Treatment of Thoracic Disk Herniation

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CHAPTER 283 Treatment of Thoracic Disk Herniation

Samer Ghostine, Srinath Samudrala, J. Patrick Johnson

Management of benign extradural lesions of the thoracic spine has evolved considerably in the past few decades owing to the increased sophistication of radiographic techniques, greater clinical suspicion, and refinement of surgical techniques. This chapter discusses the management of thoracic disk herniation.

The incidence of thoracic disk herniation ranges from 7% to 37%.^1,² However, only 0.25% to 0.57% of all disk herniations are symptomatic.³ Thoracic disk herniation may present with neurological manifestations that include pain; sensory loss; bowel, bladder, or sexual dysfunction; paraparesis; and paraplegia. In this chapter we review the evolution of surgical techniques that can be used to perform thoracic diskectomies.

History and Epidemiology

Middleton and Teacher ⁴ performed the first thoracic diskectomy in 1911 on a paraplegic man who subsequently died. In those days, diagnosis was based on the identification of calcification in the disk space and clinical acumen. The limited diagnostic resources made it difficult to diagnose early disease and localize it accurately. Many patients presented with frank myelopathy and severe neurological deficits.⁵

The advent of computed tomography (CT) and later magnetic resonance imaging (MRI) dramatically improved the ability to diagnose and localize the level of the herniated thoracic disk.⁶ With the further development of MRI techniques, clinicians can now accurately diagnose and pinpoint the level of disk herniation in the thoracic spine. CT-myelography provides additional information in certain cases, especially when the disk is calcified or when reoperation is being performed at the same level to determine the extent of prior bone resection. Currently, MRI is considered the first-line modality to diagnose thoracic disk herniation. It is noninvasive and provides a precise image of the herniated disk and its relationship to the dural sac and the nerve; it provides additional information about the conformation of the cord and whether an intramedullary signal change, and hence cord injury, is present.

Most thoracic disk herniations occur in patients between the fourth and sixth decades of life, with a slight male predominance.⁷ A history of trauma is reported in 22% to 50% of symptomatic patients.⁸ It is usually associated with a fall landing on the feet or buttocks, combined with an axial spinal rotation. Thoracic disk herniations are much less common than herniations of the lumbar and cervical spine. This is because of the limited mobility of the thoracic spine, the smaller disks, and the stabilizing effect of the rib cage.^9,¹⁰

Early surgical attempts to treat thoracic disks involved a posterior laminectomy, dural sac retraction, and completion of the diskectomy. These operations were associated with a high rate of neurological deterioration and death. Published series quoted neurological deterioration in 18% to 66% of patients and mortality rates of 14% to 50%.^9,¹¹^–¹⁵

The high rates of morbidity and mortality associated with thoracic laminectomies and diskectomies were ascribed largely to cord injury secondary to intraoperative dural sac retraction. The development of anterior, anterolateral, and posterolateral surgical approaches has allowed the performance of safe and efficacious thoracic diskectomies.

Clinical Presentation and Differential Diagnosis

Pain is the most common symptom associated with thoracic disks. The pain is dorsal and midline in 57% to 88% of patients but may be dermatomal in 9% to 57%. When dermatomal, the pain is lancinating and often unilateral, but it may be bilateral in some cases. The next most common complaint is sensory changes in a radicular pattern, occurring in 39% to 100% of patients. Dermatomal sensory loss is quite rare because of the overlap in sensation from adjacent-level nerve roots. In addition, patients may present with findings associated with spinal cord compression, including myelopathy (9% to 100% of patients), weakness (41% to 100%), and bowel and bladder dysfunction (18% to 78%).^8,¹⁶^–²⁰

Unusual presentations have been reported as well. A herniated disk at the level of C7-T1 or T1-2 has been reported to cause Horner’s syndrome.²¹^–²⁴ Another unusual presentation is dysesthesia in the medial arm, which may erroneously be associated with myocardial infarction, angina, thoracic aortic dissection, or bronchogenic tumor.²⁵ Also, far lateral thoracic disk herniation may present as flank pain.²⁶

