The craniovertebral junction is the region of the neural axis spanning from the foramen magnum of the skull base to the first and second cervical vertebrae (the atlas and axis, respectively). The bones of this region encompass neural structures, including the medulla, cervicomedullary junction, and upper cervical spinal cord.
The second most common location for chordomas to occur is in the spheno-occipital region of the skull base. In fact, 35% of chordomas arise in the clivus. 1,2,3,4,5 Although there is a 2:1 male predominance for chordomas, those located at the craniovertebral junction are distributed more equally. Sacral chordomas occur most commonly in the sixth decade, whereas craniovertebral chordomas have a peak incidence in the fourth or fifth decade. 6
Originally, tumors of the craniovertebral junction were treated by a posterior decompression with or without fusion. However, this practice resulted in poor outcomes. 7 It was not until later that wide resection as a treatment for chordomas in this region was appreciated. 7,8 We will present an overview in this chapter of the surgical techniques to approach and fixate the craniovertebral junction.
21.2 Clinical Features
Patients presenting with chordoma of the craniovertebral junction can have symptoms manifesting form compression of the brainstem, cranial nerves, cervical spinal cord and its roots, and the vasculature in this area. Chordomas are insidious and often slow growing. Oftentimes the first presenting symptom is mechanical neck pain. 7 Tumors in the craniovertebral junction can cause mechanical destabilization, resulting in cranial settling, basilar impression, and atlantoaxial instability. Slow-growing tumors, such as chordomas, can have a classic clockwise motor presentation with involvement of the ipsilateral arm then ipsilateral leg, then contralateral leg, and finally contralateral arm. 9 However, this is not seen often, and patients are more likely to present with other symptoms, including neck stiffness/pain, lower cranial nerve dysfunction, upper extremity atrophy and weakness, ataxia, dysmetria, gait disturbances (i.e., spastic gait), pyramidal tract findings, and paresthesias of the extremities. 10 Patients can present with pain in the C2 dermatome or in the suboccipital region. Weakness and hand clumsiness secondary to spasticity are the most common motor symptoms experienced by these patients. 11 In one series, it was found that as much as 90% of patients experienced myelopathic symptoms/signs. 12 A syndrome consisting of neck pain, hand atrophy and weakness, and leg stiffness can be seen in some patients with cervicomedullary junction lesions. 13 Bladder incontinence is unusual, but patients may experience urgency. Some cases of rapid deterioration and death can result from respiratory arrest and apnea caused by lesions in this region. 14
21.3 Surgical Approaches
In general, there are five general approaches to the craniovertebral junction: (1) posterior, (2) anterior, (3) anterolateral, (4) lateral, and (5) and posterolateral. A midline posterior approach is heavily utilized to directly access the posterior aspects of the craniovertebral junction and to establish stabilization with posterior fixation prior to destabilizing the spine with en bloc chordoma resection. The anterior and anterolateral approaches are also heavily utilized, as the anterior spinal elements are frequently affected by chordomas of the craniovertebral junction and thus the en bloc specimen is delivered ventrally away from the spinal cord. Anterior approaches include the transoral approach as well as its variants. Anterolateral approaches include extrapharyngeal transcervical and mandibular swing transcervical approaches. Posterolateral approaches include far/extreme lateral transcondylar access. Lateral approaches can directly access the vertebral artery.
21.3.1 Posterior Midline Approach
Little explanation is needed for the posterior midline approach, as this is one of the most commonly used approaches in neurosurgery. It allows exposure for the posterior foramen magnum and the posterior and lateral portions of the cervical vertebrae. The posterior approach allows for a posterior decompression of the neural structures. It also provides access to posterior cuts for an en bloc tumor specimen that is circumscribing the spinal canal incompletely. This approach is good for lesions of the posterior elements but inappropriate for more anteriorly situated lesions, as it would result in excessive manipulation of the brainstem and the cervical spinal cord. Regardless of whether the chordoma involves the posterior elements, the posterior approach is the very commonly utilized, as it provides excellent exposure for posterior occipitocervical instrumentation and fusion if it is required.
