Transoral Approach to the Craniovertebral Junction

10.1055/b-0034-84452

Transoral Approach to the Craniovertebral Junction

Curtis A. Dickman, Robert F. Spetzler, Volker K. H. Sonntag, Nicholas C. Bambakidis, and Paul J. Apostolides

The transoral approach to the craniovertebral junction (CVJ) provides versatile, direct access to extradural midline pathology. This transmucosal approach allows excellent decompression of the ventral medulla and upper cervical spinal cord. In most circumstances, the transoral approach permits access from the inferior third of the clivus to the C3 vertebra. The operative exposure is constrained by the patient′s ability to open his or her mouth and by the soft tissue boundaries of the nasopharynx, the oropharynx, the mandible, and the skull base. Although multiple techniques have been described both in the literature and elsewhere in this text,1–4 in this chapter we discuss our preferred technique, which has proven to be efficacious in a large number of patients.

General Considerations

Transoral access to the CVJ can be performed with a simple, uncomplicated approach that involves retracting the soft palate and the tongue without incising these soft tissue structures. Dysphagia, dysphonia, and nasal regurgitation of fluids (velopharyngeal incompetence) can occur after palatal or lingual incisions. Extended transoral exposures include the transmaxillary, transpalatal, transfacial, and transmandibular exposures ( Fig. 21.1 ). The extensions of the transoral exposure provide broader access to more extensive pathology and are fully discussed in Chapters 22, 23, and 24. The extended transoral exposures increase the morbidity rates associated with the surgical procedures and, therefore, are reserved for pathology that is more extensive than can be accessed by a simple transoral exposure.

Typically, transoral decompression is indicated for irreducible compressive pathology of the ventral brainstem and spinal cord ( Fig. 21.2 ). This was recommended for all cases of ventral compression as the initial procedure of choice. Yet, in many cases of pannus formation in which compression is purely from inflammatory fibrous tissue, a posterior fusion alone may result in resorption of the compressive lesion and neurological improvement.5–7 In cases where reduction is attempted, as in cranial settling associated with bone softening diseases or rheumatoid arthritis, a magnetic resonance imaging (MRI) compatible halo ring is best utilized. The vector of the traction should be neutral, or the neck should be extended slightly. For axial traction, weights are applied, beginning with 4 pounds. Slowly and progressively, the weight is increased to a maximum of 10 to 12 pounds. Traction should be applied carefully to avoid distraction, which can cause neurological or vascular injury. Flexion of the neck should be avoided because it can increase the compression associated with cranial settling. The duration of traction should be limited to a few days to avoid decubitus ulcers, venous thrombosis, infections, or other complications associated with prolonged bed rest. As an alternative in selected cases, manual cervical distraction and extension followed by posterior fixation alone may be attempted, particularly in patients with basilar invagination associated with Chiari malformation.8

The progress of the reduction is monitored with radiographs. The final decompressive effect of the traction is assessed with MRI. If full reduction can be achieved with traction and no residual compression exists, the patient′s instability is treated with posterior occipitocervical fusion. However, if the compressive pathology is irreducible and consists of bony or noninflammatory elements ( Figs. 21.3 and 21.4 ), decompression and staged internal fixation are required.

Access to the clivus provided by combined exposures of the skull base and craniovertebral junction: (1) frontobasal approach; (2, 3) transfrontal, transethmoidal, and transmaxillary approaches; (4) transoral approach combined with transmaxillary, transfacial approach; (5) transoral approach combined with transmaxillary approach allows access from the upper clivus to the C2-C3 disk space; and (6) transoral–transpalatal approach provides access to the middle and lower clivus. The transoral approach alone usually provides access from the lower third of the clivus to the C2-C3 disk space. (Reprinted with permission from Barrow Neurological Institute.)

Algorithms for treating **(A)** atlantoaxial subluxations and **(B)** vertical migration. Positioning and traction are used to attempt to reduce the deformities into normal anatomical positions. If compressive pathology is irreducible, then decompressive surgery is needed to remove the offending pathology. This can be done **(C)** either anteriorly or posteriorly, depending on the nature and location of the compressive lesion. The extent of the stabilization procedures to treat the pathological motion depends on the patient′s anatomy, the extent of the pathology, and the surfaces available for fixation. (Figs. 21.2A and B reprinted from Dickman CA, Ronderos JF, Sonntag VKH. Stabilization of the craniovertebral junction in rheumatoid arthritis. Part I: Pathophysiology, diagnosis and surgical criteria. Contemp Neurosurg 1995;17[12]:1–6.)

