Endoscopic Transnasal Approaches to the Craniocervical Junction

41 Endoscopic Transnasal Approaches to the Craniocervical Junction

Sarfaraz Mubarak Banglawala, Jenna Rebelo, Kesava (Kesh) Reddy, and Doron Sommer

41.1 Introduction

The craniovertebral junction is considered a challenging anatomical region for surgical access due to the deep location and close proximity of multiple important neural and vascular structures.

German first demonstrated the feasibility of a transoral approach in dogs in 1930.1 However, the approach was not used for treatment of spinal pathology until the 1940s and only gained wide acceptance with the advent of the operating microscope in the 1960s.² The transoral microscopic approach went on to become the gold standard for odontoidectomy.³ Despite offering a wide field of view, however, the transoral approach is limited vertically, often requiring a palatal split and/or mandibulotomy to afford access to higher cervical and clival lesions.^4,5,6 The addition of endoscopic assistance to the transoral route was thus described by Frempong-Boadu et al in 2002 to improve visualization while minimizing the need for palate splitting and mandibulotomy.²

The anatomical feasibility of an endoscopic, transnasal approach was demonstrated in cadavers by Alfieri et al,⁷ and a fully endoscopic transnasal odontoid resection was first described by Kassam et al in a patient with cervicomedullary compression secondary to rheumatoid arthritis.⁸

This chapter describes the endoscopic transnasal approach and its indications, advantages, and limitations in relation to the transoral (described in Chapter 32) and transcervical approaches.

41.2 Indications for Surgery of the Craniovertebral Junction

• Basilar invagination (Fig. 41.1), radiologically defined as:

Odontoid tip protrusion³ 4.5 mm above McGregor’s line (line drawn from the posterior hard palate to base of the occiput on sagittal imaging)

Tip protrusion³ 6 mm above Chamberlain’s line (line drawn from the posterior hard palate to the anterior lip of the foramen magnum)^9,10

• Soft tissue pannus due to rheumatoid arthritis (Fig. 41.2)^3,8

• Biopsy or resection of odontoid tumors (Fig. 41.3, Fig. 41.4)^8,11

Primary or metastatic

Intradural or extradural

• Odontoid fracture or nonunion⁸

• Vertebrobasilar aneurysm⁸

• Other craniovertebral junction pathologies, including lesions due to gout, ganglion cyst, and os odontoideum¹²

Fig. 41.1 (a,b) Basilar invagination.

Fig. 41.2 Soft tissue pannus due to rheumatoid arthritis.

Fig. 41.3 A 7-year-old boy with an osteolytic C2 lesion.

Fig. 41.4 Resection of odontoid tumors.

41.3 Approaches

Transnasal Endoscopic Approach

Preoperative Planning

CT angiography is done to study the anatomy of the tumor and to facilitate the use of stereotactic image guidance. The patient is positioned in a slight neck flexion position (as tolerated) to simulate neck position during surgery, as any significant difference will affect the accuracy of the image guidance system. Inferior extent of surgical access may be estimated by the nasopalatine line (Fig. 41.3), a line extending from the bottom of the nasal bones to the back of the hard palate.⁶

Preoperative Preparation

The patient is endotracheally intubated.

Using a headlight and nasal speculum, the surgeon prepares the nasal cavity by gentle packing with 1:1000 epinephrine ribbon gauze. This is done very soon after intubation to give the epinephrine ample time to decongest the nasal cavity prior to surgery. There is an option to gently retract the soft palate inferiorly using a small rubber catheter inserted via a nostril and exiting via the oral cavity.

The patient’s head is rigidly fixed (via pin fixation) to the operating table in slight neck flexion (as tolerated, trying to emulate the patient’s preoperative CT scan position to optimize access and image guidance system accuracy).

The table is placed in reverse Trendelenburg position to decrease venous return and to reduce intraoperative bleeding.