For the posterior midline approach, the patient is positioned prone head fixation in Mayfield clamps. The head should be flexed slightly and translated back, bearing in mind that whatever position the head is in during the posterior fixation will heavily influence the alignment postoperatively. A midline incision is made from the inion extending caudally to the upper cervical segments. The avascular midline plane is carefully identified and dissected down between the trapezius and posterior neck muscles to minimize bleeding. The occipital bone, posterior boundaries of the foramen magnum, and the posterior elements of the cervical vertebrae are subperiosteally dissected. Bony releases are performed to aid in the eventual removal of the en bloc specimen. Because the fragility of the spinal cord, chordomas should not be removed from a posterior approach. However, posterior decompression, posterior osteotomies for eventual en bloc resection, and posterior fixation can all be performed with this approach.
21.3.2 Anterior Approaches
The anterolateral and anterior approaches are very frequently utilized in the resection and en bloc delivery of chordomas in the craniocervical junction. The transoral transpharyngeal approach (also known as the buccopharyngeal approach) provides a direct ventral approach to the craniovertebral junction from the inferior third of the clivus down to the C2 vertebral body. 15 It is an excellent approach for midline chordomas arising from the bone elements ventral to the brainstem and upper cervical spine. The transoral transpharyngeal approach is limited laterally by the vertebral arteries and the eustachian tubes. Vascular structures within or anterior to the lesion can prevent the approach, as good vascular control may be difficult to obtain.
Since the introduction of flexible orotracheal tubes, tracheostomy is now rarely required. 16 Advances such as the operating microscope and the development of the McGarver and Crockard retractors have aided the technique. Image-guided stereotactic navigation, 17,18,19 intraoperative magnetic resonance imaging (MRI), 20 and endoscopes 21 are other more recent advances in the development of the transoral transphayrngeal technique to improve visualization of the operative field without the need for further osteotomies. Extension of the approach down to C4 without tongue splitting 16 is also another development that has decreased the morbidity of the procedure.
This approach has a high risk of potential technical complications and high morbidity but has been improved over the years by many. 15,16,22 In over to gain access to the ventral spinal elements, the surgeon must go through an inherently contaminated zone. Patients should be screened for nasopharyngeal infections, as these increase the risk of postoperative infection to unacceptable levels. The transoral transpharyngeal approach should be avoided for intradural lesions due to the difficulty to achieve watertight dural closure in many cases 23,24,25,26,27,28 and the high incidence of postoperative meningitis, especially when there is intradural involvement of the lesion or dural violation. 29,30,31 Furthermore, a jaw opening of less than 2.5 cm or severe malocclusion may make this approach not a feasible option. Palatal sectioning may improve the access but results in postoperative oropalatal dysfunction.
Postoperative spine mechanical instability is common after en bloc resection of a midline chordoma in the craniovertebral junction, 32 with more than two thirds requiring posterior fusion after transoral surgery. 16,33 The literature is conflicting in regards to whether fixations should be done immediately 33 versus in a separate stage. However, it is critical that the spine be destabilized prior to any significantly destabilizing procedure.
