3: Anterior Odontoid Resection: The Transoral Approach

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Procedure 3 Anterior Odontoid Resection

The Transoral Approach

George M. Ghobrial, Eli M. Baron, David Choi, Harminder Singh, James S. Harrop, J. Patrick Johnson, Alexander R. Vaccaro, H. Alan Crockard

Indications

Generally, for the correction of irreducible, ventral compression of the cervicomedullary junction.

Specifically, for ventral extradural, midline pathology from the lower clivus to the C2-3 disk. Anticipated dissection should not extend laterally more than 11 mm on either side of the midline, as this may result in damage to the eustachian tubes, hypoglossal nerves, or vertebral arteries.

Commonly used to decompress neural elements, typically in patients with rheumatoid arthritis. Cervicomedullary neural compression may be due to

• Craniovertebral settling resulting from rheumatoid or degenerative disease

• Pseudotumor or rheumatoid pannus

• Extradural primary bone or soft tissue tumors

• Congenital basilar invagination

• Irreducible chronic nonunion of a fractured odontoid process causing neural compression

As part of a staged procedure, may be used to excise a chordoma or other midline extradural tumor at the craniocervical junction

May very occasionally be used for midline intradural pathology, such as meningiomas and schwannomas, usually as part of a staged procedure.

Examination/Imaging

Neurologic and musculoskeletal examination

• Rotary subluxation is a relative contraindication to this procedure, as is irreducible torticollis.

• Careful examination of the oral and pharyngeal region

♦ The relationship of the hard palate to the pathology must be studied: a hard palate located above the level of pathology allows for good access.

♦ The mouth should be able to be opened more than 25 mm. This is required to obtain adequate visualization of the pathology, and provide adequate access for surgical instruments.

♦ Close attention must be paid to the patient’s teeth: Root abscesses and periodontal sepsis may be significant risk factors for postoperative infection. Any irregularities in dentition should be noted, as they may make retractor placement difficult.

♦ A gum guard, which fits both the irregular dentition and the retractors, can be fashioned before surgery.

♦ Temporomandibular pathology should be taken into consideration as this may limit mouth opening and hinder a transoral approach.

• Good neck extension is required. Fixed flexion deformities of the neck can prevent sufficient mouth opening, and limit surgical access.

• A preoperative otorhinolaryngologic assessment should be performed to rule out any lower cranial nerve dysfunction. If there is vocal cord, pharyngeal, or brainstem dysfunction, then a preoperative tracheostomy should be considered.

Preoperative imaging should include multiplanar radiographs of the cervical spine, computed tomography (CT) with sagittal and coronal reformatting, and magnetic resonance imaging (MRI) to clearly define any soft tissue pathology and the degree of neural compression (Figure 3-1).

CT reformatted images provide detailed information about the bony elements and can be beneficial in planning posterior instrumentation procedures.

Image guidance has been used as an adjunct for anterior odontoid resection, including frameless stereotaxy and intraoperative MRI. However, frameless stereotaxy may be inaccurate because of the mobility of the craniocervical junction.

Magnetic resonance angiography (MRA) may be beneficial in defining the vascular anatomy and relationship of the vertebral arteries to the midline, as well as dominance of one vessel.

In the treatment of patients with rheumatoid arthritis, it is suggested that anti-tumor necrosis factor be held 2 to 4 weeks before surgery and up to 2 weeks after. There is no definitive evidence to suggest methotrexate should be discontinued perioperatively.

FIGURE 3-1, A-B

Treatment Options

• Anterior odontoid resection through the transoral approach (transoral-transpharyngeal, with or without palatotomy)

• Combined anterior odontoid resection through the transoral approach, followed by posterior stabilization with possible decompression

• Standalone posterior stabilization with possible decompression

• Adjunctive traction reduction (in setting of reducible basilar invagination or atlantoaxial subluxation), followed by posterior stabilization

Surgical Anatomy

Understanding the ligaments of the craniovertebral junction is vital when operating in this region.

The atlas is united to the occipital bone by the anterior and posterior atlanto-occipital membranes.

