The anatomy of the parapharyngeal segment of the internal carotid artery for endoscopic endonasal approach

Injury to the internal carotid artery (ICA) is a life-threatening complication of endoscopic endonasal approaches. The objective of this study is to illustrate the detail anatomy of the parapharyngeal segment of the ICA (PPICA) to safe endoscopic endonasal surgery. The anatomical dissection was performed in 10 cadaveric specimens and several crucial anatomical landmarks were identified and measured. In addition, 50 dry skulls were studied to further assess the relationship between the pharyngeal tubercle and carotid foramen. From the endoscopic endonasal perspective, in the median plane, the pharyngeal tubercle and the carotid foramen on both sides were located on a line. The average distance between the pharyngeal tubercle and anterior border of the external orifice of the carotid canal was measured as 25.2 ± 3.2 mm. In the paramedian plane, the PPICA was located between the levator veli palatini muscle (LVPM) and the stylopharyngeal muscle (SPM) in upper parapharyngeal space in all specimens, and the distance from the posterior border of the LVPM to the anterior border of the SPM was recorded as 15.1 ± 2.8 mm at the level of the carotid foramen. The distance from the attachment of the LVPM to the anterior border of the external orifice of the carotid canal was about 5.1 ± 0.2 mm. The fully developed stylopharyngeal fascia (SPhF) was observed in 10 cases, and the PPICA was always anteriorly enclosed by and adhered to the SPhF.