Overview
Thoracic disk herniations are heterogeneous with respect to presenting symptoms, anatomic relationship to the spinal cord, and intrinsic tissue characteristics. Accordingly, thoracic diskectomy exists along a continuum of surgical complexity that has mandated the development of a wide array of surgical techniques to treat this pathology. Ultimately, the choice of surgical approach depends heavily on the individual characteristics of each disk herniation and the expertise of the surgeon.
Early experience with surgical outcomes reflected the limitations of the treatment of thoracic disk herniations with dorsal laminectomy and diskectomy. This approach led to unacceptably high rates of neurologic injury. Poor outcomes were largely attributed to spinal cord retraction, particularly in cases where the disk herniation was calcified and centrally located. Accordingly, the evolution of thoracic disk surgery has been driven by an emphasis on adequate surgical exposure with minimal spinal cord manipulation. This has led to the development of posterolateral, lateral, and anterolateral approaches that have mitigated the neurologic morbidity seen with laminectomy but often at the expense of approach-related morbidity. As imaging technology has become more refined and less invasive techniques and equipment have become available, it has become apparent that many thoracic disk herniations do not require large, open exposures for safe removal.
The most important guiding principle in thoracic disk surgery is that no single, optimal approach for every thoracic disk herniation exists. It is of paramount importance that each thoracic disk herniation be evaluated individually to assess its internal consistency and relative position to neural elements. Ultimately the choice of approach is dependent not only on these factors but also on individual preferences and the expertise of the operating surgeon. In this chapter, we will review the advantages and disadvantages of the principal approaches to thoracic disk herniations, and we will describe the fundamental surgical techniques used.
Prevelance and Presentation
Prompt diagnosis of a thoracic disk herniation can be challenging given the heterogeneity of presenting signs and symptoms, potential similarities to lumbar disk herniation presentations, and an often insidious early course. Fortunately, advances in imaging quality and availability have expedited the diagnostic process. Manifestations include pain that may be localized, axial, or radicular; sensory loss or paresthesias; hyperreflexia and spasticity; bowel, bladder, or sexual dysfunction; and lower extremity weakness that can lead to paraplegia. Patients usually come to medical attention with a combination of these symptoms.
Thoracic disk herniations are rare and account for only 0.25% to 0.75% of all disk herniations. This is likely due to the stabilizing effect of the rib cage and the resultant limited mobility of the thoracic spine. A history of trauma is reported in 22% to 50% of symptomatic patients, most of whom are between the fourth and sixth decades of life, with a nearly even sex distribution. Thoracic diskectomy accounts for less than 4% of all spinal diskectomy procedures.
Anatomic Considerations
Thoracic intervertebral disks are less prone to degradation, compared with cervical and lumbar regions, because of the relative lack of motion that results from the stabilizing effect of the rib cage. In contrast, the blood supply to the thoracic spinal cord renders it relatively vulnerable; this is due to a watershed zone at the upper thoracic levels, which is fed by small radicular arteries, and the dominance of the artery of Adamkiewicz, a large radicular artery that supplies the ventral cord from the lower thoracic levels down to the conus. Although highly variable, this artery usually enters the spinal canal at T8–L2 on the left side. This variability has led some to advocate spinal angiograms before thoracic diskectomy to delineate major feeders; however, this is not common practice.
Approximately 90% to 94% of symptomatic thoracic disk herniations are located either centrally or paracentrally. Intradural extension of herniated thoracic disks is not uncommon and occurs in 7% to 12% of cases. Thoracic diskectomy is further complicated by the consistency of thoracic disks, the majority of which contain a calcified component. Even in the absence of intradural extension, the incidence of dural adhesion is much greater with calcified disks, further arguing the importance of a surgical approach that adequately exposes the ventral spinal canal.
Imaging
The widespread use of magnetic resonance imaging (MRI) has had a profound impact on the accurate and timely diagnosis of thoracic diskectomy; it has led to earlier treatment and has likely resulted in improved prognosis. MRI facilitates precise localization of the offending pathology, provides an excellent depiction of the relationship of the disk herniation to the neural elements, and gives information as to the consistency or “softness” of the herniated disk material ( Fig. 30-1 ). Contrast may be useful to distinguish such lesions from a spinal tumor. Abnormal signal within the cord—hyperintensity on T2-weighted images and, more specifically, hypointensity on T1-weighted sequences—suggest parenchymal injury or gliosis. Although MRI is very sensitive for discerning thoracic disk herniations, it is important to keep in mind that the false-positive rate is estimated to be as high as 14.5%; this makes appropriate clinical correlation paramount to treatment decisions.
