Endoscopic anatomy of parapharyngeal segment of the internal carotid artery

Objective To explore the localization and protection of the parapharyngeal segment of the internal carotid artery, and to provide anatomical data for clinical surgery. Methods Five adult cranial specimens (10 sides) were dissected by simulating the preauricular sub-temporal fossa approaches under microscope and the endoscopic endonasal transclival approaches, and the relevant data were measured by vernier calipers. Results Microscopically, the parapharyngeal internal carotid artery was located between the levator veli palatini anteriorly and the stylopharyngeal muscle posteriorly. The distance between the two muscles was 14.7±0.4 mm (14.2-15.3 mm). From the endoscopic perspective, the parapharyngeal segment of internal carotid artery was located behind the levator veli palatini muscle, and the distance from its attachment to the anterior border of the carotid canal was 5.1±0.2 mm (4.9-5.5 mm). The parapharyngeal internal carotid artery was located in the sheath of the carotid artery with sympathetic nerve attached on its surface. The posterior group nerves descended behind the sheath of the artery. The hypoglossopharyngeal nerve and hypoglossal nerve crossed the internal carotid artery in the posterior part of the styloid muscle groups and moved forward. There was a constant stylopharyngeal fascia on the surface of the carotid sheath, which extended to the fascia on the surface of the long cephalic muscle in front of the carotid sheath. The parapharyngeal internal carotid artery gradually approached the midline from the external orifice of the carotid artery. At the level of the carotid canal, the level of pharyngeal tubercle, and the level of the atlantooccipital junction, the distances from the anterior border of the parapharyngeal segment of the internal artery to the middle line of the clivus were 23.2±2.5 mm (20.6-25.8 mm), 19.3±1.1 mm (17.9-20.7 mm) and 15.5±1.3 mm (14.1-16.9 mm) respectively. Conclusions The levator veli palatini muscle could act as the landmark of the parapharyngeal segment of internal carotid artery. The stylopharyngeal fascia and the fascia of the longus capitis major are anatomical barriers to protect parapharyngeal segment of internal carotid artery under the endoscopic endonasal approach. Key words: Carotid artery, internal; Neuroanatomy; Natural orifice endoscopic surgery; Levator veli palatini muscle; Stylopharyngeal fascia