Upper Cervical and Craniocervical Decompression

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Chapter 37 Upper Cervical and Craniocervical Decompression

The posterior fossa and craniocervical junction house the structures vital for basic human functions. Deformities and pathology in this region place these structures at risk. Compression in this region may cause neurologic deficits related to the cerebellum, brainstem, and spinal cord. Operative decompression of endangered structures helps alleviate neurologic dysfunction. On radiography the presence of an obvious pathology in this region that correlates with a neurologic deficit makes the decision to operate straightforward. A more difficult question arises when there is discordance among a patient’s films, history, and neurologic examination. The operative approach is dictated by the location of the pathology and the anatomy of local structures. Complication avoidance and management are paramount to good surgical outcomes. This chapter focuses on the choice of operation (ventral, lateral, dorsal, or combined) and on potential pitfalls associated with operating on complex pathologies in the posterior fossa, craniocervical junction, and upper cervical spine.

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.24 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.

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

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.

Pitfalls and Complication Avoidance

Preoperatively, many patients requiring ventral decompression may be severely debilitated. Postoperatively, they may need a course of parenteral nutrition, long-term rehabilitation or skilled-nursing care placement, and a long convalescent period. The surgeon should make it a priority to ensure that patients and their loved ones have appropriate and realistic expectations about outcomes and that they understand the possible risks and complications associated with the procedure.

Checking and rechecking midline orientation and depth of resection are key to safety. Dissection planes may be obscured by local pathology and may never emerge during the course of a case. As the resection proceeds deeper, meticulous dissection is crucial. A clean and bloodfree field must be maintained. Should the dura become lacerated, the surgeon should make every effort to repair it primarily. Fibrin glue or a fascial graft should be considered for adjuncts. Postoperatively, a lumbar subarachnoid drain should be placed and left for several days. The patient should be under constant surveillance, and fluid cultures should be followed to observe for signs of meningitis. Preoperative antibiotics should be maintained postoperatively if contamination is suspected. Before extubation, upper airway and tongue swelling should have abated enough to avoid obstruction and the precipitous decline of a patient with a difficult, swollen airway. Should this situation develop, an emergent tracheostomy or cricothyrotomy is option for reestablishing the airway.