Endoscopic and Transnasal Approaches to the Craniocervical Junction

Summary of Key Points

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The endoscopic transnasal approaches provides a direct surgical trajectory to anteriorly located lesions at the craniocervical junction.
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Clinical series demonstrate low rates of postoperative infection after endoscopic transnasal approaches to intradural pathology despite nasal contamination.
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Endoscopic transnasal odontoidectomy allows preservation of the soft palate and patients can restart an oral diet on the first postoperative day.
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On sagittal imaging, a line drawn from the anterior inferior nasal bone through the posterior aspect of the hard palate—the nasopalatine line—can predict the caudal limit of exposure of the upper cervical spine with a transnasal approach.
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Lesions extending lateral to the lower cranial nerves cannot fully be treated via an endonasal approach.
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A vascularized nasoseptal flap has dramatically reduced the incidence of postoperative cerebrospinal fluid leak.
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We recommend a two-surgeon, four-hand approach with collaborative expertise in rhinology and neurosurgery.

Neoplasms, infections, trauma, and inflammatory and degenerative conditions can all affect the craniocervical junction. Lesions located anterior or anterolateral to the medulla and upper cervical spinal cord present a formidable challenge given the proximity of critical neurovascular structures. Early attempts to address these lesions via a posterior approach resulted in considerable morbidity and mortality due to retraction-related morbidity and poor visualization. Various surgical approaches have been developed to treat these lesions more effectively while minimizing morbidity. These include the far lateral transcondylar, the extreme lateral, the lateral transatlantal or direct lateral, the transoral, and various endoscopic and transnasal approaches. At the craniocervical junction, endoscopic and transnasal approaches have been utilized primarily to treat lesions located anterior to the brain stem and upper cervical spinal cord.

Endoscopic and transnasal approaches were developed because they provide a direct surgical trajectory to anterior craniocervical junction pathologies with excellent operative visualization. The direct route reduces the need to manipulate surrounding neurovascular structures and can therefore reduce the risk of retraction-related morbidity. The benefit of the endoscope is that it increases illumination of the operative field, provides higher magnification with a wider angle of view, and increases depth of field. This chapter reviews common endoscopic transnasal approaches to the craniocervical junction and highlights important intraoperative and perioperative details.

Preoperative Evaluation

Routine preoperative imaging includes thin slice (1-mm) computed tomography (CT) and magnetic resonance imaging (MRI). This is necessary to fully evaluate both the bony anatomy and the neurovascular relationships to the pathology. In addition, fusion of both the thin slice CT and the MRI is performed for intraoperative computer-assisted navigation. Finally, the addition of a high-resolution constructive interference in steady state (CISS) sequence can provide unparalleled detail of the relationship of cranial nerves to the pathology. In addition to radiographic evaluation, a critical component of preoperative evaluation is dedicated bilateral sinonasal endoscopy in the office. This evaluation is performed by the participating otolaryngologist to identify any anatomic variations, such as septal deviation, spur formation, or perforation, which would affect the operative approach or reconstruction. In addition, screening for concurrent paranasal sinus disease is needed to determine if preoperative antibiotic treatment is necessary. For pathology affecting the lower cranial nerves, a preoperative swallow evaluation and direct laryngoscopy can be performed to provide baseline function and counsel patients on expected postoperative risks if preoperative dysfunction exists.

Endoscopic Transnasal Surgical Technique

Operating Room Setup, Patient Positioning, and Equipment

The patient is positioned supine and is placed near the edge of the right side of the operative table. The head is placed in a neutral position using a rigid three-point fixation device. This is particularly important when cervical instability is present or expected after surgery. For access to the odontoid process, the head is elevated slightly to align the surgical trajectory with the surgeon. Frameless stereotactic image guidance is used with all endoscopic transnasal cases. Most navigational systems have suctions that can be registered and navigated. Malleable suctions are also useful during the resection stage, as they can be manipulated to reach the surgical target and avoid conflict with the endoscope.

