Table 2.

Description of the CT-based analyses of the VC and pICA anatomical relationship

Measurement	Description
Antero-posterior measurement between the VC and the pICA	AP distance (mm) from the mid-posterior opening of the VC (in the trajectory of the canal) to the mid AP point of the pICA cross-section (Figs. 1, 2). A positive figure was recorded if the pICA was posterior to the VC
Craniocaudal measurement between the VC and the pICA	Vertical perpendicular distance (mm) between a line extrapolated posteriorly from the mid-posterior opening of the VC (in the trajectory of the canal) to the central point of the pICA cross-section (Figs. 1, 2). A positive figure was recorded if the pICA was superior to this line
Craniocaudal intersection	Whether the line extrapolated from the posterior opening of the VC (in the trajectory of the canal) intersected the pICA cross-section or if it was superior/inferior to the pICA cross-section (Figs. 1, 2)
Coronal relationship between the anterior genu of the pICA and Vidian canal	The reformatted image was scrolled antero-posteriorly and the location of the anterior genu of the pICA was defined by its quadrant (inferomedial, inferolateral, superomedial, superolateral) relative to the VC (Fig. 3)