Pathology Overview

The pathologies possible at the craniocervical junction are varied.¹ Most lesions requiring surgery are approached dorsally through a posterior fossa craniectomy and C1 laminectomy. Table 37-1 lists the pathologies encountered by category. In a more basic organization, the abnormalities can be divided into congenital abnormalities and developmental/acquired pathologies. In Box 37-1 the material is reorganized in an empirical fashion.

Ventral Approaches

Several routes to the ventral clivus and upper cervical spine are accepted. Standard approaches to the ventral cervical spine are limited by the mandible and oropharynx.^2–4 Transoral routes to the lower clivus and upper cervical spine are acceptable and safe for addressing pathologies that cause craniocervical instability and that compress neurovascular structures. In 1917 Kanavel⁵ described the first transoral procedure, which he performed to remove a bullet lodged between the clivus and ventral atlas. In 1962 Fang and Ong⁶ reported the first series of six patients who underwent transoral decompression for atlantoaxial instability or congenital anomalies. Their high complication rate contributed to the slow acceptance of this approach.

A resurgent interest in the transoral approach led to the development of better techniques and instrumentation.⁷ Current techniques and practices have lowered complication rates considerably.⁸ Modern antibiotics and instruments have revolutionized and revitalized this operation. An extrapharyngeal approach for exposing the high cervical region is technically difficult but a reasonable alternative when the transoral approach cannot be used.⁹ The transoral approach remains an excellent tool in the surgeon’s armamentarium for ventral decompression. It is also versatile in that the upper clivus rostrally and C3 vertebral body caudally can be accessed. The authors prefer this route for extradural pathology. Dural closure is difficult in the transoral setting, and a lateral approach is preferable for intradural lesions. The far-lateral approach is quite robust for this purpose.

As minimally invasive surgery becomes more prevalent and patient demand for it increases, approaches to the upper cervical spine and clivus have become the target of efforts to minimize incisions and complications. In 2008 an endoscopic endonasal approach to odontoid resection was reported.¹⁰

Surgical Technique

General anesthesia is used for all ventral cases. A reinforced endotracheal tube is used to preserve the airway. Cervical stability is maintained by using fiberoptic endoscopy or awake-intubation techniques. At the authors’ institution they routinely monitor somatosensory evoked potentials (SSEPs), and often motor evoked potentials (MEPs), intraoperatively. Baseline recordings are obtained before final positioning of the patient.

The patient is placed in the supine position on a standard operating room table with the head fixated in a Mayfield three-pin head holder (Codman, Inc., Randolph, Mass.) or a halo-ring adapter. A Spetzler-Sonntag transoral retractor (Aesculap, San Francisco) is positioned over the mouth. Retractors are used to form a rectangle of exposure. The palate is elevated cephalad, and the tongue and endotracheal tube are retracted caudally. The tonsils and lateral oropharyngeal walls are covered with moist gauze and retracted outward (Figs. 37-1 and 37-2). Transnasal catheters and palatal retraction sutures can be used in lieu of the Spetzler-Sonntag retractor. If the mouth cannot be opened sufficiently, a mandible-splitting approach can be used¹¹ and a tracheostomy performed before the surgical approach begins.

FIGURE 37-1 Placement of the Spetzler-Sonntag retractor system. The reinforced endotracheal tube and tongue are held by the lower blade. The upper blade retracts the soft palate away from the oropharynx. The depth of the lateral “fork” retractors can be adjusted to retract the tonsils first and then the soft tissue of the back wall of the oropharynx as the operation progresses.

(Used with permission from Barrow Neurological Institute.)

FIGURE 37-2 Lateral view of the retractor system in place. The lateral retractors lift the soft tissue up and away from the resection bed. Retraction of the palate and tongue provides excellent exposure.

(Used with permission from Barrow Neurological Institute.)

After the retractor is placed in its final position, the oral cavity is cleansed with povidone-iodine (Betadine). A preoperative dose of antibiotics that includes coverage for oral flora should be administered. The authors prefer cefepime and metronidazole. The surgeon sits at the patient’s head, necessitating an adjustment in orientation for the duration of the case. An operating microscope is brought into the field. Stereotactic guidance may be used to guide the angle of approach and to confirm the location before the palatal incision is made.¹² Alternatively, fluoroscopy can be used for confirmation. Electrocauterization is used, and the incision proceeds down to bone. Subperiosteal dissection is used to expose the lower clivus, atlas, and axis. The authors seldom find it necessary to divide the soft palate unless the upper clivus is the target. Self-retaining retractors are placed to maintain exposure.

