MIS Endoscopic Approaches for OC–C1–C2 Pathology

21 MIS Endoscopic Approaches for OC–C1–C2 Pathology

Rafael Uribe, Sertac Kirnaz, and Theodore H. Schwartz

Summary

Craniocervical junction is closely related to critical neurovascular structures including the carotid and vertebral arteries, brainstem, and upper spinal cord, as well as critical prevertebral structures including the oropharynx, esophagus, and trachea. Anterior craniocervical pathology is complicated by virtue of the many important anatomic structures that reside in that region. This chapter will illustrate possible anterior MIS approaches to the OC–C1–C2 region. These approaches are: the endoscopic endonasal approach, the transoral approach, and the endoscopic transcervical approach. Each of these have their own indications, advantages, and limitations, but all MISS approaches share the common goal of minimizing local tissue disruption and maximizing effectiveness in a confined working window.

Keywords: anterior cervical spine craniocervical junction endoscopic endonasal approach endoscopic transcervical approach transoral approach

21.1 Introduction

The craniocervical junction (CCJ) is a highly complex anatomic region. It is closely related to critical neurovascular structures including the carotid and vertebral arteries, brainstem, and upper spinal cord, as well as critical prevertebral structures including the oropharynx, esophagus, and trachea. The CCJ is seat to a myriad of pathologies including primary and metastatic tumors, degenerative and autoimmune spinal diseases, traumatic lesions, infections, and congenital malformations.1^,²^,³^,⁴^,⁵ Surgical approaches to this region vary depending on the pathology being addressed but generally fall into two broad categories depending on the anatomic route that is used: anterior and posterior approaches. This chapter will focus on minimally invasive treatment approaches to the ventral CCJ: the endoscopic endonasal approach (EEA), the transoral approach, and the endoscopic transcervical approach.

Anterior approaches to the craniovertebral junction have undergone significant evolution with the introduction of less invasive open microsurgical techniques using the operating microscope and especially more recently using minimally invasive endoscopic technology.

21.2 Indications

21.2.1 Endoscopic Endonasal Approach

The EEA to the skull base and CCJ is the result of the technological evolution that allowed ear, nose, and throat (ENT) surgeons and neurosurgeons to access the ventral skull base through natural orifices. As suggested in the introduction to the chapter, ventral approaches to the CCJ can address primary extradural (e.g., metastatic tumors, inflammatory conditions,² degenerative spine disease, basilar impression),⁶^,⁷^,⁸ infections, osteomyelitis, epidural abscess⁹^,¹⁰, or congenital malformations (e.g., retroflexed odontoid),¹¹ extra- and intradural diseases (e.g., chordomas,¹² chondrosarcomas¹³) or intradural tumors (e.g., brainstem gliomas,⁴ epidermoid/dermoid tumors,¹⁴ meningiomas¹⁵), and vascular lesions.¹⁶^,¹⁷ The upper limit of this approach is the highest of all approaches, reaching up to the frontal sinus, while the inferior limit is generally the base of the odontoid.

21.2.2 Transoral Approach

The indications for the transoral approach are similar to those mentioned for the EEA.¹⁸^,¹⁹^,²⁰^,²¹ However, a potential advantage of the transoral approach compared with the EEA is the possibility of reaching more lesions. This approach allows limited superior access not only above the odontoid but also the base of C2 and often C3. When further exposure is necessary, the sphenoid and inferior clivus can be accessed cranially through an open-door maxillotomy. However, that approach is invasive and can be replaced by EEAs for rostrally located lesions. C3 and C4 can be exposed via a median transmandibular and transglottic approach.²²^,²³ The transoral approach is not ideal for patients who have mouth opening limitations (e.g., temporomandibular joint pathologies) or restrictions of cervical spine flexion (e.g., deformity).

21.2.3 Endoscopic Transcervical Approach

The indications for the endoscopic transcervical approach are basilar invagination and atlantoaxial dislocations with high cervical myelopathy.²⁴^,²⁵^,²⁶^,²⁷ In contrast with the transoral approach, the entire cervical spine can be accessed with this approach with the advantage of a sterile surgical corridor. Obese patients and patients with thoracic abnormalities (such as barrel chest, severe kyphosis) are not suitable for this technique.

21.3 Techniques

21.3.1 Endoscopic Endonasal Approach

The EEA approach to the CCJ proceeds in the same way that is used for other approaches along the sagittal plane of the skull base. Patients are placed in supine position with the head fixed in a Mayfield three-pin head holder.²⁸ The head is usually rotated approximately 15 degrees in three planes: lateral rotation, lateral tilt, and neck extension. For a conventional approach to the sellar region, the patient’s chin will point to the patient’s right foot. However, for clivus and craniocervical approaches, the head has to be flexed more than usual in order to provide comfortable visualization. It is our practice for the surgeon to stand on the right side of the patient (i.e., for right-handed surgeons). An endoscope holder is placed on the contralateral side of the bed, opposite from the surgeon. Fiberoptic orotracheal intubation is preferred if there is evidence of craniocervical instability. The tube is secured to the left side of the mouth to provide an unobstructed view of the surgical field. Neuromonitoring will be used depending on the type of pathology being addressed; we do not use neuromonitoring for routine extradural cases. Doppler ultrasound and frameless stereotactic navigation are commonly used and become especially relevant to appropriately identify the trajectory of the carotid arteries which may be unusually displaced. Close attention must be paid to the final location of the navigation system reference array. We routinely place it contralateral to the side where the surgeon is standing and make sure it does not obstruct the surgical field. The abdomen is always prepped in the event when a fat graft needs to be harvested for closure. The leg is also prepped for a fascia lata graft in cases where a large intradural opening is expected and there is a chance for a high-flow cerebrospinal fluid (CSF) leak. After registration and surgical site prepping is completed, the nasal phase of the procedure is begun by the ENT surgeon who will harvest a nasoseptal flap if needed at the end of the case for reconstruction. For cases that involve resection of the dens, a vertical incision is made in the basopharyngel fascia in the midline between the Eustachian tubes. Intraoperative computed tomography scanning is a useful adjunct in order to ensure complete resection of the odontoid process.⁶ The underlying longus colli and longus capitis muscles are mobilized laterally in order to expose the anterior arch of C1 and the body of C2. Anatomical landmarks are identified including the C1/2 interspace, anterior ring of the atlas, inferior edge of the clivus, and the odontoid process (Fig. 21.1 and Fig. 21.2). The apical and alar ligaments are sharply divided. A diamond drill may be used with care to avoid any injury to the dura. When the bone has been thinned, pituitary and Kerrison rongeurs can be used to remove the remaining bony elements. If a rheumatoid pannus is present, it must be removed with special care to avoid any injury to the dura. For larger approaches that involve intradural exploration, the pharyngeal mucosa can be incised in an inverted U shape to improve lateral visualization. At the end of the procedure, if there is no CSF leak such as with an odontoid resection, nonabsorbable stitches are placed to reapproximate the mucosa and a bioresorbable nasal dressing is left in place (Nasopore® Stryker Corporation, Kalamazoo, MI). If there is a small leak, fat can be placed over the defect and covered with fibrin glue before closing the mucosa. If a large CSF leak occurs as a result of removing intradural pathology, a button or gasket seal closure is performed and covered with a nasoseptal flap (Fig. 21.3).²⁹^,³⁰ Temporary lumbar drainage is also often used to decrease pulsatile pressure on the closure.