The atlantoaxial joint consists of four articulations and two key ligaments. Two synovial joints for each lateral mass and two odontoid joints, on the anterior and posterior aspects.

The alar ligament arises laterally from the odontoid to attach to the occipital condyles. The apical ligament runs from the odontoid process to the anterior margin of the foramen magnum. Disruption of any of the aforementioned ligamentous structures runs an increased risk for basilar invagination.

The cruciate ligament runs from the atlas to the axis anteriorly. Atlantoaxial dissociation results from damage to this ligament, requiring surgical intervention.

Below the foramen magnum, the oropharynx is separated from the prevertebral fascia by a well-defined areolar plane (Figure 3-2). The oropharyngeal mucosa heals remarkably well after surgical incision and repair.

The most important bony anatomic landmarks for the transoral approach are the midline structures: rostrally, the septal attachment to the sphenoid, the pharyngeal tubercle on the clivus; and caudally, the anterior tubercle of the C1 arch. The longus colli muscles flank the dens on each side and, more laterally, the longus capitis muscles.

The anterior longitudinal ligament extends caudally in the midline.

• Knowledge of the location of the vertebral arteries is requisite before performing a transoral procedure.

• The vertebral arteries are located 24 mm laterally from the midline at the level of the arch of C1, and approximately 11 mm from the midline at the C2-3 disk space as well as the level of the foramen magnum.

• Pathology such as atlantoaxial rotary subluxation can significantly distort the relationship of the vertebral arteries to the midline.

• Visually, the anatomic midline can be accurately defined by examining the symmetry of the anterior longitudinal ligament and the longus colli muscles.

FIGURE 3-2, A-C

Positioning

Neurophysiologic monitoring electrodes for somatosensory-evoked potential and transcranial motor-evoked potential monitoring are placed first.

Fiberoptic nasotracheal intubation is then performed.

A nasogastric tube should also be placed for intraoperative gastric drainage and postoperative feeding.

The patient’s head can be fixed in a three-pin fixation system with slight extension. Alternatively, a horseshoe with Gardner-Wells traction or the head resting on a circular headrest can be used.

Extension should not be used in patients with fixed cervical kyphosis. Rather, they should be placed in slight Trendelenburg position to assist in the rostral extent of the dissection. One caveat to this would be the limitations in positioning caused by cervical instability or cervicomedullary compression; in this case, positioning is done cautiously with neuromonitoring.

Positioning Pearls

• Because many patients have inherent spinal instability, perisurgical neck immobilization may be required. Halo immobilization, however, will limit neck extension and surgical exposure.

• The placement of topical 1% hydrocortisone on the oral mucosa, before and after surgery, may reduce the incidence of lip and tongue swelling.

Positioning Pitfalls

• Inability to widely open the mouth is a relative contraindication to this procedure. As a general rule, in the adult population, if you cannot place three fingers into the mouth of a patient with his or her mouth fully opened, the transoral approach should be avoided. Otherwise, splitting the mandible and tongue may be needed for adequate exposure.

• Alternatively, patients may be positioned laterally in a Mayfield clamp (Figure 3-3). The advantages of this position are that blood and washings drain out of the operative field. The head is placed in slight extension, which improves exposure. The table may be tilted laterally, allowing optimal positioning for the patient and surgeon. After the initial procedure, a posterior stabilization can be performed after reversing the lateral tilt.

• A fluoroscopy unit is then brought in following positioning to confirm adequate positioning and spinal alignment.

FIGURE 3-3

Portals/Exposures

Oral swabs can be obtained for culture to identify bacterial colonization before preparation of the mouth and oropharynx with 1% Betadine or cetrimide.

The upper esophagus should be packed with a collagen sponge or gauze to minimize the ingestion of saline and blood.

The midlines of the oropharyngeal mucosa and soft palate are infiltrated with 1% lidocaine with epinephrine (1:100,000). A Crockard transoral retractor system (Codman, Raynham, Mass.) is used to maintain adequate exposure of the posterior oral cavity and to keep the nasotracheal and nasogastric tubes to one side, out of the surgeon’s way (Figures 3-4 and 3-5).

