INTRODUCTION

Spinal tumors around the atlantoaxial spine are very rare, and most of them are metastatic. Patients with tumors in this area present with severe mechanical neck pain that is elicited in flexion, extension, and lateral rotation. Pain on lateral rotation distinguishes atlantoaxial tumors from tumors occurring in the subaxial cervical spine. In the subaxial spine, mechanical pain generally is a late manifestation indicating a compression or burst fracture with resultant instability.¹ Neurological symptoms resulting from a tumor at C1 and C2 are rare. Patients with C2 nerve root involvement or compression may present with occipital neuralgia. Cranial nerve involvement suggests a tumor extension to the skull base. Myelopathy is rare, given the wide mid-sagittal canal diameter at this spine level. Most cases of spinal cord compression at this level result from pathological fracture subluxations rather than an epidural tumor.

Patients with normal spine alignment or minimally displaced fractures can be treated with radiation therapy and immobilization in a hard collar, and those with marked displacement are treated with surgery. Osteolytic destruction of multiple atlantoaxial spine elements results in pathological fractures, which are somewhat different from the patterns of traumatic fractures. However, instability, defined in the trauma literature by degree of displacement and angulation, may be applicable. Patients are considered to have significant subluxations resulting in instability if they have odontoid displacement that is more than 5 mm or angulation that exceeds 11 degrees with displacement of more than 3.5 mm. As with tumors of the subaxial spine, atlantoaxial tumors generally involve the anterior spine elements (i.e., odontoid and body of C2). Although recent studies advocate aggressive anterior resection and stabilization for atlantoaxial tumors, posterior instrumentation without anterior resection can result in immediate stabilization, deformity reduction, and neurological preservation.

TOTAL SPONDYLECTOMY FOR UPPER CERVICAL TUMORS (TUMOR MASS ON C2–4 LEVELS)

POSTERIOR APPROACH

After the airway is maintained with a tracheostomy, the patient is positioned prone with skeletal fixation. A midline skin incision is made, and subperiosteal muscle dissection is accomplished from the external occipital protuberance to the upper thoracic levels to expose the multiple level laminae and facet joints (Fig. 19-1). Complete bilateral laminectomies and facetectomies of C2–4 are performed with wide exposure of the exiting nerve roots.

Fig. 19-1 Posterior decompression from C2 to C4.

Modified from Jackson RJ, Gokaslan ZL: Occipitocervicothoracic fixation for spinal instability in patients with neoplastic processes J Neurosurg 1999;91[1 suppl]:81–89.

Using a high-speed drill with a diamond burr, the vertebral artery (VA) is freed from C2 to C4 on both sides. When the facetectomy is complete, the cut surface of the pedicle is exposed (Fig. 19-2). The pedicle forms the posteromedial wall of the transverse foramen. Continuous drilling of the pedicle can open the transverse foramen. During drilling, the exiting nerve root on the upper level may be injured. The exiting nerve root is located on the upper portion of the exposed pedicle (see Fig. 19-2). If the VA on the unilateral side is encased within the tumor mass, the cephalad and caudal portions out of the tumor mass are exposed.³ An initial dissection plane is created around the lateral aspect of the tumor.

Fig. 19-2 For the VA transposition, the posterior wall of the transverse process should be removed.

For the easier dissection, the C2 and C3 nerve roots may be sacrificed without significant functional loss. If necessary, the C4 root also can be included. A Silastic sheet is then placed between the tumor and the ventral dura to protect the neural structures during the subsequent anterior procedure. Occipitocervical fixation is performed using the contoured titanium rods.⁴

ANTERIOR PROCEDURE—TRANSMANDIBULAR, CIRCUMGLOSSAL, RETROPHARYNGEAL APPROACH

The patient is positioned supine with the neck in extension. The anterior neck dissection can be made via either side, and transmandibular, circumglossal, retropharyngeal exposure is performed.

Upper Neck Dissection

A curvilinear incision is begun below the mastoid tip and extended 2 cm inferior and parallel to the lower margin of the mandible inferiorly and medially to the mentum. The incision continues to the vertical incision to the midline of the lower lip. The turning point of the incision lies on the hyoid bone. The lower lip is incised with a zigzag incision. A mucosal incision is made at the alveolar margin under the lower lip. After the skin incision, a vertical incision of platysma is made on the mental symphysis to the superior notch of the thyroid cartilage (Fig. 19-3, A). The platysma can then be transected across its fibers parallel to the direction of the primary incision for the full length of the exposure. Subplatysmal flaps are elevated to expose the upper neck, the submandibular gland, and surrounding tissue.

