Modifications of the transoral approach to the craniovertebral junction: anatomic study and clinical correlations

The rhinopalatine line as a reliable predictor of the inferior extent of endonasal odontoidectomies

OBJECT

The endoscopic endonasal approach (EEA) provides a minimally invasive corridor through which the cervicomedullary junction can be decompressed with reduced morbidity rates compared to those with the classic transoral approaches. The limit of the EEA is its inferior extent, and preoperative estimation of its reach is vital for determining its suitability. The aim of this study was to evaluate the actual inferior limit of the EEA in a surgical series of patients and develop an accurate and reliable predictor that can be used in planning endonasal odontoidectomies.

METHODS

The actual inferior extent of surgery was determined in a series of 6 patients with adequate preoperative and postoperative imaging who underwent endoscopie endonasal odontoidectomy. The medians of the differences between several previously described predictive lines, namely the nasopalatine line (NPL) and nasoaxial line (NAxL), were compared with the actual surgical limit and the hard-palate line by using nonparametric statistics. A novel line, called the rhinopalatine line (RPL), was established and corresponded best with the actual limit of the surgery.

RESULTS

There were 4 adult and 2 pediatric patients included in this study. The NPL overestimated the inferior extent of the surgery by an average (± SD) of 21.9 ± 8.1 mm (range 14.7-32.5 mm). The NAxL and RPL overestimated the inferior limit of surgery by averages of 6.9 ± 3.8 mm (range 3.7-13.3 mm) and 1.7 ± 3.7 mm (range -2.8 to 8.3 mm), respectively. The medians of the differences between the NPL and NAxL and the actual surgery were statistically different (both p = 0.0313). In contrast, there was no statistically significant difference between the RPL and the inferior limit of surgery (p = 0.4375).

CONCLUSIONS

The RPL predicted the inferior limit of the EEA to the craniovertebral junction more accurately than previously described lines. The use of the RPL may help surgeons in choosing suitable candidates for the EEA and in selecting those for whom surgery through the oropharynx or the facial bones is the better approach.

Videoassisted anterior surgical approaches to the craniocervical junction: rationale and clinical results

PURPOSE

In this narrative review, we aim to give an update on the anatomic fundamentals of endoscopic assisted surgery to the craniocervical junction (transnasal, transoral and transcervical), and to report on the available clinical results.

METHODS

A non-systematic review and reporting on the anatomical and clinical results of endoscopic assisted approaches to the craniocervical junction (CVJ) is performed.

RESULTS

Pure endonasal and cervical endoscopic approaches still have some disadvantages, including the learning curve and the lack of 3-dimensional perception of the surgical field. Endoscopically assisted transoral surgery with 30° endoscopes represents an emerging alternative to standard microsurgical techniques for transoral approaches to the anterior CVJ. Used in conjunction with traditional microsurgery and intraoperative fluoroscopy, it provides a safe and improved method for anterior decompression with or without a reduced need for extensive soft palate splitting, hard palate resection, or extended maxillotomy.

CONCLUSIONS

Transoral (microsurgical or video-assisted) approach with sparing of the soft palate still remains the gold standard compared to the "pure" transnasal and transcervical approaches due to the wider working channel provided by the former technique. Transnasal endoscopic approach alone appears to be superior when the CVJ lesion exceeds the upper limit of the inferior third of the clivus. Combined transnasal and transoral procedures can be tailored according to the specific pathological and radiological findings.

