Overview
Anterior lesions of the thoracic spine can present a challenging clinical scenario. Unlike the cervical spine, at which anterior approaches are commonplace, the generally unfamiliar surrounding anatomy can make thoracic anterior approaches seem daunting. Reaching the anterior column through a posterior approach, particularly to address central lesions, requires that the surgeon avoid manipulation of the thoracic cord to avoid potentially severe neurologic complications; this was shown by Love and Kiefer, who found that over a third of patients undergoing laminectomy for thoracic disk herniation had either no improvement or experienced worsening of neurologic symptoms.
Knowing that the thoracic spinal cord is intolerant to manipulation, the spine surgeon may inadequately expose or undertreat an anterior compressive lesion from a posterior approach. Anterolateral thoracotomy has been in general use for more than a century, although its use in the spine was described more recently by Hodgson in 1956 for débridement and fusion in the setting of Pott disease. Since that time, thoracotomy has been considered the “gold standard” for decompression of anterior spinal lesions. Although multiple alternative posterior and posterolateral approaches to the anterior column have been described elsewhere (transpedicular, costotransversectomy, lateral extracavitary), as have thoracoscopic and miniopen approaches, in response to the perceived morbidity associated with thoracotomy, transthoracic approaches remain a safe and effective option in treating anterior pathology in the thoracic spine.
Anatomic Considerations
Superficial (Extrapleural)
The anterolateral transthoracic approach begins superficially with an incision oriented along the rib, which is covered superficially by loose connective tissue and periosteum. Posteriorly, the fibers of the latissimus dorsi muscle cross the ribs nearly perpendicularly. Deep to the latissimus, the erector spinae muscle group—the iliocostalis, longissimus, and spinalis, from lateral to medial—run vertically on either side of the spinous processes. The scapula limits the posterior extent of the exposure, because it overlies the posterior aspect of the second through seventh ribs. Following the rib posteriorly will lead first to the tip of the transverse process, which covers the angle of the rib, and subsequently to the rib head, articulating with paired demifacets over the intervertebral disk.
Because the ribs angle caudally on leaving the spine, careful attention to selection of level is crucial; the rib to be exposed and resected will often originate one or two levels cranial to the spinal pathology to be addressed. The inferior edge of each rib has a costal groove that contains the intercostal artery, nerve, and vein. After rib resection, the rib bed is encountered, consisting of the deep periosteum and adherent parietal pleura, along with the remaining intercostal vessels and nerve. Incision of the rib bed will allow entry into the pleural potential space.
Deep (Intrapleural)
Incision of the rib bed opens the pleural space, created by a continuous layer of connective tissue covering the inner surface of the thoracic wall (parietal pleura) and the outer surface of the lungs (visceral pleura). In the normal anatomic state, the pleural space is a potential space; the visceral and parietal pleura held in close approximation by negative hydrostatic pressure allows for thoracic wall excursion to expand the lung during respiration. Incision of the parietal pleura, however, temporarily disrupts this negative pressure and allows the lung to collapse.
Once the pleural space is entered, several important structures are encountered. The arch of the aorta is normally at the T4 vertebral level, and it becomes the descending aorta, traveling inferiorly along the left side of the vertebral bodies from T5–T12 before passing through the diaphragm and becoming the abdominal aorta. The thoracic duct is the main avenue for lymphatic drainage for three quarters of the body. It ascends on the anterior aspect of the vertebral bodies, crossing from right to left of midline between T4 and T6. The duct is dull white in color and sometimes appears beaded because of multiple valves. The duct is thin-walled and fragile, and if the anterior aspect of the spine is exposed, care should be taken to identify and protect it, because treatment of a persistent chyle leak can be problematic. The thoracic sympathetic trunk and its associated ganglia lie along the rib heads and are generally safe in the upper thoracic spine. In the lower thoracic spine, however, these structures become more anterior and may lie along the sides of the vertebral bodies.
The thoracic spine itself lies posterior to the posterior mediastinum and is covered in parietal pleura. Segmental vessels from the aorta and vena cava run from anterior to posterior at the midportion of the each vertebral body. The intervertebral disk is generally identified by its shiny white annulus fibrosis and by the fact that it is generally more prominent than the midvertebral body (i.e., a “hill” rather than a “valley”).
