Thoracic Disc Herniation

Thoracic disc herniation is rare, accounting for only 0.25-0.75% of all symptomatic disc herniations (Arce and Dohrmann 1985, PMID 3975822). The rib cage makes the thoracic spine inherently stable and protects its discs from the degenerative change common in the cervical and lumbar regions. When a thoracic disc does herniate, the narrow canal and the closeness of the spinal cord make both diagnosis and treatment difficult.

History. Mixter and Barr described the first surgical treatment in 1934. Early posterior decompressive laminectomy gave poor results, only 57% success against over 80% for the posterolateral, lateral and transthoracic approaches (Arce and Dohrmann 1985, PMID 3975822). The anterior and anterolateral approaches pioneered in the 1960s to 1980s define the modern era, and outcomes have improved significantly with proper approach selection.

Who and where. Symptomatic herniations requiring surgery are estimated at about 1 per 1,000,000 population a year (Stillerman et al 1998, PMID 9525706). Presentation peaks in the fourth to sixth decades, with a slight male predominance of about 1.5:1. 75% occur at T8-T12 in the lower thoracic spine and 25% at T1-T7.

Why the lower thoracic spine. The lower thoracic spine moves relatively more than the upper. Its anatomy is transitional as it approaches the thoracolumbar junction, the rib cage constrains it less, mechanical stress concentrates at the change from kyphosis to lordosis, and it carries greater axial load than the upper thoracic spine.

Associated conditions. Four conditions are associated with thoracic disc disease:

• Scheuermann's disease may predispose to thoracic disc degeneration
• Ankylosing spondylitis brings an increased fracture risk but also disc disease
• Degenerative scoliosis produces asymmetric loading
• Trauma can cause an acute herniation, which is rare but possible with a high-energy mechanism

The canal. The thoracic canal is the narrowest region of the vertebral column, 12-14mm in diameter at its narrowest point, T5-T8, around a cord of 8-10mm. The cord fills 40-50% of the canal, against 25% in the cervical spine; the lumbar canal holds the cauda equina. The CSF space dorsally is limited, so the cord lies close to the posterior elements.

The artery of Adamkiewicz. The arteria radicularis magna is the largest anterior segmental medullary artery, supplying the lower two-thirds of the spinal cord through the anterior spinal artery (standard anatomical teaching). Damaging it causes an anterior spinal artery syndrome with paraplegia, so segmental vessels at these levels are ligated with care. Some surgeons obtain preoperative CT angiography to identify it, though this is not routine.

The disc. Thoracic discs are thinner than lumbar discs, 5-7mm high against 10-12mm, less mobile because of the rib cage, and have a smaller nucleus pulposus relative to the annulus. They are more prone to calcification with age: 65% of surgical cases were calcified in Stillerman's series (Stillerman et al 1998, PMID 9525706).

Biomechanics. The thoracic spine is stabilised by:

• The rib cage articulations, costovertebral and costotransverse
• Longer spinous processes in a shingled arrangement
• Coronal facets, which limit rotation and allow lateral flexion
• The kyphosis, which loads the anterior column

Motion is relatively limited in the upper and mid thoracic spine, 2-4 degrees per level, and increases towards the thoracolumbar junction to 6-8 degrees at T11-T12.

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Where the disc goes. A thoracic disc herniates centrally, centrolaterally or laterally into the foramen, and the location decides both the syndrome and the approach (see Classification). A giant herniation is a rare variant with extensive canal compromise.

Calcification. Thoracic disc pathology differs from the lumbar disc, where extrusion through the posterior annulus is common. Thoracic discs undergo dystrophic calcification more often than cervical or lumbar discs; lower metabolic activity and vascularity, chronic mechanical stress with minimal motion (repetitive microtrauma), age-related degeneration with calcium deposited in the nucleus and annulus, and the association with Scheuermann's disease, whose endplate irregularities promote degeneration, are the reasons given.

Why calcification matters. A calcified disc behaves like bone at surgery and cannot be removed with rongeurs or curettes, so it needs a high-speed burr (see Surgical Approaches), and its removal carries an increased risk of dural tear and cord injury. With high-energy trauma a calcified disc may act as a missile and cause an acute traumatic herniation.

How the cord is injured. The disc flattens the cord against the posterior canal by direct mechanical compression, and compresses the anterior spinal or radicular arteries. Cord oedema is reversible in its early stages; chronic compression leads to myelomalacia, necrosis of the cord, which is irreversible.

Compared with the cervical and lumbar spine. The thoracic cord is a tight fit with no CSF buffer, so it tolerates compression worst of the three, and the thoracic disc calcifies most often.

Thoracic disc herniation presents as one of three syndromes: myelopathy, radiculopathy, or axial pain alone.

