THORACIC DISC HERNIATION
Rare | T8-T12 Common | Cord at Risk | Anterior Approach Preferred
ANATOMICAL CLASSIFICATION
Critical Must-Knows
- Rare pathology - only 0.5-1% of all symptomatic disc herniations
- Lower thoracic predominance - 75% occur at T8-T12 where relatively more motion
- Myelopathy is primary concern - narrow canal, cord cannot be retracted
- Posterior laminectomy CONTRAINDICATED for central discs - high paraplegia risk
- Anterior/anterolateral approaches - transthoracic, costotransversectomy, thoracoscopic
- Artery of Adamkiewicz at T9-L2 (usually left) - major blood supply to cord
Examiner's Pearls
- "40-70% of thoracic discs are calcified (complicates surgical removal)
- "Central disc from posterior = catastrophic cord injury
- "Many thoracic discs asymptomatic (incidental MRI findings)
- "Transthoracic approach provides best visualization but requires thoracotomy
High-Yield Thoracic Disc Exam Points
Why Posterior is Contraindicated
Thoracic spinal cord CANNOT be safely retracted. The canal is narrow with limited CSF space. Attempting to access a central disc posteriorly requires cord manipulation - this causes irreversible paraplegia. This is the most important exam point.
Artery of Adamkiewicz
The major radicular artery (arteria radicularis magna) supplying the lower two-thirds of the spinal cord. Located T9-L2 in 80%, predominantly left side (75-80%). Damage causes anterior spinal artery syndrome and paraplegia.
Approach Selection
Central disc: Transthoracic, thoracoscopic, or costotransversectomy. Centrolateral: Anterior or posterolateral. Lateral: Transpedicular or lateral extracavitary. Location determines approach.
Calcification Challenge
40-70% of thoracic discs are calcified (increases with age). Calcified discs are harder to remove surgically (like concrete). Requires high-speed burr. CT essential for surgical planning. Increases cord injury risk.
THORACICTHORACIC - Why Central Discs Need Anterior Approach
Memory Hook:THORACIC reminds you why posterior approach to central disc = paraplegia
APPROACHESAPPROACHES - Surgical Approach Selection
Memory Hook:APPROACHES covers all surgical options and critical technical points
T8-T12T8-T12 - Most Common Levels
Memory Hook:T8-T12 is the zone - lower thoracic has relatively more motion than upper
Overview and Epidemiology
Thoracic disc herniation is a rare spinal pathology accounting for only 0.5-1% of all symptomatic disc herniations. [1] The thoracic spine's inherent stability from rib cage articulation protects the discs from the degenerative changes commonly seen in cervical and lumbar regions. However, when thoracic disc herniations do occur, they pose unique diagnostic and therapeutic challenges due to the narrow spinal canal and proximity to the spinal cord.
Historical Context:
- First surgical treatment described by Mixter and Barr in 1934
- Early posterior approaches resulted in high rates of neurological deterioration (up to 33%) [2]
- Modern era defined by anterior and anterolateral approaches pioneered in 1960s-1980s
- Current outcomes significantly improved with proper approach selection
Geographic and Demographic Distribution:
- Incidence: Estimated 1 per 1,000,000 population annually [1]
- Age: Peak presentation in 4th-6th decades (40-60 years)
- Gender: Slight male predominance (male:female ratio approximately 1.5:1)
- Level distribution: 75% occur at T8-T12 (lower thoracic), 25% at T1-T7 (upper/mid thoracic)
Why Lower Thoracic?
The lower thoracic spine experiences relatively more motion than the upper thoracic due to:
- Transitional anatomy approaching thoracolumbar junction
- Reduced rib cage constraint
- Mechanical stress concentration at kyphosis-lordosis transition
- Greater axial loading compared to upper thoracic
Asymptomatic Disc Herniations
Studies using MRI screening of asymptomatic individuals found thoracic disc abnormalities in 37% of subjects under 40 years and 73% over 40 years. [3] Not all thoracic disc herniations are symptomatic or require treatment. Clinical correlation is essential.