Heights of the table and monitors are adjusted to the surgeon’s comfort level. Otolaryngologist and neurosurgeon positioning is similar to that for other expanded endonasal cases (Fig. 41.5).

Image guidance is registered, calibrated and verified prior to draping the patient.

Neurophysiologic monitoring is set up at this time.

The patient is given preoperative antibiotics to cover for nasal contamination into the surgical field.

Operative Steps

Exposure

1. Using a 0° endoscope, the middle turbinate is lateralized or partially resected. Inferior turbinates are lateralized.

2. Sphenoid ostia are identified and wide sphenoidotomies are performed.

3. Use of a long, insulated needle cautery gives the option to develop a large, posteriorly based, nasoseptal flap. This may be performed routinely or only in cases of likely CSF leak. The flap can be raised from the sphenoid face to as far anterior as just behind the columella, extending inferiorly to include partial floor of the nose. Care is taken not to remove the olfactory mucosa superiorly by staying at the level of the sphenoid ostia until the middle turbinate is reached, before then heading superiorly. The flap may be stored in the maxillary sinus to avoid injury during surgery.

4. A posterior, inferior septectomy is performed to allow greater freedom of movement with two-nostril instrumentation.

5. The rostrum is drilled down with a size-4 diamond drill bit or fractured out with Kerrison rongeurs. Bleeding may ensue at the palato-vaginal canal region.

6. A wide exposure is now obtained, with soft palate caudal, and eustachian tubes lateral, to the field.

7. Care should be taken not to injure the vidian nerve or to violate the carotid canals.

8. An inferiorly based U-shaped flap is raised in the nasopharynx and is reflected caudally to the level of the soft palate. The flap is planned well medial to the eustachian tubes—i.e., medial to the internal carotid arteries. See Fig. 41.6 and Video 41.1.

9. The pharyngobasilar fascia is elevated from the inferior sphenoid floor to the ventral clivus.

10. The sphenoid floor is drilled flush with the clivus.

11. Using insulated cautery and periosteal elevators/Freer elevators, the fascia and paraspinal muscles/longus capitis and longus colli are reflected inferiorly (this is partially achieved during step 8, above). Care is taken to avoid heat injury posteriorly to the spinal cord by limiting the cautery setting and avoiding prolonged cautery during this step. Ensure that the trajectory is inferior (not posterior along the clivus) toward C1.

12. The ring of C1 is identified and is verified with image guidance.

Resection

1. Depending on the pathology, various portions of the C1 ring and odontoid process are resected (Fig. 41.7, Fig. 41.8). This is generally performed with an elongated diamond drill and irrigation. It is advisable to perform the vast majority of drilling prior to freeing up most ligamentous attachments of odontoid, so as to avoid drilling a mobile structure. Other instruments, including Kerrison rongeurs, are also utilized. See Video 41.2 and Video 41.3.

2. The amount of dens that will need to be removed depends on the location and extent of the compression. This predicts how much overlying ring of C1 will need to be resected.

3. The dens is followed from the C2 body to its tip and is removed laterally. The cap is removed using sharp dissection.

4. Drilling and dissection are kept to a median and paramedian location (medial to the occipital condyles). Anatomical landmarks and image guidance are used to ensure the correct trajectory. Surrogate landmarks for the parapharyngeal carotid artery include the eustachian tube orifice. Midline landmarks include the posterior hard palate notch and the rostral portion of the nasal septum/sphenoid (although this is partially excised for access). The tubercle of C1 is also confirmed via image guidance.

5. In rheumatoid disease, as C1 ligaments and odontoid are removed, hypertrophic pannus (Fig. 41.9) is identified, which is removed with an ultrasonic aspirator.

6. Decompression is adequately achieved when good CSF pulsations (seen through intact dura) are re-established along the entire length of the affected region.

7. The nasopharyngeal flap is re-approximated with fibrin glue. The nasoseptal flap is used if CSF leak is encountered; otherwise, the flap is replaced onto the septum where it was originally raised.