An Endonasal Approach to the Craniocervical Junction

40 An Endonasal Approach to the Craniocervical Junction

Juan Barges Coll, Luis Alberto Ortega-Porcayo, and Gabriel Armando Castillo Velázquez

40.1 Background

Several surgical approaches have been used to reach the craniovertebral junction (CVJ), which has a unique anatomy and important vital structures that need to be preserved. The surgical approach utilized depends on the type of lesion, its extent, and its location. The endonasal endoscopic approach (EEA) to reach the CVJ is ideal for ventral and ventrolateral lesions, while posterior and posterolateral lesions are better reached through posterior approaches. The EEA provides adequate medial exposure from the frontal crest to the CVJ. With chordomas, which could have a lateral extension, the corridor can be expanded through maxillary osteotomies or a midline mandibulotomy.1 The extent of ventral exposure can be anticipated by the nasopalatine, naso-axial, and palatine lines, while the exposure of the CVJ is delineated by the dorsal position of the hard palate (Fig. 40.1).^2,3,4 In children, the size of the nares in some cases limits the approach; they may require a sublabial incision to facilitate endoscopic passage into the nose.⁵ After the description of expanded endonasal endoscopic odontoidectomy by Kassam et al⁶ and the anatomical endoscopic study by Messina et al,⁷ a substantial number of publications have described an EEA to reach the CVJ.

Assessment of CVJ stability and motion must be performed prior to surgery. The occipitoatlantal junction contributes 23 to 24.5° of flexion and extension, 3.4 to 5.5° of lateral bending, and 2.4 to 7.2° of axial rotation. The atlantoaxial joint contributes 10.1 to 22.4° of flexion and extension, 6.7° of lateral bending, and 23.3 to 38.9° of axial rotation.^8,9 The atlantoaxial joint is the most mobile of all joints in the body¹⁰ and is potentially the most unstable in response to trauma, tumor, and inflammatory or degenerative processes. Disruption of the craniovertebral complex joints (i.e., occipitoatlantal and atlantoaxial joints) and/or principal ligaments (i.e., the transverse cruciate ligament, alar ligament, or the tectorial membrane) determines the need for internal fixation before or after EEA of the ventral CVJ. Recently, in the case of degenerative and inflammatory processes, we prefer to perform a C1–C2 fixation because these pathologies are associated with atlantoaxial instability, and it is unnecessary to include the occipital bone if there is no occipitoatlantal joint involvement. Furthermore, with tumor pathology in which one condyle has been invaded more than 75%,¹¹ a craniocervical fusion is preferred before EEA.

40.2 Craniocervical Junction Endoscopic Anatomical Landmarks

The CVJ is a complex region defined by the axis, atlas, and occiput. It protects the cervicomedullary junction and the vertebral arteries. The majority of the spine’s flexion, extension, and rotation occur in the CVJ.⁹ Understanding the complex anatomy of the ventral CVJ is essential to safe performance of an extended EEA.

The CVJ contains several important neurovascular structures: the cervicomedullary junction, the vertebrobasilar system, and the lower cranial nerves and the cranial nerve VI, which is medially located during EEA and seems to be frequently involved in chordoma pathology.¹² Therefore, total resection of any tumors involving these structures is difficult to accomplish without significant morbidity. A standard preoperative work-up, including computed angiotomography (CT) and gadolinium-enhanced MRI, helps to precisely delimit the tumor and its position in relation to neural and vascular structures.

Fig. 40.1 A schematic representation of the naso-axial, nasopalatine, and palatine lines in the midsagittal plane. The nasopalatine line is created by connecting the inferior border of the nasal bone to the posterior edge of the hard palate. The extrapolation of the line shows the inferior extension of the endonasal approach. The naso-axial line begins at the midpoint of a line between the rhinion and the anterior nasal spine to the posterior edge of the hard palate. The palatine line is drawn parallel along the superior edge of the palatine process.

