Operative Considerations

Patients with nonreducible craniocervical junction bony compression or ventral soft tissue compression with spinal cord contusion are candidates for transoral odontoidectomy. The body habitus of the individual patient must be taken into account before embarking upon the procedure. The patient should be able to open his or her mouth widely enough to accommodate the transoral retraction systems. In our experience, the minimal jaw excursion to perform an odontoidectomy is 3 cm or, as a good rule of thumb, two fingerbreadths. A working corridor of this size will provide the surgeon with access from the inferior clivus to the C2–C3 interspace. Some patients with more limited jaw excursion may require transmaxillary or transmandibular approaches. Patients must have good dentition, and oral hygiene must be optimized to minimize the risk of infectious complications. Patients who satisfy these criteria are good candidates for transoral odontoidectomy.

Operating Room Configuration and Patient Positioning

Operating room setup and positioning of the patient are critical to the success of the transoral approach. Prior to intubation, the patient is positioned on the operating table awake with his or her head in extension on a horseshoe headrest in the position required for surgery. In rare instances, a Mayfield head holder or halo ring may be used if instability is of concern. Awake hyperextension allows the surgeon to optimally position the neck while also ensuring the safety of positioning from a neurological standpoint. Maintaining a neutral, nonrotated head position is critical to maintaining orientation intraoperatively. Subsequently, an awake, fiberoptic oral intubation is performed with an armored endotracheal tube.

In general, tracheostomy is rarely necessary in patients who will undergo transoral surgery. Prophylactic tracheostomy is performed only in patients who have Down syndrome or those with small oral apertures (~3 cm diameter, depending on the rostrocaudal extent of the pathology to be decompressed). These patients have both redundant posterior pharyngeal wall tissue and a decreased ability to coordinate their pharyngeal musculature following odontoidectomy.

Patients are given high-dose penicillin or clindamycin prior to starting surgery and in the perioperative period. Dexamethasone may also be given prior to surgery to decrease both neural and airway edema.

In patients with severe myelopathy, neural monitoring consisting of somatosensory evoked potentials (SSEPs) and/or motor evoked potentials (MEPs) is employed. When neuromonitoring is used, a preoperative baseline study is obtained prior to incision.

Cranial traction may be used if necessary to optimize anatomical reduction of the craniocervical junction ( Fig. 16.1 ); in most cases, we do not need to employ traction.

To maximize ergonomics for a right-handed surgeon, the patient is positioned with his or her left side toward the anesthesiologist. The endotracheal tube is placed in the midline of the mouth. The C-arm fluoroscope is positioned to obtain cross-table lateral cervical images. The surgeon stands behind the patient, and the scrub nurse is positioned to the right side of the patient. The operating microscope base is positioned to the left-hand side of the surgeon ( Fig. 16.2 ).

Surgical Technique for Transoral Odontoidectomy

A Spetzler-Sonntag or similar retractor is placed with an appropriate tongue blade to retract the tongue and endotracheal tube inferiorly. Care is taken to avoid trapping the tongue against the teeth. The retractor is opened as widely as possible to allow maximum exposure of the posterior pharyngeal area ( Fig. 16.3 ). The anesthesiolo-gist administers agents that create neuromuscular blockade to allow for wider mandibular opening.

Once the Spetzler-Sonntag retractor is in place, a red rubber catheter is placed through one of the nares and is sutured to the uvula ( Fig. 16.4 ). The catheter is then pulled up through the nose, thus retracting the uvula and soft palate superiorly; this retraction improves exposure of the upper portion of the posterior pharyngeal wall overlying the tip of the odontoid and prevents secretions from flowing into the incision. This maneuver is a critical step, allowing the surgeon to avoid making soft palate incisions in most cases. It is the soft palate incision that results in postoperative dysphagia and dysphonia in some patients.

The superior soft palate retractor on the SpetzlerSonntag system is applied after the uvula is retracted superiorly to provide even further superior exposure ( Fig. 16.5 ). At this point, a clear view from the inferior clivus to C2 is obtained.

The posterior pharynx is then infiltrated with 1% lido-caine with epinephrine. Subsequently, lateral fluoroscopy is used to identify the area of the posterior pharyngeal mucosal wall overlying the odontoid process. The anterior tubercle of C1 may also be palpated. The incision is typically 1.5 to 2 cm in length and is carried through the posterosuperior pharyngeal constrictor muscle in the midline raphe ( Fig. 16.6 ) over C2 and the anterior tubercle of C1. A full-thickness incision must be made through the mucosa, and the integrity of the superficial mucosa should be maintained to facilitate closure. Our initial incision is shorter than what is ultimately needed for the odontoidectomy because the retractors that are subsequently placed tend to extend the rostrocaudal length of the incision when they are opened. Once the incision has been created, we do not touch the remainder of the oral cavity outside the incision. We avoid tracking secretions and oral bacteria into the incision with this “no touch” technique.

The Crockard self-retaining retractor is placed in the midline pharyngeal incision to retract the mucosal and pharyngeal constrictor muscles and spread laterally to expose the anterior arch of C1. We then use electrocautery to skeletonize, in a subperiosteal fashion, the anterior surface of the arch of C1 ( Fig. 16.7 ). The fluoroscope is again used to confirm anatomical landmarks. The use of image guidance is optional, and in most cases we do not use computerized neuronavigation systems.

Once the arch of C1 has been exposed ( Fig. 16.8 ), we identify the midline and drill and remove the anterior arch of C1 to expose the anterior portion of the odontoid process. The arch removal should be wide enough to expose the shoulders of the odontoid process; this typically requires removal of two thirds of the anterior arch of C1. Inadequate resection of the anterior portion of the C1 ring is a common mistake. The shoulders of the odontoid process are a critical landmark for the surgeon and must be visualized. Preoperative computed tomography (CT) scans should be obtained to ensure that there are no variations in the normal anatomical course of the vertebral artery in the foramen transversarium of C1 and C2.