In regards to the technique for the transoral transpharyngeal approach for craniovertebral junction chordomas, the patient is positioned supine with the neck in slight extension. The flexible fiber-optically placed orotracheal tube is retracted away from view. To improve exposure, rubber catheters may be placed through the nares out to the pharynx and secured in a manner that pulls back the soft palate. A self-retaining retractor keeps the mouth open, but it is imperative to do frequent checks of the soft tissue to avoid excessive and prolonged compression during the retraction. For localization, the anterior arch of C1 can be palpated through the pharyngeal wall in addition to fluoroscopic verification. After localization, the posterior pharyngeal wall is incised at the midline, and the mucosa along with the prevertebral muscles is elevated via subperiosteal dissection as a mucoperiosteal layer. The soft palate can be divided in the midline if the exposure needs to be extended superiorly or laterally. To expose the inferior clivus and the arch of C, the longus and capitis muscles are dissected free. At this point, the anterior arch of C1 and the odontoid process are exposed for resection of the chordoma. Bony resection can also be continued caudally to C2. In the dissection and eventual delivery of the tumor, the utmost care must be taken to avoid the lower cranial nerves, the carotid artery, and the jugular vein. At the tumor resection, fat graft is oftentimes placed in the resection cavity before closure. In the closure, the mucosa and posterior pharyngeal tissue are reapproximated with interrupted absorbable sutures.
Transoral Translabiomandibular Transpharyngeal Approach
The transoral translabiomandibular transpharyngeal approach allows for more caudal exposure than the previous approach, allowing exposure of the inferior one third of the clivus down to the upper cervical levels. The transoral approach can be extended caudally by splitting the mandible, thus allowing a larger exposure. 11,34,35,36,37,38,39,40 The indications and contraindications are similar to the transoral transpharyngeal approach, but the transoral translabiomandibular transpharyngeal approach has higher risks of infection. Preoperatively, a feeding tube is placed to avoid later difficulties associated with pharyngeal swelling. A tracheostomy is required with this approach due to the increased orophayngeal swelling. Furthermore, this approach carries the risk of malocclusion, tongue dysfunction, swallowing difficulties, dysphonia, and infection.
At the time of surgery, the patient is positioned supine with the neck in slight extension, and the entire jaw, upper neck, and pharynx are prepared. An incision is made in a zigzag fashion, and an incision into the mucosa is made at the alveolar margin in the lower lip. Subperiosteal dissection is done to expose the mandible laterally to the mental foramen. A staircase osteotomy is done to split the mandible. If the exposure provided by the splitting of the mandible is insufficient, then the tongue can be split inferiorly in the midline, allowing exposure down to the level of the arytenoids. Afterwards, the posterior pharyngeal wall is opened, and the surgery is carried out as described in the previous approach. After tumor resection, the posterior pharyngeal wall and tongue are reapproximated. The mandible is plated and carefully reapproximated. The alveolar margin is closed with absorbable sutures, and the lip is reapproximated, with special attention to achieving a well-approximated vermilion border. Soft tissue swelling can be expected postoperatively, potentially compromising the airway. Thus, tracheostomy is often needed. Enteral nutrition may be necessary as well.
Transoral Transpharyngeal Extended Maxillotomy Approach
Just as mandibular splitting allows for more caudal exposure, Le Fort maxillotomies extend the rostal limit of the transoral exposure, allowing for exposure of the majority of the clivus down to the upper cervical levels. 11,35,36,37,39,41,42,43 Three types of maxillotomy can be used. Le Fort I osteotomy involves fracturing of the maxilla and hard palate en bloc inferiorly into the oral cavity. However, downfracturing of the maxilla in the Le Fort I osteotomy can obscure the operative field, results in dental occlusion, and has a higher rate of oropalatal morbidity. Another method is Le Fort I osteotomy combined with a midline osteotomy and division of the hard and soft palate. This is followed by swinging away both maxilla inferolaterally. The third method is a unilateral Le Fort I osteotomy combined with midline osteotomy of the hard palate. Here, the single cut maxilla is swung inferolaterally while attached to the still intact soft palate. It should be noted that the advantage of this third method is that the unilateral Le Fort I is associated with quicker recovery of oropalatal function because it preserves the soft palate. 13 Thus, it is preferable given that it has lower morbidity while still having adequate exposure.
The downside to the transoral transpharyngeal with maxillotomy approach is that it carries a greater risk of wound infection as with the other transoral approaches. It also can lead to swallowing and speech difficulties, especially with division of the soft palate.
