Transoral and Transnasal Approaches to the Craniocervical Junction

17 Transoral and Transnasal Approaches to the Craniocervical Junction

Matthew L. Rontal, Daniel Roy Pieper, and Mick J. Perez-Cruet

Abstract

This chapter discusses both the traditional transoral approach and the endoscopic transoral and transnasal approaches to the craniocervical junction or craniovertebral junction. These approaches are extremely versatile for the treatment of a variety of anterior pathology affecting the craniocervical junction. This chapter discusses the anatomy as well as operative nuances to help make these approaches safe and effective.

Keywords: craniocervical junction, craniovertebral junction, rheumatoid pannus, nasopharyngeal carcinoma, chordoma, chondrosarcoma, osteogenesis imperfecta, Klippel–Feil syndrome, Down’s syndrome, achondroplasia, mucopolysaccharidoses, transoral, velopharyngeal insufficiency, transnasal

17.1 Introduction

Management of disease of the craniocervical junction (CCJ), or craniovertebral junction (CVJ), is evolving.¹^,² This evolution largely results from the simultaneous development of the technology and the techniques of approach and resection of disease. This chapter discusses both the traditional transoral approach and the endoscopic transoral and transnasal approaches to the CCJ.

17.1.1 Anatomy

Approach to the CCJ is founded in an understanding of the correlated pharyngeal and spinal anatomy, the function of the CCJ and velopharynx, and the required surgical exposure.

The CCJ consists of the occipital bone, the atlas, and the axis. Together these bony structures house the junction of the brainstem and spinal cord and transmit the vertebral arteries and proximal derivatives of the spinal cord. The bony and ligamentous anatomy of the CCJ creates the structural basis of the majority of the flexion, extension, and rotation of the head. An understanding of the complex anatomy of the cranial vertebral junction, soft palate, and transoral approach is critical to safe and effective surgical intervention ( Fig. 17.1).

Occipital-C1

The junction of the occipital bone and atlas is an articulation of the occipital condyles of the occipital bone and the concave surfaces of the lateral masses of C1 which confers flexion and extension of the head. Just above this articulation are two discrete portions of the occipital bone:

1. Clivus, anteriorly.

2. Squamous portion of the occipital bone, posteriorly.

The pontomedullary junction lies approximately 1 cm above the inferior tip of the clivus. The hypoglossal nerves exit through their canals in the squamous portion of the occipital bone just superior and medial to the condyles.

The atlanto-occipital membrane (AOM) spans from the posterior aspect of the atlas ring to the occipital bone. The vertebral arteries ascend through their foramina in the lateral masses of the cervical vertebrae, and then run over the posterior ring of atlas and pierce the AOM to enter the foramen magnum. The AOM does not confer stability to the CCJ.

Fig. 17.1 Anatomical illustration of the craniocervical junction.

C1–C2

The atlantoaxial junction is defined by the unique articulation of the odontoid process and C1, which permits rotation of the head. The dens extends superiorly from the anterior aspect of C2 and articulates with the posterior aspect of the anterior ring of C1. A complex arrangement of the transverse ligament and its vertically oriented superior and inferior crura (together comprising the cruciate ligament) and the alar ligaments restrict flexion/extension and rotation, respectively, stabilizing the CCJ. The role of the tectorial membrane, which fans upward from the anterior aspect of C2 to the dura mater within the anterior aspect of the foramen magnum, remains controversial. The anterior longitudinal ligament guards the anterior aspect of the CCJ and contributes stability, but does not confer any of the regions’ specialized range of movement. The longus colli and longus capitis muscles lie anterior to the anterior longitudinal ligament and just behind the mucosal, muscular, and fascial planes of the posterior pharyngeal wall.

The velopharynx is the name given to the region at the junction of the nasopharynx and oropharynx that operates to restrict the flow of air through the nose during speech. It is composed of the soft palate, the lateral pharyngeal walls, and the posterior pharyngeal wall. The soft palate projects posteriorly from the posterior edge of the hard palate and then assumes a posteroinferiorly curved posture at rest. The midline aspect of the inferior-most edge of the soft palate extends further inferiorly as the bullet-shaped uvula.

Deep to the mucosa and minor salivary glands of the soft palate are the muscles of the palate. Most important, the levator veli palatini is the principal elevator of the palate. It descends from the inferior aspect of the greater wing of the sphenoid to the lateral aspect of the palate and then turns 90 degrees to run transversely in the substance of the palate, inserting on the palatal aponeurosis. Contraction of the levator muscles elevates the palate in the coronal plane and creates a posterior superior movement in the sagittal plane such that the palate obturates against the posterior pharyngeal wall.

