The endoscopic endonasal approach provides a direct surgical trajectory to anteriorly located lesions at the craniovertebral junction. The inferior limit of surgical exposure is predicted by the nasopalatine line, and the lateral limit is demarcated by the lower cranial nerves. Endoscopic endonasal odontoidectomy allows preservation of the soft palate, and patients can restart an oral diet on the first postoperative day. Treating the condition at the craniovertebral junction using this approach requires careful preoperative planning and endoscopic endonasal surgical experience with a 2-surgeon 4-handed approach combining expertise in otolaryngology and neurosurgery.
Key points
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The endoscopic endonasal approach provides a direct surgical trajectory to anteriorly located lesions at the craniovertebral junction.
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Endoscopic endonasal odontoidectomy allows preservation of the soft palate, and patients can restart an oral diet on the first postoperative day.
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Lesions extending lateral to the lower cranial nerves cannot fully be treated via an endonasal approach.
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The use of vascularized pedicled flaps, such as the nasoseptal flap, has dramatically reduced the incidence of postoperative cerebrospinal fluid leak.
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A 2-surgeon 4-hand approach is recommended with collaborative expertise in rhinology and neurosurgery.
Introduction
Pathologic lesions located anterior or anterolateral at the craniovertebral (CVJ) pose a surgical challenge given their deep location and proximity to critical neurovascular structures. Historically, surgical treatment of these lesions using a standard midline suboccipital approach resulted in significant morbidity and mortality. Over the last several decades, numerous alternative approaches have been described to treat these lesions more effectively. These include the far lateral, extreme lateral, direct lateral, transcervical, transoral, and transnasal approaches.
The endonasal approach to the CVJ was originally described by Kassam and colleagues. The advantage of the endonasal approach is that it provides direct surgical access to anterior and anterolateral CVJ lesions without the need to mobilize or retract cranial nerves, the lower brainstem, or upper cervical spinal cord. In addition, the endoscope can provide high illumination with a wide field of view. However, the endoscopic endonasal approach to the CVJ requires substantial experience to overcome the learning curve associated with the technique and to minimize the risk of potential complications. In this article, the authors outline the surgical technique for the endoscopic endonasal approach to the CVJ, present illustrative cases, review outcomes, and discuss complication avoidance.
Introduction
Pathologic lesions located anterior or anterolateral at the craniovertebral (CVJ) pose a surgical challenge given their deep location and proximity to critical neurovascular structures. Historically, surgical treatment of these lesions using a standard midline suboccipital approach resulted in significant morbidity and mortality. Over the last several decades, numerous alternative approaches have been described to treat these lesions more effectively. These include the far lateral, extreme lateral, direct lateral, transcervical, transoral, and transnasal approaches.
The endonasal approach to the CVJ was originally described by Kassam and colleagues. The advantage of the endonasal approach is that it provides direct surgical access to anterior and anterolateral CVJ lesions without the need to mobilize or retract cranial nerves, the lower brainstem, or upper cervical spinal cord. In addition, the endoscope can provide high illumination with a wide field of view. However, the endoscopic endonasal approach to the CVJ requires substantial experience to overcome the learning curve associated with the technique and to minimize the risk of potential complications. In this article, the authors outline the surgical technique for the endoscopic endonasal approach to the CVJ, present illustrative cases, review outcomes, and discuss complication avoidance.
Treatment goals
The goals of surgery and the anticipated outcomes are discussed with the patient preoperatively. Goals may include obtaining a diagnosis (if not already known), decompression of neural structures, and maximizing survival and quality of life. The latter requires minimizing collateral damage to both nasal and neural structures and lessening the risk of complications.