For the approach, the patient is positioned supine with the neck slightly extended, and the face, jaw, upper neck, and oropharynx are prepared. Using local anesthetic injection, the mucosa is elevated off the upper alveolar margin. The mucosa is then incised under the upper lip along the alveolar margin and around the maxillary tuberosity, and the alveolar tissue is subperiosteally elevated to the extent of the nasal opening. An incision is also made along the midline of the mucosa over the hard palate, and the mucosa is elevated. Unilateral Le Fort I osteotomy cuts are made in addition to a midline parasagittal osteotomy made between the front incisors through the hard palate. The mobilized maxilla is separated from the pterygoid process and swung inferolaterally while still attached to the intact soft palate. This exposes the posterior nasopharynx. The posterior nasal septum is removed only if it is necessary to obtain sufficient exposure. Next, the posterior pharyngeal wall can be opened. The rest of the exposure is performed as described in the earlier approaches. After tumor resection, the posterior pharyngeal wall is closed and the mobilized maxilla is meticulously reapproximated to its original position with plating. The hard palate mucosa and sublabial mucosa are reapproximated with absorbable sutures. The nares are packed, making sure to reapproximate the nasal septum back to the midline. Postoperatively, special attention is paid to make sure that the nasal and oral mucosae heal well. Tracheostomy may be required until pharyngeal swelling subsides. Enteral nutrition is necessary as well.
21.3.3 Anterolateral Approaches
Mandibular Swing Transcervical Approach
Although the anterior transoral approaches provide direct access to the resection of many ventral chordomas, they provide limited exposure and high morbidity. The anterolateral approaches utilize a transcervical approach and allow for access to the craniovertebral junction through the tissues of the neck. The mandibular swing transcervical approach splits the mandible and swings it outward with an upper cervical myocutaneous flap. The exposure can be extended rostrally to the infratemporal fossa and caudally to the upper cervical spine vertebral bodies. It provides access to the infralabyrinthine space, inferior clivus, anterior and lateral portions of C1, the dens, and the upper cervical vertebrae. 44 The approach offers excellent vascular control as well. The mandibular swing transcervical approach is most appropriate for resecting chordomas that are either too lateral or too large for the standard transoral approach. Unlike the standard transoral approach, the mandibular swing transcervical approach also allows for resection of chordomas that have vascular involvement. The approach also allows for en bloc resection of chordoma, anterior reconstruction, and fusion (to a limited extent) to occur in the same operation as the tumor resection.
The mandibular swing transcervical approach is very technically challenging with multiple potential complications, including injury to the lingual nerve or eustachian tube. It can also result in malocclusion, oropharyngeal dysfunction, or dysphonia. Postoperatively, a temporary tracheostomy is required, and a gastrostomy may also be necessary.
To perform the mandibular swing transcervical approach, the patient is positioned supine with the neck slightly extended, and the neck and oropharynx are prepared. An incision is made from the midline of the lower lip and caudally extended down to the level of the hyoid. There, it is extended laterally to the border of the sternocleidomastoid muscle and then turned cephalad towards the mastoid process along the border of the sternocleidomastoid muscle. The submandibular gland is exposed with subplatysmal dissection, and then dissection is continued deep to the submandibular gland. By retracting the sternocleidomastoid muscle laterally, the carotid sheath is exposed. In the dissection, the digastric muscle is divided, and then the mylohyoid muscle is separated from the hyoid while the geniohyoid muscle is separated from the mandible. This exposes the hypoglossal nerve, which should be identified and avoided. Subperiosteal dissection is used to expose the mandible. A staircase osteotomy is performed to split the mandible. After splitting the mandible, an incision around the floor of the mouth is made by starting an incision at the midline underneath the tongue and extending it around the tongue to the tonsillar pillar. The tongue can then be retracted, as the mandibular half along with the cervical myocutaneous flap are swung out laterally, bringing the oropharynx and the upper cervical pharyngeal spaces into communication. Note that the swung mandible may be tethered by the palatine muscles and the eustachian tube. The branches of the external carotid artery may need to be ligated and divided if they are obstructing the operative field. Muscles attached to the styloid process are also detached if they are limiting exposure. It is imperative that the lower cranial nerves be identified and avoided. The eustachian tubes, soft palate, and palatine muscles should be sectioned only if they are obstructing the field, as these maneuvers increase the morbidity of the operation. An incision is made in the posterior pharyngeal wall, and the anterior cervical muscles are retracted. At this point, the clivus and the upper cervical spine are fully exposed and the chordoma can be resected with good vascular control. After tumor resection, the pharyngeal structures as well as the divided mylohyoid and digastric muscles are reapproximated. The split mandible is reapproximated with plates. Next, the oral mucosa is reapproximated with absorbable suture as well as the lip incision. In the neck, the platysma muscle is reapproximated and the skin closed.