Patients may present with spinal cord syndromes associated with thoracic disk herniation. The specific presentation is dependent on the pattern of neural compression on the cord. Brown-Séquard syndrome may occur when the herniated disk is lateral and compressing one side of the spinal cord, whereas anterior spinal artery syndrome occurs when the herniated disk is central and compressing the anterior spinal artery; conus medullaris syndrome is caused by a herniated disk compressing the conus medullaris at the thoracolumbar junction.^13,^16,¹⁹ Other differential diagnoses include primary and metastatic neoplasm, demyelinating disease, primary motoneuron disease, neuromuscular disease, myopathy, muscular dystrophy, motor neuropathy, spinal cord infarction, and spinal cord vascular malformation. Other entities that need to be considered are those related to visceral referred pain, such as renal colic, gallbladder colic, colitis, intercostal neuritis, and costochondritis.²⁵

Radiologic Evaluation

Magnetic Resonance Imaging

The primary care physician often performs MRI of the thoracic spine in the evaluation of back pain. It is the best screening method for thoracic disk herniation, given its noninvasive nature and high sensitivity. However, it is also associated with 14.5% false-positive rate, making it crucial to correlate the MRI information with the clinical examination.^27,²⁸ The exaggeration of disk herniation (which is not unique to the thoracic spine), especially in sagittal images, has been attributed to the edge effect, which occurs when two substances of different proton densities are next to each other. The edge effect is most pronounced on T2-weighted images between the disk substance and the adjacent cerebrospinal fluid. Axial images provide further information about the level of stenosis caused by the herniated thoracic disk. Increased signal on T2-weighted images may be seen in the spinal cord when it is significantly compressed. In addition, MRI can distinguish herniated disks in the thoracic spine from neoplastic, demyelinating, or infectious pathologies. It can also distinguish intradural versus extradural lesions. When the accuracy of MRI is in doubt, it is best to obtain a thoracic myelogram and postmyelogram CT to further delineate the extent of dural sac compression, presence of calcification in the herniated disk, and presence of posterior osteophytes and their relation to the dural sac.^29,³⁰ Thoracic myelograms and postmyelogram CT scans are most useful for extradural lesions.

Myelography and Postmyelography Computed Tomography

Some clinicians still consider the combination of myelography and postmyelography CT the “gold standard” in patients with calcified herniated disks. It typically shows an indentation caused by an extradural mass compressing the dural sac at the level of the disk. Postmyelography CT allows the distinction among bone, calcified soft tissue, soft tissue, dural sac, and spinal cord. It also allows the visualization of posterior osteophytes and disk material and their relationship to the dural sac. Twelve percent of thoracic disk herniations are associated with calcifications in the spinal canal, which suggests an intradural extension of the herniated disk.^22,^29,^31,³² CT-myelography, like MRI, has a high false-positive rate (13.5%) in diagnosing symptomatic thoracic disk herniation.³³

Radiography

Radiographs are useful to evaluate the alignment of the vertebral column to rule out a kyphotic or scoliotic deformity, the disk spaces for diskitis, the end plates for degenerative disk disease, the vertebrae for osteomyelitis, compression or burst fractures, and osteolytic or osteoblastic lesions such as primary or metastatic neoplasms. In addition, they may suggest a calcified disk when the disk space is collapsed, the end plates are eroded with posterior osteophyte formation, and there is localized kyphosis. Calcification within the spinal canal is highly suspicious of a thoracic herniated disk and is sometimes associated with an intradural extension of the disk. Also, lumbar and thoracic films are always ordered preoperatively to determine the number of lumbar vertebrae and identify the last thoracic rib in relation to the herniated disk level.

Management

Management of symptomatic disk herniation is illustrated in Figure 283-1. Nonsurgical management should be instituted first, unless there is an associated neurological deficit or intolerable pain. Surgical intervention is indicated when there is radiographic evidence of spinal cord compression and clinical examination findings of myelopathy, weakness, or bowel, bladder, or sexual dysfunction, or when the patient is experiencing severe back or radicular pain. Patients with mild to moderate pain that is refractory to conservative management may be good surgical candidates as well. The aim of conservative therapy is to allow the herniated disk to resorb³⁴ and the inflamed nerve root to heal.^18,^28,^29,³⁵

FIGURE 283-1 Treatment algorithm of herniated thoracic disks.