After exposure of the odontoid process, an angled curet is used to detach the apical and alar ligaments at the top of the odontoid process. Fluoroscopy is used to identify how far posteriorly the angled curet may be placed without violating the spinal canal. These ligaments act as a tether and will prevent removal of the tip of the dens if they are not severed. Removal of these ligaments at the apex of the dens establishes the superior boundary for bone removal and allows for subsequent resection of the top of the odontoid process. In patients with significant basilar invagination, accessing and removing these ligaments can be difficult; traction is often necessary in these cases to gently mobilize the top of the odontoid process inferiorly.

Once the ligaments have been detached, a “top-down” removal of the odontoid process is performed by drilling the dens using an eggshell drilling technique with the Midas Rex AM-8 drill bit (Midas Rex Pneumatic Tools, Inc., Forth Worth, Texas). The AM-8 drill bit has a smooth tip, which prevents it from catching and tearing soft tissue. The drill is then used to carry the bony resection all the way through the odontoid process up to the transverse ligament.

The odontoid is not disarticulated at its base with the drill, as it would result in a free-floating odontoid fragment. Such a “bottom-up” drilling procedure allows the odontoid to float freely and does not provide resistance to the drill bit for further removal of the bone. The “top-down” drilling technique ensures that the apex of the dens (which often causes significant spinal canal compromise) is removed first, and the surgeon can then proceed in a stepwise fashion (in a superior to inferior direction) to remove the remainder of the dens without leaving floating bone fragments behind. In cases where the apex of the dens cannot be reached with the drill tip, we use Kerrison rongeurs and/or curets to reach around the top of the dens and complete the bony resection. Upon removal of the dens, the cruciate ligament is identified. It is also critical to examine the degree of compression attributable to the rostral C2 body, and the bony resection should be carried further caudally into the body of C2 to ensure no residual cord compression exists after the odontoid resection.

In patients with rheumatoid arthritis or with fibrocartilaginous lesions of the odontoid area, soft tissue pannus is encountered typically once the bone of the dens has been resected. Some portion of the soft tissue pannus may be resected. Several studies have shown spontaneous resorption of the soft tissue pannus following posterior fixation13,19–21; therefore, aggressive resection of the pannus may not be necessary if posterior fixation is to be placed. Because posterior fixation is indicated for most patients, complete resection of the soft tissue pannus, if present, is not required. All loose fragments of soft tissue pannus are resected, but the deeper layers on the surface of the dura are left behind. Aggressive removal of soft tissue pannus risks injury of the underlying dura and potential leakage of cerebrospinal fluid (CSF). CSF leakage in the setting of the transoral odontoidectomy may result in meningitis, which can be fatal.

Once we feel that we have achieved an adequate removal of bone and pannus, we then inject iohexol dye into the resection cavity and obtain a lateral fluoroscopic radiograph to confirm the extent of our decompression. The spread of the dye helps to reveal any remaining remnant of the dens. In cases where neuronavigation is used, the image guidance system is helpful to identify any remnants of the dens. If we are satisfied with the bone removal, we then proceed with closure.

The posterior pharyngeal mucosa and muscle are closed by reapproximating them with interrupted 3.0 chromic suture in a single- or double-layer fashion. The posterior pharynx is irrigated with a small amount of antibiotic solution. Bone wax is not used, as the wound is considered contaminated, and the wax theoretically could provide a nidus for infection. Only the incision is irrigated, not the entire oral cavity. Excessive oral irrigation may allow fluid to enter the airway and lungs.

The nasal red rubber catheter is removed. The uvula falls into its original place. To allow for nutrition after a surgery, a Dobbhoff feeding tube is then passed through one of the nares and down into the esophagus under direct vision while the Spetzler-Sonntag retractor is still in place. The Dobbhoff tube is stitched to the lateral wall of the nostril to prevent accidental dislodgment. The retractor systems are then removed, and the tongue and lips are inspected. Cortisone cream is typically applied to the tongue and lips to reduce postoperative swelling. The tongue is massaged to restore circulation. Typically, the tongue retractor is not released during the procedure because the operation can be performed in ~90 minutes. Instances of tongue edema following surgery typically resolve within 2 or 3 days.

The instability created by the removal of the odontoid process9,10,22 has been established in several previous studies. Therefore, posterior stabilization is performed as a second procedure on the same day, immediately following the transoral odontoidectomy. This is performed without changing the endotracheal tube. The patient is fixated in skull clamps and positioned prone onto chest rolls, on a separate operating table for the posterior portion of the procedure. For cases with significant basilar invagination or occipitocervical instability, an occipitocervical fusion is indicated.23 For cases without significant basilar invagination and only C1–C2 instability, Magerl’s transarticular C1–C2 screw fixation or Goel’s C1 lateral mass screws with C2 pars/pedicle screw constructs15,23–26 are preferable. Posterior fusions should incorporate iliac crest autograft or rib autograft.

After completion of both anterior and posterior procedures, the patient is monitored in the intensive care unit (ICU). Patients typically remain intubated in the ICU for 2 or 3 days. They are extubated only after a cuff leak (breathing around a deflated endotracheal cuff) is confirmed in the ICU on postoperative day 2 or 3. The anesthesiologist typically removes the endotracheal tube over a tube changer, which is left in place for a minimum of 1 hour. The tube changer allows for easy reintubation should the need arise.