Summary of Key Points
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A diverse set of pathologies affects the craniocervical junction, including traumatic, congenital, degenerative, vascular, and neoplastic pathologies.
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Traditionally, the craniocervical junction has been treated via transoral, lateral extrapharyngeal, and posterior approaches.
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Improved instrumentation and endoscopic techniques now allow for a broadened number of less invasive approaches to the craniocervical junction.
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Advances in surgical adjuncts, neuroimaging, anesthesia, and postoperative care have improved treatment outcomes of craniocervical junction pathologies.
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Minimization of vascular injury and cerebrospinal fluid fistulae formation may contribute to improved surgical outcomes.
The posterior fossa and craniocervical junction (CCJ) house critical neurovascular structures; their compromise may result in devastating injury. Neural and vascular compression in this region may cause deficits related to the cerebellum, brain stem, and spinal cord. Operative decompression of endangered structures alleviates neurologic dysfunction. Radiographically, the presence of obvious correlative pathology in this region makes the decision to operate straightforward. Discordance between imaging, history, and neurologic examination is more challenging and requires further workup. Complication avoidance and management are paramount to good surgical outcomes. This chapter focuses on indications for surgical intervention, choice of approach, and pearls for complication avoidance when addressing pathologies in the posterior fossa, CCJ and upper cervical spine.
Pathology Overview
The CCJ may be the site of complex and diverse pathologies ( Table 51-1 ). In general, most surgical lesions can be approached dorsally through a posterior fossa craniectomy with or without a C1 laminectomy. Abnormalities can be divided into two basic categories: congenital/developmental abnormalities and acquired pathologies. The various pathologies are summarized in Table 51-2 .
| Location | Congenital | Acquired | Primary Neoplastic | Secondary Neoplastic | Intra/Extradural | Neural “Tumors” |
|---|---|---|---|---|---|---|
| Clivus and foramen magnum | Segmentation failure |
|
|
|
|
|
| Atlas | Assimilation with segmentation failure | Stenosis (e.g., achondroplasia), chronic dislocation (e.g., Morquio syndrome, Down syndrome, rheumatoid arthritis, other arthropathies) |
|
|
|
|
| Axis |
|
|
|
|
|
|
| Congenital |
|---|
| O ccipital B one M alformations |
| Occipital vertebrae |
|
| Basilar invagination |
| Condylar hypoplasia |
| Assimilation of atlas |
| A tlas M alformations |
| Atlas assimilation |
| Atlantoaxial fusion |
| Incomplete arch |
| A xis M alformations |
| Segmentation abnormalities |
| Dens dysplasias |
|
| C2-3 segmentation failure |
| Developmental or Acquired |
| F oramen M agnum A bnormalities |
| Secondary basilar invagination |
|
| Foraminal stenosis (e.g., achondroplasia) |
| A tlantoaxial I nstability |
| Metabolic errors (e.g., Morquio syndrome) |
| Down syndrome |
| Infectious |
| Inflammatory (e.g., rheumatoid arthritis) |
|
| Tumors (e.g., neurofibromatosis, syringomyelia) |
| Miscellaneous |
Ventral Approaches
There are several accepted routes to the ventral clivus and upper cervical spine. Standard approaches to the ventral cervical spine are limited by the mandible and oropharynx. Transoral and endonasal routes to the lower clivus and upper cervical spine are safe for addressing pathologies that cause craniocervical instability and that compress neurovascular structures from the clivus to the C4 vertebral body. In 1917, Kanavel described the first transoral procedure, removal of a bullet lodged between the clivus and ventral atlas. Fang and Ong later reported the first series of six patients who underwent transoral decompression for atlantoaxial instability or congenital anomalies; a high complication rate contributed to slow adoption of this approach.
A resurgent interest in transoral and endonasal approaches led to the refinement of techniques and instrumentation. Modern antibiotics and instruments have revolutionized and revitalized this operation. Most notably, improvements in dural repair techniques have lowered the incidence of cerebrospinal fluid (CSF) leaks and infections. Although an extrapharyngeal approach can be used to access the upper cervical region, it is technically difficult. The authors of this chapter prefer the transoral or the endoscopic approach to access extradural pathology and a lateral approach for intradural lesions.