MRI scans and plain radiographs of the thoracic spine are obtained in patients with thoracic back pain. MRI helps rule out any intrinsic or extrinsic spinal cord lesion that could require surgical intervention. Plain films help rule out neoplastic, infectious, or unstable fractures that need further urgent evaluation to determine whether surgical intervention is indicated. When both MRI and plain films are negative, conservative management is tried in patients with tolerable back pain.

Nonsurgical Management

Nonsurgical management includes restricted activity, immobilization with a hyperextension brace, oral steroids, nonsteroidal anti-inflammatory drugs, oral pain medications, and epidural injections.^18,^28,^29,³⁵ Figure 283-1 summarizes the nonsurgical management protocol.

If the patient does not improve after 2 or 3 weeks of medical management (including epidural steroid injections), and if MRI shows a herniated thoracic disk compressing a nerve root, he or she may be a surgical candidate. CT-myelography is performed in all patients with intradural calcification on plain films or when further information about the bony elements or evaluation of posterior osteophytes is required.

Surgical Management

Three surgical approaches can be used: posterior, posterolateral, and anterior (Fig. 283-2). The posterior approach includes dorsal laminectomy and a transpedicular approach. The posterolateral approach includes costotransversectomy and lateral extracavitary and lateral parascapular approaches. The anterior approach includes transthoracic and thoracoscopic approaches. Table 283-1 summarizes the pros and cons of each approach.

FIGURE 283-2 Possible surgical approaches to perform thoracic diskectomy.

TABLE 283-1 Pros and Cons of Surgical Approaches for Thoracic Diskectomy

APPROACH	PROS	CONS
Laminectomy	Simple to perform	High morbidity and mortality Limited exposure Need to retract dural sac
Transpedicular	Simple to perform Minimally invasive Good for lateral disks; may be used for paracentral disks with poor visualization	Difficult to visualize ventral dural sac Difficult to dissect midline calcified disks Limited exposure for multilevel OPLL
Costotransversectomy	Extrapleural Good for lateral disks; may be used for paracentral disks with better visualization than transpedicular approach	Difficult to visualize ventral dural sac Difficult to dissect midline calcified disks Limited exposure for multilevel OPLL
Lateral extracavitary	Extrapleural Best visualization of midline structures among posterior and posterolateral approaches Access to multiple levels Adequate exposure to resect multilevel OPLL Allows fusion if needed	Limited visualization of ventral dural sac Painful Potentially higher risk for radicular artery injury leading to spinal cord infarction⁴⁵
Transthoracic (open)	Best visualization of large midline calcified or soft herniated disks Access to multiple levels Adequate exposure to resect multilevel OPLL Access for fusion if needed	Painful Potential morbidity Need for chest tube
Thoracoscopic	Best visualization of large midline calcified or soft herniated disks Access to multiple levels (up to three) Minimally invasive	Limited exposure for multilevel OPLL Need for chest tube Steep learning curve

OPLL, ossification of the posterior longitudinal ligament.

Identification of Surgical Level

Identification of the correct surgical level may be challenging. Preoperative lumbar and thoracic films are helpful in determining the number of lumbar vertebrae and identifying the last thoracic rib in relation to the herniated disk level. Intraoperative identification of the surgical level is performed with high-quality fluoroscopy, anteroposterior and lateral films, or imaging guidance when available.^36,³⁷

Posterior Approach

Posterior thoracic laminectomy was the first approach described for thoracic diskectomies. However, it provides inadequate exposure of midline herniated disks, and significant retraction of the dural sac is almost always needed. It is estimated that 70% to 90% of thoracic disk herniations that cause spinal cord or nerve compression are central or paracentral.^22,^29,^31,³² This explains the necessity of dural sac retraction to reach the herniated disk. There are reports that thoracic laminectomy performed for thoracic diskectomy is associated with unacceptably high rates of morbidity and mortality. It is estimated that there is at least a 45% chance of experiencing neurological deterioration or no benefit with this approach.^14,^38,³⁹ Currently, this approach is completely contraindicated in the management midline calcified herniated thoracic disks,⁴⁰ and surgeons should consider the other approaches discussed.