After nasal access is obtained, a two-surgeon approach is used for the remainder of the case. The endoscope is positioned at the apex of the right nostril and navigated by one surgeon. For a right-handed surgeon, a suction is placed underneath the endoscope in the right nostril and a dissecting instrument is placed in the left nostril. Endoscopes are 4 mm in diameter and the 0- and 30-degree lens angles are most commonly used for these approaches. An irrigation sheath on the endoscope can improve efficiency by reducing the time needed to clean the lens.

Anesthetic Considerations

The endotracheal tube is placed along the left side of the mouth. A nasogastric tube or a throat pack is placed to prevent the pooling of blood in the stomach, which can provoke postoperative emesis and disrupt the reconstruction. Neurophysiology monitoring is routinely used, including somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), and lower cranial nerve electromyography (EMG). Electrodes may be placed in the trapezius muscle and tongue to monitor the accessory and hypoglossal nerves, respectively. In addition, a neural integrity monitor (NIM) electromyogram endotracheal tube (NIM 3.0, Medtronic, Minneapolis, MN) allows one to stimulate the vagus nerve and assess for motor response within the vocal cords. Local anesthetic gels must be avoided with this endotracheal tube. The use of nondepolarizing neuromuscular blocking agents should be avoided in addition to any local anesthetic gels when using the NIM EMG tracheal tube. Lastly, arterial hypotension, which is often used to help control nasal mucosal bleeding, is avoided when entering the intracranial space or when brain stem or upper cervical spinal cord compression is present.

Nasal Approach

The nasal mucosa is injected with local vasoconstrictors. The inferior turbinates are outfractured and one or both of the middle turbinates are resected if necessary to provide a wider corridor for passage of instruments. In approaches to pathology limited to the craniocervical junction, resection of the middle turbinate is frequently not necessary unless significant platybasia is present. The posterior choanae can be visualized by following the nasal cavity floor back to the nasopharynx. The natural sphenoid ostium is identified medial to the superior turbinate. A nasoseptal flap, if required, is harvested by first identifying the pedicle of the flap, which contains the posterior septal artery, a branch of the sphenopalatine artery. Using needle-tip bovie electrocautery, an inferior cut is made from the posterior choanae extending inferior and anterior along the floor of the nasal cavity. A superior cut is then made from the natural os of the sphenoid extending superior and anterior along the nasal septum. Normally, the nasoseptal flap can be tucked down into the nasopharynx during most endoscopic endonasal cases, but when working in the region of the craniocervical junction, this becomes obstructive and can be easily damaged. Therefore, on the side of the nasoseptal flap harvest, a maxillary antrostomy is performed by removing the uncinate process, and the nasoseptal flap can be tucked into the maxillary sinus until it is needed at the time of reconstruction. Again, it should be noted that approaches for pathology limited to the craniocervical junction might not require initial nasoseptal flap harvest. Rather, an inferior posterior septectomy that spares the pedicle to the nasoseptal flap can be employed, allowing subsequent harvest if warranted by intraoperative findings.

Wide sphenoidotomies can then be performed if warranted by the pathology or at the discretion of the surgeon. The posterior nasal septum is disarticulated from the rostrum of the sphenoid sinus and the rostrum is removed with a 4-mm coarse diamond bur Kerrison rongeurs. Roughly 1 to 2 cm of the posterior septum is removed as well. Wide bilateral sphenoidotomies create a large, singular surgical cavity with adequate room for the passage of the endoscope and surgical instruments without conflict.

For access to the lower clivus and upper cervical spine, additional nasal work is required as follows. The floor of the sphenoid sinus is drilled down to create a wide communication between the sphenoid sinus and the nasopharynx. The nasopharyngeal mucosal and muscular layers along the midline are cauterized and lateralized. This exposes the buccopharyngeal fascia, which is also elevated off the clivus and lateralized. The longus capitus (lower clivus), longus coli (upper cervical spine), and anterior atlanto-occipital membranes are also cauterized at the midline and lateralized to provide access to the lower clivus, anterior ring of C1, and odontoid process.