Myelopathy (50-70% of symptomatic cases). Progressive cord compression produces an upper motor neuron pattern:

• Lower limb weakness with spasticity
• A spastic, wide-based, scissoring gait
• A sensory level at or below the level of the herniation
• Hyperreflexia below the level of the lesion and a positive Babinski sign
• Loss of the abdominal reflexes at the level of compression
• Bowel and bladder dysfunction (urgency, frequency, retention), a late finding

Radiculopathy (25-40%). Thoracic radicular pain is band-like, running around the chest or abdomen in the distribution of the intercostal nerve, and worse with coughing, sneezing and Valsalva, which raise intraspinal pressure. It mimics visceral pathology, cardiac chest pain or abdominal conditions such as pancreatitis and cholecystitis. Thoracic dermatomes are less distinct than limb dermatomes, so there is no classic dermatomal pattern, though there may be hypoaesthesia or hyperaesthesia in the thoracic dermatome.

Axial pain alone (10-20%). Chronic midline thoracic back pain with a mechanical pattern, worse with activity and better with rest. It may be the only symptom for years and often delays the diagnosis.

Natural history. Without treatment, a substantial proportion of established myelopathic cases progress to more severe deficit. Worsening is gradual, over months to years, and acute deterioration is rare but possible, especially with a traumatic herniation. Once myelopathy develops, spontaneous improvement is uncommon.

Examination. The neurological examination finds the level and the tracts involved, the functional assessment sets the baseline against which surgery is judged, and the red flags decide the urgency.

MRI is the diagnostic modality of choice. It shows the herniation, whether protrusion or extrusion; the cord compression, as flattening or displacement of the cord; any cord signal change; whether the disc is central, centrolateral or lateral; and whether one level or several are involved.

CT is essential for surgical planning. It is indicated in all operative candidates to assess calcification, when MRI is contraindicated (pacemaker, claustrophobia), and as CT myelography with water-soluble contrast via lumbar puncture if MRI is not available. It shows calcification as high-density material and its extent, which decides burr against rongeur; pedicle size for a transpedicular approach; and whether ossification is OPLL or calcified disc.

Plain radiographs have limited value and are not diagnostic, but may raise suspicion in the appropriate clinical context. They may show disc space narrowing, a calcified disc on the lateral view (pathognomonic when present), Scheuermann's changes (irregular endplates, Schmorl's nodes) and the overall alignment, kyphosis or scoliosis.

Electrodiagnostics. Somatosensory evoked potentials establish a preoperative baseline of cord function; their use in theatre, with motor evoked potentials, is covered under Surgical Approaches. EMG and nerve conduction studies have a limited role in thoracic radiculopathy, because the intercostal muscles are difficult to study, but may help exclude a peripheral nerve lesion.

Other causes of thoracic myelopathy and pain. Tumour, infection, demyelination and dural arteriovenous fistula are separated by the investigations in the table. For a metabolic cause, check B12, copper and vitamin E levels.

Algorithm

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The decision. Management turns on whether the cord is threatened. Red flags (progressive weakness, myelopathy, bowel or bladder dysfunction) call for an urgent MRI; when it confirms a herniation with myelopathy, a CT for calcification follows, and the approach is chosen by disc location. Radiculopathy or axial pain alone gets a conservative trial of 6-12 weeks, and worsening or developing myelopathy during it means a repeat MRI and reconsideration of surgery.

Conservative management is indicated for:

• Mild radiculopathy without motor weakness
• Axial pain only, with no neurological deficit
• An asymptomatic incidental finding
• Medical comorbidities that preclude surgery
• Patient preference after informed discussion

The protocol:

• Analgesia - NSAIDs, paracetamol, neuropathic agents (gabapentin, pregabalin)
• Activity modification - avoid provocative activities, ergonomic adjustments
• Physiotherapy - core strengthening, posture training, with a limited role in thoracic disc
• Monitoring - serial neurological examinations, MRI if worsening

Many patients with mild radiculopathy or axial pain and no myelopathy improve with conservative care. It is abandoned for:

• Development of myelopathy
• Progressive motor weakness
• Bowel or bladder dysfunction
• Intractable pain despite optimal management

Intraoperative neuromonitoring. Every thoracic disc operation should have SSEPs, as a baseline and continuously, to detect cord ischaemia, and MEPs, which are more sensitive than SSEPs to motor pathway injury and guide safe decompression. The alarm criteria are a 50% fall in amplitude or a 10% rise in latency. The response is to stop manipulation, increase the MAP and consider aborting.

The rates differ by approach, and the table sets them side by side.

Neurological deterioration (5-15%). Paraplegia is the most feared complication, and myelopathy may worsen through cord manipulation or ischaemia. The mechanisms are direct cord injury, vascular injury to the artery of Adamkiewicz and spinal cord ischaemia. Prevention means avoiding cord retraction, neuromonitoring, gentle technique and an anterior approach for a central disc; high-dose steroids are controversial, and management is supportive care and rehabilitation.