Alternatively, the transpedicular approach allows better exposure of the paracentral herniated disk, with minimal dural sac retraction and sparing of the facet (Fig. 283-3). The foramen of the affected level is unroofed by drilling the medial half of the inferior facet of the above vertebra and the medial half of the superior facet along with the superior part of the pedicle of the lower vertebra. A trough is created with a high-speed diamond drill in the posterior inferior vertebrae overlying the relevant disk space; in the posterior superior vertebrae below the disk space, including the end plates; and in the lateral aspect of the disk space laterally. The resultant trough should be large enough to pull the disk material into the trough without significant manipulation of the dura. (See Video 283-1.)

FIGURE 283-3 A, Computed tomography scan of a patient with left-sided radiculopathy showing a small paracentral calcified disk on the left. B, Magnetic resonance imaging shows nerve root compression with mild rotation of the spinal cord. The arrows show the approach options. We would perform this particular diskectomy using a facet-sparing transpedicular approach. Other anterior and lateral approaches could be considered as well.

The transpedicular approach reportedly yields satisfactory results for both soft and calcified disks in the lateral and centrolateral position. However, it is inadequate for central herniated thoracic disks.² Fusion is rarely needed with the transpedicular approach because it spares the facet and maintains the integrity of the anterior column, anterior longitudinal ligament, posterior longitudinal ligament, and posterior band. One report described a delayed compression fracture after a transpedicular approach,⁴¹ but we have encountered no such adverse complications. This approach has been performed through an endoscope⁴² and through a minimally invasive tube,⁴³ with favorable outcomes.

Posterolateral Approach

In the costotransversectomy approach, the transverse process and a proximal piece of the rib head are resected, providing further direct midline exposure of the ventral dura. Hulme ⁴⁴ reported good results with the costotransversectomy approach to thoracic diskectomy.

The lateral extracavitary and lateral parascapular approaches involve much more lateral exposure and dissection than the costotransversectomy approach. They allow better visualization of midline structures and may be especially useful when an extensive exposure is required for the placement of cages or the performance of vertebrectomy for infectious, neoplastic, or traumatic lesions.^25,⁴⁵ The lateral extracavitary approach as described by Maiman and coworkers¹⁷ involves cutting the head of the rib as well as 8 cm of the rib distal to the dorsal root ganglion. The intercostal nerve is sacrificed by tying it 3 cm distal to the dorsal root ganglion. A posterior vertebral body trough is created with a drill, into which calcified disk and osteophytes are fractured, decompressing the dura. The lateral extracavitary approach has yielded satisfactory results in thoracic diskectomy.¹⁷ In addition, it allows an extrapleural approach to the anterior elements without the need for postoperative chest tubes, as well as the option of anterior or posterior instrumentation in the same setting if needed. A modified lateral extracavitary approach has been described whereby the neurovascular bundle is preserved, avoiding the potential complication of intercostal neuralgia or anesthesia dolorosa secondary to intercostal nerve resection²⁵ or spinal cord infarction secondary to a radicular artery injury.⁴⁶ The extracavitary approach can be performed in a minimally invasive fashion by using the METRx tube (Medtronic Sofamor Danek, Memphis, TN) and an endoscope, as described by Lidar and associates.⁴⁷

The costotransversectomy and lateral extracavitary approaches are not facet-sparing; therefore, fusion should be considered for some patients, especially in the lower thoracic levels, where the rib cage does not provide as much support (Figs. 283-4 to 283-6).

FIGURE 283-4 Right paracentral calcified herniated thoracic disk in a patient presenting with myelopathy. The arrows delineate the exposure afforded by a lateral approach (either a costotransversectomy or a lateral extracavitary approach) and the anterior approaches. We favor the anterior approach, but the lateral approach is acceptable as well. Fusion may be needed if the lateral approach is chosen.

FIGURE 283-5 A, Large central soft disk compressing the spinal cord in a patient with severe myelopathy. Note the increased signal change in the spinal cord. B, Large centrolateral soft disk in the midthoracic area displacing and compressing the spinal cord significantly to the left. This disk could be approached from an anterior, lateral, or partial facet-sparing transpedicular approach without fusion. Arrows delineate the exposure of each approach.

FIGURE 283-6 A, Large paracentral herniated disk at the T10-11 level, leading to significant spinal cord compression in a myelopathic patient. Note the signal change of the spinal cord. B, Right paracentral herniated disk is pushing the spinal cord to the left. A laminectomy with facet and pedicle resection may provide adequate exposure of the herniated disk, but fusion with instrumentation may be required. The posterior, lateral, and anterior approaches are alternatives that may be considered. The arrows delineate the working channels.