A tongue blade and soft palate retractors maximize the exposure.

To extend superior and lateral exposure, the soft palate may be split at the midline from hard palate to the uvula.

The uvula may be secured with a red rubber catheter and retracted along with the soft palate through the nares to avoid problems with swallowing and phonation postoperatively. After incision of the posterior pharyngeal wall, a Crockard toothed self-retaining retractor is inserted for lateral retraction to expose the underlying anterior longitudinal ligament and longus colli muscles.

With or without the aid of lateral fluoroscopy, the extent of the incision is from the base of the clivus to the upper border of the C3 vertebra.

Alternative techniques

• Another technique is to use endotracheal intubation with the Spetzler-Sonntag retractor system (Aesculap, San Francisco). This system protects and retracts the endotracheal tube and tongue, whereas the Crockard system displaces the nasotracheal tube out of the way.

• The soft palate may also be retracted using sutures through the soft palate, which are brought out via the nares after they are secured to vessel loops that were passed through the nostrils into the nasopharynx (Spetzler technique) (Hadley et al, 1988). Alternatively, the soft palate may be divided in the midline (offset to avoid the uvula) and retracted with sutures hanging out of the mouth (Crockard, 1995).

FIGURE 3-4, A-B

FIGURE 3-5

Procedure

Step 1

The anterior ridge or tubercle of the atlas is palpated. At this point, a confirmatory lateral localizing image may be taken. An operating microscope can then be used, or a surgeon may choose loupe magnification with directed illumination.

A vertical incision is made extending approximately 2.5 cm superiorly and 2.5 to 3.0 cm inferiorly along the midline of the posterior oropharynx (Figure 3-6).

The extent of the exposure obtained with this incision will be approximately 15 to 20 mm bilaterally from the midline incision.

Dissection is taken through the posterior pharyngeal mucosa, the superior constrictor muscles of the pharynx, and the anterior longitudinal ligament.

Incising the soft (and sometimes hard) palate can provide additional visualization of the lower clivus if needed.

Using periosteal elevators and electrocautery, a subperiosteal dissection exposes the arch of C1, as well as the anterior bodies of C2 and C3.

The longus colli and longus capitis muscles are detached medially to laterally from the cervical vertebra.

In the presence of instability, there may be a large amount of granulation tissue at the level of the inferior margin of the atlas and its junction with the anterior odontoid peg. Toothed retractor blades are then used to retract the dissected soft tissues laterally. This allows excellent visualization of the midline inferior clivus, the atlas, and the axis.

FIGURE 3-6

Step 1 Pitfalls

• Great care should be taken to avoid cerebrospinal fluid (CSF) leakage in order to minimize the risk of postoperative meningitis. A preoperative lumbar drain should be placed when an intradural approach is anticipated. In such procedures, fat, muscle, fascia lata, or a dermal fat graft should be used in the repair of any dural opening, followed by the application of fibrin glue.

• With an incision from the inferior clivus to the superior border of C3, an operating field of 15 to 20 mm bilaterally can be exposed. Beyond that, there is an increased risk of trauma to the eustachian tube, hypoglossal nerve, vidian nerve, and vertebral artery at the C1-2 interspace.

• Given the large vascular channels and venous sinusoids in this region, postoperative hematoma formation may be a problem. This can be minimized by meticulous hemostasis, using Avitene, Surgicel, Gelfoam, or fibrin glue, and postoperative nursing in the head-up position. Bleeding from the rheumatoid pannus or small arterial feeders can be controlled with bipolar electrocautery. If an intradural procedure is performed, watertight dural closure is very important to minimize the risk of infection. Suturing or clipping the dura will rarely close the defect completely. A free dermal fat graft, pharyngeal mucosal rotation flaps, or nasal septal mucosal flaps help provide a watertight closure, and a lumbar drain may also be used.

Step 2

A match-head burr is used to remove the anterior arch of the atlas out laterally approximately 1 cm to each side of the midline (about two thirds of the arch, exposing the shoulder of the dens bilaterally) (Figure 3-7). The odontoid mass and pannus (if present) are then resected in a rostrocaudal direction (starting at the top of the odontoid process) using a combination of drilling and curetting.