Anterolateral Retropharyngeal Transcervical Approach
The risk of infection and postoperative difficulties associated with transoral or transpharyngeal approaches motivated the development of the anterolateral retropharyngeal transcervical approach. With the anterolateral retropharyngeal transcervical approach, the oropharynx is avoided. The anterolateral retropharyngeal transcervical approach allows for exposure of the inferior clivus, the anterolateral portion of C1, the dens, and the upper cervical vertebrae.
This approach can either be taken medial to the carotid sheath 45,46,47,48,49 or lateral. 46,50,51,52 Going medially to the carotid sheath allows more direct access to the spine but requires exposure of the carotid artery, the hypoglossal nerve, and the laryngeal vessels and nerves and risks potential injury to these structures. Approaching laterally to the carotid sheath only requires dissection of the accessory nerve. However, this approaches the anterior region of the spine tangentially and makes this more appropriate for lateral approaches.
Common complications associated with the anterolateral retropharyngeal transcervical approach include pharyngeal swelling as well as injury to the hypoglossal and marginal mandibular nerves. 53 Important structures to be very careful of during the approach include the internal carotid and vertebral arteries, internal jugular vein, lower cranial nerves, and the eustachian tube.
To perform the anterolateral retropharyngeal transcervical approach, the patient is positioned supine with the neck in slight extension and the head rotated 30 degrees facing away from the surgeon. The skin is incised with a horizontal incision starting from the midline below the chin and carried out laterally under the body of the mandible over to the mastoid before curving caudally and medially along the posterior border of the sternocleidomastoid muscle down to the clavicle. After the platysma is opened, dissection is carried down through the submandibular triangle, retracting the carotid sheath laterally and the esophagus and trachea medially. During the dissection, the submandibular gland should be gently mobilized. In order to protect the marginal mandibular branch of the facial nerve, the facial vein may need to be divided and reflected rostrally. The hypoglossal nerve passes underneath the stylohyoid and posterior digastric muscles, and care must be taken to preserve the nerve. In order to improve the exposure, it may be necessary to ligate and divide branches of the external carotid artery that are obscuring the field. It is also important to be cognizant of and preserve the superior laryngeal nerve, as it travels deep to the carotid arteries. The anterior arch of C1 can be palpated for localization. Dissection is carried out along the midline with a kitner to develop the retropharyngeal plane. The pharyngeal mucosa and longus colli are reflected medially away from the tumor. At this point, the surgical team can proceed with en bloc resection. Anterior arthrodesis can be performed for ventral reconstruction. The neck muscles are reapproximated, and the skin is closed.
