Table 2.

Definitions of the measurements.

Measurements	Definitions
VC diameters
Anterior	The anterior opening of the vidian canal on posterior wall of the pterygopalatine fossa
Middle	The middle part of the vidian canal
Posterior	The posterior opening of the vidian canal on anterior margin of the foramen lacerum
VC length (A–P)	The distance from the anterior to posterior openings of the vidian canal
VC location
PVC-vomerine crest	The distance from the palatovaginal canal to the vomerine crest
VC-vomerine crest	The distance from the vidian canal to the vomerine crest
VC-FR	The distance from the vidian canal to the foramen rotundum
SPF diameter
Posterior to the middle turbinate	The diameter between the perpendicular plate of the palatine bone (inferior) and the sphenoid bone (superior)
Endoscopic endonasal approach angle
VC-MTP Angle	The angle between the posterior end of the middle turbinate and the most lateral margin of the anterior opening of the vidian canal