Reduction with traction is attempted primarily in patients with rheumatoid arthritis, infections, neoplasms, and bone softening diseases.1–3,9–16 Congenital malformations of the CVJ usually are static and cannot be reduced with traction.13,17,18 Patients with ventral CVJ tumors or infections may require transoral surgery for resection or debridement of their pathology in addition to neural decompression. If instability is associated with the pathology or develops postoperatively, a staged posterior approach is used for occipitocervical or atlantoaxial fixation ( Fig. 21.2 ).

**(A)** Postmyelogram computed tomography scan of an irreducible congenital malformation of the craniovertebral junction. The odontoid process is compressing and distorting the medulla. **(B)** Sagittal magnetic resonance image provides an excellent perspective of the pathoanatomical relationships. This patient has platybasia, failure of segmentation, occipitalization of C1, fusion of C2-C3, compression of the pons and medulla, and a Chiari malformation.

**(A)** Lateral cervical radiograph of a myelopathic patient with rheumatoid arthritis. This patient′s deformity was irreducible with traction and neck extension. The anterior arch of C1 (*arrow*) and skull base are displaced ventrally and inferiorly. **(B)** Magnetic resonance image demonstrates the soft tissue pannus, bone erosion, and compression and distortion of the medulla and spinal cord. The lax ligaments in the subaxial spine create a “staircase” effect with the vertebral bodies.

Myriad symptoms occur with compression of the CVJ.1–3,9,10,12,14,15,19,20 These symptoms can be nonspecific and difficult to localize. The diagnosis often is delayed and mistaken for demyelinating diseases or other types of pathology. Ischemic symptoms may develop if the vertebrobasilar system, posterior inferior cerebellar artery, or anterior spinal artery is involved. Compressive symptoms can occur if the lower cranial nerves, brainstem, spinal cord, or cerebellum is involved. Spinal instability can be superimposed on the compression, causing severe neck pain, occipital neuralgia, radicular pain, or worsening neurological symptoms.

Transoral odontoidectomy provides a midline ventral extradural exposure of the CVJ that avoids traction or manipulation of critical anatomical structures such as the cranial nerves, brainstem, spinal cord, or vertebral arteries. In comparison, during the high retropharyngeal approach to the anterior CVJ, the lower cranial nerves are retracted, branches of the external carotid arteries are sacrificed, and the pharynx is mobilized extensively. These maneuvers result in extensive, prolonged dysphagia and can be avoided with the transoral approach. The retropharyngeal approach has the relative advantage of being extramucosal and is better suited for ventral bone grafting or application of anterior screw plate fixation devices because bacterial contamination is avoided.

Transoral surgery is contraindicated if an active nasopharyngeal infection is present or if any vascular structures (i.e., vertebral or basilar arteries) are within or ventral to the lesion. Typically, the transoral approach is inappropriate for intradural pathology because of the risks of meningitis and cerebrospinal fluid (CSF) leakage.11,20,21 These complications reflect the inability to obtain a watertight dural closure transorally. Patients with compressive pathology posterior or lateral to the spinal cord and brainstem or with reducible anterior compressive lesions can be treated with alternative approaches. They do not need transoral decompression.

Operative Technique

Transoral odontoidectomy is performed with simple techniques designed to facilitate the ease and safety of the procedure. Custom designed instrumentation is used for exposure, retraction, and tissue dissection ( Fig. 21.5 ). Self retaining retractor systems are used. The tongue and endotracheal tube are retracted caudally with a wide blade retractor, and the soft palate is retracted superiorly with a malleable blade retractor. A tracheostomy is avoided unless severe, preoperative bulbar or respiratory disturbances exist. If possible, a palatal incision is avoided because it can cause nasal regurgitation, dysphagia, and a nasal tone of voice.

Positioning

The patient is positioned supine on the operating table with the head slightly extended. Reverse Trendelenburg positioning of the operating table and neck extension provide the surgeon with direct visualization of the pathology ( Fig. 21.6 ). The skull is rigidly fixated with a Mayfield head holder; however, a halo brace can be used if the patient has preoperative spinal instability. The anterior bars of the halo brace can be removed temporarily to allow room for the retractors and to bring the surgeon′s hands closer to the patient′s mouth. The surgeon is seated at the top of the patient′s head. Surgery is enhanced by the precise visualization, magnification, and illumination provided by a binocular surgical microscope. A microscope with a 350 mm or 400 mm lens is used to allow for the depth of the working field.