Video-Assisted Thoracoscopic Discectomy: Indications and Techniques

Thoracic Disc Disease

The surgical management of disorders of the thoracic spine began in 1814 when H. J. Cline attempted to treat a fracture of the thoracic spine by laminectomy. In 1911, Middleton and Teacher attempted the first surgical procedure for a thoracic disc herniation, which was later described by Benjamin. In this case the patient was paraplegic and subsequently died.

Historically, the diagnosis of a thoracic disc herniation has been a challenge. Given the lack of imaging, the diagnosis was required to be made solely on clinical history and physical findings. In addition, early surgical results were quite dismal. The evolution of diagnostic imaging and surgical techniques in the latter half of the 20th century has resulted in a significant improvement in the diagnosis and outcome of patients with thoracic disc herniation.

Thoracic disc herniation is a relatively infrequent clinical diagnosis, accounting for 0.25% to 0.75% of all disc herniations and approximately 4% of surgical cases. ^, The symptoms of thoracic disc herniation are variable and often nonspecific, and many patients experience a protracted clinical course with a delay in diagnosis. Radiologic studies focused on computed tomography myelography and magnetic resonance imaging have demonstrated an 11% to 14.5% incidence of thoracic disc herniations. ^, Woods and colleagues found disc herniations in 37% of the 60 asymptomatic patients evaluated by magnetic resonance imaging.

There has been a significant evolution in the surgical management of thoracic disc herniation. Early surgical therapy consisted of laminectomy alone, which often resulted in paraplegia due to excessive neural element retraction and carried a combined operative mortality as high as 10%. In 1969, Perot and Munro reviewed 91 laminectomies for thoracic disc herniations and found no neurologic improvement in 40 of the patients and progressive paraplegia in 16 of these patients. Others have also reported similarly poor outcomes with laminectomies for thoracic disc herniation. Variations on the surgical technique were used with laminectomies, including the use of decompression alone, decompression and transdural removal of disc material, and decompression with transdural rhizotomy and sectioning of the dentate ligaments, but all these successive approaches had similarly poor outcomes. The only exception to this pattern of poor surgical outcomes was the series reported by Horwitz and colleagues in 1955 in which five consecutive cases of thoracic disc herniation treated with laminectomy resulted in a good outcome. In 1998, Fessler and Sturgell reviewed and reported on 60 years of the literature in which they compared the mortality and morbidity rates with the various surgical approaches to the thoracic spine. They concluded that laminectomy alone does not provide adequate access to safely treat thoracic disc herniations.

In response to the uniformly poor outcomes after midline dorsal approaches to thoracic disc disease, surgical alternatives were developed using the anterior or extended posterolateral approaches with the costotransversectomy, transpedicular, and the lateral extracavitary approach. ^, Maiman and colleagues, in their report on the lateral extracavitary approach for thoracic disc herniation, reviewed 23 cases. None of the patients in the review experienced any new deficits postoperatively. However, this surgical technique required significantly more soft-tissue dissection and manipulation, with the paraspinous muscles being mobilized medially, resulting in devascularization and denervation. This was found to contribute to poor wound healing and increase in perioperative kyphosis. In addition, the lateral parascapular extrapleural approach, as developed by Fessler and colleagues, provided exposure to the upper thoracic spine, which was comparable with the lateral extracavitary approach. However, it presents the risk of significant shoulder girdle dysfunction due to lateral scapular mobilization. These approaches, despite their complexity, yielded significantly improved surgical and neurologic outcomes when compared with laminectomy for thoracic disc herniations.

The transpleural approach to the thoracic spine dates to 1958, when Craffoord and colleagues reported the use of this technique for herniated thoracic discs. In 1969, Perot and Munro reported the use of this approach in two patients, and in the same year Ranasohoff and colleagues reported the results of a similar approach for three patients. Since that time, the benefits of the anterior transthoracic approach have been supported by other published series.

In 1988, Bohlmann and Zdeblick recommended the anterior transthoracic approach over the costotransversectomy to treat herniated thoracic discs. This anterior transthoracic approach required a thoracotomy with rib resection and often resulted in significant perioperative morbidity including pulmonary dysfunction, intercostal neuralgia, and shoulder girdle dysfunction.

Spinal Endoscopy

Spinal endoscopy began in 1931 when Burman published a report on a technique he called myeloscopy. He described the use of an arthroscope to explore the lumbar thecal sac in cadaveric specimens. In 1938, Pool ^, expanded on Burman’s work and used a hot lamp system with improved visualization of the thecal space to examine more than 400 patients between 1938 and 1942. Despite the initial success of Barman and Pool, spinal endoscopy did not immediately gain widespread acceptance. Optical resolution and the light intensity were poor, and the instruments were far too large to easily explore and work in the confines of this small surgical space. Advances in fiber optics and the development of modern video technology have led to resurgence in interest in endoscopic approaches to the spine. Small cold light sources and video display monitors have replaced the older hot reflected light and lens tube systems.