Indications
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Treatment of anterior compressive lesions
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Tumor
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Thoracic disk herniations
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Bony fragments resulting from trauma
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Treatment of spinal instability resulting from infection (vertebral osteomyelitis/diskitis), tumor, or trauma
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Mobilization of the thoracic spine for deformity correction
Operative Technique
- 1.
The patient is positioned on a radiolucent operating room (OR) table in the straight lateral decubitus position on a vacuum beanbag; all bony prominences must be well padded. A dual-lumen endotracheal tube is used to allow for selective deflation of one lung. The entire hemithorax, from the midline of the sternum to the spinous processes, is draped into the surgical field. If the approach is to be proximal (T4 or above), the arm may need to be draped into the field to allow for manipulation of the scapula. Regarding the side of approach, if the pathology is clearly one-sided, that side should be chosen. If not, we generally prefer to approach the low thoracic spine (T10 and below) from the left side, because the liver and elevated hemidiaphragm make the right-sided approach more difficult this low. Above T10, the right-sided approach is preferred, because the heart and descending aorta can make the left-side approach more difficult.
- 2.
Care in selection of the level is especially crucial in the thoracic spine, because counting of levels can be difficult using intraoperative fluoroscopy. Ribs are most reliably counted from caudal to cranial, because the first rib can be medial to the second rib and may be difficult to palpate. If any doubt exists as to the correct level, intraoperative fluoroscopy should be compared with preoperative imaging, which may include either sagittal magnetic resonance imaging (MRI) showing both the sacrum and the herniation on a single cut or a computed tomography (CT) scan with coronal reconstruction to demonstrate the ribs at each level; this allows a precise count of thoracic and lumbar vertebrae. The interventional radiologist can place a marker on the spine at the level of pathology before the CT that can act as an intraoperative guide for identification using fluoroscopy. For lesions of the vertebral body, we typically resect two ribs higher (e.g., we resect the sixth rib for a T8 lesion). For disk herniations, if rib head resection is required for adequate exposure, the rib head over the affected disk space is resected (the ninth rib head is resected for a T8–T9 disk herniation).
- 3.
Once the appropriate level is selected, the skin is incised from the lateral border of the paraspinal musculature to the costochondral junction in line with the selected rib. Less skin can be taken if less exposure is needed. Using a slightly more transverse incision tangential to the rib allows for skin mobilization in the event that the next cranial or caudal rib must be resected for greater exposure ( Fig. 28-1 ).
Figure 28-1
Patients are positioned in the lateral decubitus position. Skin incisions are made longitudinally along the planned rib resection ( dashed lines B or C ), unless the planned exposure is proximal such that the scapula overlies the targeted rib. In this case, the skin incision follows the medial border of the scapula ( dashed line A ).
- 4.
Using electrocautery and maintaining meticulous hemostasis, the chest wall musculature is divided to expose the superficial surface of the rib. For proximal exposures with planned resection of the third or fourth rib, the retraction of the scapula cranially and medially may be required to adequately expose the rib ( Fig. 28-2 ).
Figure 28-2
Exposures proximal to T6 may require mobilization of the scapula. Mobilization proceeds in a cranial and medial direction.
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Once the periosteum covering the superficial surface of the rib is exposed, and the appropriate level has been confirmed, the periosteum is incised sharply, and curved-tip elevators are used to strip the periosteum circumferentially as far posteriorly as possible. To avoid injury to the intercostal vessels, caution should be exercised during this step, particularly when dissecting under the caudal surface of the rib. In cases of a thoracic disk herniation, when the approach is to be limited to a single disk space, rib resection may not be necessary. In this case, the dissection can be limited to the superior aspect of the rib, and the spine can be exposed through the intercostal space without resection of the rib.
- 6.
The rib cutter is then used to resect the exposed portion of rib ( Fig. 28-3 ). This resection should be performed anteriorly at the costochondral junction and as far posteriorly as possible. If a need for autogenous bone graft is anticipated, the resected portion is saved, and bone wax is applied to the remaining cut ends of the rib.
Related posts:
Craniovertebral Junction Instabilities and Surgical Fixation Techniques
Surgical Approaches to the Craniovertebral Junction in Rheumatoid Arthritis
Thoracic Microdiskectomy: Lateral and Posterolateral Approaches
Lumbar Facet Screw Fixation Techniques
Surgical Management of Scheuermann Kyphosis
Primary Malignant and Benign Tumors of the Spine
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