Associated Conditions:
- Scheuermann's disease - may predispose to thoracic disc degeneration
- Ankylosing spondylitis - increased fracture risk but also disc disease
- Degenerative scoliosis - asymmetric loading patterns
- Trauma - acute disc herniation rare but possible with high-energy mechanism
Anatomy and Biomechanics
Thoracic Spinal Canal Anatomy:
The thoracic spinal canal is the narrowest region of the vertebral column:
- Spinal cord fills 40-50% of canal (cervical: 25%, lumbar: cauda equina)
- Limited CSF space dorsally - cord is close to posterior elements
- Canal diameter: 12-14mm at T5-T8 (narrowest point)
- Cord diameter: 8-10mm in thoracic region
Why Cord Cannot Be Retracted
In the cervical spine, the cord occupies only 25% of the canal with ample CSF allowing safe posterior retraction. In the thoracic spine, the cord occupies 40-50% of the canal with minimal CSF dorsally. Attempting to retract the cord posteriorly causes direct mechanical injury and vascular compromise leading to irreversible paraplegia. This is the fundamental reason posterior laminectomy is contraindicated for central thoracic discs.
Vascular Anatomy - Artery of Adamkiewicz:
The arteria radicularis magna (artery of Adamkiewicz) is the largest anterior segmental medullary artery supplying the lower two-thirds of the spinal cord via the anterior spinal artery. [4]
| Feature | Details |
|---|---|
| Location | T9-L2 in 80% of population (range T5-L4) |
| Side | Left side in 75-80% of cases |
| Most common level | T9-T11 |
| Supply | Lower thoracic and lumbosacral cord segments |
| Clinical significance | Injury causes anterior spinal artery syndrome (paraplegia, loss of pain/temperature, preserved proprioception) |
Adamkiewicz Critical Points for Viva
Examiner: "What is the artery of Adamkiewicz and why is it important in thoracic surgery?"
Answer: "The artery of Adamkiewicz is the major anterior radicular artery supplying the lower two-thirds of the spinal cord. It's located at T9-L2 in 80% of individuals, more commonly on the left side. During thoracic surgery, especially at these levels, we must be careful with segmental vessel ligation as damaging this artery causes anterior spinal artery syndrome with paraplegia and loss of pain and temperature sensation below the lesion. Some surgeons obtain preoperative CT angiography to identify it, though this is not routine."
Thoracic Disc Anatomy:
Thoracic intervertebral discs are:
- Thinner than lumbar discs (height 5-7mm vs 10-12mm lumbar)
- Less mobile due to rib cage constraints
- More prone to calcification with age (40-70% of symptomatic herniations are calcified) [5]
- Smaller nucleus pulposus relative to annulus compared to lumbar
Biomechanical Considerations:
The thoracic spine is stabilized by:
- Rib cage articulations (costovertebral and costotransverse joints)
- Longer spinous processes (shingled arrangement)
- Coronal plane facet orientation (limits rotation, allows lateral flexion)
- Thoracic kyphosis (anterior column loading)
Relatively less motion in upper/mid thoracic (2-4 degrees per level) increases at thoracolumbar junction (6-8 degrees at T11-T12).
Pathophysiology
Mechanisms of Disc Herniation:
Unlike lumbar discs where extrusion through posterior annulus is common, thoracic disc pathology has distinct features:
- Central herniation - nucleus migrates posteriorly compressing cord centrally
- Posterolateral herniation - most common pattern (60-70%), may cause myelopathy or radiculopathy
- Lateral/foraminal - pure radiculopathy without myelopathy (15-20%)
- Giant herniation - rare, extensive canal compromise
Calcification Pathophysiology:
Thoracic discs undergo dystrophic calcification more frequently than cervical or lumbar discs due to:
- Lower metabolic activity and vascularity in thoracic discs
- Chronic mechanical stress with minimal motion (repetitive microtrauma)
- Age-related degenerative changes with calcium deposition in nucleus and annulus
- Scheuermann's disease association (endplate irregularities promote degeneration)
Clinical Significance of Calcification
Calcified thoracic discs:
- Identified on CT scan (essential preoperative imaging)
- Behave like bone during surgery - cannot be removed with rongeurs or curettes
- Require high-speed burr for safe removal (diamond burr reduces heat)