Alternatively, the odontoid process may be initially drilled at its base and disarticulated from the C2 body. The odontoid peg is hollowed out gradually with a 3-mm cutting burr down to the cortical bone, which is then thinned and removed with a match-head or diamond burr. The alar and apical ligaments are sharply divided, taking care not to cause a CSF leak. The proximal peg is then removed after circumferentially elevating off all soft tissue attachments. This is facilitated by grasping the odontoid peg with special forceps and pulling it down from the foramen magnum while elevating the dura off it. This allows complete removal of the dens. This technique has a greater potential for durotomy, particularly in the pediatric population, in whom the odontoid process may have a hook at its apex that can tear the dura during peg removal.

The posterior longitudinal ligament is seen behind the dens, which has now been removed. The fibers of the transverse ligament are also visualized at the level of the removed C1 anterior arch. With division of these ligaments, the dura should be clearly seen. Ligament and soft tissue removal can be accomplished with a series of small angled curettes, transsphenoidal punches, and transoral bayoneted forceps. Typically, a gap exists between the ligaments and dura. Decompression is considered adequate when the dura pulsates freely and the lateral curvature of the dura is seen bilaterally. Fluoroscopy may be used to confirm adequate decompression.

Any venous bleeding can be controlled with Surgicel and fibrin glue (Figure 3-8, A).

Extended approaches

• In addition to the standard transoral technique, extended approaches can be performed to widen the surgical exposure of the craniocervical junction.

• A mandibulotomy can be made to increase the cervical exposure by first incising the lip in the midline, then more inferiorly through the gingival, mandible, and finally the hyoid. The mucosa is divided beneath the tongue, sparing the submaxillary ducts, with retraction of the mandible laterally to allow for the depression of the tongue to maximize the exposure of the craniocervical junction superiorly and inferiorly.

• A mandibuloglossotomy extends the above approach to include the middle clivus to the C3-4 vertebral bodies inferiorly.

• A palatotomy can be made by extending the midline incision of the soft palate, sparing the uvula. The posterior connection of the vomer can be disconnected, as well as the hard palate separated then retracted laterally.

• A more extensive bilateral mucogingival extension can be performed along the maxilla, with a subperiosteal dissection, effectively degloving the face. The superior limit of muscle and mucosa dissection off of the maxilla is the infraorbital nerve. Bilateral osteotomies are made from the piriform aperture to the maxillary alveolus. The maxilla is disarticulated from the pterygomaxillary fissure. An inferior turbinectomy is made. The nasal mucosa is reflected off of the nasal septum as well as the sphenoid bone for a superior exposure. Concern for this extensive approach is preservation of the vascular supply namely via the palatine arteries.

FIGURE 3-7, A-B

FIGURE 3-8, A-B

Step 3

The posterior pharyngeal wall is then closed with a two-layered closure using 3-0 Vicryl sutures (Figure 3-8, B).

Despite the presence of bacterial flora in the oral cavity, a low infection rate of less than 3% is to be expected if the dura is not breeched. In the presence of a durotomy, great efforts should be made to close the dura in a watertight manner.

A double layer closure of both the pharyngeal musculature and mucosa is less susceptible to dehiscence.

In the presence of durotomy, a watertight closure may be aided with the application of fat, fascia, dermal fat graft, and fibrin glue. Additionally, a lumbar drain should be used for about 5 days with regular drainage of CSF (10 to 15 mL/hr).

Postoperative Care and Expected Outcomes

Postoperatively, the nasotracheal tube is left in place for 24 to 48 hours. It should only be removed if there is no evidence of significant labial or lingual swelling.

The patient should be left in a halo vest, Minerva jacket, rigid collar, or traction if a posterior stabilization has not been performed at the initial procedure.

The patient should be encouraged to sit up and to ambulate, if possible, to minimize saliva pooling in the pharynx and the potential for breakdown of the incision.

The patient should take nothing by mouth for 5 days after the operation. Nasogastric feeding may commence after 5 hours.

