Endoscopic Approach to the Craniocervical Junction

42 Endoscopic Approach to the Craniocervical Junction

Vincent Dodson, Neil Majmundar, Wayne D. Hsueh, Jean Anderson Eloy, and James K. Liu

Abstract

Endoscopic surgical approaches to the craniocervical junction (CCJ) may offer advantages over the current gold standard, the microsurgical transoral approach. Recent advances in endoscopic technology have allowed neurosurgeons and otolaryngologists to approach the CCJ via an endonasal, transoral, or transcervical route. Although the endoscopic approaches are less familiar to most surgeons, these novel approaches are less morbid than the microsurgical transoral approach. The endoscopic endonasal approach (EEA) involves the navigation through the nasal cavity to access the CCJ via an incision made to the posterior pharyngeal wall. The endoscopic transoral route also provides access to the posterior pharyngeal wall through the oral cavity. The endoscopic transcervical approach is similar to other procedures which require access to the anterior cervical spine and makes use of an angled tubular retractor to access the CCJ. Although the endoscopic approaches are not without limitations, their success in being able to reach lesions in the CCJ without significant postoperative complications has been well reported in the literature. This chapter covers the advantages of the endoscopic approaches, their special surgical considerations, and their limitations.

Keywords: endoscopic, endonasal, transcervical, craniocervical junction, craniovertebral junction, odontoidectomy

42.1 Introduction

The craniocervical junction (CCJ) is comprised of the occiput, the foramen magnum, and the upper cervical spine. Pathologies affecting this region include acquired diseases (rheumatoid arthritis and Paget’s disease), congenital abnormalities (Chiari malformation, Klippel-Feil malformation, and atlantoaxial instability secondary to Down syndrome), and neoplasms (meningiomas, chordomas, and metastases). All of these conditions may potentially cause abnormalities of the CCJ. Symptomatic and compressive pathologies occurring at the CCJ often require surgical intervention. Therefore, an optimal surgical approach which treats the patient’s symptoms while limiting morbidity and mortality is imperative for skull base surgeons to achieve successful patient outcomes.

Historically, the transoral or transpharyngeal approach had been considered the “gold standard” route for access to the CCJ, tracing its origins to the 1930s.1 This approach involves retraction of the uvula, soft palate, and the posterior pharyngeal wall.² In addition to being a well-studied procedure for several decades, the transoral approach provides excellent surgical exposure and the most direct route to the ventral CCJ.³ ^, ⁴ However, this approach exposes the patient to an increased risk for velopharyngeal insufficiency due to the necessary retraction of the soft palate and resection of the hard palate. This approach also requires the use of a retractor to maximize the space between the upper and lower jaw and to displace the tongue, increasing the patient’s risk of damage to teeth, ischemic necrosis or swelling of the tongue, and/or upper airway obstruction.⁴ Thus, the approach carries high rates of extended postoperative intubation as well as dysphagia.⁴

Advances in endoscopic technologies have allowed neurosurgeons to navigate to the CCJ using minimally invasive approaches through the nose (endonasal), mouth (transoral), and neck (transcervical) (Fig. 42.1). These approaches have been shown to avoid several of the pitfalls associated with the microsurgical transoral approach and are slowly becoming the preferred approaches as familiarity with them increases.⁵

Fig. 42.1 (a) Endoscopic endonasal corridor, (b) endoscopic transoral corridor, and (c) endoscopic transcervical corridor.

42.2 The Endoscopic Endonasal Approach

The endoscopic endonasal approach (EEA) eliminates the need to split the soft palate, avoiding the increased risk of velopharyngeal insufficiency associated with the microsurgical transoral approach.⁵ Feeding complications after the endonasal approach have been found to be reduced compared to the transoral approach. Patients who undergo the endonasal approach resume normal feeding earlier than those undergoing a transoral approach.⁵ ^, ⁶ Furthermore, as the endonasal approach does not cause trauma to the oropharyngeal soft tissues, the risk of postoperative breathing complications and the need for postoperative tracheostomy are reduced.⁵ ^, ⁷ Some case reports have also described the preferred use of the endonasal approach for pediatric patients because the transoral approach requires resection of the hard palate for greater rostral exposure owing to their smaller mouths.⁸ ^, ⁹ ^, ¹⁰