In 1983, Hausmann and Forst used a nucleoscope to inspect the disc space for loose fragments after an open discectomy, and in 1992, Schreiber and Leu successfully performed a percutaneous discoscopy. The procedure was rapidly applied to surgery for thoracic disc herniations. ^,

The anterior approaches provide an unsurpassed exposure of the ventral aspect of the spinal column. It not only provides a large working area in which the adjacent anatomic structures became clearly identified but also provides the optimal angle for removal of intervertebral discs and allows easy inspection of the spinal cord. If necessary, repair of the dura in cases of intradural disc herniations can be performed via this approach. The anterior approach has become the preferred approach for most thoracic spinal pathology other than far lateral lesions. ^{, ,}

The main risk associated with the anterior transpleural approach is injury to vital vascular and visceral structures. There is associated morbidity with prolonged pulmonary dysfunction, incisional pain, and pain associated with thoracostomy tube drainage, which is a requirement after transpleural approaches. Comparative studies have shown a lower rate of pulmonary morbidity with thoracoscopic procedures when compared with open thoracotomy.

Landreneau and colleagues reported 106 such cases in 1993 in which they compared video-assisted thoracoscopic surgery (VATS) with thoracotomy. The patients who underwent VATS had less pain, improved pulmonary function, and had superior shoulder girdle function when compared with thoracotomy patients. That year, Mack and colleagues published a report demonstrating the potential of VATS to provide reliable access to the ventral surface of the thoracic spine. In 1995, Caputy and colleagues demonstrated the successful use of VATS in performing thoracic discectomy on both cadaveric and porcine models. In that study, the clinical use of thoracoscopic dissection was also reported.

Although the benefit of VATS is usually compared only with the alternative thoracotomy, data also suggest that it is a less morbid procedure than a costotransversectomy. Rosenthal and Dickman reported a series of 55 patients who underwent thoracoscopic discectomy and compared the rate of complications of the thoracoscopic procedures with both the patients undergoing open thoracotomy and the patients undergoing costotransversectomy for thoracic disc herniations. There were no instances of postoperative neurologic deterioration in either the thoracoscopic or thoracotomy group, but of those patients undergoing costotransversectomies, 7% experienced new neurologic deficits after surgery. Intercostal neuralgia, both temporary and permanent, has been a significant problem associated with thoracotomy. The use of VATS has significantly reduced the incidence of this painful disorder. In that series, there was a 16% rate of intercostal neuralgia in the VATS group compared with 50% in patients who had a thoracotomy. In all patients in the thoracoscopic group with intercostal neuralgia, the condition was temporary and resolved completely within 1 to 2 weeks. In patients undergoing costotransversectomy, there was a 20% rate of intercostal neuralgia.

Thoracic Cavity Anatomy

The surgical anatomy includes the external anatomy of the chest, the intrathoracic visceral and vascular anatomy, the contents of the posterior mediastinum, the ribs, the vertebrae, and neural elements.

A thorough knowledge of the anatomy of the thoracic cavity is critical for a successful procedure as well as for avoiding complications. The muscles of the chest wall, primarily the serratus anterior, pectoralis major, and latissimus dorsi, form important landmarks for thoracoscopic port placement. The serratus anterior forms the medial wall of the axilla. The pectoralis major demarcates the anterior axillary line and serves as the anterior border for trocar insertion, whereas the latissimus dorsi denotes the posterior axillary line and the posterior border for trocar placement. Attention should also be paid to the mammary gland overlying the anterior and lateral thoracic wall. Its origin just anterior to the midaxillary line, from the second to the sixth rib, is at risk during trocar introduction.

Inside the thoracic cavity, transparent parietal pleura covers the anterior, posterior, and superior aspects of the chest cavity. It reflects over the great vessels, trachea, esophagus, and spinal column and is easily separated from these structures. Commonly, the parietal pleura is studded with anthracotic pigment, indicating exposure to smoke or other inhaled pollution over the patient’s lifetime. Chronic inflammation of the pleura can render it opaque and prevent visualization of the underlying structures.

The right lung is composed of three lobes, whereas the left has two lobes. Each is divided by one or two fissures. Deflation and retraction of the lung permit visualization of the majority of the intrathoracic structures.

In the center of the chest cavity lies the mediastinum, containing the heart and great vessels. The heart is enclosed within the pericardial sac, and the phrenic nerve overlies the lateral surface. Accessing the right side of the thoracic cavity permits visualization of the right subclavian and brachiocephalic vessels. The right pulmonary artery, right main stem bronchus, and distal trachea can also be seen with retraction of the lung. Inspection of the left side of the chest cavity demonstrates the left subclavian artery, descending aorta, and internal mammary vessels. The left carotid artery is difficult to visualize in its position deep to the brachiocephalic venous trunk.