- Increased risk of dural tear and cord injury during removal
- May cause acute traumatic herniation (calcified disc acts as missile with high-energy trauma)
Cord Compression Pathomechanics:
Thoracic disc herniation causes myelopathy through:
- Direct mechanical compression - cord flattened against posterior canal
- Vascular compromise - compression of anterior spinal artery or radicular arteries
- Cord edema - seen as T2 hyperintensity on MRI (reversible in early stages)
- Myelomalacia - chronic compression leads to cord necrosis (irreversible)
Difference from Cervical and Lumbar:
| Feature | Cervical | Thoracic | Lumbar |
|---|---|---|---|
| Neural structure | Cord with space | Cord (tight fit) | Cauda equina (nerve roots) |
| Compression tolerance | Moderate (CSF buffer) | Poor (no buffer) | Good (roots mobile) |
| Posterior approach | Often safe | CONTRAINDICATED | Standard approach |
| Calcification rate | 10-20% | 40-70% | 5-10% |
Classification Systems
Anatomical Location Classification (most clinically relevant)
This classification determines surgical approach selection:
Anatomical Location and Approach Selection
| Location | Definition | Frequency | Clinical Features | Preferred Approach |
|---|---|---|---|---|
| Central | Midline, posterior central canal | 20-30% | Myelopathy, bilateral findings, no radiculopathy | Anterior only (transthoracic, thoracoscopic) |
| Centrolateral | Paracentral, eccentric | 60-70% | Myelopathy plus radiculopathy, most common | Anterior or posterolateral |
| Lateral/Foraminal | Far lateral, in or beyond foramen | 10-15% | Radiculopathy only, no myelopathy | Posterolateral safe (transpedicular, lateral extracavitary) |
This classification is critical for determining surgical approach and predicting outcomes.
Clinical Presentation
Symptom Patterns:
Thoracic disc herniation presents with three main clinical syndromes:
1. Myelopathy (50-70% of symptomatic cases):
Progressive spinal cord compression causes:
- Lower extremity weakness - UMN pattern (spasticity, hyperreflexia)
- Gait dysfunction - spastic, wide-based, scissoring gait
- Sensory level - at or below level of herniation
- Bowel/bladder dysfunction - urgency, frequency, retention (late finding)
- Positive Babinski sign - UMN lesion
- Hyperreflexia - below level of lesion
- Loss of abdominal reflexes - at level of compression
Brown-Séquard Syndrome
Lateral thoracic disc herniations may cause Brown-Séquard syndrome (hemicord syndrome):
- Ipsilateral: Motor weakness (corticospinal tract), loss of proprioception and vibration (dorsal columns)
- Contralateral: Loss of pain and temperature (spinothalamic tract crosses) This is classic exam material for thoracic spine pathology.
2. Radiculopathy (25-40%):
Thoracic radicular pain has unique features:
- Band-like pain around chest or abdomen following intercostal nerve distribution
- Mimics visceral pathology - cardiac (chest pain), abdominal (pancreatitis, cholecystitis)
- Worse with cough, sneeze, Valsalva - increased intraspinal pressure
- No classic dermatomal pattern - thoracic dermatomes less distinct than limb dermatomes
- May have sensory changes in thoracic dermatome (hypesthesia or hyperesthesia)
3. Axial Pain Alone (10-20%):
- Chronic midline thoracic back pain
- Mechanical pattern (worse with activity, better with rest)
- May be the only symptom for years
- Often leads to delayed diagnosis
Natural History:
Without treatment:
- 25-50% progress to more severe myelopathy [6]
- Gradual worsening over months to years (slow progression)
- Acute deterioration rare but possible (especially traumatic herniation)
- Spontaneous improvement uncommon once myelopathy develops
Physical Examination:
Motor Examination:
- Lower extremity strength testing (hip flexion, knee extension, ankle dorsi/plantarflexion)
- Spasticity assessment (increased tone, clonus)
- Gait evaluation (spastic, ataxic patterns)
Sensory Examination:
- Pinprick and light touch to identify sensory level
- Proprioception and vibration (dorsal column function)
- Temperature sensation (often lost with pain in spinothalamic dysfunction)
Reflex Examination:
- Lower extremity reflexes (hyperreflexia below lesion)
- Pathological reflexes (Babinski, Hoffman's if cervical involvement)
- Abdominal reflexes (T8-T12 - may be absent at level of lesion)
This completes the neurological examination findings.