The superior pharyngeal constrictor bounds the lateral and posterior aspects of the velopharynx. It takes its origin from the medial pterygoid plate, the mandible, and the pterygomandibular raphe. And it inserts on the midline raphe in the posterior pharyngeal wall and the pharyngeal tubercle at the base of the occipital bone. More superiorly, the posterior wall of the nasopharynx is created by the mucosal covering of the anterior aspect of the inferior portion of the clivus.

Together the posterior superior movement of the palate and the purse-string movement of the superior constrictor function to close the velopharynx during swallowing and during speech. During swallowing, these movements are slow and large in amplitude, preventing the egress of food and liquids into the nasopharynx. During speech, these movements work to open and close the velopharynx several times per second, appropriately permitting and restricting nasal flow of air in the creation of particular phonemes of speech. Inadequacy in these movements results in hypernasal resonance and inability to create the sounds of the letters P, B, D, K, G, Z, and S. The consequence is a constellation of abnormal voice and misarticulations known as velopharyngeal incompetence (VPI).³ VPI is most commonly seen in some patients with cleft palate in whom palatal length and/or movement is insufficient to obstruct the velopharynx during speech. Correction of VPI involves adding partially obstructive tissue in the region of the velopharynx to aid in closure. The authors’ preferred technique is the superiorly based pharyngeal flap, which creates a myofascial-mucosal bridge from the posterior pharyngeal wall to the palate.⁴ Improved closure of the velopharynx is then accomplished by inward movement of the lateral pharyngeal walls up to the lateral margins of the bridge, without significant movement of the palate.

The function of the velopharyngeal sphincter is essential to maintaining normal, intelligible speech, and should be preserved in approaching the CCJ.

17.1.2 Pathology

Disease of the CCJ resulting in compression of the spinal cord and brainstem and/or instability of the complex bony and ligamentous anatomy threatens severe neurologic impairment. Historically, the most common presenting etiology has been compression due to a rheumatoid pannus involving the atlantoaxial junction.¹^,⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰^,¹¹ Other pathologies of the CCJ include neoplastic processes such as nasopharyngeal carcinoma, chordoma, and chondrosarcoma, infectious processes, and trauma. Congenital disease affecting craniofacial growth such as osteogenesis imperfecta,⁹ Klippel–Feil syndrome, Down’s syndrome,¹² achondroplasia, and mucopolysaccharidoses may result in basilar invagination.¹³ Acquired diseases of bone such as rickets, osteogenesis imperfecta, cretinism, and parathyroid disease may result in softening of the occipital bone and basilar impression resulting from settling of the skull and a relative odontoid elevation.¹⁴ Interestingly Choi et al¹¹ reported that with improved management of rheumatoid arthritis, the incidence of rheumatoid pannus of the CCJ is more recently markedly reduced and that resection of tumor has ascended to the most common indication.¹^,¹⁵ While most inflammatory and benign neoplastic presentations can be managed with piecemeal resection, some malignant processes indicate a need for en bloc resection. The required exposure and thus the chosen approach vary based on these indications¹⁶ ( Fig. 17.2).

17.1.3 Relative Anatomy

Key to choosing an approach is understanding an individual patient’s CCJ anatomy relative to the structures of the palate. This provides an understanding of the angle of attack that may be expected through the nose and the mouth.

On lateral cephalogram, the tip of the odontoid has long been compared to the level of the hard palate. McGregor’s line is drawn from the posterior aspect of the hard palate to the base of the occiput. Chamberlain’s line is drawn from the posterior aspect of the hard palate to the anterior lip of the foramen magnum. The tip of the dens is found at or below Chamberlain’s line in roughly 50% of individuals. Basilar invagination is said to be present if the tip of the dens is 4.5 mm above McGregor’s line or 6 mm above Chamberlain’s line. As the approach to the CCJ has evolved, CCJ anatomy relative to the hard palate has been studied with respect to the angle of attack in the transnasal approach ( Fig. 17.3).

Fig. 17.2 Illustration of pathology affecting the odontoid process, which is typically a chordoma.

Fig. 17.3 Illustration showing Wackenheim’s, McRae’s, Chamberlain’s, and McGregor’s lines used to define craniovertebral junction anatomy and pathology.