40.2.1 Anatomical Landmarks

Sphenoid Sinus Ostium and Sphenopalatine Foramen

The sphenoid sinus ostium is located in the anterior sphenoid sinus wall approximately 12 mm from the upper edge of the posterior choanae at the entrance to the sphenoid sinus. The sphenopalatine foramen is ~ 7 mm from the ostium; it is an important landmark for the prevention of bleeding from the sphenopalatine artery.13

Vidian Canal

The vidian canal is an important landmark below the floor of the sphenoid sinus between the pterygoid process and the body of the sphenoidal bone. The canal follows the anterolateral edge of the anterior genu of the petrous carotid artery. The anterior genu and the foramen lacerum are medial to the posterior end of the vidian canal.¹⁴

Torus Tubarium and Fossa of Rosenmüller

The torus tubarium is a prominence derived from the medial cartilaginous end of the eustachian tubes. Behind the torus is the lateral pharyngeal recess or the fossa of Rosenmüller, and at the apex of this fossa, a layer of fibroconnective tissue separates the nasopharyngeal mucosa from the internal carotid artery (ICA).¹⁵ Near the ICA is the anterior pharyngeal artery, which gives rise to three or four branches that supply the parapharyngeal structures.¹⁶ The ICA is an average of 23.7 mm from the midline (minimum 11.5 mm). The eustachian tube is 23.5 mm from the ICA (minimum 10.4 mm), and the distance between the fossa of Rosenmüller and the ICA is minimal, with the closest distance being 0.2 mm.¹⁷ The foramen lacerum is positioned above the fossa of Rosenmüller, and the tensor veli palatini muscle and the levator palatini muscle sit laterally behind the medial pterygoid plate.¹⁶

The medial working space needed to access the ventral CVJ is limited caudally by the soft palate, rostrally by the floor of the sphenoid sinus, and laterally the eustachian tubes surrounding the nasopharyngeal mucosa.⁶

Longus Capitis

Posterior to the nasopharyngeal mucosa is the basipharyngeal fascia, which covers the longus capitis, a key muscular landmark medial to the internal carotid artery. The longus capitis has its origin at the anterior tubercles of the transverse processes of the third to sixth cervical vertebrae and has its insertion at the ventral surface of the lower clivus. Deep and lateral to the longus capitis is the rectus capitis anterior, which has its origin at the transverse process and lateral mass of C1 and its insertion at the inferior surface of the lower clivus. The hypoglossal nerve and branches of the ascending pharyngeal artery course along the lateral borders of these muscles.¹⁸ The longus colli muscles are encountered deep at the level of the anterior arch of C1. Behind these muscles the craniocervical junction is exposed, including the inferior clivus, the anterior arch of C1, and the dens.

40.3 Indications for an Endonasal Approach to the Craniocervical Junction

• Cervicomedullary ventral compression

Irreducible bone compression

Rheumatoid pannus compression

Lesion above the nasopalatine line

• Extradural tumors (chordoma, chondrosarcoma, nasopharyngeal carcinoma)

• Intradural tumors with limited lateral extension and no vascular encasement (anterior foramen meningiomas)

40.3.1 Endonasal Approach to the Craniocervical Junction

Preoperative Planning

All patients should have a complete medical history, CT, MRI, and otoneurological evaluation. MRI allows for the complete identification and determination of the position of the nerves and vascular structures. Instability must be addressed prior to surgery. Large tumors and extensive drilling of the lower clivus can cause chronic instability. Stability of the occipitoatlantal joint is provided by the configuration of the occipitoatlantal joint and the thick articular capsule, along with the anterior and posterior atlantooccipital membranes. If instability is detected, a second staged surgery must be performed.

The nasal mucosa is prepared with topical 0.05% oxymetazoline. The surgical field is prepared by applying povidone-iodine to the nose and the lateral thigh region, in the event that an autologous fascia lata free graft is required for reconstruction. Broad-spectrum prophylactic perioperative antibiotics (ceftriaxone 1 g and clindamycin 600 mg) are administered and continued for the next 5 days. The operating room setup is demonstrated in Fig. 40.2.

Fig. 40.2 An efficient and organized operating room setup is critical for success. Two monitors are used for the comfort of the surgeon and the assistant. Neurophysiology and anesthesia are usually performed at the feet of the patient to allow sufficient space for the fluoroscope to maneuver freely. We use a two-surgeon binostril technique. No endoscopic holder is used, and the first assistant drives the endoscope and irrigates when needed. This setup allows for an extra hand from the assistant to help with graspers or suction.

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