Fig. 19-3 Illustration of the mandibular swing transcervical approach. A, After the skin incision, subplatysmal dissection continues to expose the submandibular gland. The digastric and mylohyoid are divided to expose the hypoglossal nerve. B, After the mandible is split, the floor of the mouth is incised around the tongue. C, The mandible is swung away but is tethered by the palatini muscles and the eustachian tube. D, Once the mandibular flap is dissected free, the exposure reveals the clivus down to the upper cervical vertebra.

A supraomohyoid neck dissection (usually by an otolaryngologist) provides access to the lingual and hypoglossal nerves as well as the internal carotid artery (ICA), external carotid artery, and internal jugular vein.⁵ The sternocleidomastoid muscle is retracted laterally to expose the carotid sheath. The digastric muscle is then divided, and the mylohyoid muscle is freed from the hyoid bone and the geniohyoid from the mandible. The hypoglossal nerve should be identified and saved.

Mandibulotomy

A stairstep mandibulotomy is performed between tooth 24 and 25 (lower two mandible molars).⁶ The mandible is exposed by subperiosteal dissection laterally to the mental foramen. For accurate alignment, the mini-plates should be pre-bent and fitted, and screw holes should be predrilled. Only then is the mandible split with a staircase osteotomy.

Dissection follows the floor of the mouth posteriorly toward the glossopharyngeal sulcus, which allows the mandible to swing laterally and the tongue medially (Fig. 19-3, B). An incision is made from the midline under the tongue where the mandible has been divided and is continued around the tongue to the tonsillar pillar. The tongue is retracted away from the field as the mandible half is swung out laterally with the cervical myocutaneous flap. The oropharynx and the upper cervical pharyngeal space communicate. The styloid process is palpated and the muscular attachments are separated. The ICA, internal jugular vein, and the 9th, 10th, 11th, and 12th cranial nerves are identified superiorly to the skull base.

As the incision approaches the anterior tonsillar pillar, it splits into two limbs. The upper limb of incision extends to the soft palate. This incision is then carried onto the hard palate approximately 1 cm medial to the alveolar ridge. It then passes anteriorly around to the contralateral hard palate. The lower limb of the incision extends into the hypopharynx, passing lateral to the tonsil and the orifice of the eustachian tube. The levator and tensor veli palatini muscles and the eustachian tube are transected, and a retropharyngeal dissection is used to elevate the pharynx off of the longus colli muscles and expose the clivus and upper cervical spine (Fig. 19-3, C). This pharyngeal flap is elevated and rotated medially. The longus capitis muscle and the prevertebral fascia cover the clivus and upper cervical spine. The posterior pharyngeal wall is incised, and the longus capitis and rectus capitis muscles are retracted (Fig. 19-3, D).

En Bloc Resection

The C4–5 discectomy is performed, the uncovertebral joints are drilled away, and the posterior longitudinal ligament is removed. The soft tissue is freed from the anterior arch of C1. On the intact side, the longus colli and longus capitis muscle insertions are released from C2–4. The transverse processes are drilled away with a diamond burr, completing the circumferential exposure of the VA from C2 to C4. On the tumor-involved side, the longus colli muscle is cut above and below the tumor, and the VA is dissected above C2 and below C4 such that the tumor capsule is not violated. Additional dissection is then performed around the lateral aspect of the tumor mass, medial to the carotid sheath, which communicates with the dissection plane already made in the posterior side. The tumor-involved VA is then ligated and transected both rostral and caudal to the tumor mass, freeing the specimen along its lateral aspect (Fig. 19-4). Finally the high-speed drill is used to cut across the base of the dens, and Kerrison rongeurs are used to resect the ligamentous complex behind the dens.

Fig. 19-4 Anterior resection of the C2–4 body mass and reconstruction.

Modified from Rhines LD, Fourney DR, Siadati A, et al: En bloc resection of multilevel cervical chordoma with C-2 involvement. Case report and description of operative technique. J Neurosurg Spine 2005;2:199–205.