Endoscopic Transoral Approaches to the Craniocervical Junction

42 Endoscopic Transoral Approaches to the Craniocervical Junction

James H. Stephen and John Y. K. Lee

42.1 Introduction

Surgical access to the craniovertebral junction (CVJ) is challenging because of its deep, anatomically protected location. The pathology that can involve the CVJ is diverse and includes rheumatoid odontoid pannus, basilar invagination, congenital skull base malformations, lower clival chordomas and chondrosarcomas, metastatic disease, infection, and even intradural pathologies, such as meningiomas. The most direct route to the anterior CVJ is by the ventral transoral approach.1,2 This approach was refined by Menezes, Crockard, and Hadley^3,4,5 and was adopted as the preferred approach for treating pathology of the anterior CVJ. However, the traditional transoral approach has several limitations. Given the deep, narrow working channel, the operating microscope may not provide adequate visualization of the pathology. While the extended transoral variants may achieve improved visualization and greater access, they are achieved at the expense of greater morbidity.

Given the significant morbidity with the traditional transoral approach, endoscopic approaches to the CVJ have been pioneered. Compared with the narrow column of illumination and visualization provided by the operative microscope, the endoscope can provide direct illumination deeper and closer to the target. Modern endoscopes can capture a field of view up to 80° and provide a panoramic view of the anatomy. Another current advantage of endoscopes is their worldwide availability. Unlike microscopes, however, most endoscopes remain two-dimensional, with resolution that is limited by the camera and the display screen, but these limitations are being addressed with three-dimensional endoscopes and improved video technology. The feasibility of transoral robotic surgery (TORS) as a tool to address pathology of the craniocervical junction has been demonstrated.⁶ In TORS, the dual-channel endoscope provides stereoscopic (3D) visualization with excellent illumination and there are two articulating robotic arms to work at depth in the deep narrow channel. However, there are limitations to TORS that prevent the entire procedure, especially bony removal, from being performed endoscopically by the robot. As surgeons continue to pioneer the endoscopic transoral approach, improvements in technology and instrumentation over time will allow a greater range of pathology to be tackled through this approach (Video 42.1).

42.2 Surgical Anatomy

• The endoscopic transoral approach provides access from the lower third of the clivus down to the C2–C3 disk space.

• Surgical exposure and the size of the working channel are limited by mouth opening. In addition, the hard palate is the physical barrier that limits superior access, while the mandible and tongue limit inferior access. However, given that endoscopy provides panoramic illumination and visualization not limited to the line of sight, these geometric limitations are less of a hindrance than in traditional transoral approaches.⁷

• Identification of the midline is very important for the transoral approach. The anterior arch of the atlas can be palpated and visualized behind the pharynx.

• Aberrant vertebral arteries or retropharyngeal carotid arteries are a possibility, although both usually lie more than 1 cm off the midline. This affords a safe working zone up to 1 cm laterally on either side of the midline.

42.3 Preoperative Planning

• Patients with trismus (inability to fully open the mouth), prior temporomandibular joint (TMJ) injuries, or prior TMJ surgery may not be candidates for transoral surgery. An inability to open the mouth at least 25 mm (average mouth opening is 40 mm) preoperatively is a relative contraindication to transoral surgery.

• A fixed chin-on-chest deformity is also a contraindication to the transoral approach. Other contraindications include dental/periodontal infections or anomalous anatomy that results in vital neurovascular structures’ being ventral to the pathology.

• Lesions that are reducible from a posterior approach should undergo a simple posterior decompression and fusion rather than undergoing a transoral approach.

• Preoperative CT may be utilized to assess the limits of surgical access in each individual patient. The length of the hard palate and the position of the CVJ relative to the hard palate help determine access. If the pathology is located above the hard palate, then an endonasal approach may be a better choice.

• Vascular imaging with CT angiography (CTA) may be helpful where a tumor has distorted the anatomy or when lateral dissection is required.

• The transoral approach is limited by providing decompression only. Pathology at the CVJ may lead to instability, and this can be further destabilized by the procedure. Often, posterior surgical stabilization may also be required, and reconstruction/stabilization should be considered preoperatively.

• Preoperative trach or percutaneous endoscopic gastrostomy (PEG) may be required in patients with existing lower cranial nerve dysfunction, and this possibility should be evaluated as part of the preoperative work-up.

• A lumbar drain can also be placed preoperatively if intradural pathology is the surgical target or if a CSF leak is expected.

• The patient should be adequately counseled preoperatively about the potential complications and morbidities of the transoral approach.

42.4 Patient Positioning and Anesthesia

• The patient is positioned supine with slight neck extension. Care should be taken to avoid head rotation to prevent surgical disorientation that may result from rotation of the atlas—and vertebral artery—in relation to the midline.

• The patient’s head may be fixed in a Mayfield head holder or a halo vest, depending on the stability of the CVJ.

• The airway is of critical importance, and collaboration with anesthesia should ensure proper choice of, and technique for, the endotracheal tube (ETT). We prefer a midline armored ETT that exits inferiorly toward the patient’s feet.

• Intraoperative monitoring, including somatosensory evoked potentials and motor evoked potentials, is utilized to prevent any positioning-related neurological compromise.

• Lateral fluoroscopy is utilized for localization of the bony anatomy. Neuronavigation may also be used for intraoperative localization.

• For endoscopic procedures, surgeons are positioned on either side of the head, with the display monitor at the head of the bed.

• For TORS, the da Vinci surgical robot (Intuitive Surgical, Sunnyvale, CA) is positioned at the head of the bed. A 12-mm, 0° endoscope is used, although a 30° endoscope may be used to enhance the superior or inferior visualization as needed. The binocular endoscopic arm is kept midline, with one articulating arm on either side.

42.5 Surgical Procedure

• There are several options for retraction during the transoral approach, including the Dingman retractor or a Crowe-Davis retractor.

• Care should be taken not to overdistract the jaw, dislocating or injuring the TMJ. We limit the opening to 4 cm.

• The soft palate can also obscure the view, but it may be retracted superiorly using two red rubber catheters placed through the nose and out of the mouth (Fig. 42.1). Alternatively, a stitch can be placed in the uvula, which is then retracted out through the nose.

• While it is rarely necessary, the soft palate may be split, incising from the uvula up to the hard palate.

• Teeth guards should be used and care should be taken to avoid tongue compression against the teeth by the retractor or ETT tube.

• The anterior arch of the atlas may be palpated with gentle pressure.

• We prefer a midline incision in the posterior pharyngeal mucosa, where there is a relatively avascular plane. This avoids critical vascular and neural structures that may be damaged with a U-shaped incision (Fig. 42.2).

• Using TORS, a midline incision is taken down to the anterior arch of C1 and then is extended inferiorly to the body of C2. At this point, localization is confirmed with lateral fluoroscopy. The anterior longitudinal ligament is taken down to expose the anterior atlantooccipital membrane, the arch of C1, and the base and dens of C2 (Fig. 42.3).