7 Technique of Transoral Odontoidectomy

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7 Technique of Transoral Odontoidectomy

P.J. Apostolides, A.G. Vishteh, R.M. Galler, V.K.H. Sonntag

Modified from Operative Techniques in Neurosurgery, 1:58 – 62, Apostolides, Vishteh, and Sonntag,

a

b Fig. 7.1. a Routine transoral

exposure. This exposure may be increased superiorly with a transpalatal extension or inferiorly with a transman- dibular extension. b Sagittal view showing routine transoral exposure with normal and pathological anatomy (inset). With permission from Barrow Neurological Insti- tute

7.1

Terminology

The transoral approach to the craniovertebral junction is an excellent surgical technique for treating ventral midline extradural compressive pathology. The target region is reached by an approach crossing the oral cavity through the open mouth (“transoral”).

7.2

Surgical Principle

The transoral operation provides direct midline access to the ventral craniovertebral junction to facilitate decompression of the lower brain stem and upper cervical spinal cord. The surgical exposure typically extends from the inferior third of the clivus to the top of the C3 vertebra (Fig. 7.1) and is limited primarily by the pa-

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tient’s ability to open his or her mouth. The standard transoral exposure can be extended superiorly with a transpalatal or transmaxillary approach [3 – 5, 16 – 23], or inferiorly with a mandibulotomy and median glossotomy (Fig. 7.1a, b) [3, 8, 14, 16 – 20].

7.3 History

The approach was described first by Kanavel in 1917 [15]. Since then and especially since the application of the surgical microscope, the approach has been described by many authors mainly for the extirpation and treatment of extradural lesions [3, 7, 8, 11, 13, 18, 22].

7.4

Advantages

This approach is the direct and unobstructed way to the anterior part of the craniocervical junction. The anteri- or bony structures (inferior third of the clivus, anterior arch of C1, and anterior part of C2 and C3) can be exposed by dissection of the posterior wall of the pharynx. The apex of the odontoid process as well as the anterior part of the foramen magnum can be exposed after resection of the anterior arch of C1.

7.5

Disadvantages

The approach is limited by the surgical corridor provided through the open mouth. There is a considerable risk of severe complications such as infection with or without involvement of the meninges, disturbances of wound healing, cerebrospinal fluid (CSF) leakage as well as complications arising from trauma to the uvula and soft palate. In patients with rheumatoid arthritis involving the mandibular joints, the approach is occasionally limited by the inability to open the mouth suf- ficiently (> 2.5 cm).

7.6

Indications and Contraindications

The primary indication for a transoral procedure is an irreducible midline extradural lesion that compresses the cervicomedullary junction. A transoral procedure occasionally may be required to obtain a tissue diagno- sis or to debride an infection.

Transoral surgery is contraindicated if the patient has an active nasopharyngeal infection or reducible ventral lesion, or if the vertebral or basilar arteries are

located within or ventral to the lesion. The transoral approach is usually inappropriate for intradural pathology because of the significant risks of CSF leakage and meningitis associated with the frequent inability to achieve a watertight dural closure [7, 10 – 12, 21].

7.7

Patient’s Informed Consent

Informed consent of the patients should include explana- tions of the potential complications such as lesions to the tongue, postoperative hematoma, irritation, and sensory deficits in the oral cavity. It should also include the risk of disturbed senses of taste and smell or swallowing due to postoperative swelling of the intraoral structures. The risk of postoperative infection and the necessity for antibiotic medication should be emphasized.

7.8

Surgical Technique

7.8.1

Preoperative Preparation

All transoral surgeries are performed under general anesthesia administered via a fiber-optically placed orotracheal tube that can be retracted from the surgical field to provide optimal exposure of the posterior oropharynx. Routine tracheostomy is rarely necessary un- less severe preoperative bulbar or respiratory disturbances are present [1, 2, 9, 13, 23]. All patients receive routine perioperative antibiotics (cefuroxime, 1.5 g).

Unlike some authors, [6, 18, 23] we do not obtain routine preoperative nasal and oropharyngeal cultures un- less an active infection is suspected based on the patient’s history or clinical examination.

Continuous intraoperative somatosensory evoked- potential monitoring and brain stem auditory evoked- potential monitoring are used to assess the physiologic status of the spinal cord and brain stem during the procedure.

7.8.2 Positioning

The patient’s head is secured with a Mayfield clamp and the patient is placed in the supine position. The head is placed in a neutral position and the neck is slightly extended.

