Lateral Retropleural Thoracic Discectomy and Corpectomy

27 Lateral Retropleural Thoracic Discectomy and Corpectomy

David S. Xu, Jakub Godzik, S. Harrison Farber, Shashank V. Gandhi, Ernest J. Wright, Courtney Hemphill, Sebastian Uribe, and Juan S. Uribe

Summary

Lateral retropleural thoracic discectomy and corpectomy is a minimally invasive surgical strategy to treat thoracic disc herniations. Open anterolateral transthoracic approaches have traditionally been the gold standard surgical strategy to perform thoracic discectomies, but perioperative morbidity and postoperative chest wall pain syndromes are significant associated risks. In efforts to reduce the morbidity associated with open thoracotomy, the mini-open lateral retropleural approach has been developed to achieve maximal exposure of the herniated disc without obstruction by the thecal sac. In this chapter, we outline patient selection, preoperative planning, and intraoperative workflow to safely and efficiently execute a mini-open lateral retropleural thoracic discectomy.

Keywords: corpectomy discectomy minimal invasive surgery mini-open lateral retropleural spine thoracic

27.1 Introduction

Thoracic disc herniations are uncommon and comprise less than 1% of all symptomatic disc herniations.1^,² Based on historical studies, less than 25% of patients with herniated thoracic discs are symptomatic.³ When symptoms do present, the clinical manifestations are protean and depend on the anatomic configuration of the herniated disc. Large central herniations may cause spinal cord compression, leading to motor deficits and myelopathy, while paracentral herniation may impinge on thoracic nerve roots leading to radiculopathy or dysesthetic pain along the chest wall, abdomen, or viscera.⁴^,⁵

Early surgical management of thoracic disc herniations relied on laminectomy alone and resulted in high rates of major morbidity ranging from 18 to 75% in different series.¹^,⁶ These poor results are most likely due to iatrogenic injuries incurred during manipulation of the thecal sac to visualize the disc space. Consequently, in the 1960s, anterior approaches via thoracotomy quickly became the gold standard by permitting wide exposure of herniated discs, unimpeded by neural structures, allowing the removal of even heavily calcified and transdural lesions.⁷ However, an open thoracotomy carries a risk of morbidity, with over 30% of patients developing significant thoracic pain more than 4 years postoperatively.⁸ Thoracoscopic discectomy emerged to reduce the morbidity of open transthoracic exposures but has had limited acceptance due to the specialization and high cost of equipment, the steep learning curve, and limitations of the technique in managing intraoperative complications such as hemorrhage or cerebrospinal fluid (CSF) leaks.⁹^,¹⁰

Recently, a lateral mini-open retropleural approach to the thoracic spine was developed as an intermediate option between open thoracotomy and minimally invasive thoracoscopy.¹¹^,¹² Through specialized retractors, the lateral mini-open approach enables direct visualization of the thoracic disc with less exposure-associated morbidity, while enabling the use of standard instruments in a familiar operative corridor. In this chapter, the authors provide a detailed description of the operative planning, execution, and postoperative care of patients undergoing a mini-open lateral thoracic retropleural discectomy.

27.2 Indications

Thoracic discectomy is indicated in patients with declining motor function or progressive myelopathy attributable to spinal cord or conus compression by a herniated thoracic disc. Furthermore, intractable pain or discomfort caused by thecal sac or nerve root compression that is unresponsive to conservative measures is also an indication for discectomy.

27.3 Contraindications

Significant scoliosis is a contraindication for a lateral approach because the coronal deformity may prevent a perpendicular approach to the disc space. Previous thoracic surgery is a relative contraindication due to the presence of scar tissue between the parietal pleura and the endothoracic fascia, forcing an intrapleural approach. Knowledge of and familiarity with lateral approach surgeries are paramount and are the primary determinant of what types of disc herniations are amenable to surgical resection. Small, paracentral disc herniations are less technically demanding and can be undertaken by surgeons early in the learning curve. Removal of large central disc herniations or those that are heavily calcified should be undertaken only by surgeons well accomplished with the approach and equipment.