Investigations
Imaging Modalities:
MRI - Diagnostic Modality of Choice:
| Sequence | Purpose | Key Findings |
|---|---|---|
| T2-weighted sagittal | Assess cord signal, CSF, disc | Disc appears dark, cord compression visible, T2 hyperintensity in cord indicates edema/myelomalacia |
| T2-weighted axial | Determine herniation location | Central vs centrolateral vs lateral classification |
| T1-weighted | Anatomical detail | Disc-cord relationship, vertebral body marrow |
| T1 post-contrast | Rule out tumor, infection | Enhancement suggests neoplasm or infection vs bland disc |
MRI Findings:
- Disc herniation - posterior disc protrusion or extrusion
- Cord compression - flattening or displacement of spinal cord
- Cord signal change - T2 hyperintensity indicates edema (reversible) or myelomalacia (irreversible)
- Location - central, centrolateral, or lateral
- Levels involved - single or multiple
T2 Hyperintensity Prognostic Value
Cord signal change on T2-weighted MRI has prognostic significance:
- No signal change - better surgical outcomes, more reversible compression
- Faint/mild hyperintensity - cord edema, still potentially reversible
- Intense hyperintensity - myelomalacia (cord necrosis), poor prognosis, likely permanent deficit
This helps counsel patients on expected recovery and surgical urgency.
CT Scan - Essential for Surgical Planning:
Indications:
- All operative candidates - assess for calcification
- MRI contraindicated - pacemaker, claustrophobia
- CT myelography - if MRI not available (water-soluble contrast via lumbar puncture)
CT Findings:
- Disc calcification - appears as high-density material (40-70% of cases)
- Bony anatomy - pedicle size for transpedicular approach
- Ossification - OPLL vs calcified disc
- Extent of calcification - plan for burr use vs rongeur removal
Plain Radiographs:
Limited value but may show:
- Disc space narrowing at affected level
- Calcified disc - visible on lateral radiograph (pathognomonic when present)
- Scheuermann's changes - irregular endplates, Schmorl's nodes
- Overall alignment - kyphosis, scoliosis
Not diagnostic but may raise suspicion in appropriate clinical context.
Electrodiagnostic Studies:
Somatosensory Evoked Potentials (SSEPs):
- Baseline - establish preoperative cord function
- Intraoperative monitoring - detect cord ischemia during surgery
Motor Evoked Potentials (MEPs):
- More sensitive than SSEPs for detecting motor pathway injury
- Used during thoracic discectomy to guide safe decompression
EMG/NCS:
- Limited role in thoracic radiculopathy (intercostal muscles difficult to study)
- May help exclude peripheral nerve lesions
Differential Diagnosis Investigations:
Consider other causes of thoracic myelopathy:
- Tumor - MRI with contrast (enhancement)
- Infection - inflammatory markers (CRP, ESR), blood cultures, MRI
- Demyelination - brain MRI, CSF analysis
- Vascular - dural arteriovenous fistula (spinal angiography)
- Metabolic - B12, copper, vitamin E levels
Management
Conservative Management:
Indications:
- Mild radiculopathy without motor weakness
- Axial pain only (no neurological deficit)
- Asymptomatic incidental finding
- Medical comorbidities precluding surgery
- Patient preference after informed discussion
Treatment Protocol:
- Analgesia: NSAIDs, acetaminophen, neuropathic pain agents (gabapentin, pregabalin)
- Activity modification: Avoid provocative activities, ergonomic adjustments
- Physical therapy: Core strengthening, posture training (limited role in thoracic disc)
- Monitoring: Serial neurological examinations, MRI if worsening
Success Rate: 30-50% of patients with mild symptoms improve with conservative care [7]
When to Abandon Conservative Treatment:
- Development of myelopathy
- Progressive motor weakness
- Bowel/bladder dysfunction
- Intractable pain despite optimal management
Myelopathy is NOT a Conservative Diagnosis
Progressive myelopathy from thoracic disc herniation is a surgical indication. Unlike cervical myelopathy where some mild cases may stabilize, thoracic myelopathy has a narrow canal with less compensatory capacity. Delaying surgery risks irreversible cord damage. Do not attempt prolonged conservative management in the presence of myelopathy.