Microscopic Transoral Odontoidectomy
Surgical Technique
General anesthesia is used for all ventral cases, including a reinforced endotracheal tube to preserve the airway. Cervical stability is maintained by using fiberoptic endoscopy or awake-intubation techniques if required. The institutional policy of the authors requires intraoperative monitoring of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs). 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, MA) or a halo-ring adapter. A Spetzler-Sonntag transoral retractor (Aesculap, San Francisco, CA) is positioned into the mouth to form a rectangle of exposure. The palate is elevated cephalad, while the tongue and endotracheal tube are retracted caudally. The tonsils and lateral oropharyngeal walls are covered with moist gauze and retracted laterally ( Figs. 51-1 and 51-2 ). 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 used along with a tracheostomy before the surgical approach begins.
After the retractor is placed in its final position, the oral cavity is cleansed with Betadine. A preoperative dose of antibiotics that covers for oral flora is administered; the authors prefer cefepime and metronidazole. The surgeon stands at the patient’s head; adjustments in orientation will be necessary for the duration of the case. An operating microscope is brought into the field. Stereotactic guidance or fluoroscopy may be used to guide the angle of approach and to confirm the location before the palatal incision is made. Electrocautery is used, and the incision proceeds down to bone. Subperiosteal dissection exposes the lower clivus, atlas, and axis. It is seldom necessary to divide the soft palate unless targeting the upper clivus. Self-retaining retractors maintain the exposure.
A high-speed drill is used to remove the ventral arch of C1, which is the load-bearing portion of the bone. A portion of the arch should be preserved 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, reaching 90% in patients with rheumatoid arthritis. The remaining anterior tubercle of C1 is left as a landmark for posterior fixation ( Fig. 51-3A-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. Long-handled curettes and rongeurs as well as bipolar cautery are useful adjuncts for removing bone and tissue ( Figs. 51-4 through 51-6 ). The average distance between the vertebral arteries is approximately 3 cm. The anatomic “safe zone” is within 1.5 cm on either side of midline ( Fig. 51-7 ). Preoperative radiographs must be evaluated carefully. In many cases, computed tomography (CT) angiography can delineate aberrant or asymmetric vasculature. Further lateral dissection places the hypoglossal nerve, vertebral artery, and cervical neurovascular bundle at risk.
During a transoral odontoidectomy, cautious dissection and a methodical approach are essential to minimize the risk of CSF fistula. The superior ligamentous complex (consisting of the apical and paired alar ligaments) must first be sectioned to remove the dens, which can be done with curved curettes. This region often strongly adheres to the dura, and great care must be taken to avoid durotomy. 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.
Hemostasis is achieved using bipolar cautery and thrombin hemostatic matrix. Dural integrity is assessed with a Valsalva maneuver 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 should it become necessary. A feeding tube is placed under microscopic vision to avoid violating the mucosal suture line; fluid intake is allowed 1 week postoperatively. 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.
Endoscopic Transnasal Odontoidectomy
Surgical Technique
The expansion in endoscopic endonasal approaches allows for novel approaches to the clivus and upper cervical spine. Image guidance is of paramount importance in planning and executing endoscopic endonasal approaches to the clivus. Thin-cut computed tomography (CT) and magnetic resonance imaging (MRI) of the cervical spine are useful for assessing the bony anatomy and other critical structures during the approach. If necessary, patients are placed in halo traction for immobilization to prevent risk of injury during positioning.
Intubation is performed using an armored (reinforced) oral endotracheal tube, and the patient is affixed to the table using a standard Mayfield head holder. The patient is typically in a neutral position. Fluoroscopy is then used to obtain a true lateral view, and CT- or MRI-based intraoperative image guidance is registered for optimal trajectory to the clivus or upper spine.
Although both nostrils can be used for access, a right-handed surgeon commonly prefers to access endonasal pathology via the right nostril ( Fig. 51-8A ). Various endoscopes, including 0-degree, 30-degree, and 45-degree endoscopes, can be used to visualize the surgical field ( Fig. 51-8B ). A mounted digital camera system is used for most cases (Karl Storz GmbH & Co., Tuttlingen, Germany). The middle turbinate can be resected or outfractured to expose the nasal mucosa, which is then mobilized using cautery in a vertical incision 1.5 cm from the root of the nasal septum. Periosteal dissection is continued, and the bony nasal septum is fractured to expose the sphenoid rostrum. The optimal trajectory to the clivus can be confirmed using intraoperative navigation.
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