27.4 Preoperative Planning

A preoperative magnetic resonance imaging (MRI) or computed tomography (CT) myelography of the thoracic spine is required to define the neural elements and level to be treated. In addition, noncontrast CT imaging of the thoracic spine should be done to determine the degree of disc calcification as well as to facilitate accurate level localization. In patients with variant anatomy or large body habitus that the surgeon anticipates might cause difficulty with intraoperative localization, a radiopaque fiducial can be placed in the pedicle or rib head adjacent to the treated level before surgery. In all patients, neuromonitoring with somatosensory and motor evoked potentials is mandatory.

27.5 Patient Positioning

After induction of general anesthesia and intubation, the patient is positioned in the lateral decubitus position with the side of the approach facing upward (Fig. 27.1a). The patient’s height on the bed should be adjusted to ensure that the thoracic level to be treated rests above the table break. An axillary roll is placed to decompress the brachial plexus, and an optional roll can be placed just above the underlying iliac crest to promote torso bending. The table is then subtly broken to increase the intercostal distance. At this point, the fluoroscope is brought in to verify the level of localization, and the bed should be repositioned to achieve perfect anteroposterior (AP) and lateral radiographs of the level to be treated, without requiring changes to the tilt or arc of the fluoroscope. A 16-gauge needle can be inserted into the spinous process overlying the level to be treated, which acts as an in-situ fiducial (Fig. 27.1a, b).

Fig. 27.1 Patient positioning and fiducial placement. (a) The patient is positioned for a right-sided approach with the left flank facing downward and the head on the left-hand side of the image. A purple foam roll is placed under the axilla to decompress the brachial plexus and above the downfacing iliac crest to facilitate torso bending during table breakage. A 14-gauge needle (arrow) is inserted into the spinous process directly overlaying the disc space to act as a fiducial. (b) Lateral radiograph shows the fiducial (arrow) in line with the disc space to be treated. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.)

Incision planning proceeds by drawing the lateral projection of the disc space and adjacent vertebra on the patient’s flank (Fig. 27.2a, b). A 5-cm incision begins at the posterior margin of the disc space and runs parallel to the underlying rib or intercostal space. This incision ensures that the retractor will be centered on the interface between the disc space and thecal sac (Fig. 27.2c).

Fig. 27.2 Incision planning. (a) Lateral radiograph shows a reference cross on the patient’s skin in line with the posterior margin of the vertebral body and the disc space to aid in planning the incision. (b) Photograph of the planned incision shows the outline of the disc space to be treated as well as the adjacent vertebra. The incision itself is a slanted line that intersects the posterior margin of the disc space and runs along the groove of the underlying rib or intercostal space. (c) The illustration shows the superimposed image of the planned incision and the underlying thoracic structures. The incision is centered posterior to the disc space to allow easier dissection of the retropleural plane and anterior retraction of the pleura and lung. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.)

27.6 Step-by-Step Surgical Technique with Example

27.6.1 Incision and Exposure

Step 6: The planned incision is made, and the underlying intercostal space is exposed. If the intercostal space is not large enough to accommodate a working corridor, a 5- to 7-cm segment of the bordering rib is resected. Upon removal of the rib, the parietal pleura is visualized and deflected anteriorly along with the underlying lung by digital or blunt retraction (Fig. 27.3a).

Step 6: A retropleural corridor is then created by carefully dissecting the medial and deep planes of the parietal pleura from the adjacent endothoracic fascia in an extracavitary fashion (Fig. 27.3b).

Step 6: Once the dissection approaches the rib head attached to the vertebral body inferior to the disc space, sequential blunt dilators are inserted to allow placement of a split blade retractor (MaXcess, NuVasive Inc.) that is then docked and opened.

Step 6: The rib head is then resected to expose the underlying pedicle (Fig. 27.4a, b), and the retractor is opened to the final working diameter. The size of the final exposed operative field consists of a superior-inferior border delimited by the inferior margin of the pedicles of the vertebral bodies adjacent to the disc space to be treated, the posterior border marked by the transverse processes of the spine, and the anterior border marked at the midpoint of the disc space (Fig. 27.4c).