Relationship between the posterior septal artery and the upper edge of the choana
ConclusionAlthough the distance between the choanal edge and PSA is 8.5 mm on average, due to its variability, a distance of at least 12.45 mm for the opening of the sphenoidal sinus in the ETA approach should be considered as a safety margin.
Source: Surgical and Radiologic Anatomy - Category: Anatomy Source Type: research