Preoperative planning
Preoperative evaluation begins with thorough radiographic assessment of pathologic and anatomic variations. Thin-slice (1.0 mm) computed tomography (CT) scan of the sinuses, CVJ, and upper cervical spine and volumetric MRI are performed. In addition to the volumetric T1 sequence with gadolinium, a high-resolution constructive interference in steady state sequence can be invaluable in showing the relationship of cranial nerves to the condition and the competency of dural membranes. A preoperative CT angiogram may be performed in certain cases to further evaluate any anatomic variations in the paraclival carotid arteries (the segment of the carotid artery between the foramen lacerum and the cavernous sinus) and to assess intracranial collateralization patterns. These images may be fused and uploaded into a frameless stereotaxy image-guidance unit, which is used on all endoscopic endonasal cases.
In addition to radiographic evaluation, preoperative direct bilateral sinonasal evaluation is imperative. This evaluation is usually performed in the office by the participating otolaryngologist. Anatomic variations, such as septal deviation, spur formation, or perforation, may directly impact the operative approach or reconstruction technique. In addition, screening for concurrent paranasal sinus disease is necessary to determine the need for preoperative antibiotic treatment. If preoperative voice or swallowing symptoms exist, a preoperative swallow evaluation or direct laryngoscopy may be performed to provide baseline function and to appropriately counsel the patients on potential risks of exacerbation after surgery.
Patient positioning
The patient is placed in supine position toward the right edge of the surgical bed. The arms are tucked to the side allowing sufficient access to the abdomen and right thigh should fat or fascia lata harvest be necessary. Accordingly, the monopolar electrocautery grounding pad is placed on the left thigh. For transclival approaches, the head may be placed on a donut or in a 3-point fixation device and secured to the bed. For cases of odontoidectomy before a posterior cervical fusion, placing the patient in a 3-point fixation device is imperative given that significant spinal instability will be present after odontoidectomy. The head may be placed in a neutral position for transclival cases, but gentle neck flexion is beneficial for odontoidectomy cases to align the approach trajectory with the surgeon.
The endotracheal tube is placed along the left side of the mouth. A throat pack or nasogastric tube is placed to avoid the collection of blood in the stomach, which may provoke postoperative emesis and affect the reconstruction. Neurophysiology monitoring may also prove helpful in select cases. Somatosensory and motor-evoked potentials may be used as well as monitoring of lower cranial nerves if affected by the condition. A neural integrity monitor 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. In addition, it cannot be used in cases of intraoperative MRI, as it is MRI incompatible. Electrodes may also be placed in the trapezius muscle and tongue to monitor the accessory and hypoglossal nerves, respectively.
Procedural approach
Nasal Approach
The nasal mucosa is injected with local vasoconstrictors. Using a 0° endoscope, the inferior turbinates are out-fractured. Resection of one or both of the middle turbinates can be performed to provide a wider corridor for passage of instruments. However, middle turbinectomy is typically not necessary when the approach is limited to the CVJ, unless there is significant platybasia. The choanae can then be visualized by following the nasal cavity floor back to the nasopharynx. The natural ostium of the sphenoid sinus is identified medial to the superior turbinate. In cases requiring vascularized reconstruction, a nasoseptal flap is harvested by first identifying the pedicle of the flap, which contains the posterior septal artery. Using needle-tip bovie electrocautery, the inferior cut is made from the posterior choana extending inferior and anterior along the floor of the nasal cavity. The superior cut is then made starting at the natural sphenoid ostium and extending superior and anterior along the nasal septum. During most endoscopic endonasal cases, the nasoseptal flap is tucked into the nasopharynx. However, when approaching the CVJ, the flap must be placed into the maxillary sinus to maximize visualization and avoid damaging the flap. Therefore, a maxillary antrostomy is performed on the side of the nasoseptal flap harvest by removing the uncinate process, and the nasoseptal flap is tucked into the maxillary sinus until needed for the reconstruction. Again, it should be noted that approaches for pathologic conditions limited to the CVJ might not require initial nasoseptal flap harvest. Rather, an inferior posterior septectomy that spares the pedicle to the nasoseptal flap can be used, which allows subsequent harvest if needed.
Wide sphenoidotomies can then be performed if warranted by the pathologic findings 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 burr or Kerrison rongeurs. Roughly 1 to 2 cm of the posterior septum is removed as well. Wide bilateral sphenoidotomies creates 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 exposure is performed. 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 process exposes the nasopharyngeal 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 the odontoid process.