Surgical Approaches
Indications:
- Central or centrolateral disc herniation
- Best visualization of disc-cord interface
- Gold standard for calcified central discs
Approach:
- Position: Lateral decubitus, affected side up
- Incision: Posterolateral thoracotomy at rib level corresponding to disc (e.g., 9th rib for T8-T9 disc)
- Single lung ventilation: Deflate ipsilateral lung for exposure
- Rib resection: Remove rib, divide intercostal muscles
- Pleural entry: Enter pleural cavity, pack lung anteriorly
- Identify level: Count ribs, confirm with intraoperative radiograph
- Expose vertebral bodies: Dissect parietal pleura, identify disc space
- Segmental vessels: Ligate at disc level (beware Adamkiewicz)
- Discectomy: Remove disc anterior and posterior longitudinal ligament
- Decompress cord: Remove all herniated material, ensure cord decompression
- Fusion: Consider corpectomy and cage if extensive removal (optional)
- Closure: Chest tube, layer closure
Advantages:
- Excellent visualization
- Direct access to disc without cord manipulation
- Can remove calcified disc safely
Disadvantages:
- Requires thoracotomy (post-thoracotomy pain)
- Single lung ventilation (pulmonary complications)
- May need cardiothoracic surgery assistance
- Longer hospital stay
This completes the transthoracic approach description.
Surgical Pearls:
Managing Calcified Disc
Calcified thoracic disc removal:
- Use high-speed diamond burr (reduces heat compared to cutting burr)
- Thin posterior shell of calcified disc first (like eggshell)
- Micro-rongeurs to remove fragments through thin shell
- Avoid levering against cord - this causes direct injury
- Copious irrigation during burring to reduce heat
- Monitor SSEPs/MEPs throughout to detect early cord ischemia
Intraoperative Neuromonitoring:
All thoracic disc surgeries should have:
- SSEPs - baseline and continuous monitoring
- MEPs - more sensitive for motor pathway
- Alarm criteria: 50% amplitude decrease or 10% latency increase
- Response to changes: Stop manipulation, increase MAP, consider aborting
Complications
Surgical Complications:
Approach-Specific Complications
| Complication | Transthoracic | Thoracoscopic | Costotransversectomy |
|---|---|---|---|
| Neurological deterioration | 5-10% | 5-8% | 10-15% |
| Pulmonary complications | 15-20% | 10-15% | Less than 5% |
| CSF leak/dural tear | 5-10% | 5-8% | Less than 5% |
| Vascular injury | 2-5% | 2-4% | Less than 2% |
| Post-thoracotomy pain | 20-30% | 10-15% | 5-10% |
Major Complications:
1. Neurological Deterioration (5-15%):
- Paraplegia - most feared complication
- Worsening myelopathy - cord manipulation or ischemia
- Mechanisms: Direct cord injury, vascular injury (Adamkiewicz), spinal cord ischemia
- Prevention: Avoid cord retraction, neuromonitoring, gentle technique, anterior approach for central disc
- Management: High-dose steroids controversial, supportive care, rehabilitation
2. Pulmonary Complications (10-20% with thoracotomy):
- Pneumothorax - inadequate chest tube drainage
- Pleural effusion - post-thoracotomy inflammation
- Pneumonia - single lung ventilation, atelectasis
- Prolonged air leak - pleural space issues
- Prevention: Chest physiotherapy, incentive spirometry, adequate chest tube management
- Management: Chest tube management, antibiotics if pneumonia, supportive care
3. CSF Leak and Dural Tear (5-10%):
- Incidental durotomy - especially with calcified disc removal
- CSF fistula - persistent leak through wound
- Pseudomeningocele - CSF collection
- Prevention: Careful dural dissection, burr away from dura
- Management: Primary repair if identified, oversew with 6-0 Prolene, consider lumbar drain if persistent, revision surgery if pseudomeningocele symptomatic
4. Vascular Injury (2-5%):
- Artery of Adamkiewicz - anterior spinal artery syndrome (paraplegia)
- Segmental arteries - bleeding, cord ischemia
- Aorta - rare but catastrophic (anterior approaches)
- Prevention: Identify Adamkiewicz preoperatively (CT angiography), careful vessel ligation, maintain MAP during surgery
- Management: Control bleeding, vascular surgery consultation if major vessel, supportive care for cord ischemia
Post-Thoracotomy Pain Syndrome
Chronic post-thoracotomy pain affects 20-30% of patients after open transthoracic approach. This is intercostal neuralgia from rib retraction and nerve injury. It can be severe and persistent, affecting quality of life. Counsel patients preoperatively. Consider thoracoscopic approach to reduce this risk. Manage with neuropathic pain medications, nerve blocks, and pain clinic referral if severe.