As an adjunct to MRI, computed tomography (CT) is particularly useful in the evaluation of calcification of disk material. This cannot be reliably ascertained with MRI. Although rarely used, CT myelogram can be more sensitive at ruling out intradural extension ( Fig. 30-2 ).
Surgical Indications
Radiographic studies suggest that the prevalence of thoracic disk herniation may be as high as 20%, yet the vast majority of these lesions are asymptomatic and require no surgical intervention. Like comparable lesions in the cervical and lumbar spine, herniated thoracic disks should be treated conservatively in the absence of myelopathy or intractable pain. Conservative therapy may include nonsteroidal antiinflammatory medications, analgesics, and epidural steroid injections in cases of thoracic radiculopathy. Patients with radiographic evidence of nerve compression who do not improve following 4 to 6 weeks of conservative treatment are candidates for surgical intervention. However, patients with radiographic evidence of spinal cord compression and signs or symptoms of myelopathy usually require surgery.
Once the decision has been made to proceed with surgery, the optimal approach to the thoracic spine must be selected based on the characteristics of the individual disk herniation and the comfort level and expertise of the operating surgeon. Effective surgical management is contingent on an understanding of the various approaches to the thoracic spine and the advantages and disadvantages associated with each. Primary considerations related to approach include adequate exposure of the herniated disk, limited manipulation of the dura, potential iatrogenic instability from surgical exposure, preservation or sacrifice of the intercostal neurovascular bundle, postoperative pain, approach-related morbidity, and patient health and age.
Although no precise algorithm exists for selecting which surgical approach is optimal for each patient, useful guidelines based on large clinical series highlight the efficacy of anterior, lateral, and posterolateral approaches in different clinical scenarios ( Table 30-1 ). Posterior thoracic laminectomy for diskectomy has been associated with unacceptably high rates of neurologic deterioration and is contraindicated. Midline and calcified disk herniations are relative indications for lateral or anterolateral approaches, given the degree of ventral exposure needed for safe decompression. Soft and lateral disks are potentially amenable to less invasive posterolateral approaches. The extent of bone removal and approximate operative angles for each approach are illustrated in Figure 30-3 .
| Approach | Indications (+) and Contraindications (–) | Advantages | Disadvantages |
|---|---|---|---|
| ANTERIOR | |||
| Transthoracic |
|
|
|
| Thoracoscopic |
|
|
|
| ANTEROLATERAL | |||
| Retropleural |
|
|
|
| POSTEROLATERAL | |||
| Lateral extracavitary |
|
|
|
| Costotransversectomy |
|
|
|
| POSTERIOR | |||
| Transpedicular |
|
|
|
| Transfacet |
|
|
|
| Dorsal laminectomy |
|
|
|
To date, objective comparisons of different approaches are limited by the low incidence of symptomatic thoracic disk herniation, the varying appropriateness of certain approaches given disk location and consistency, and a paucity of standardized outcome measures. For this reason, surgeon familiarity is an important factor in decision making, because often more than one alternative can effectively address the pathologic disk.
Anterolateral Approaches
Transthoracic Approach
The transthoracic approach allows for midline exposure of the ventral cord without dural retraction, making it particularly advantageous in the treatment of densely calcified centrally herniated disks. Of note, reoperation following thoracic diskectomy is most often attributed to incomplete diskectomy as a result of inadequate visualization of calcified midline disks. When feasible, an anterior exposure should be used in the context of calcified midline disks, particularly if the spinal cord is draped over the disk herniation. However, it is important to note that the standard transthoracic approach is an extensive undertaking associated with potential morbidity; this may make it unsuitable for medically ill patients with poor cardiac or pulmonary function.
With this is mind, less invasive thoracoscopic diskectomy techniques have evolved rapidly in recent years. Proponents of the thoracoscopic approach argue that excellent endoscopic visualization and reductions in morbidity make this the ideal approach for central disk herniations. Small clinical series that have compared thoracoscopic and “open” transthoracic approaches have reported equivalent operative time, reduced postoperative pain, and comparable clinical results. However, it should be noted that thoracoscopic disk surgery is associated with a steep learning curve and requires specialized equipment and training.
Anterior approaches to the thoracic spine, including transthoracic and thoracoscopic techniques, are discussed in detail in Chapter 28 .
Lateral Approaches
Retropleural Approach
Indications and History
The modern retropleural approach, as described by McCormick, provides the shortest direct route to the thoracic spine and leaves the pleura intact. In doing so, the retropleural approach avoids some of the shortcomings of the transthoracic approach—including direct retraction of the lung, creation of a deep surgical field, and postoperative closed-chest drainage—while achieving comparable ventral access to the thoracic spine.
