Once the internal jugular vein is entered, a hand injection close to the superior jugular bulb, with Valsalva and bilateral compression at the root of neck, fills the petrosal and other veins of the craniovertebral junction. Any anatomical variations and the position of the inferior petrosal sinus opening are noted. a) Lateral view. Note the normal sized inferior petrosal sinus (arrowhead), the anterior condylar vein (open arrowhead) and external vertebral venous plexus (arrow). Tributaries of the internal jugular are seen (asterisks). b) AP view. The inferior petrosal sinus opening is located a centimeter or more below the jugular bulb (arrowhead), and is in the anteromedial aspect, running superomedially.