21.3.4 Lateral Transcervical Approach
The lateral transcervical approach allows for exposure of the lower clivus, lateral portion of the foramen magnum, and lateral portion of C1 and upper cervical levels. An extensive resection of the petrous bone may be required for exposure of the clivus, but, ultimately, the ventral and ventrolateral regions of the brainstem and the upper cervical spinal cord can be accessed for chordomas in the craniovertebral junction. This approach allows for exposure of the vertebral artery, allowing for good vascular control. It is a good approach for lateral tumors involving the vertebral artery. A benefit of the approach is that it minimizes the depth of the approach, provides a large working area, and avoids spinal cord manipulation for chordomas ventral or ventrolateral to the cord. Destabilization of the spine may also potentially be avoided with this procedure if the vertebral bodies, intervertebral discs, and contralateral facets are preserved, as unilateral removal of bone on the side ipsilateral to the tumor should not significantly affect stability. 52,54,55 Performing a simultaneous fusion procedure may be difficult with this approach, but it can be used to perform atlantoaxial fusion when posterior fusion attempts have failed or are not feasible. 56
For the lateral transcervical approach, the patient is positioned in a lateral decubitus position with the neck extended. The incision is made along the anterior border of the sternocleidomastoid muscle from the cricoid cartilage to the mastoid, and then the incision is continued posteriorly along the base of the skull for approximately 8 cm. The platysma is dissected open and the sternocleidomastoid muscle then divided. The platysma, sternocleidomastoid, and divided splenius capitus muscle are reflected posteriorly, and the accessory nerve is dissected out to avoid injury. The jugular vein and deeper cervical muscles are gently retracted, and the transverse processes of C1 and C2 are palpated caudal to the mastoid. The fascia overlying the C1 and C2 transverse processes is opened and subperiosteally dissected, detaching the muscles to expose the bony element. Great care must be taken to identify and avoid the vertebral artery. Bone can be drilled off from the foramen magnum down to C3 with this approach. After tumor resection, closure is done by reapproximating the divided muscles and skin.
21.3.5 Posterolateral Approach
The posterolateral approach provides exposure of the ventrolateral foramen magnum and upper cervical levels. It allows for occipitocervical fusion to be performed if the tumor resection causes destabilization. This approach should not be performed if the lesion is directly ventral to the brainstem or cervical spinal cord, as it would risk excessive manipulation of these structures to achieve full tumor resection.
21.3.6 Far/Extreme Lateral Transcondylar Suboccipital Approach
The far lateral transcondylar approach provides access to the caudal third of the clivus, the pontomedullary junction, and the anterolateral foramen magnum. It also allows for a wide lateral exposure of the anterolateral brainstem. 23,57,58,59 The extreme lateral approach can provide anterior access to the foramen magnum, with the ability to extend across the midline to the contralateral atlanto-occipital joint and lower clivus. The extreme lateral approach allows for resection of anterior midline chordomas even with contralateral extension. The far/extreme lateral transcondylar approach also allows for good control of the proximal and distal portions of the intradural and extradural vertebral arteries as well as good exposure of the lower cranial nerves with minimal brain retraction.
The far lateral transcondylar approach and the extreme lateral transcondylar approach differ from one another primarily in the extent of muscle dissection. These approaches can be combined with other approaches to further increase the exposure of the posterior fossa. 60,61 These approaches alone are not destabilizing. However, if additional resection of the spinal elements is performed, occipitocervical fusion can still be performed if stabilization is needed. 62 Dens resection can be performed with these approaches. 62 Likewise, one must be cautious in drilling the occipital condyles, as the hypoglossal nerve lies in the anterior third and superior portions of the occipital condyle. The posterior two thirds of the occipital condyle can be removed safely, but the surgeon must be aware that extensive resection of the occipital condyle will lead to destabilization. In general, stability is maintained as long as less than one third of the occipital condyle is resected.