Endoscopic Transnasal Transclival Approach

This chapter focuses on the transclival approach for access to the lower clivus and craniocervical junction. Common pathologies at this level include anteriorly located foramen magnum meningiomas and clival chordomas. Proper preoperative evaluation includes radiographic evaluation of the lesion pathology in relation to the lower cranial nerves and carotid arteries. Lesions extending lateral to the lower cranial nerves cannot fully be treated via an endonasal approach. The paraclival carotid arteries, or the segment of the carotid artery between the foramen lacerum and the cavernous sinus, is at risk during a midclival approach. The lacerum segment of the internal carotid artery (ICA) roughly corresponds to the pontomesencephalic junction. Therefore, the risk of carotid injury is lower in an approach to the lower clivus and foramen magnum. However, preoperative imaging should be carefully evaluated to rule out any major anatomic variation that may put the ICA at increased risk. In general, the ICA is lateral to the occipital condyle and the superior pharyngeal constrictor muscle. However, anatomic variations exist that may place the ICA at risk during this surgical approach, particularly in elderly patients and in patients with significant congenital bony deformity of the craniocervical junction.

After appropriate nasal access has been carried out as previously outlined, the clivus is drilled with a 4-mm coarse diamond bur between the occipital condyles inferiorly and the lacerum segments of the ICA superiorly. Between the two layers of clival dura, the basilar plexus, which communicates with the inferior petrosal sinus and cavernous sinus, can often result in brisk bleeding that can be controlled with injectable hemostatic agents. When the basilar sinus has been invaded by tumor, the basilar plexus is often already thrombosed.

For lesions extending lateral to the occipital condyle, the anteromedial aspect of the occipital condyles may be drilled down to provide further lateral access. First, the rectus capitus anterior and the atlanto-occipital joint capsule are removed to expose the atlanto-occipital joint. The superior aspect of the condyle has a small groove, which estimates the level of the hypoglossal canal. Below this groove is bone of the occipital condyle, and above this groove is bone of the jugular tubercle. The condyle can be removed down to the level of the hypoglossal canal. The inferior portion of the condyle with the alar ligament insertion is left intact as its resection provides little additional surgical exposure but can result in increased craniocervical instability. Angled endoscopes can be used to help broaden the lateral extent of surgical exposure. Inferior clivectomy, transection of the tectorial membrane, and resection of up to 75% of the anteromedial condyle for exposure of the anterior foramen magnum do not result in enough significant craniocervical instability to warrant fusion.

Case 52-1

Pediatric Clival Chordoma

A 10-year-old male with a history of bilateral severe to profound sensorineural hearing loss underwent an uncomplicated left cochlear implantation at 2 years of age. He subsequently represented for consideration of a right-sided implant, and during his preoperative evaluation, a history of intermittent epistaxis for approximately 2 years was noted. Given this report and the planned surgical procedure, a CT of the sinuses was obtained revealing a heterogeneous mass about the sella and clivus concerning for a clival chordoma ( Fig. 52-1 ). An endoscopic endonasal resection was planned.

The patient was placed supine with the head in neutral position on a gel headrest. Stereotactic image guidance was utilized, and the nasal cavities were prepared with pledgets soaked with a topical vasoconstrictor. The inferior turbinates were then lateralized and the right middle turbinate was removed, allowing easy visualization of the sphenoid rostrum. A right-sided nasoseptal flap was then harvested with cold instruments, as monopolar cautery is contraindicated in the presence of a cochlear implant. Once harvested, a small right maxillary antrostomy was performed and the flap was tucked into the right maxillary sinus for future use. To facilitate a two-surgeon, four-handed approach, a posterior septectomy was performed. Wide bilateral sphenoidotomies were then performed to allow a panoramic view of the planum, tuberculum, sella, clival recess, and clivus.

With this view obtained, the mucosa of the sphenoid was stripped to improve visualization of the osseous anatomy. The bone of the inferior sella, clival recess, and clivus was progressively thinned using a 4-mm rough diamond bur until the dura was exposed. Given the location of the mass, the medial aspect of the right carotid canal extending from the posterolateral aspect of foramen lacerum to the paraclival segment was progressively drilled to expose the ICA ( Fig. 52-2 ).