Positioning
The patient is positioned in the lateral position and supported by a beanbag. A soft roll is placed in the inferior axilla, and the lower leg is flexed at the knee and hip. When possible, thoracolumbar lesions should be centered over the break in the table to help maximize exposure of the lesion. For laterally herniated disks, ipsilateral exposure provides the most direct surgical route. In cases of central or paracentral herniations, the side of approach is often dependent on the vertebral level. Rostral thoracic lesions are best approached from the right, limiting exposure to cardiovascular structures. Conversely, for more caudal thoracic lesions, a left-sided approach allows the surgeon to avoid the inferior vena cava and liver. When exposing the caudal thoracic spine from the left, the artery of Adamkiewicz is an important consideration. When approaching the upper thoracic spine, rostral to T6, a double-lumen endotracheal tube should be used to allow for ipsilateral lung deflation.
Incision, Dissection, and Diskectomy
Intraoperative fluoroscopy should be used to confirm the level of pathology and proper positioning before marking the course of the incision. In the rostral thoracic spine (T3–T4), a paramedian “hockey stick” incision is made, curving lateral in parallel with the medial and caudal border of the scapula. This incision can be carried through the trapezius and rhomboid muscles, allowing for superior rotation of the scapula and exposure of the underlying rib. For lesions between T5 and T10, a curvilinear incision is made that extends from the posterior axillary line to a point approximately 4 cm lateral the dorsal midline along the caudal rib of the involved segment. When approaching the thoracolumbar junction, the incision is usually made two levels rostral to the surgical target ( Fig. 30-4, A ).
A subperiosteal dissection of the intercostal musculature is then carried out to expose 8 to 10 cm of the rib. This exposed portion of the rib is resected and saved for later autograft, if needed, leaving the proximal rib attached to the vertebral body and transverse process. Cut rib edges are waxed to prevent lung injury. Removed rib exposes the underlying endothoracic fascia, which lines the thoracic cavity and lies flush to the ventral border of the vertebral body (see Fig. 30-4, B ). The intercostal neurovascular bundle, azygous vein, thoracic duct, and sympathetic chain all lie within this important layer of fascia. With this in mind, the fascia is incised in line with the imprint of the resected rib and is then carefully separated from the underlying parietal pleura via blunt dissection to create a potential space between the layers (see Fig. 30-4, C ). A retractor distracts adjacent ribs. For lesions rostral to T6, the ipsilateral lung should be deflated. For more caudal lesions, a table-mounted malleable retractor can be used to protect the lung and clear it from the operative field, avoiding the need for deflation.
The endothoracic fascia opening can then be followed posteriorly to the proximal rib head and anterior vertebral column (see Fig. 30-4, D ). When incising fascia over the involved disk space, the sympathetic chain will be divided. This rarely has clinically significant repercussions in the thoracic spine. The fascia and vertebral periosteum are subsequently dissected free from the ventral spine and proximal rib and are reflected rostrally and caudally, away from the disk space ( Fig. 30-4, E ). The intercostal vascular pedicle runs in the fascia layer at the level of the midvertebral body. It is possible to preserve this structure in single-level diskectomies.
Costotransverse ligaments are divided to free the rib head and proximal rib, which are removed. The underlying neural foramina and pedicle are then visualized. Removal of the transverse process further exposes the neural foramen and lateral dura. The rostral portion of the pedicle directly caudal to the disk space can also be drilled down to improve exposure of the disk space.
The pathologic disk can now be incised and removed with rongeurs and curettes (see Fig. 30-4, F ). A high-speed drill is used to extend the dissection into the adjacent vertebral bodies (see Fig. 30-4, G ). Next, the caudal pedicle is removed with Kerrison rongeurs, further exposing the lateral spinal canal and dura. Drilling of the posterior vertebral bodies is extended to create a cavity that lies roughly 1.5 cm rostrally and caudally from the disk space and 3 cm medially. Drilling is carried out until only a thin shell of bone remains on the posterior border of the vertebral body, along with the posterior longitudinal ligament (PLL).
The PLL is then divided with a reverse-angled curette, with all applied force directed away from the spinal cord into the vertebral body trough. Remaining bone and ligament can then be evacuated through this cavity, and a nerve hook is used to survey the thecal sac for residual disk fragments. Final decompression should be performed in a timely fashion to limit the effects of epidural bleeding, which can be addressed with electrocautery. Resected rib can be placed in the vacated disk space in the form of a strut autograft, and additional vertebral body drilling may be needed to establish proper disk height and to allow the graft to sit flush (see Fig. 30-4, H ). The fusion can be augmented with vertebral body screws.