21.4 Biomechanics of the Craniovertebral Junction
The craniovertebral junction is composed of the occiput (O), atlas (C1), and axis (C2) along with their associated ligaments and articulations. Collectively, these structures have unique biomechanical properties, which confer greater mobility than any other segment of the cervical spine. 63
The occipital condyles are located lateral to the foramen magnum and rest on the superior articular surfaces of the C1 lateral masses, forming the bilateral O–C1 joints. The occipital bone contains a thick midline keel that runs from the external occipital protuberance to the foramen magnum, which may provide ample bony fixation when considering constructs extending to the skull. The atlas does not have a vertebral body, as its embryological remnant forms the odontoid process (dens) of C2. Instead, C1 is composed of two lateral masses that are connected by an anterior and a posterior arch, thus forming a ring. The lateral masses contain articulations for the O–C1 joints on their rostral surfaces and for the C1–C2 joints caudally. A notch on the dorsal surface of the anterior arch provides an articular surface for the odontoid process of C2. These four-facet articulations (bilateral O–C1 and C1–C2) and the atlantodental articulation are the five synovial joints of the craniovertebral junction.
C2 contains a vertebral body with an odontoid process that protrudes rostrally through the ventral portion of the C1 ring to articulate with the anterior arch of C1 as described above. The lateral masses of C2 contain superior and inferior articular surfaces for the C1–C2 and C2–C3 joints, respectively. The transverse processes extend laterally from the midpoint of the lateral masses and form the transverse foramen. The vertebral artery traverses these foramina, and injury to these vessels must be avoided when considering C2 fixation.
Further stability to O–C2 is provided by numerous ligaments, which include capsular ligaments, apical ligament, alar ligaments, cruciform ligament, tectorial membrane, accessory atlantoaxial ligament, and the anterior and posterior atlanto-occipital membranes. 64
The capsular ligaments maintain correct alignment and contain the synovial fluid of the facet joints. The cruciform ligament, as its name suggests, is composed of vertical and transverse portions, which cross behind the dens. The transverse portion, or transverse ligament, extends laterally behind the dens to attach on bony tubercles located of the medial surfaces of the C1 lateral masses. This structure fixes the dens to its articular surface of the anterior arch of C1 and is critical in conferring C1–C2 stability. The rostral fibers of the cruciform ligament attaches to the clivus between the tectorial membrane and the apical ligament, whereas the caudal extension attaches to the dorsal body of C2. Collectively, the fibers of the cruciform ligament allow axial rotation and lateral bending of the C1–C2 joints while limiting flexion.
The alar ligaments are paired structures, which insert on the posterior aspect of the rostral dens and attach to the lateral masses of C1 and occiput. They stabilize the head during axial rotation, lateral bending, and flexion–extension movements. The tectorial membrane is the rostral extension of the posterior longitudinal ligament and attaches to the basion, becoming indistinguishable from the dura mater. Prior investigations hypothesized that the tectorial membrane played a critical role in stabilizing the craniovertebral junction. However, recent evidence suggests that it does not necessarily limit cervical flexion but rather acts primarily to prevent anterior impingement of the odontoid process on the cervical canal. 65 The accessory atlantoaxial ligament attaches to the dorsal vertebral body of C2, the lateral masses of C1, and the basion. It functions to maintain rotational stability along with the alar ligaments.
The anterior atlanto-occipital ligament attaches from the basion to anterior arch of the atlas, whereas the posterior longitudinal ligament attaches from the opisthion to the posterior arch of the atlas. The apical ligament attaches from the tip of the dens to the basion. These three ligaments confer marginal stability to the craniovertebral junction.
21.5 Craniovertebral Junction Reconstruction
In planning to fixate the craniovertebral junction, one must bear in mind that the occipitocervical joints under normal circumstances provide a wide range of motion, and with alteration and/or fixation of these joints, the patient’s range of motion in this region may be significantly altered and limited. In circumstances where stability of the craniovertebral junction has been minimally affected, the patient may be observed after surgery without fixation. However, if the patient becomes symptomatic from craniovertebral instability or if significant destabilization occurs at the time of surgery, then the patient may require fixation at the time of chordoma resection. Fixation and fusion most commonly is done from a posterior midline approach, although it is also technically feasible to do this with the far lateral suboccipital or posterolateral approaches at the time of tumor resection.