Anterior Approach

The anterior approach is favored for central or paracentral herniated disks, especially if the disk is calcified and intraspinal. It allows an anterior dissection of the disk without the need to manipulate or retract the dura.

At the T11-L1 region, the diaphragm limits the surgeon’s working channel and must be retracted. At those levels, either a retroperitoneal approach and release of the diaphragm or a thoracoscopic approach may be indicated.⁴⁸ A right-sided approach at the level of the third rib may be performed for the upper levels when using a transthoracic approach.⁴⁹ In contrast, the thoracoscopic approach may be performed from either side from T2 down to T12, and the choice of the surgical side is determined by the lesion’s laterality (Figs. 283-7 and 283-8).

FIGURE 283-7 Preparation for a typical thoracoscopic approach. A, Positioning of the patient in a lateral decubitus fashion with an axillary roll placed under the left shoulder. Positioning and skin preparation must take into consideration the possible conversion to open thoracotomy. B, Insertion of the three ports—one in the posterior axillary line at the level of the lesion, and two in the anterior axillary lines. C, Intraoperative positioning of staff and monitors. D, Using the universal dynamic registration hardware and software, standard endoscopic instruments are registered for real-time image-guided surgery. The drill, curets of different sizes and angles, and Kerrison rongeurs are registered in this fashion and monitored in real time on the screen as the surgery is proceeding.

FIGURE 283-8 A, The image-guided monitor is placed just adjacent to the endoscopic one. The surgeon is able to acquire real-time information about the tip of the instruments from both the image-guided system and the endoscope camera. B, Picture of the exposure provided by the thoracoscopic approach.

Understanding the anatomy is paramount. Each rib articulates with the superior posterior part of the same level vertebra and with the inferior posterior part of the above vertebra (except the 1st, 11th, and 12th ribs, which articulate only with the same level vertebrae).⁴⁸ Hence, from an anterior lateral approach, the posterior part of the disk and the neural foramen are parallel and behind the rib head. Therefore, access to the herniated disk and neural foramen necessitates drilling the rib head.

Few ligaments are encountered; the radiate, costotransverse, intertransverse, and capsular ligaments and their relation to the surgical site are illustrated in Figure 283-9.^22,^48,⁵⁰ The radiate ligament attaches the tip of the rib head in a web-like fashion to the vertebra of the above level, the same level vertebra, and disk space between them. The different costotransverse ligaments attach the rib head to the transverse process, and the capsular ligament (not shown in Fig. 283-9) connects the ventral part of the transverse process to the dorsal portion of the articulating rib.

FIGURE 283-9 Diagram illustrating the surgical site and its relationship to the surrounding ligaments from an anterior approach.

A curvilinear incision is performed after identifying the proper level with fluoroscopy or an image-guided system, following the course of a rib. The musculature is sequentially divided with the Bovie electrocautery. A subperiosteal rib dissection is performed; the rib is cut with specific attention given to leaving the neurovascular bundle intact with Cobb and Doyen elevators. The bed of the rib is entered, and retractors are placed to spread the space open into the intrapleural space after deflating the ipsilateral lung (a double-lumen endotracheal tube is used).

The proximal 2 cm of the rib head is skeletonized with the electrocautery and then drilled with a high-speed coarse diamond drill, exposing the pedicle and neural foramen (Fig. 283-10). The pedicle is subsequently drilled until the dura and nerve sleeve are visualized. At that time, the surgeon will be able to recognize the posterior part of the overlying vertebra and same level vertebra. A trough is created with the high-speed coarse diamond drill in the posterior inferior vertebra above the relevant disk space and in the posterior superior vertebra below the disk space, until reaching the midline. The posterior cortex of the vertebra is left to avoid compression on the dural sac. With a curet, the herniated disk and the posterior longitudinal ligament are dissected off the dural sac and pushed anteriorly, along with the posterior cortical bone that was left undrilled. Using pituitary and Kerrison rongeurs, the herniated disk, posterior longitudinal ligament, and posterior cortex of the vertebra are removed. A chest tube is placed, and the patient is weaned off it postoperatively per protocol.

FIGURE 283-10 A, Drilling of the rib head. B-D, Drilling the posterior edges of the posterior part of the disk space and the vertebrae overlying and underlying it. E, Dissection of the herniated disk. F, Resection of the posterior longitudinal ligament with Kerrison rongeurs.