The endothoracic fascia is released back over the ventral vertebral body, and the pleura is inspected for injury. If no appreciable injury is present, chest tube drainage is unnecessary. Chest tubes should be placed in the case of significant intrathoracic air or persistent pleural leakage, which can be better assessed during positive-pressure ventilation. Chest wall deformity is reduced by approximating ribs adjacent to the resection site with suture, taking special care not to injure underlying intercostal nerves, which might cause intercostal neuralgia.
Minimally Invasive Considerations
Tubular retractors have made possible a less invasive retropleural approach. The surgery is performed essentially as described but requires a smaller incision (3 to 4 cm) placed over rib that lies directly over the posterior aspect of the disk space and ventral canal. Depending on the level of the disk herniation and the patient’s individual anatomy, the initial thoracotomy in a minimally invasive retropleural approach may be at the level of the disk space of interest or one to two levels above. The more caudal the segment, the more angulated the rib and the more likely the initial thoracotomy will need to be performed at the level above. In contrast to the open retropleural approach, a smaller window of rib is resected in the initial thoracotomy, which mitigates potential postoperative morbidity from pain or a chest wall deformity. If greater exposure is needed, this approach is easily converted to an open retropleural thoracotomy.
Advantages
- ▪
Achieves access to the ventral spinal canal comparable to that achieved with transthoracic approaches
- ▪
Does not penetrate the pleura, avoiding the need for routine chest tube drainage
- ▪
Provides the shortest direct route to the ventral thoracic spine, facilitating smaller incisions and less invasive soft-tissue dissection compared with other anterolateral and lateral approaches
- ▪
Preserves the intercostal neurovascular bundle and minimizes the risk of postoperative neuralgia and radicular artery injury
Disadvantages
- ▪
This approach requires more bone resection and soft-tissue manipulation than a posterolateral transpedicular-transfacet approach.
- ▪
The sympathetic chain is divided, which may result in a Horner syndrome in the rostral thoracic spine. This approach should not be used above the T3 level.
Costotransversectomy
Indications and History
Original descriptions of costotransversectomy for Pott disease were later adopted and refined by Hulme for the treatment of thoracic disk herniation. Resection of the rib head and transverse process provides more exposure to the ventral thecal sac for the removal of paracentrally herniated disks. Achieving good clinical results, costotransversectomy became the first safe alternative to laminectomy for thoracic diskectomy. With time, the technique described by Hulme would be expanded on to provide surgeons with more options to individualize treatment.
Positioning
Positioning for costotransversectomy varies. The procedure can be performed in the prone, semiprone, and modified lateral decubitus positions. If the disk is laterally herniated, an ipsilateral approach is generally taken. When laterality is clinically arbitrary some advocate a right-sided approach to minimize risk of injury to the artery of Adamkiewicz, which usually originates from the lower left intercostal arteries.
Incision, Dissection, and Diskectomy
Similar to positioning, skin incisions for costotransversectomy vary. Most surgeons prefer a midline incision, with or without a hockey stick extension, although semilunar and paramedian incisions are also described. Following a midline incision, a traditional midline subperiosteal dissection of the paraspinal muscles is performed, extending the dissection laterally to expose the transverse processes, facets, and rib heads. The rib head below the level of the disk herniation sees the most lateral exposure. Alternatively, a paramedian incision can be made; the lateral border of the erector spinae muscle is identified, and the fascial plane is followed to the costovertebral junction. The muscle belly is then mobilized laterally, exposing the transverse process and facet.
Before initiating bone work, intraoperative fluoroscopy should be compared with preoperative imaging to confirm the level of pathology. An initial laminectomy or laminotomy is performed to effect dorsal spinal cord decompression. Next, the transverse process is removed to expose the rib head of the segment below the disk herniation. The proximal rib is carefully dissected out from the parietal pleura, taking care to preserve the neurovascular bundle that lies along the caudal ventral margin. The lateral aspect of the rib is cut using a drill or narrow Leksell rongeur. The rib head is disarticulated from the spine using curettes and Kerrison rongeurs to expose the lateral cortex of the pedicle, and the proximal rib is removed and saved if arthrodesis is to be performed. If not readily apparent, the neural foramina can be localized by tracing the intercostal nerve medially under the rib bed. The pleura is then dissected subperiosteally along the lateral aspect of the disk space and end plates of the adjacent vertebral body and is retracted with a malleable retractor. The pedicle and facet can then be removed with a drill and rongeurs to afford a complete dorsal and lateral skeletonization of the spinal canal. The neurovascular bundle can be sacrificed to provide more exposure.