Endoscopic Endonasal Transclival Approach
For the purpose of this article, the discussion focuses on the transclival approach for access to the lower clivus and CVJ. Common conditions treated with these approaches include clival chordomas and ventrally located foramen magnum meningiomas. The relationship between the tumor, the lower cranial nerves, and carotid arteries should be carefully studied on preoperative imaging. Lesions extending lateral to the lower cranial nerves cannot fully be treated via an endonasal approach. During a midclival approach, the paraclival carotid arteries are at risk. An important anatomic landmark is the lacerum segment of the internal carotid artery (ICA), which roughly corresponds to the pontomesencephalic junction. In lower clival and foramen magnum approaches, which take place below the lacerum segment of the ICA, the risk of carotid artery injury is lower. In general, the ICA is lateral to the superior pharyngeal constrictor muscle and occipital condyle. However, major anatomic variations of the ICA can occur, particularly in elderly patients and in patients with significant congenital bony deformity of the craniocervical junction, and should be accounted for when planning the operation.
After the nasal corridor has been accessed as previously described, the clivus is drilled with a 4-mm coarse diamond burr between the lacerum segments of the ICA superiorly and the occipital condyles inferiorly. The basilar plexus, which lies between the 2 layers of clival dura and communicates with the inferior petrosal sinus and cavernous sinus on each side, can often result in brisk bleeding when encountered. This bleeding is controlled with injectable hemostatic agents and gentle pressure with cotton patties. When this region has already been invaded by tumor, the basilar plexus is often already thrombosed.
For lesions that lie lateral to the occipital condyle, the anteromedial portion of the occipital condyles may be removed to gain additional lateral access. First, the rectus capitus anterior and the atlanto-occipital joint capsule are removed to expose the atlanto-occipital joint. A small groove is found on the superior aspect of the condyle, which estimates the level of the hypoglossal canal. Above this groove is bone of the jugular tubercle, and below this groove is bone of the occipital condyle. The condyle can be removed up to the level of the hypoglossal canal. The inferior portion of the condyle that contains the alar ligament insertion is left intact as removal of this portion results in very little additional exposure but can increase risk of craniocervical instability. In addition, the lateral extent of surgical exposure can be better visualized using angled endoscopes. Inferior clivectomy, transection of the tectorial membrane, and resection of less than 75% of the anteromedial condyle for exposure of the anterior foramen magnum does not result in significant craniocervical instability enough to warrant fusion.
Case Illustration
A 60-year-old man with a history of smoking and diabetes presented with headaches and double vision. His examination was remarkable for left abducens nerve palsy. MRI of the brain found a 3.0- × 2.5- × 3.8-cm enhancing clival mass extending laterally along bilateral petrous apices behind the horizontal petrous carotid arteries ( Fig. 1 ). CT scan found destruction of the clival bone in the location of the mass ( Fig. 2 ). An endoscopic endonasal resection was planned.
The patient was positioned supine with the head positioned neutral in a donut. Stereotactic image guidance was used. Nasal cavities were prepared with topical vasoconstrictor. The inferior turbinates were outfractured and the right middle turbinate was resected. A right nasoseptal flap was harvested using needle-tip electrocautery. A right maxillary antrostomy was performed, and the nasoseptal flap was tucked into the maxillary sinus to allow unimpeded access to the clivus. Wide bilateral sphenoidotomies, in addition to a posterior septectomy, was performed. The mucosa of the sphenoid sinus was stripped.
The sella and clinoidal ICAs were identified ( Fig. 3 ), and the tumor, which had invaded much of the clival bone, was resected. The paraclival arteries were dissected out bilaterally. Angled endoscopes and instruments were used to remove the tumor extending posterolateral to the paraclival ICAs on both sides. The paraclival arteries and clivus were covered with the nasoseptal flap. Postoperative imaging confirmed gross total resection ( Fig. 4 ). The patient did well after surgery and in follow-up had improvement in his abducens palsy.
