Fig. 9.1
Surgical approches to CVJ
Anterior Approach
Transcranial (transfrontal, orbitozygomatic, pterional)
Transnasal (transsphenoidal, transmaxillary, endoscopic)
Transoral (transpalatal, buccopharyngeal, translabiomandibular, translabioglossomandibular, endoscopic)
Transcervical
Posterior Approach
Suboccipital, retrosigmoid, extreme lateral
Lateral Approach
Translabyrinthine, transcochlear, presigmoid, subtemporal transpetrosal, preauricular infratemporal, preauricular transtemporal
The anterior approaches are best suited for extradural lesions. Attacking intradural pathology through one of these approaches risks contamination with pharyngeal organisms, meningitis, and cerebrospinal fluid (CSF) leaks.
Consequently, intradural lesions located laterally and lesions involving the temporal bone are better treated through a lateral approach, while intradural posterior lesions are reached through a posterior approach [7, 12].
Details are shown in Fig. 9.2.
Fig. 9.2
Selection of the approach according to the site of the lesion
Our objective is to describe the anterior approaches performed by ENT and orthopedic surgical team, in particular, the minimally invasive endoscopic-assisted approaches.
Posterior and lateral approaches are not described in this chapter.
9.2 Anterior Approaches
CVJ is a complex region which can harbor neoplastic, degenerative, or inflammatory lesions that can cause compression of the cervicomedullary junction and craniovertebral instability. Treatment may require surgical decompression and subsequent craniocervical stabilization.
Several surgical approaches provide anterior access to the craniocervical junction and the upper cervical spinal including transnasal, transoral, and high transcervical approaches.
In particular, anterior or anterolaterally located CVJ lesions have traditionally been most difficult to resect with high morbidity and mortality resulting from anterior traditional approaches. Recently the development of endoscopic surgery allowed to perform decompression of the craniovertebral junction with endoscopic transnasal-transoral techniques, even in patients with challenging anatomic features [14].
Preoperatively, estimate the superior extent of the exposure by drawing an imaginary line in the plane of the hard palate toward the craniovertebral junction on a sagittal MRI. If the lesion is midline and is situated above this line, a transnasal approach may be suitable. If, however, the lesion is situated below the plane of the hard palate, a transoral approach alone may be sufficient. Alternatively, consider a Le Fort I maxillotomy with or without a palatal split if the lesion extends above and below the plane of the hard palate. If the lesion extends inferiorly beyond the line of sight of a standard transoral approach (roughly beyond the lower body of C2 to the C2–C3 disk space in most cases), a labiomandibular median glossotomy (transmandibular split) or cervical approach may be appropriate to gain more inferior exposure (Fig. 9.3) [11].
Fig. 9.3
Preoperative estimate of exposure and choice of the approach: lesions suitable for transnasal approach (green), for transoral approach (orange), for maxillotomy with or without palatal split (blue), for labiomandibular median glossotomy or cervical approach (yellow), and for transoral robotic surgery (red)
Transoral robotic surgery gets the opportunity to extend the approach along all upper cervical spine.
Prophylactic antibiotics are administered intraoperatively in transnasal and transoral approaches.
A high-resolution stereotactic computed tomography scan and MRI of the craniovertebral junction are necessary for preoperative planning. Moreover dynamic plain cervical radiographs in flexion and extension views to evaluate for preexisting instability at the craniovertebral junction are suggested. In some cases, the CVJ pathology has destabilized the occipitoatlantal or atlantoaxial joints, thus requiring a subsequent or prior stabilization procedure. If severe deformity or cranial settling is detected preoperatively, attempt reduction with cervical traction using Gardner-Wells tongs and mobilization in halo vest is recommended. Even if no instability is present, however, most cases will require stabilization after surgery because of postoperative iatrogenic instability [11]. Either occipitocervical or atlantoaxial stabilization can be performed postoperatively or simultaneously to the main procedure. Rarely ventral bone graft is placed intraoperatively into the bony defect because of high risk of infection, reabsorption, and dislodgement.
Take Home Massages
Advantages
Low morbidity (endoscopic approaches)
Direct extradural approach that does not require any brain retraction
Low morbidity and mortality (traditional and extended approaches)
Disadvantages
Risk of cerebrospinal fluid leak
Contraindications
Intradural lesion (risk of meningitis)
Lateral or posterior lesions
9.2.1 Radiological Planning of Anterior Approaches to Craniovertebral Junction [5]
It is possible to evaluate and compare the minimally invasive techniques to the anterior craniocervical junction using exclusive endoscopic approach or endoscopic-assisted approaches:
Endonasal (exclusive endoscopic)
Transoral (endoscopic assisted)
Transcervical (endoscopic assisted)
9.2.1.1 Angles of Attack
The angles of attack were created with the use of a single entry point. The entry point selected allows the best “angle” to reach the surgical lesion (e.g., angled inferiorly as much as possible for the endonasal approach and anteriorly to posteriorly as much as possible for the transcervical approach).
