The Contralateral Transcaruncular Approach to the Parapharyngeal Space and Craniocervical Junction: An Anatomical Study

Introduction: The treatment of skull base lesions located in the parapharyngeal space or craniocervical junction (CCJ) is a challenge. The endoscopic endonasal approach (EEA) is limited inferiorly by the hard palate and laterally by the Eustachian tubes (ET). Access to the parapharyngeal space may require an extensive transpterygoid approach and resection of the medial ET. The base of the odontoid process is the inferior limit of the EEA. This study investigates the feasibility of a contralateral transcaruncular approach (CTA) to access the parapharyngeal space more directly and to reach the lower levels of the CCJ.

Material and Methods: Eight human heads with colored-latex injection and thin-sliced CT scans for navigation were dissected (16 sides). The parapharyngeal space and the CCJ were dissected through a CTA bilaterally. A right transcaruncular approach was used to dissect the left parapharyngeal space. The working distances were measured from the caruncle for the CT and the anterior nasal spine for EEA using navigation to compare the two approaches. The base of the styloid process was the target point for the parapharyngeal space. The inferior limit of each approach in the craniocervical junction was similarly measured.

Results: (Surgical Technique) A posterior ethmoidectomy and sphenoidotomy were performed contralateral to the side to be approached. A conventional transcaruncular approach was made ipsilaterally. The medial wall of the orbit was removed after sacrifice of the ethmoidal arteries. From the CTA, dissection of the sphenoid sinus, the inferior clival region, and the parapharyngeal space were sequentially performed. The fossa of Rosenmuller was fully exposed on both sides; the parapharyngeal segment of the carotid artery, the contents of the jugular foramen, and the styloid process were visualized. This exposure did not remove the resection of the ET. The condyle, the lateral mass, and the anterior arch of C1 were then identified. Removal of the anterior arch of C1 allowed resection of the body of C2 and C3 in all specimens.

Measurements: The working distance of the CTA to the right parapharyngeal space was 96.1 (± 6.1) mm and 94.2 (± 7.1) mm on the right and left sides respectively. The EEA showed a working distance of 97.9 (± 5.4) mm and 97.8 (± 5.5) mm to the right and left parapharyngeal spaces, respectively. The difference between these distances was not statistically significant. While the body of C3 was accessed from the CTA, an EEA did not allow dissection of the C3 body in any specimen.

Conclusion: The CTA is feasible and can be used to access the parapharyngeal space and the upper cervical spine as low as the C3 body. The working distances of the CTA and EEA are similar. In the scenario of extensive extradural lesions, the CTA may play a role helping to avoid a separate surgery such as a transoral or a transcervical procedure while preserving of the ET.