Minor Complications:
- Wound infection (2-5%) - superficial or deep, antibiotics or debridement
- Seroma - fluid collection, usually self-limiting
- Intercostal neuralgia - rib retraction injury, chronic pain
- Horner's syndrome - sympathetic chain injury (upper thoracic), ptosis/miosis/anhidrosis
- Chylothorax - thoracic duct injury (left-sided approaches above T6), milky chest tube output, conservative management or ligation
Complications of Non-Operative Management:
- Progressive myelopathy (25-50%) - delayed surgery may have worse outcomes
- Irreversible cord damage - myelomalacia from prolonged compression
- Chronic pain - persistent radiculopathy or axial pain
- Functional decline - loss of ambulation, wheelchair dependence
Postoperative Care and Outcomes
Immediate Postoperative Management:
Rehabilitation Protocol:
Phase 1 (Weeks 0-6):
- Goals: Pain control, wound healing, basic mobility
- Activities: Walking, gentle range of motion, respiratory exercises
- Restrictions: No lifting over 5kg, no twisting, no strenuous activity
Phase 2 (Weeks 6-12):
- Goals: Restore function, improve strength
- Activities: Progressive resistance training, core strengthening, balance
- Restrictions: Gradual increase in lifting, avoid high-impact activities
Phase 3 (Weeks 12+):
- Goals: Return to full activities, work, sports
- Activities: Sport-specific training, unrestricted activities as tolerated
- Monitoring: Serial neurological examinations, functional outcome measures
Outcome Measures:
| Measure | Description | Use |
|---|---|---|
| mJOA score | Modified Japanese Orthopaedic Association (0-11) | Myelopathy severity and improvement |
| Nurick Grade | 0-5 scale of myelopathy | Simple grading system |
| VAS | Visual Analog Scale for pain (0-10) | Pain assessment |
| ODI | Oswestry Disability Index | Functional limitation |
| SF-36 | Quality of life measure | General health status |
Surgical Outcomes:
Based on systematic reviews and case series [9,10]:
Neurological Improvement:
- 60-80% improve or stabilize after surgery
- 15-20% no change
- 5-10% worsen (neurological deterioration)
Factors Associated with Better Outcomes:
- Shorter duration of symptoms (less than 12 months better than over 24 months)
- No preoperative T2 signal change on MRI (myelomalacia predicts poor recovery)
- Younger age (under 60 years better outcomes)
- Soft disc (calcified discs more difficult, higher complication rate)
- Lateral location (central discs more challenging, worse outcomes)
Factors Associated with Worse Outcomes:
- Long-standing myelopathy (over 24 months)
- Severe preoperative deficits (non-ambulatory, Nurick grade 4-5)
- Cord signal change (myelomalacia on MRI)
- Older age (over 70 years)
- Multiple medical comorbidities
Recovery Timeline
Neurological recovery after thoracic discectomy:
- Immediate - decompression relieves mechanical pressure
- Weeks to months - cord edema resolves, early motor return
- 6-12 months - continued improvement (cord remyelination)
- 12-18 months - plateau of recovery
Counsel patients that maximum recovery takes 12-18 months. Early postoperative neurological status may not reflect final outcome. Continue therapy and rehabilitation throughout recovery period.
Return to Activities:
- Desk work: 6-8 weeks (sooner if minimally invasive approach)
- Manual labor: 12-16 weeks
- Contact sports: 6 months (after full recovery and rehabilitation)
- Driving: 4-6 weeks (when off narcotics and able to perform emergency stop)
Evidence Base
- Historical series of 38 thoracic disc herniations
- Posterior laminectomy resulted in 33% neurological deterioration
- Anterior and anterolateral approaches superior outcomes
- Established that posterior approach contraindicated for central discs
- Large series of 100 thoracic discectomies
- Transthoracic and costotransversectomy approaches compared
- Transthoracic better for central, costotransversectomy for lateral
- 70% good to excellent outcomes with appropriate approach selection
- Review of surgical approaches to thoracic disc
- Thoracoscopic outcomes comparable to open transthoracic
- Less morbidity with minimally invasive approaches
- Steep learning curve for thoracoscopic technique
- Systematic review of thoracic discectomy outcomes
- Overall neurological improvement in 60-80% of patients
- Calcified discs associated with higher complication rates
- Preoperative myelomalacia (T2 signal) predicts poor recovery
Current Controversies:
1. Calcified Disc Management:
- Some advocate leaving small calcified fragments vs complete removal
- Risk of incomplete decompression vs risk of cord injury during aggressive removal
- No high-quality comparative data
2. Fusion After Discectomy:
- Some surgeons perform fusion after extensive discectomy or corpectomy
- Others perform discectomy alone without fusion
- Thoracic spine stability from rib cage may allow discectomy without fusion
- No RCT data comparing outcomes
3. Asymptomatic Disc Treatment:
- Incidental thoracic disc herniations common on MRI
- No clear consensus on surveillance vs prophylactic surgery
- Generally observe unless developing symptoms
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Central Calcified Thoracic Disc with Myelopathy
"A 55-year-old male presents with 6-month history of progressive lower limb weakness and gait dysfunction. MRI shows a central T10-T11 disc herniation with cord compression and T2 signal change. CT confirms the disc is heavily calcified. How would you manage this patient?"