9.2.1.2 Endonasal
For the endonasal approach, the entry point was defined as a point in the midline at the inferior edge of the nasal bone. The most superior access within the surgical field was arbitrarily defined as the point on the clivus at the base of the sella (the superior aspect of the clival recess). The most inferior access within the surgical field was then approximated by fashioning a straight line starting from the inferior midline of the nasal bone and ending at the lowest point on the odontoid or C2 while remaining tangential to, but not crossing, the hard palate. This approximates the most inferior point within the surgical field, but does not take into account the use of angled instruments that allow a more inferior reach of approximately 5 mm or an increase in the angle obtained by hard palate drilling.
9.2.1.3 Transoral
For the transoral approach, the entry point was defined as a point in the midline at the inferior edge of the incisors. The most superior access within the surgical field was defined as the point in the midline at the superior aspect of the lower third of the clivus. This was chosen based on the anatomic dissections as the point of superior access without splitting the soft palate. The most inferior access within the surgical field was chosen as the inferoposterior aspect of the body of C2.
9.2.1.4 Transcervical
For the transcervical approach, the entry point was defined as the midline on the skin at the C4–C5 cervical disk level. The most superior access within the surgical field was defined as the point in the midline at 1 cm above the basion. The most inferior access within the surgical field was the inferoposterior aspect of the body of C2.
The surgical goals of lower clival and odontoid (craniocervical) decompression were achieved using the endonasal and transoral approaches.
The transcervical approach was unable to achieve more than 1 cm of lower clival resection without undue retraction or was limited by the constraints of the mock chest on the angle of attack. Furthermore, it was difficult to maintain a midline dissection trajectory. This approach, like the endonasal and transoral approaches, did allow complete odontoid resection (Table 9.1).
Table 9.1
Summary of the angles of attack, surgical working distance, and working area in each endoscopic approach
Approach | Distance to surgical target (mm) | Angle of attack, sagittal (degrees) | Working area (mm2) |
|---|---|---|---|
Transnasal | 94 | 28 | 1305 |
Transoral | 102 | 30 | 1406 |
Transcervical | 100 | 15 | 743 |
The working angles and the overlapping working areas of each approach are illustrated in Fig. 9.4.
Fig. 9.4
Computed tomography scans demonstrating the surgical trajectory and angles for the endonasal approach (a), the transoral approach (b), and transcervical approach (c). (d) Common surgical area of the 3 approaches is represented by the overlapping illumination
9.3 Transnasal Approach
9.3.1 Standard Transnasal/Transsphenoidal Approach
9.3.1.1 Operative Positioning
The procedure is performed under general anesthesia with the patient positioned supine and intubated orally. Sometimes neuromonitoring with somatosensory-evoked potentials is used, and spinal traction is applied as needed to get the odontoid process into a more normal position. Neuronavigation is always used for surgical guidance.
The oropharynx is packed to prevent blood and secretions from the operative site from reaching the stomach. The patient is supine with the head slightly extended on a doughnut pad or fixated with a Mayfield head holder. The operating table is adjusted to provide a semirecumbent position for the patient.
9.3.1.2 Surgical Principles
In 2005 Kassam et al. [1] published the first report on endoscopic endonasal approach being used to perform odontoidectomy.
The endoscopic transnasal approach consisted of a bilateral approach to the nostril.
Kassam [1] described an expanded endonasal approach to perform resection of the odontoid process that consists in an elevation of a nasal septal flap that will be used for closure, a bilateral maxillary antrostomy, ethmoidectomy, middle turbinate resection posterior septectomy, and a wide sphenoidectomy to reach the CVJ. Actually not all patients require sphenoidectomy or middle turbinectomy. Depending on the location of the lesion, the sphenoid floor and/or clival bone were drilled if necessary. After cauterization the posterior nasopharyngeal mucosa was incised in the midline, and the prevertebral muscles were dissected vertically and elevated laterally to expose the anterior tubercle of the atlas. Decompression can be performed using a drill, curettes, and/or Kerrison rongeur [8, 13].
Neuronavigational devices can provide more accurate information and guidance. CSF leak and venous bleeding from the epidural venous plexus are common in this procedure. A fat graft is used to pack with fibrin glue which is used to pack the cavity. If CSF leak occurs, fat should be used to pack the entire sphenoid sinus, and fascia lata may also be necessary to enhance the closure. The graft is held in place with a plate or stent of nasal bone or cartilage. A Merocel sponge is packed in the nose bilaterally (Figs. 9.5, 9.6, and 9.7).
Fig. 9.5
From Presutti et al. eight descriptions of transnasal/transsphenoidal approach. (a) Creationof a U shape nasopharyngeal flap to identify the prevertebral structures (b) Exposure of odontoid process and anterior tubercle of the atlas
Fig. 9.6
Nasopharyngeal U-shaped flap to expose prevertebral plane