Before decompression, a space is made ventral to the spinal canal, into which the compressive disk material can be delivered. This requires at least a partial diskectomy and often necessitates extension into the adjacent vertebral bodies. The thecal sac is then carefully defined in relationship to the disk herniation, and disk material is delivered into the ventral space with minimal manipulation of the dura. One technique uses a down-angled curette and gentle and judicious use of a mallet. Resection of the PLL is preferable, when technically feasible, because it allows for confirmation of complete disk resection and adequate decompression. The ventral dural surface should then be inspected for any residual disk fragments or osteophytes. This may be accomplished with endoscopic assistance or with the use of angled mirrors. Stabilization and fusion can then be performed as indicated; this is required for lower thoracic exposures.
Advantages
- ▪
Better exposure of the ventrolateral spinal cord than can be achieved via the transpedicular-transfacet approach
- ▪
Less soft-tissue and muscle manipulation and rib resection compared with the lateral extracavitary approach (LECA), resulting in less postoperative pain
Disadvantages
- ▪
Limited visualization of the ventral spinal canal compared with LECA; not advised for calcified centrally herniated disks, particularly those with intradural extension
- ▪
Significant postoperative pain, although less painful than transthoracic approaches and LECA
Lateral Extracavitary Approach
Indication and History
The lateral extracavitary approach was originally developed by Capener for the treatment of tuberculous spondylitis and was later applied to thoracolumbar fractures. Its safety and efficacy for thoracic diskectomy has since been consistently proven in clinical series. Although it shares many similarities to costotransversectomy, the LECA provides better exposure of the ventral spine while maintaining an extrapleural trajectory. The exposure provided by the LECA is particularly useful when corpectomy is indicated for the treatment of infectious, neoplastic, or traumatic disease.
Positioning
Patients are traditionally placed in a prone position with arms taped to the sides. However, a “three-quarter” prone position with slight lateral rotation away from the surgeon may improve operative line of sight.
Incision, Dissection, and Diskectomy
A “hockey stick” incision is made with the vertical segment centered at the level of the herniated disk. Caudally, the incision curves laterally 8 to 12 cm toward the side of the herniated disk to facilitate soft-tissue reflection and increase the amount of rib that may be exposed and removed. Paramedian lunar-shaped incisions may also be used. A flap consisting of skin, subcutaneous tissue, and superficial fat is reflected and rotated laterally to expose the ipsilateral erector spinae muscles. The erector spinae are isolated circumferentially, joining a typical subperiosteal dissection medially and ventrally along the spinous processes, laminae, transverse processes, and ribs with a blunt dissection along the lateral fascial border of the muscle. Once mobilized, the muscle belly is translocated medially, providing a continuous exposure of the posterior elements and rib heads up to several centimeters lateral to the tip the transverse process.
Once the muscle mobilization has been performed, the surgical approach mimics costotransversectomy. The key difference is that mobilization of the erector spinae permits more rib to be resected, enabling more pleural retraction and a more lateral view of the canal and disk space. Accordingly, greater rib resection facilitates greater exposure of the ventral spinal cord.
Advantages
- ▪
Extrapleural exposure of anterior spinal elements is allowed without pleural violation.
- ▪
The dura may be directly visualized during decompression of the disk space and PLL, enhancing the safety and efficacy of decompression.
- ▪
Ventral spinal canal exposure can be augmented by extending rib resection.
- ▪
LECA exposure may provide the requisite ventral exposure for midline calcified disks.
Disadvantages
- ▪
Risk of postoperative neuralgia and radicular artery injury
- ▪
Relatively high rate of exposure-related postoperative morbidity
- ▪
Suboptimal for medically ill patients who may respond poorly to prolonged anesthesia or prone positioning
Minimally Invasive Considerations
Minimally invasive variations of costotransversectomy and the lateral extracavitary approach have been reported with encouraging results ( Fig. 30-5 ). Here the angle of approach is selected according to the patient’s pathology, the paraspinal musculature is dilated instead of mobilized, and the surgery is performed essentially as described in the text. This is a technically demanding procedure that requires specialized equipment and extensive experience with minimally invasive techniques.
Related posts:
Craniovertebral Junction Instabilities and Surgical Fixation Techniques
Surgical Approaches to the Craniovertebral Junction in Rheumatoid Arthritis
Anterior and Posterior Cervicothoracic Junction Stabilization Techniques
Lumbar Facet Screw Fixation Techniques
Surgical Management of Scheuermann Kyphosis
Primary Malignant and Benign Tumors of the Spine
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