Scenario 2: Lateral Thoracic Disc with Radiculopathy
"A 45-year-old female presents with 3-month history of band-like chest pain around the left T8 dermatome. No lower limb weakness. MRI shows a lateral T7-T8 disc herniation in the left foramen. How would you manage this?"
Scenario 3: Approach Selection Dilemma
"A 60-year-old patient with significant COPD and FEV1 of 45% predicted has thoracic myelopathy from a centrolateral T9-T10 disc herniation. How do you approach surgical decision-making?"
MCQ Practice Points
Why Posterior is Contraindicated
Q: Why is posterior laminectomy contraindicated for central thoracic disc herniation?
A: The thoracic spinal cord cannot be safely retracted. The thoracic canal is narrow (12-14mm diameter) with the cord occupying 40-50% of the space. There is minimal CSF dorsally. Attempting to access a central disc from behind requires retracting the cord posteriorly, which causes direct mechanical injury and vascular compromise resulting in irreversible paraplegia. In contrast, the cervical canal has more space (cord occupies only 25%) allowing safer posterior retraction. The lumbar spine has nerve roots (cauda equina) which can be retracted. This is the single most important concept in thoracic disc surgery.
Artery of Adamkiewicz
Q: What is the artery of Adamkiewicz and why is it clinically important?
A: The arteria radicularis magna (artery of Adamkiewicz) is the largest anterior segmental medullary artery supplying the lower two-thirds of the spinal cord via the anterior spinal artery. It is located at T9-L2 in 80% of individuals, most commonly at T9-T11, and enters from the left side in 75-80%. Clinically, it's important because injury during thoracic surgery (especially when ligating segmental vessels during transthoracic approach or anterior spinal procedures) can cause anterior spinal artery syndrome with paraplegia, loss of pain and temperature sensation below the lesion, but preservation of proprioception (dorsal columns spared). Some surgeons obtain preoperative CT angiography to identify its location, though this is not routine.
Calcification Assessment
Q: What imaging modality best assesses calcification in thoracic disc herniation and why is this important?
A: CT scan is the best modality for assessing disc calcification. 40-70% of symptomatic thoracic disc herniations are calcified, and this is critical surgical information because calcified discs behave like bone - they cannot be removed with standard rongeurs or curettes. The surgeon must use a high-speed diamond burr to carefully thin the posterior shell of the calcified disc (like an eggshell) and then remove fragments. This increases operative time, difficulty, and risk of dural tear and cord injury. Preoperative knowledge of calcification allows proper surgical planning and patient counseling about increased risks.
T2 Signal Change Prognosis
Q: What is the prognostic significance of T2 hyperintensity in the spinal cord on MRI?
A: T2 hyperintensity (increased signal) in the spinal cord indicates cord edema or myelomalacia:
- Mild/faint hyperintensity suggests cord edema which is potentially reversible with decompression
- Intense hyperintensity suggests myelomalacia (cord necrosis) which is irreversible
- Patients with no T2 signal change have better surgical outcomes
- Patients with myelomalacia have poor recovery potential - many deficits will be permanent despite adequate surgical decompression
This information helps counsel patients about realistic expectations. A patient with severe myelomalacia should understand that surgery prevents further deterioration but may not restore lost function.
Approach Selection Algorithm
Q: How do you select surgical approach for thoracic disc herniation?