42.3 Surgical Technique and Anatomic Landmarks

When the endoscope is advanced through the nasal vestibules, the nasal septum is medial, while the turbinates are encountered laterally. The inferior ends of the middle and inferior turbinates are the landmarks for the lateral aspects of the choana.11 The ostium of the Eustachian tube is also found on the lateral aspect of the choana and is a useful landmark for the lateral limit of the endonasal approach. If identified bilaterally, the midpoint between the ostia can be used to determine the midline of the posterior pharyngeal wall, where the incision is made to access the CCJ.¹² To increase the area of the surgical working corridor, it is often necessary to perform a posterior septectomy. We have previously described a mucosal sparing septectomy technique to access the CCJ so that the septectomy is performed in a way that spares the vascular supply and surface area of the septal mucosa, as these may be needed as a flap for reconstruction in the event of an intraoperative cerebrospinal fluid (CSF) leak.¹³ ^, ¹⁴ ^, ¹⁵ ^, ¹⁶ ^, ¹⁷ ^, ¹⁸ To do this, a pedicled nasoseptal flap (PNSF) is constructed on both sides of the septum. Each PNSF should be harvested in different sizes so that the flaps on either side are offset. Each PNSF is then tucked into the ipsilateral middle meatus for protection. Constructing the flaps in this way maintains their vascular supply, preserving them for future use.¹² ^, ¹⁹

Superior to the choana is the caudal aspect of the sphenoid sinus, where the septal branch of the sphenopalatine artery can be visualized as it courses medially to the nasal septum.¹¹ Advanced further, the soft palate is visualized caudally. To expose the CCJ, an incision is made at the midline of the posterior pharyngeal mucosal wall with monopolar cautery, and the underlying longus capitis and longus colli muscles are dissected laterally. As the incision is extended vertically, the structures exposed in a rostral-to-caudal order are the inferior clivus, the anterior atlanto-occipital membrane, the anterior arch of the atlas, and the body of C2. For exposure of the odontoid process, the anterior arch of the atlas is removed with a high-speed drill.¹¹ Care is taken not to drill laterally into the C1 lateral masses. After removal of the anterior arch of C1, the odontoid process is defined with a monopolar cautery and angled curette. The odontoidectomy is then performed with a high-speed drill by hollowing out the center much like a canoe so that an eggshell thickness of cortical bone remains. The remaining bone is removed with angled curettes and Kerrison rongeurs. Attention is then directed toward resecting the transverse ligament, tectorial membrane, and any residual ligaments to remove any compressive pannus. The underlying compressive pathology is removed to decompress the dural sac of the CCJ. Any remnants of tissue that are adherent to the dural sac should be trimmed and left intact in order to avoid intraoperative dural tears and CSF leak. An adequate decompression is typically manifested by reinflation of the dural sac. Image guidance is also helpful in determining the extent of ventral decompression. In some cases of severe basilar invagination, it may be necessary to drill off the inferior clivus in order to access the odontoid process (Fig. 42.2 and Fig. 42.3).¹²

Fig. 42.2Case 1. (a) Preoperative T2-weighted sagittal MRI of the cervical spine demonstrating atlanto-occipital assimilation, basilar invagination, and fusion of the C3 and C4 vertebral bodies consistent with a Klippel-Feil anomaly. Obvious compression of the medulla and upper cervical cord is seen. (b) Immediate postoperative T2-weighted sagittal image of the cervical spine demonstrating successful endoscopic endonasal resection of the anterior arch of C1 and the odontoid process of C2. (c) Preoperative CT of the cervical spine demonstrating tip of dens 5 mm above McGregor’s line. (d) Immediate postoperative CT of the cervical spine demonstrating successful occipitocervical fusion. Note the amount of decompression achieved through the endoscopic endonasal approach.

Fig. 42.3Case 2. (a) Preoperative T2-weighted sagittal image of the cervical spine demonstrating Chiari malformation type 1 and basilar invagination causing severe compression of the lower brainstem and upper cervical spinal cord. (b) Immediate postoperative T2-weighted sagittal image of the cervical spine demonstrating successful endoscopic endonasal decompression of the craniocervical junction. (c) Cervical spine demonstrating cerebrospinal fluid space ventral to the lower brainstem and upper cervical cord in 3-month postoperative T2-weighted sagittal image, which was not present on preoperative imaging. (d) Preoperative CT of the cervical spine demonstrating a retroflexed odontoid as well as an os odontoideum. (e) Immediate postoperative CT of the cervical spine demonstrating successful endoscopic endonasal resection of the clivus, anterior arch of C1, and a portion of the odontoid process. Also note the posterior occipitocervical instrumentation. (f) Resolution of the acute postoperative changes seen in 3-month postoperative CT.

Only gold members can continue reading. Log In or Register to continue