Hydrocortisone ointment should be applied to the tongue and mucosa for the first 48 hours.

In the event of a durotomy, lumbar drainage should be maintained for 5 to 10 days. Prophylactic antibiotic therapy directed against gram-positive, gram-negative, and anaerobic oral flora may be administered by some surgeons. For example, Menezes (1991) recommended CSF cultures for the initial 5 days, at which point, if the cultures remain negative, antibiotics may be stopped. Occasionally, a lumbar-peritoneal shunt may be required for persistent CSF leakage.

The main predictor of outcome is the degree of preoperative neurologic impairment. Rheumatoid patients who are unable to walk due to myelopathy (Ranawat classification IIIb) have a much higher mortality.

Complications

• Airway complications are always a concern with the transoral approach. It is the practice of the senior author to leave the endotracheal tube in place for a minimum of 24 hours following surgery. If after this time there is evidence of swelling of the tongue or oral cavity, the endotracheal tube is left in situ until the swelling subsides. The occurrence of lingual swelling may be minimized by intermittent intraoperative release of the retractor, and ensuring the tongue is not trapped between the retractor blade and the lower teeth.

• Delayed complications may include tongue swelling, meningitis, palatal/pharyngeal dehiscence, neurologic deterioration, retropharyngeal abscess, late pharyngeal bleeding, and velopalatine incompetence. Pharyngeal dehiscence may occur either early or late. Early dehiscence (during the first 7 days after surgery) is typically due to inadequate closure or starting oral feeding too early. This can be minimized by encouraging the patient to sit up and walk as soon as possible to prevent pooling of saliva at the apex or weakest point of the pharyngeal incision. If early dehiscence occurs, closure should be attempted (with the assistance of head and neck specialists if required), followed by hyperalimentation and intravenous antibiotics. In cases of late dehiscence, infection needs to be ruled out. The differential diagnosis of late dehiscence includes osteomyelitis, retropharyngeal abscess, and poor nutrition. Management of retropharyngeal abscess includes lateral drainage (rather than transoral), followed by appropriate intravenous antibiotics, hyperalimentation through a nasogastric feeding tube, and neck immobilization.

• Neurologic deterioration after transoral odontoid resection is most likely to be due to craniocervical instability. The vast majority of patients who undergo this procedure require a posterior stabilization procedure.

• In patients with altered mental status following the transoral approach, meningitis must be kept at the forefront of the differential diagnosis. This is particularly true in the elderly population with rheumatoid arthritis, in whom this diagnosis may be overlooked because confusion in this age group can be common in the critical care setting.

• Late retropharyngeal bleeding may indicate an underlying infection. Osteomyelitis and pseudoaneurysm of the vertebral artery must also be ruled out. MRI/MRA evaluation of the craniovertebral junction should be performed in addition to angiography to rule out vascular involvement. This diagnostic process also allows for potential therapeutic endovascular treatment in cases of vertebral artery compromise.

• Velopalatine incompetence (incorrect closure of the soft palate muscle during speech resulting in a nasal voice) occurs more commonly in children than in adults. It typically occurs 4 to 6 months after the transoral procedure and probably occurs secondary to contracture of the soft palate and nasopharynx. This requires otorhinolaryngologic evaluation. Usually it is treated with pharyngeal retraining, but a palatal prosthesis or a pharyngeal flap may also be used.

Although little evidence exists as to the long-term efficacy of anterior odontoid resection, with proper indications, diligent planning, and an understanding of the anatomy of the craniovertebral junction, the procedure appears to be a highly effective and safe method of addressing anterior compressive pathology at the craniocervical junction. A few small studies support the different steps outlined in this technique.

Apuzzo ML, Weiss MH, Heiden JS. Transoral exposure of the atlantoaxial region. Neurosurgery. 1978;3:201-207.

This paper reviews the positioning, surgical technique, and postoperative care related to transoral odontoid resection (Level V evidence [expert opinion]).

Crockard HA. Transoral surgery: some lessons learned. Br J Neurosurg. 1995;9:283-293.