7.8.3

Surgical Steps

A low-profile self-retaining transoral retractor system (Spetzler-Sonntag, Aesculap, San Francisco, CA) is

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a Fig. 7.2. Superior (a) and lateral

(b) views of patient positioning and the retractor system used in the transoral approach. The patient’s head is secured with a Mayfield clamp. The patient is placed in the supine position with the head in the neutral position and the neck slightly extended. The rectangular retractor frame is placed over the patient’s mouth and attached to the operating room table via crossbars.

With permission from Barrow Neurological Institute

used to achieve wide exposure of the posterior oropharynx. The rectangular retractor frame is placed over the patient’s mouth and attached to the operating room table via crossbars to stabilize the instrumenta- tion and to allow the table to be rotated during the procedure (Fig. 7.2a, b ). The tongue and endotracheal tube are retracted caudally with a rigid wide-blade retractor.

To avoid severe swelling or necrosis, the tongue should be inspected carefully to ensure that it is not pinched between the retractor blade and the patient’s teeth. The soft palate and uvula are retracted superiorly with a malleable-blade retractor. Adjustable, telescoping tooth-bladed retractors are attached to the retractor frame and inserted into the oropharynx to retract the pharyngeal flaps laterally to widen the exposure.

The oropharynx and the retractors are sterilized with Betadine solution. An intraoperative radiograph often is obtained to judge spinal alignment after positioning and to confirm the extent of the rostral and cau- dal exposure provided by the retractor system. The table is often placed in the Trendelenburg position to provide the best perspective of the craniovertebral junction. The surgical microscope is used immediately to improve lighting, to provide variable magnification, and to allow the co-surgeon to observe and assist during the procedure. The surgeon sits above the patient’s head and has a direct view of the patient’s mouth and oropharynx (Fig. 7.3a).

The C1 tubercle is palpated to verify the position of the midline (Fig. 7.3b). The midline posterior oropharyngeal mucosa is infiltrated with 0.5 % or 1 % lido- caine with 1/200,000 epinephrine. A vertical midline

b

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a

Fig. 7.3. a Surgeon’s view of patient’s mouth and oropharynx after placement of the low-profile, self-retaining re- tractor system. b Anatomical relationships of the anterior aspects of the clivus, C1-C2, and the adjacent vascular structures underlying the posterior oropharynx mucosa and muscles. The C1 tubercle is a key landmark that veri- fies the position of the mid- line. c Anatomical relation- ships of the alar and apical ligaments fixating the dens to the occiput. With permission from Barrow Neurological Institute

b c

a b

Fig. 7.4. Transoral odontoidectomy. a A vertical midline incision is made in the median raph´e of the posterior oropharynx to ex- pose the anterior arch of C1 and the body of C2. b The inferior portion of the anterior C1 arch is resected to expose the base of the odontoid process.

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c

d

e

Fig. 7.4. (cont.) c The dens is transected at its base. d The dens is removed to complete the decompression. e The incision is closed in a single layer with a running 2 – 0 vicryl suture. With permission from Barrow Neurological Institute

incision is made in the median raph´e of the posterior pharyngeal wall mucosa, pharyngeal muscles, and the anterior longitudinal ligament using either monopolar cauterization or a Shaw scalpel (Fig. 7.4a). If possible, a palatal incision is avoided because it can cause nasal re-

gurgitation, dysphagia, and a nasal tone of voice. The layers of the posterior oropharynx are maintained as a single thick layer to facilitate a strong tissue closure.

Periosteal elevators are used to dissect the anterior longitudinal ligament subperiosteally and to separate the tissue flap from the anterior surfaces of the C1 arch, the C2 vertebral body, and the inferior clivus.

Curettes and periosteal elevators are used to define the boundaries of the clivus, the anterior arch of C1, the base of the odontoid process, and the C2 vertebral body. The inferior one-third to two-thirds of the anteri- or C1 arch is resected to expose the base of the odontoid process using a high-speed air drill and Kerrison ron- geurs (Fig. 7.4b). We try to limit the resection of the anterior C1 arch to preserve the structural integrity of the C1 ring. However, enough bone must be removed to expose the dens adequately. If necessary, the anterior C1 arch should be resected completely.

After the base of the dens has been exposed satisfac- torily, the lateral margins of the odontoid are defined.

The alar and apical ligaments are detached sharply with curved curettes. The base of the dens is partially transected with a cutting burr (Fig. 7.4c); the osteotomy is completed by removing the posterior cortex with a small Kerrison rongeur or diamond burr. The dens is grasped with a toothed odontoid rongeur and removed en bloc (Fig. 7.4d). The dens can be removed in a piece- meal fashion, but it is often more difficult to access its apex.

