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S239: COMBINING SIMPLIFIED RETROPHARYNGEAL AND ENDONASAL ROUTES TO MAXIMIZE VENTRAL SKULL BASE EXPOSURE: A QUANTITATIVE CADAVERIC STUDY
Chiara Angelini; Marco Obersnel; Hao Tang; Roberto Rodriguez Rubio, MD; UCSF

Objective: The anterior surface of the craniovertebral junction (CVJ) and lower clivus represent one of the most challenging regions in neurosurgery due to their depth and proximity to critical neurovascular and glandular structures. Traditional transoral approach—with or without extended modifications—offers adequate exposure but at the cost of extensive dissection, retraction, or resection. The simplified retropharyngeal approach (SRPhA) has recently been proposed as a rapid, safe, and straightforward technique, but its cranial limits and potential combinations with other minimally invasive routes remain unexplored. This anatomical feasibility study investigated whether the simplified SRPhA can be extended cranially. We further evaluated whether combining it with an endoscopic endonasal approach (EEA) could overcome anatomical limitations and optimize ventral skull base exposure.

Methods: Ten embalmed cadaveric heads (thirty dissections: twenty retropharyngeal, ten endonasal) were studied under an operative microscope and a 4-mm 30° rigid endoscope. Intraoperative neuronavigation system (iNtellect [Stryker Inc.]) was used to perform all measurements. Key metrics included surgical exposure area, corridor depth (CD), and horizontal angles of attack (AA). The surgical areas were calculated using MorphoNeuro, a novel open-source tool that semiautomatically calculates 2D/3D surgical morphometrics. A 3D printer (Bambu Lab P1S, USA) was employed to print a customized tubular retropharyngeal retractor with semiflexible 90A thermoplastic polyurethane (TPU) filaments. (Figure 1).

Results: The SRPhA from both sides yielded significantly wider exposure of the lower clivus (right 349.31 ± 20.11 mm², left 456.24 ± 80.13 mm² vs. EEA 227.57 ± 38.44 mm²; p<0.001) and a shorter CD to the basion (76.55 ± 4.08 mm vs. 88.71 ± 3.11 mm; p<0.002) and C1 (61.76 ± 6.05 mm vs. 87.54 ± 2.65 mm; p<0.001). The SRPhA also provided a significantly wider horizontal AA at the pharyngeal tubercle (80.32° ± 8.36° vs. 64.24° ± 7.88°; p=0.0218). However, the AAs at the basion (87.11° ± 12.17° vs. 73.22° ± 11.61°; p=0.126) and the anterior tubercle of C1 (69.71° ± 12.94° vs. 78.5° ± 6.22°; p=0.226) were not statistically different between the two approaches. Exposure of the anterior arch of C1 was comparable (right p=0.860, left p=0.399).

Conclusion: The SRPhA offers superior area of exposure and surgical control of the extracranial lower clivus (Figure 2), whereas the EEA provides better access to the foramen magnum and anterior arch of C1 (Figures 3 and 4). When combined, these complementary routes broaden the operative corridor and enhance exposure across the ventral skull base. Despite the limitation of a deep working distance and narrow corridors that require long and slim instruments, this integrated strategy may represent a promising advancement in the minimally invasive management of the anterior CVJ and the lower clival lesions. Moreover, novel emerging tools such as a semiautomatic morphometric calculation (MorphoNeuro) and the use of tailored 3D printed retractors, contribute to the innovation of this study.

 

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