Different Perspectives of Internal Carotid Artery in Transnasal Endoscopic Surgery

BACKGROUND: Several endoscopic landmarks for the internal carotid artery (ICA) have been identified, but they have always been proposed in a "static" perspective. The aim of this study was to investigate how the surgical corridor and optical distortion can influence the perception of carotid landmarks in transnasal endoscopic surgery. METHODS: Computed tomography images of skulls in 20 subjects were analyzed. The petrous carotid angle (PCA) was calculated as the angle between the petrous carotid axis and the coronal plane connecting stylomastoid foramina. The angle of incidence (AI) on the anterior carotid genu of 3 different surgical corridors (contralateral nostril, ipsilateral nostril, and transmaxillary ipsilateral route) was evaluated. PCA, AI, and their differences were studied by Spearman's correlation test. Two cadaver heads were dissected, simulating the studied surgical corridors. The fish-eye effect was empirically quantified. RESULTS: Mean PCA was 31° (range, 21-41°). PCA and AI are linked by an inverse proportion relationship. A transmaxillary approach always ensures the highest value of AI on the target. The cadaveric dissection qualitatively confirmed the radiologic data. The fish-eye effect can cause a compression of distance perception as high as 37%. CONCLUSIONS: The surgical corridor and endoscope optic distortion can influence ICA visualization and the perception of its anatomic landmarks. In a 2-nostril, 4-handed approach, it is advisable to place the endoscope and instrument for dissection in the nostril that is ipsilateral to the lesion. Awareness of the different perspectives and related optical distortions is essential when working in proximity to the ICA.