Soft tissue pathology often must be resected to de- compress the neural elements adequately. The trans- verse ligament and tectorial membrane also may need to be removed to adequately visualize the dura and normal pulsation of the thecal sac. However, the surgeon must beware of attenuated dura and ligaments that ad- here to the dura. Meticulous microsurgical techniques are necessary to avoid a CSF leak from inadvertent dural entry, which is associated with a high risk of postoperative morbidity and mortality. If an intraoperative CSF leak occurs, a fascial patch is placed directly over the dura and secured with fibrin glue. A lumbar drain is inserted postoperatively, and antibiotic coverage and the lumbar drain are maintained for at least 5 – 7 days.

The boundaries of the decompression can be as- sessed intraoperatively by placing iodinated contrast material into the decompression site and obtaining a lateral cervical radiograph or by employing stereotac- tic navigation. Adequate decompression is confirmed when the dura bows into the wound and assumes its usual anatomic contour. Once the brain stem and spinal cord have been decompressed, the wound is irrigated with antibiotic solution and hemostasis is achieved.

The wound is closed with interrupted or running 2 – 0 vicryl suture in a single layer that includes the mucosa, pharyngeal muscles, and ligaments (Fig. 7.4e). Multi- layer closures are more difficult to perform and can at-

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tenuate the tissue layers and weaken the incision line. A nasogastric feeding tube is inserted while directly visu- alizing the oropharyngeal incision to avoid inadvertent malpositioning of the tube.

7.9

Postoperative Care

Moderate tongue and pharyngeal swelling can be expected for the first 24 – 72 hours after surgery. The endotracheal tube should be maintained until the swelling subsides because premature extubation can lead to respiratory distress, respiratory arrest, and death. In our experience, topical steroids provide little if any benefit in minimizing soft tissue swelling and therefore are not used routinely.

Enteral nutrition via the indwelling feeding tube is started on postoperative day 1 and continued 3 – 5 days.

The patient’s diet is slowly advanced from liquids to soft regular foods and then to regular foods usually within 14 days. If the feeding tube is inadvertently removed before oral feedings have been started, appropriate par- enteral nutrition should be provided. Replacing the feeding tube risks penetration of the healing mucosal incision and inadvertent malpositioning of the tube.

Postoperative spinal instability should be expected after transoral odontoidectomy. Patients should therefore remain in an external orthosis until spinal stability can be restored. Although some authors advocate im- mediate posterior fixation of the spine after transoral decompression, we prefer to wait several days to reduce the risk of infection in the posterior cervical wound.

7.10

Hazards and Complications

Medical complications, including pneumonia, urinary tract infections, deep venous thrombosis, pulmonary emboli, and myocardial infarctions, are common after transoral surgery, particularly in patients with severe preoperative neurological deficits or debilitating medical illnesses. Therefore, it is important to optimize the patient’s general medical condition before surgery and to use prophylaxis for deep venous thrombosis during and after surgery. Postoperatively, pulmonary toilet should be aggressive, and the patient should be mobi- lized early after stabilization to limit the development of these potential complications.

Wound infections should be treated with broad- spectrum antibiotics until culture sensitivities are available. Wound dehiscence at any time requires reoperation and reclosure. Wound dehiscence occurring after the first week should raise the suspicion of a possible underlying retropharyngeal infection or abscess.

CSF leakage represents a significant risk to the patient and should be addressed promptly. Appropriate treatment includes dural patching, meticulous pharyngeal wound closure, and placement of a lumbar drain. If a CSF leak stops with lumbar drainage but recurs after the drain has been closed or discontinued, the patient requires a lumboperitoneal shunt. If CSF leakage per- sists despite lumboperitoneal drainage, reoperation and dural patching are required. Postoperative meningitis should raise the suspicion of a CSF leak. Proper treatment includes intravenous antibiotics and placement of a lumbar drain.

Neurological deterioration after transoral surgery is rare. Patients with new neurological deficits should be evaluated for loss of spinal alignment, persistent cervicomedullary compression, epidural hematoma, epidural abscess, meningitis, or vertebrobasilar occlusion.

7.11 Conclusions

The transoral approach is an effective surgical method for the direct decompression of irreducible ventral midline extradural compressive pathology of the craniovertebral junction. Specialized low-profile retractor systems, the surgical microscope, contemporary microsurgical dissection and dural closure techniques, and meticulous postoperative radiographic assessment of spinal stability minimize perioperative complications and facilitate good long-term outcomes.

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