Pulmonary complications (10-20% across the open and thoracoscopic transthoracic approaches). Pneumothorax from inadequate chest tube drainage, pleural effusion from post-thoracotomy inflammation, pneumonia from single lung ventilation and atelectasis, and a prolonged air leak from pleural space problems. Chest physiotherapy, incentive spirometry and adequate chest tube management are the prevention; treatment is chest tube management, antibiotics for pneumonia and supportive care.

CSF leak and dural tear (5-10%). Incidental durotomy happens especially during calcified disc removal and can lead to a CSF fistula, a persistent leak through the wound, or a pseudomeningocele. Careful dural dissection and burring away from the dura are the prevention. Repair primarily if identified, oversewing with 6-0 Prolene; consider a lumbar drain if the leak persists, and revision surgery if a pseudomeningocele is symptomatic.

Vascular injury (2-5%). Injury to the artery of Adamkiewicz causes an anterior spinal artery syndrome with paraplegia; segmental artery injury causes bleeding and cord ischaemia; aortic injury is rare but catastrophic in anterior approaches. Preoperative identification of the artery by CT angiography, careful vessel ligation and maintaining MAP during surgery are the prevention. Control the bleeding, consult vascular surgery for a major vessel, and give supportive care for cord ischaemia.

Minor complications include:

• Wound infection (2-5%), superficial or deep - antibiotics or debridement
• Seroma - a fluid collection, usually self-limiting
• Intercostal neuralgia - rib retraction injury, chronic pain
• Horner's syndrome - sympathetic chain injury in the upper thoracic spine, with ptosis, miosis and anhidrosis
• Chylothorax - thoracic duct injury in left-sided approaches above T6, with milky chest tube output; conservative management or ligation

Complications of not operating. Non-operative management has its own list:

• Progressive myelopathy (25-50%), and 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

Rehabilitation. Three phases carry the patient from mobility to full activity:

• Weeks 0-6 - pain control, wound healing and basic mobility through walking, gentle range of motion and respiratory exercises; no lifting over 5kg, no twisting, no strenuous activity
• Weeks 6-12 - restore function and strength with progressive resistance training, core strengthening and balance; lifting increases gradually and high-impact activities are avoided
• Weeks 12 onwards - return to full activities, work and sport with sport-specific training, unrestricted activities as tolerated, and monitoring by serial neurological examination and functional outcome measures

Results. In systematic reviews and case series (see Evidence Base: Stillerman et al 1998, Quint et al 2011, Brotis et al 2019, Hamid et al 2023), 60-80% improve or stabilise after surgery, 15-20% are unchanged and 5-10% worsen.

Prognostic factors. Each factor has a better and a worse end:

• Symptom duration - under 12 months does better than over 24 months, and long-standing myelopathy over 24 months does worse
• Cord signal - no preoperative T2 signal change does better; myelomalacia on MRI predicts poor recovery
• Age - under 60 years does better, over 70 years worse
• Disc - a soft disc does better; calcified discs are more difficult, with a higher complication rate
• Location - lateral does better; central discs are more challenging, with worse outcomes
• Severity and health - severe preoperative deficit (non-ambulatory, Nurick grade 4-5) and multiple medical comorbidities do worse

Return to activities. Typical milestones:

• Desk work at 6-8 weeks, sooner after a minimally invasive approach
• Manual labour at 12-16 weeks
• Contact sport at 6 months, after full recovery and rehabilitation
• Driving at 4-6 weeks, when off opioids and able to perform an emergency stop

Global Epidemiology

Guidance and Consensus, Side by Side

There is no high-level randomised guideline for this rare condition; practice is driven by case series, meta-analyses, and society/spine-unit consensus. The points where bodies genuinely converge or differ:

Registry Evidence

National joint registries (NJR, AJRR, AOANJRR, SHAR) do not capture thoracic discectomy, and no dedicated thoracic disc registry exists, reflecting the rarity of the condition. The best pooled evidence is therefore from systematic reviews and network meta-analyses rather than registry data: surgery carries minimal mortality but overall morbidity up to 29%, with approach-specific differences (PMID 31493617).

Global Practice Variation

• High-resource settings: Care concentrated in tertiary/quaternary spine units with intraoperative neuromonitoring (SSEPs/MEPs); growing use of thoracoscopic and tubular minimally invasive approaches; cardiothoracic collaboration for transthoracic exposure.
• Limited-resource settings: Open transthoracic or costotransversectomy predominate where thoracoscopic equipment and neuromonitoring are unavailable; later presentation with established myelopathy is more common, worsening prognosis.
• Regional preference: Endoscopic spine techniques have been adopted earliest and most widely in parts of Asia, while open and tubular posterolateral approaches remain standard in many Western units.
• Perioperative care (universal principles): Single-shot antibiotic prophylaxis at induction (e.g. cefazolin), mechanical and chemical VTE prophylaxis, neuropathic agents (gabapentin/pregabalin) for radicular pain, and structured rehabilitation for myelopathic patients. Outcomes converge internationally at 60-80% neurological improvement.