An inferior view of the chest cavity is defined by the diaphragm. Divided into two halves, the diaphragm originates from the xiphoid process, upper lumbar vertebrae, and lower six ribs. During full expiration, the right hemidiaphragm ascends to the level of the fourth intercostal space and the left to the level of the fifth rib. This fact must be considered at the time of trocar placement to avoid perforation of the diaphragm and violation of the peritoneal cavity.

The complex vascular anatomy of the paravertebral area as demarcated from the intrathoracic perspective requires a detailed understanding before embarking on thoracoscopic procedures. The posterior intercostal arteries of the first two vertebral segments arise from the superior intercostal artery branch of the costocervical trunk of the subclavian artery. The lower posterior intercostal arteries arise segmentally directly from the aorta. The segmental branches on the right are longer and traverse a greater distance than segmental branches on the left. These arteries leave the aorta and travel on the side of the vertebral body between the intravertebral discs. These arteries are crossed, immediately anterior to the rib head articulation, by the sympathetic chain. The arteries then course superiorly under the tip of the transverse process, merging with the vein and nerve in the costal groove. At this point, the artery gives off a branch that continues in a posterior course over the transverse process to supply the muscles of the back. However, before passing over the transverse process, it sends a spinal branch through the intravertebral foramen, which supplies the spinal cord ( Fig. 142.1 ).

The primary blood supply to the lower thoracic spinal cord is via the great radicular anastomotic artery of Adamkiewicz. This vessel most often enters from the left side between T8 and L3. Disruption of this radicular artery can lead to spinal cord infarction and paraplegia. Spinal angiography should be considered for locating this vessel before considering costotransversectomy or transpedicular approaches to the disc space at the lower thoracic spine levels. However, angiography is generally unnecessary when a thoracoscopic technique is used.

The posterior intercostal vein courses in the intercostal space adjacent to and in a rostral position with the posterior intercostal artery. Blood from the spinal cord, spine, and posterior muscles converges at the level of the rib head. The segmental vein courses over the lateral aspect of the vertebral body, merging, depending on the location, with the azygos, hemiazygos, or superior intercostal vein.

The first intercostal vein ascends over the first rib and arches above the pleura to terminate in the corresponding brachycephalic or vertebral vein. The second and third intercostal veins unite to form a superior intercostal vein. On the right, this vein drains into the terminal part of the azygos vein, and on the left, it branches into the brachycephalic vein. At all levels below the third intercostal region, the veins empty into the azygos vein on the right and into the accessory hemiazygos vein on the left. The hemiazygos and accessory hemiazygos veins cross to the right side of the thoracic cavity, emptying into the azygos vein. The azygos vein then ascends and empties into the superior vena cava just before passing through the pericardium.

To avoid injury to the phrenic nerve and subsequent diaphragm paralysis, a more thorough understanding of its course is warranted. Upon leaving the cervical plexus, the phrenic nerve accesses the thoracic cavity via the thoracic inlet and runs along the lateral border of the brachiocephalic trunk. On the right, the nerve continues along the superior vena cava, over the right side of the heart, and into the diaphragm. On the left, the nerve runs between the left common carotid and subclavian vessels until it meets the diaphragm.

The sympathetic chain and ganglia lie in the retropleural space over the rib heads in the upper chest cavity, cross the segmental vessels, and move medially to lie over the vertebral bodies in the caudal portion. The sympathetic chain is made up of ganglia linked by interganglionic cords. This chain is located anterior to the rib head of the thoracic vertebrae and crosses the segmental vessels. The medial branches of the upper five ganglia supply the thoracic aorta via the thoracic aortic plexus. The medial branches of the lower ganglia coalesce to form the splanchnic nerves. The anterior rami of the thoracic nerves form an intercostal nerve. Each nerve is connected to the ganglion of the adjacent sympathetic trunk by a gray and a white communicating ramus. They pass forward in the intercostal space below the intercostal vessels. The sympathetic preganglionic nerve fibers are conveyed through white rami to the sympathetic trunk. They in turn synapse with the cells of the sympathetic ganglia. These ganglion cells of the sympathetic chain send out postganglionic fibers through the gray rami, which return to join the spinal nerves.

The vagus nerves and their recurrent branches also lie within the thoracic cavity. The left vagus nerve runs between the left common carotid artery and subclavian artery, then passes between the left pulmonary artery and the aortic arch. It continues in close proximity to the esophagus, where it forms the anterior vagal trunk. The left recurrent laryngeal nerve arises below the aortic arch and ascends into the neck in the tracheoesophageal groove. The right vagus nerve runs anterior to the right subclavian artery and deep to the brachiocephalic vein. It then gives off its recurrent branch and continues along the trachea and ends as the posterior vagal trunk along the esophagus.