A: Location-based algorithm:
- Central disc → Anterior approach mandatory (transthoracic, thoracoscopic) - posterior contraindicated
- Centrolateral disc → Anterior or posterolateral (transthoracic, costotransversectomy) - surgeon preference and patient factors
- Lateral/foraminal disc → Posterolateral acceptable (transpedicular, lateral extracavitary) - no need for thoracotomy
Additional considerations:
- Calcified disc → Anterior approach preferred (better visualization for burr work)
- COPD/pulmonary disease → Favor costotransversectomy or VATS over open thoracotomy
- Surgeon expertise → Thoracoscopic requires specialized training
Australian Context
Thoracic disc herniation surgery is performed at tertiary spine centers in Australia given the rarity of the condition. Expertise is concentrated at quaternary hospitals with neurosurgery and orthopaedic spine services, typically requiring multidisciplinary spine units including cardiothoracic surgery collaboration for transthoracic approaches.
Perioperative antibiotic prophylaxis follows eTG Antibiotic guidelines with cefazolin 2g IV at induction for spine surgery. Neuropathic pain agents including gabapentin and pregabalin are PBS-listed for management of thoracic radiculopathy. DVT prophylaxis with enoxaparin is standard postoperatively.
Australian spinal rehabilitation units provide comprehensive postoperative care including inpatient rehabilitation for patients with significant myelopathy, outpatient physiotherapy, and occupational therapy for return to work. Limited Australian-specific registry data exists for thoracic disc surgery due to rarity, with outcomes generally consistent with international literature showing 60-80% neurological improvement.
THORACIC DISC HERNIATION
High-Yield Exam Summary
Key Epidemiology
- •0.5-1% of all disc herniations (RARE)
- •75% occur at T8-T12 (lower thoracic)
- •Peak age 40-60 years
- •40-70% are calcified (complicates surgery)
Critical Anatomy
- •Narrow thoracic canal (12-14mm diameter)
- •Cord occupies 40-50% of canal (vs 25% cervical)
- •Limited CSF space dorsally
- •Artery of Adamkiewicz at T9-L2 (usually LEFT)
Why Posterior is Contraindicated
- •Cord CANNOT be safely retracted in thoracic spine
- •Historical posterior laminectomy: 33% deterioration
- •Central disc from posterior = PARAPLEGIA
- •Must use anterior or anterolateral approach
Clinical Presentation
- •Myelopathy 50-70%: weakness, spasticity, gait dysfunction
- •Radiculopathy 25-40%: band-like chest/abdominal pain
- •Axial pain 10-20%: chronic thoracic back pain
- •T2 hyperintensity = myelomalacia (poor prognosis)
Investigations
- •MRI: Diagnostic modality of choice
- •CT: Essential for calcification assessment
- •T2 signal change: Edema vs myelomalacia (prognosis)
- •Neuromonitoring: SSEPs and MEPs intraoperatively
Approach Selection
- •CENTRAL: Anterior only (transthoracic, VATS)
- •CENTROLATERAL: Anterior or posterolateral (costotransversectomy)
- •LATERAL: Posterolateral OK (transpedicular)
- •Calcified disc: Anterior preferred (better visualization)
Transthoracic Approach
- •Lateral decubitus, single lung ventilation
- •Rib resection, enter pleural cavity
- •Ligate segmental vessels (beware Adamkiewicz)
- •Direct anterior disc access, burr for calcified disc
Calcified Disc Technique
- •High-speed DIAMOND burr (reduces heat)
- •Thin posterior shell like eggshell
- •Remove fragments through thin shell
- •Copious irrigation, NO levering against cord
Complications
- •Neurological deterioration 5-15% (paraplegia worst)
- •Pulmonary 10-20% (pneumothorax, effusion, pneumonia)
- •CSF leak/dural tear 5-10%
- •Chronic post-thoracotomy pain 20-30%
Outcomes
- •60-80% improve or stabilize
- •Recovery takes 12-18 months (counsel patient)
- •Better if: short duration, no T2 change, younger, soft disc
- •Worse if: long-standing, myelomalacia, older, calcified
Viva Killer Points
- •Posterior laminectomy for central disc = CONTRAINDICATED
- •Why: Cord cannot be retracted (narrow canal)
- •Adamkiewicz: T9-L2, LEFT side, anterior spinal artery supply
- •Calcified disc (40-70%): CT essential, requires burr