Thoracoscopic surgery is a minimally invasive approach that achieves the same results as its open counterpart, with reduced postoperative pain, morbidity, and length of stay.⁵¹^–⁵³ It was first used simultaneously by Mack and colleagues^54,⁵⁵ in the United States and Rosenthal and associates⁵⁶ in Germany. Unlike its open counterpart, the thoracoscopic technique can manage disks through a left- or right-sided approach from T5-6 down to T11-12 (Figs. 283-11 to 283-13). Its downside is the steep learning curve associated with the technique, making it less practical for surgeons who do not perform thoracic diskectomies on a regular basis. We have used the endoscopic approach in combination with an image guidance system that allows consistent correct localization of the affected level. The surgical technique is otherwise very similar to the open thoracotomy described earlier. (See Video 283-2.)

FIGURE 283-11 A, Preoperative magnetic resonance imaging (MRI) of a patient with a symptomatic midline, calcified herniated thoracic disk. Note the cord signal change. B, Postoperative MRI scan of the same patient shows complete decompression of the spinal cord and limitation of the bone work to the middle column.

FIGURE 283-12 A, Small central herniated disk in a patient with progressive myelopathy. B, This small midline herniated thoracic disk is causing the spinal cord to assume a kidney shape. Diskectomy must be performed from an anterior approach. The posterior and lateral approaches would require manipulation of the spinal cord, increasing the risk of injury.

FIGURE 283-13 A, Sagittal computed tomography scan shows a large calcified thoracic disk herniation in a myelopathic patient. B, Sagittal magnetic resonance imaging (MRI) shows mild signal change in the spinal cord. C, Axial MRI scan shows a large central herniated disk resulting in spinal cord deformity. Both posterior and lateral approaches would compromise the safety of the spinal cord. The arrows show the corridor in which the diskectomy can be performed safely with an anterior approach.

Some surgeons prefer the open thoracic approach because of its familiarity and broader application. Unlike its thoracoscopic counterpart, the open thoracic approach does not have a steep learning curve, and it can be used for multilevel vertebrectomies for neoplastic or infectious lesions requiring instrumentation and fusion, small or giant intervertebral disk herniation, and unstable traumatic fractures requiring instrumentation and fusion.^57,⁵⁸

Results and Complications

Results of thoracic diskectomy in patients with myelopathy may depend on the duration and severity of preoperative myelopathy. Hence, patients with new-onset mild myelopathy may have a better chance for improvement or recovery.⁵⁹ It is hard to compare the results of the different approaches because of the low incidence of thoracic disk herniation, the nonstandardized measurement of results, and some surgeons’ preference for one particular approach. Good results have been reported with all approaches, with the exception of laminectomy. The improvement rate for myelopathic patients ranges from 71% to 97%.^8,^18,^29,^38,⁵¹ For back and radicular pain, the improvement rate varies between 67% and 94%.^20,^25,⁶⁰

McCormick and coworkers ⁴⁶ reviewed all approaches for complications and found that neither neurological nor nonneurological complications were significantly higher with any particular approach (excluding laminectomy). They evaluated rate of infection, pneumonia, pulmonary embolism, intercostal neuralgia, and cerebrospinal fluid leak and found no significant difference among approaches. Furthermore, they found that postoperative spinal instability is most likely due to preoperative predispositions and is not directly related to any particular approach. However, they found a number of misdiagnoses and misidentifications of surgical level that could have been prevented with preoperative lumbar and thoracic plain films, CT of the thoracic spine, and use of high-quality intraoperative fluoroscopy or an intraoperative image-guided system.

The need to reoperate has been reported in patients in whom the surgical level was misidentified ^46,^61,⁶² or in whom the herniated disk was incompletely dissected owing to its inadequate visualization.^46,⁶¹ Incompletely dissected herniated disks are most often midline and calcified.⁶¹ When they are intradural, they are extremely challenging to dissect.⁶¹ Hence, an anterior approach, providing an oblique view of the posterior longitudinal ligament and herniated disk, and resection of the posterior longitudinal ligament along with the herniated disk for complete spinal cord decompression are encouraged for midline, calcified disks.^46,⁶¹^–⁶⁵