Detailed anatomy for the transoral approach to the craniovertebral junction: an exposure and safety study

Objective The aim of this study was to demonstrate the anatomical structures of the transoral approach to the craniovertebral junction. We evaluated the necessary exposure field and the safety of this approach. Methods Surgical operations with the transoral approach were performed on 36 cadaver specimens. The special anatomical structures were measured surrounding the exposure field with priorities given to measurements relating to the vertebral artery (VA). The anatomical relationships between the VA and nerves were observed. Results The exposure field partly covered the vertebral basilar system confluent. The middle clivus to upper C3 vertebral body can be exposed by transoral approach. Cranial nerves and cervical nerves emerged from the caudal of vertebrobasilar artery and circumambulated anterolaterally, and some abnormalities were observed in the intracranial segment of vertebrobasilar artery. The safe field was in an inverted trapezoid shape, of which the widest point was 25.5 ± 4.5 mm to the midline at C1 transverse process level; the narrowest point was 11.2 ± 1.5 mm to the midline at the C2-3 level. Conclusion Because the VA is the landmark of the safe field in this approach, surgeons should be very careful to avoid injuries of the VA and nerves while operating in the intracranial field or at the C2-3 level.

Technical advances in pediatric craniovertebral junction surgery

Surgery for conditions in the craniovertebral junction in the pediatric population poses unique challenges. The posterior approach has emerged as the gold standard for arthrodesis in this region. Anterior fixation or decompression also may be indicated. Intraoperative image guidance and neurophysiological monitoring improve the safety and efficacy of these procedures. The specific technical advances in surgery of the craniovertebral junction that have improved patient outcomes are reviewed.

The influence of cervical spine position on the three anterior endoscopic approaches to the craniovertebral junction: an imaging study

BACKGROUND CONTEXT

Three endoscopic anterior approaches, the transnasal, transoral, and transcervical approaches, are used for ventral lesions of the craniovertebral junction and have been compared regarding surgical working distances and approach angles. However, how the position of the cervical spine influences the depths of surgical corridors and approach angles for the three approaches has not been evaluated.

PURPOSE

To evaluate the depths of surgical corridors and the approach angles for the three endoscopic approaches, taking the influence of cervical spine position into account.

STUDY DESIGN

A radiographic study comparing three anterior endoscopic approaches to the craniovertebral junction.

PATIENT SAMPLE

Cervical extension and flexion radiographs for 34 patients and cross-sectional computed tomography scans for 30 additional patients were assessed.

OUTCOME MEASURES

The depths of the surgical corridors and the approach angles for the three endoscopic approaches in the midsagittal planes.

METHODS

We determined the mean angles of the surgical trajectories for the endoscopic transoral and transcervical approaches on cervical extension and flexion radiographs. In addition, we measured the depths of the surgical corridors and the approach angles for the three approaches in the midsagittal plane.

RESULTS

The average depths of surgical corridors were as follows: endonasal, 93.65 mm; transoral, 85.27 mm; transcervical, 62.97 mm (in extension). The average approach angles were as follows: endonasal, 31.22°; transoral, 30.87°; transcervical, 36.58° (in extension).

CONCLUSIONS

The position of the cervical spine does not influence the surgical convenience of the endoscopic transnasal approach, but it can influence the endoscopic transoral and transcervical approaches, especially the latter. The endoscopic transcervical approach offers several advantages over the endoscopic transoral and endonasal approaches.

Surgical treatment of a clival-C2 atypical teratoid/rhabdoid tumor

The authors present the case of en bloc resection of a clival-C2 atypical teratoid/rhabdoid tumor. These aggressive lesions of early childhood generally occur in the cerebellum or cerebral hemispheres. This 7-year-old boy presented with pain on turning his head and was found to have a clival-C2 mass. A metastatic workup was negative for disseminated disease. A transoral biopsy procedure revealed an atypical teratoid/rhabdoid tumor on histological examination. The tumor was resected via a transoral approach, and the patient's spine was stabilized with posterior instrumented fusion from the occiput to C-5. Postoperatively, the patient underwent 16 months of chemotherapy along with 6 weeks of overlapping radiation therapy. Twenty-seven months after the initial surgery he presented with leg pain and was found to have a solitary metastatic lesion at the conus medullaris. There was no local recurrence at the clivus. The conus tumor was resected and found to be consistent with the primary tumor. Several months later the patient presented with disseminated intrathecal disease and ultimately died 42 months after the initial resection.