Landmark for Medial Extent of Paraclival Carotid Artery at Anterior Genu
The popularity and ability of endonasal techniques for the resection of skull base tumors has increased in recent years leading to more extended resections. The rupture of the internal carotid artery is one of the most feared and devastating complications of the endonasal technique. As endonasal skull base resections have become more extended, the incidence of internal carotid injury has increased. The current surgical technique for localizing the clival portion of the carotid involves an extensive technique of drilling out the pterygoid plate and identifying and following the vidian canal to the carotid artery. The purpose of this study was to identify an intraoperative landmark that consistently marked a location medial to the anterior genu of the ascending paraclival carotid artery. The study looked at 102 CT sinus with 61 females and 41 males all over the age of 18 years old. A trajectory from the nasolacrimal duct to the sphenopalatine foramen consistently ended at the lateral portion of the anterior genu, this line was termed the nasolacrimal-sphenopalatine-carotid line (NSC line). Scans were evaluated and measured to test if 1 cm medial to this landmark was always medial to the carotid.
Measurements included: distance from the nasolacrimal duct to the lateral internal carotid artery, carotid width at the anterior genu, inter-carotid width at anterior genu, and angle from nasolacrimal duct to anterior genu across to contralateral genu. The average inter-carotid distance was 1.79 cm (SD of 0.34), the average carotid width was 0.61 cm (SD of 0.12) on the right and 0.60 (SD of 0.11) on the left, and the measured angle average was 84.9 degrees (SD of 3.19 degrees) on the right and 84.7 degrees (SD of 3.42) on the left. The average NSC trajectory length on the right was 5.77 cm (SD of 0.33 cm) and 5.79 cm (SD of 0.33) on the left. Using a 2 tailed student t-test there was no statically significant difference in the NSC angle, NSC length, or carotid diameter between the right and left sides (P > 0.5). There were some noted differences when comparing male to female patients, as females were found to have a shorter inter-carotid distance, carotid diameter, and NSC trajectory length. In all 102 studies, 1 cm medial to the lateral genu landmark was medial to the carotid artery. This study provides a safe and consistent intraoperative landmark for the carotid when drilling through the clivus.