A high-speed air drill is used to remove the ventral arch of C1. The ventral arch of the atlas is the load-bearing portion of the bone.¹³ An effort should be made to preserve a portion of the arch to prevent spread of the lateral mass and to maintain orientation relative to midline. Approximately 70% of patients undergoing ventral decompression require supplemental internal fixation. This number increases to 90% in patients with rheumatoid arthritis.¹⁴ The remaining anterior tubercle of C1 is left as a landmark for posterior screw fixation (Fig. 37-3A–C). Stereotactic navigation may be useful in cases requiring hardware fixation, especially if a large ventral portion of C1 and surrounding bone must be removed. Various instruments can be used to remove bone and tissue carefully. Long-handled curettes and rongeurs, as well as bipolar cautery, are useful adjuncts (Figs. 37-4 to 37-6). The average distance between the vertebral arteries is approximately 3 cm. The anatomic “safe zone” is 1.5 cm lateral to midline in both directions (Fig. 37-7). Preoperative radiographs must be evaluated carefully. In many cases, CT angiography can delineate aberrant or asymmetrical vasculature. Further lateral dissection places the hypoglossal nerve, vertebral artery, and cervical neurovascular bundle at risk.¹⁵

FIGURE 37-3 Stepwise resection of the odontoid. A, The back wall of the oropharynx is incised from the top of C1 to the bottom of C2. Subperiosteal dissection is extended laterally. The anterior arch of C1 is identified, and the midline is maintained by preserving part of the anterior arch. Frameless stereotactic guidance is also helpful. B, The anterior arch of C1 is partially drilled away, and the lesion encompassing the odontoid is clearly in view. C, The posterior portion of the odontoid is removed, and the dura is visible. The superior part of the anterior arch of C1 is intact.

(Used with permission from Barrow Neurological Institute.)

FIGURE 37-4 Decompression of the cervicomedullary junction by resection of the odontoid. A midline incision is made in the oropharynx, and a long, curved curette is used to resect the bone or mass. Orientation to midline is crucial during the compressive stage. A portion of C1 should be left to maintain the appropriate trajectory.

(Used with permission from Barrow Neurological Institute.)

FIGURE 37-5 Further decompression is achieved with a high-speed drill. A handpiece with an angled bur works well in the depths of the resection bed.

(Used with permission from Barrow Neurological Institute.)

FIGURE 37-6 A watertight closure of the oropharyngeal incision is important to prevent postoperative cerebrospinal fluid leakage. The brainstem is well decompressed and in anatomic position.

(Used with permission from Barrow Neurological Institute.)

FIGURE 37-7 Illustration showing the lateral “safe zone” for resection of the odontoid, the average distance of which is 1.5 cm from midline.

(Used with permission from Barrow Neurological Institute.)

During a transoral odontoidectomy, cautious dissection and a methodical approach are essential to minimize the risk of cerebrospinal fluid (CSF) fistula. The superior ligamentous complex (consisting of the apical and paired alar ligaments) must be sectioned to remove the dens. This step should be performed first with curved curettes. This region is often adherent to the dura, and great care must be taken to avoid durotomy.^16,17 A thin shell of bone can be left to avoid a dural tear. Once the last of the odontoid is removed, the frameless guidance or a lateral radiograph can be checked with a radiopaque instrument in the field.¹⁸

Hemostasis is achieved using bipolar cautery and a thrombin hemostatic matrix (Floseal, Baxter Healthcare, Fremont, Calif.). Dural integrity is checked with a Valsalva maneuver held for 10 seconds. The pharynx is closed in a single layer with an absorbable suture. An enteric feeding tube is placed before anesthesia is reversed. Patients are left intubated 24 to 48 hours to avoid the trauma of reintubation if the upper airway or tongue swells. A feeding tube is placed under microscopic vision to avoid violating the mucosal suture line. After 1 week, the patient is allowed fluids. A swallow evaluation and modified barium swallow study may be undertaken before oral feedings are resumed. Dorsal stabilization may be performed during the same sitting or delayed several days to allow reassessment.

Lateral Approaches

The lateral craniocervical region is rarely involved with bony compressive lesions. Most of these lesions are strongly associated with assimilation of the atlas into the occiput when segmentation fails between the last (fourth) occipital and first cervical sclerotomes. The sclerotomes fail to separate and remain fused, resulting in an incompletely separated atlas and sometimes a bifid lamina. This defect is associated with various syndromes (e.g., achondroplasia, Morquio syndrome) and usually occurs in conjunction with other occipitocervical bony anomalies. Astute clinicians should be wary of such entities, which may be common, such as Chiari I malformations and Klippel-Feil syndrome. Rarer but no less significant entities such as basilar invagination and congenital fusion of C2 and C3 also occur.^19,20 Thus lateral approaches may need to be part of a larger operative plan and used in conjunction with other techniques to completely address the pathologies present.