Reviews the author’s experience with the transoral approach and discusses its use in relation to different pathologies. Reviews technical pearls of preoperative patient evaluation and selection, intraoperative techniques, and postoperative management (Level V evidence).

Crockard HA, Calder I, Ransford AO. One-stage transoral decompression and posterior fixation in rheumatoid atlanto-axial subluxation. J Bone Joint Surg Br. 1990;72:682-685.

Illustrates how the lateral position can be used for anterior odontoid resection and for posterior stabilization in the same setting (Level IV evidence [case series]: retrospective series of 68 patients undergoing a combined procedure).

Crockard HA, Sen CN. The transoral approach for the management of intradural lesions at the craniovertebral junction: review of 7 cases. Neurosurgery. 1991;28:88-97. discussion 97-8

A study examining the transoral approach for intradural pathology, including meningiomas and schwannomas. Reviews the advantages and disadvantages of this approach in this clinical setting (Level IV evidence).

Fang HSY, Ong GB. Direct anterior approach to the upper cervical spine. J Bone Joint Surg Am. 1962;44:1588-1604.

Fang and Ong published a series of patients who underwent transoral decompression of the spinal cord and brainstem for irreducible compressive atlantoaxial pathology. The high complication rate with this approach tempered their enthusiasm for the procedure (Level IV evidence).

Frempong-Boadu AK, Faunce WA, Fessler RG. Endoscopically assisted transoral-transpharyngeal approach to the craniovertebral junction. Neurosurgery. 2002;51(5 Suppl):S60-S66.

A review of the endoscopic transoral approach (Level IV evidence [case series of 7 patients]).

Hadley MN, Martin NA, Spetzler RF, Sonntag VK, Johnson PC. Comparative transoral dural closure techniques: a canine model. Neurosurgery. 1988;22:392-397.

This animal study demonstrated the superiority of a fibrin glue augmented dural closure over other methods (Level I study: prospective study).

Hsu W, Wolinsky J, Gokaslan Z, Sciubba DM. Transoral approaches to the cervical spine. Neurosurgery. 2010;66(Suppl. 3):119-125.

A review article highlighting the transoral-transpharyngeal approach to the cervical spine as well as more recent use of the endoscopic endonasal and endoscopic transcervical approach as an alternative.

Kaibara T, Hurlbert RJ, Sutherland GR. Transoral resection of axial lesions augmented by intraoperative magnetic resonance imaging: report of three cases. J Neurosurg Spine. 2001;95:239-242.

Small case study supporting alternative intraoperative imaging in addition to fluoroscopy (Level IV evidence).

Krauss WE, Bledsoe JM, Clarke MJ, Nottmeier EW, Pichelmann MA. Rheumatoid arthritis of the craniovertebral junction. Neurosurgery. 2010;66(Suppl. 3):83-95.

Review of rheumatoid arthritis at the craniovertebral junction, including the evaluation, diagnosis, and surgical management.

Menezes AH. Complications of surgery at the craniovertebral junction—avoidance and management. Pediatr Neurosurg. 1991;17:254-266.

This article presents a detailed review of complications of the transoral approach, with specific reference to the pediatric population, and their management (Level IV evidence as recommendations are based on author’s case series).

Pollack IF, Welch W, Jacobs GB, Janecka IP. Frameless stereotactic guidance: an intraoperative adjunct in the transoral approach for ventral cervicomedullary junction decompression. Spine. 1995;20:216-220.

Small case study supporting alternative intraoperative imaging in addition to fluoroscopy (Level V evidence).

Singh H, Harrop J, Schiffmacher P, Rosen M, Evans J. Ventral surgical approaches to craniovertebral junction chordomas. Neurosurgery. 2010;66(Suppl. 3):96-103.

Extended transoral approaches as well as endoscopic transoral and transnasal approaches are highlighted for the treatment of craniovertebral junction chordomas.

Youssef AS, Sloan AE. Extended transoral approaches: surgical technique and analysis. Neurosurgery. 2010;66(Suppl. 3)):126-134.

A discussion of the various extended approaches available for increasing exposure of the craniovertebral junction beyond the conventional transoral approach.

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