstable; restores CSF flow
• Post-traumatic syringomyelia: Syrinx stabilization may follow treatment of associated cord tethering or deformity; some centers advocate for early decompression/stabilization of initial injury

Pharmacological Management

• Gabapentin or pregabalin: first-line for neuropathic pain (300-3600 mg/day in divided doses); mechanism is calcium channel modulation reducing neuronal excitability
• Duloxetine or venlafaxine: serotonin-norepinephrine reuptake inhibitors for neuropathic pain; also address mood symptoms
• Topical lidocaine patches or capsaicin cream: localized pain management
• Baclofen or tizanidine: for spasticity management (starting doses 5 mg TID, titrate as tolerated)
• Avoid NSAIDs and opioids as monotherapy: limited efficacy for neuropathic pain and risk of medication overuse
• Intrathecal baclofen: for severe, refractory spasticity; requires programmable pump

Non-Pharmacological Measures

• Physical therapy and occupational therapy: maintain strength, improve function, prevent contractures
• Assistive devices: bracing for instability, mobility aids as weakness progresses
• Skin care and pressure relief: prevent ulceration and Charcot joint changes
• Thermal protection: educate patients on avoiding temperature extremes given sensory loss
• Pain management programs: multidisciplinary approach including psychological support for chronic neuropathic pain

Surgical Intervention Indications

• Progressive neurological deficit despite observation
• Syrinx expansion on serial imaging (>2 mm increase or length increase)
• Intractable pain refractory to medical management
• Underlying surgically correctable cause (Chiari, tethering, tumor)
• Neurological function >2 years post-injury declining

Monitoring and Follow-Up

• Clinical assessment: Document strength, sensation, and pain severity regularly; establish baseline functional status
• Serial imaging: MRI every 6-12 months for first 2 years, then annually if stable; more frequent if progressive
• Neurophysiologic monitoring: SSEPs/MEPs to detect subclinical progression
• Symptom tracking: pain scales, functional outcome measures (ASIA Impairment Scale for spinal injury patients)

Progressive Neurological Deterioration

• Worsening weakness and paralysis from expanding syrinx
• Loss of sensory function with risk of unrecognized injury and infection
• Management: escalate to surgical intervention if progressive and not already done

Charcot Arthropathy (Neuropathic Joint Disease)

• Develops in denervated joints due to repeated trauma with loss of protective pain sensation
• Affects shoulders, elbows, wrists, and knees; characterized by progressive joint destruction, osteophyte formation, and subluxation
• Management: joint protection with bracing, activity modification; surgical arthrodesis if severely compromised

Trophic Changes and Pressure Ulcers

• Skin ulceration, nail dystrophy, and tissue necrosis in areas of sensory loss
• Risk of secondary infection, osteomyelitis, and sepsis
• Management: aggressive skin care, pressure relief, infection prevention and treatment

Spasticity

• Hypertonicity with flexor/extensor spasms causing functional impairment
• Management: stretching, physical therapy, baclofen, tizanidine, botulinum toxin, or intrathecal baclofen pump

Chronic Neuropathic Pain

• Severe, burning pain refractory to standard analgesics
• Can severely impact quality of life and psychosocial function
• Management: multimodal therapy with neuropathic agents, pain psychology, interventional pain procedures (epidural injections, cord stimulation)

Syringobulbia

• Extension of syrinx into brainstem causing bulbar dysfunction
• Results in dysarthria, dysphagia, nystagmus, ataxia, and vocal cord paralysis
• Management: addresses underlying cause; supportive care for aspiration risk

Respiratory Failure (High-Mortality Complication)

• High cervical syrinx (C1-C4) extending into brainstem or affecting phrenic nerve nuclei
• Results in hypoventilation, sleep apnea, and reduced respiratory reserve
• Management: aggressive surgical intervention if progressive; non-invasive positive pressure ventilation; monitoring for sleep-disordered breathing

Syrinx Hemorrhage

• Intramedullary hemorrhage within syrinx cavity (rare but acute complication)
• Presents with acute neurological deterioration, severe pain
• Management: emergent imaging, neurosurgical consultation; may require acute decompression

Syrinx Rupture and Arachnoiditis

• Communication between syrinx and subarachnoid space
• Can cause acute spinal cord swelling and neurological decline
• Management: identify cause; may require surgical intervention

Natural History and Progression

• Approximately 50% of syrinxes remain stable on imaging, while 30-50% progress
• Progressive syringomyelia: average expansion rate ~1-2 mm per year
• Progression more common in young patients and those with large initial syrinx diameter
• Symptoms often precede radiographic changes by months to years
• Neuropathic pain may improve or stabilize while motor deficits continue to progress

Prognostic Factors Associated with Better Outcomes

• Identification and treatment of underlying cause: post-Chiari decompression success rate 60-80% for pain, 40-60% for motor deficits
• Early intervention before significant neurological loss: functional recovery better if intervention occurs within 1-2 years of symptom onset
• Stable small syrinx (<5 mm) without progression: observation alone may be safe in asymptomatic patients
• Good baseline neurological function

Prognostic Factors Associated with Worse Outcomes

• Large syrinx diameter (>5-10 mm): associated with progressive neurological deficit
• Young age at onset: longer lifetime for progressive deterioration
• Rapid syrinx expansion: indicates aggressive underlying pathology
• Long-standing syrinx: risk of permanent axonal loss and irreversible deficits
• Severe initial neurological deficit: limited potential for recovery
• Incomplete post-traumatic spinal cord injury: syrinx formation more likely than in complete injuries

Functional Outcomes

• Many patients achieve functional stability if syrinx arrest achieved surgically
• Motor deficits often permanent and not fully reversible even after successful surgery
• Neuropathic pain shows variable response to treatment, may persist despite syrinx stabilization
• Quality of life significantly affected by pain and progressive disability
• Return to work and activities limited by weakness and pain severity

Most Important Facts

• Syringomyelia is a sign, not a diagnosis: always search for underlying etiology (Chiari malformation, tethered cord, tumor, trauma, arachnoiditis)
• Post-traumatic syringomyelia is the most common form: occurs months to decades after initial spinal cord injury; progressive deterioration years post-injury should raise suspicion
• Suspended sensory loss (cape-like distribution) is pathognomonic: indicates central cord pathology with selective spinothalamic tract involvement

Classic Board Buzzwords and Associations

• "Syrinx + Chiari": most common symptomatic association; suboccipital decompression is treatment of choice
• "Charcot joint": painless joint destruction from chronic sensory loss; classic complication requiring recognition
• "Neuropathic pain preceding motor deficits": cardinal symptom that often brings patient to attention before significant weakness

Common Clinical Traps and Pitfalls

• **Confusing cord