• Davide Mattavelli, Andrea Bolzoni Villaret, Marco Ferrari, Marco Ravanelli, Vittorio Rampinelli, Davide Lancini, Luigi Fabrizio Rodella, Marco Fontanella, Roberto Maroldi, Piero Nicolai, and Francesco Doglietto.
• Unit of Otorhinolaryngology-Head and Neck Surgery, Department of Surgical Specialties, Radiological Sciences, and Public Health, University of Brescia, Italy. Electronic address: davide_mattavelli85@yahoo.it.
• World Neurosurg. 2016 Nov 1; 95: 222-228.

BackgroundSeveral 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.MethodsComputed 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.ResultsMean 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%.ConclusionsThe 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.Copyright © 2016 Elsevier Inc. All rights reserved.

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