Fixation options include a combination of screws, rods, plates, cables, contoured loops, or wires. Instrumentation needs to be supplemented with bone graft so that bony fusion can occur and provide long-term stabilization to the region. It is important to consider that total fusion failure n the craniovertebral junction still is between 5 and 30% despite the advances in instrumentation. 66 For bony fusion, autologous bone locally (i.e., laminectomy), iliac crest, rib, or fibula can be used in addition to allograft bone.
A posterior occipitocervical fixation begins with a midline incision from the inion rostrally and extending caudally to the upper cervical segments. Care is taken to identify and dissect along the midline avascular plane between the trapezius and cervical muscles to avoid bleeding and excessive thermal injury to the muscle fibers. A subperiosteal dissection is performed to fully expose the occipital bone, edge of the foramen magnum, and the dorsal elements of the cervical vertebrae that will be included in the construct. If wiring is chosen for occipital fixation, two sets of burr holes are made along the same line on both sides of the midline keel. The occipital bone flanked by a two–burr hole set should align with the cervical fixation wires or screws to facilitate anchoring an occipitocervical rod, a bone graft, or a contoured loop. The dura is gently separated off of this bone, and a wire is passed through one burr hole and out the other. The wire ends can then be cinched over the rod or structural bone graft.
A variety of occipital plates secured with screws are available as alternatives to occipital wiring. Many of these take advantage of the thick midline keel, which ranges from 10 to 18 mm on average, with the bone thinning laterally. 67 If the lateral masses of C1 are preserved, C1 lateral mass screws can be placed with a 22-mm threaded portion and a 10-mm smooth shank. Likewise, if the C2 pedicles are preserved, 26- to 28-mm pedicle screws may be placed. For the subaxial spine, standard subaxial lateral mass instrumentation is utilized. Occipital plates are often combined with upper cervical screws affixed to bilateral contoured rods to provide craniovertebral stability. The occipital bone and dorsal cervical processes must be thoroughly decorticated before onlay profusion material is placed.
Likewise, there are a variety of options for anterior reconstruction if extensive bony resection occurred in the removal of the chordoma specimen. These include combinations of plates, cages, and bone grafts and are used in a similar fashion to extensive anterior reconstruction of the subaxial spine.
Once an instrumented fusion procedure is performed, an external cervical orthosis should be considered to enhance the rate of bony union.
21.6 Case Presentation
A 31-year-old woman diagnosed at an outside facility with a nonhealing C2 fracture treated with a halo brace presents with progressively worsening neck pain. On examination, she was neurologically intact. Imaging studies ( ▶ Fig. 21.1, ▶ Fig. 21.2, ▶ Fig. 21.3) and computed tomography (CT)-guided biopsy were consistent with cervical chordoma.
Fig. 21.1 Sagittal T2-weighted MRI revealing a T2-hyperintense lesion invading C2 and the prevertebral space. The prevertebral involvement extends to the C4–C5 disc space, with the inferior T2 intensity representing edema. The lesion did not enhance with gadolinium. A four-stage en bloc resection was planned. (1) Resection of the dorsal elements and skeletonization of the thecal sac and bilateral vertebral arteries from C1 to C5 with sacrifice of bilateral C2 and C3 nerve roots. Instrumented internal fixation from occiput to T4 with an occipital plate and bilateral pedicle screws from T1 to T4 ( ▶ Fig. 21.2). (2) Expanded endonasal endoscopic approach for a middle and inferior clivectomy, bilateral medial occipital condylectomy, resection of the anterior arch of C1, and sectioning of the craniovertebral ligaments. (3) Anterior en bloc corpectomy of C1, C2, C3, C4, and the rostral two thirds of C5. (4) Occipitocervicothoracic instrumented arthrodesis with fibular strut allografts ( ▶ Fig. 21.3).
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