Angiographic evaluation of the distance from the top of the jugular bulb to the inferior petrosal sinus–internal jugular vein junction: simple classification and identification method for the orifice of the non-visualized inferior petrosal sinus during neuroendovascular surgery

Background The inferior petrosal sinus (IPS) is the transvenous access route for neurointerventional surgery that is occasionally undetectable on digital subtraction angiography (DSA) because of blockage by a clot or collapse. This study was aimed at analyzing the distance from the jugular bulb (JB) to the IPS–internal jugular vein (IJV) junction and proposing a new anatomical classification system for the IPS–IJV junction to identify the non-visualized IPS orifice. Methods DSA of 708 IPSs of 375 consecutive patients were retrospectively investigated to calculate the distance from the top of the JB to the IPS–IJV junction, and a simple classification system based on this distance was proposed. Results The median distance from the top of the JB to the IPS–IJV junction was 20.8 ± 14.7 mm. Based on the lower (10.9 mm) and upper (31.1 mm) quartiles, IPS–IJV junction variants were: type I, 0–10 mm (22.3%); type II, 11–30 mm (45.8%); type III, > 31 mm (23.9%); and type IV, no connection to the IJV (8.0%). Bilateral distances showed a positive interrelationship, with a correlation coefficient of 0.86. The bilateral symmetry type (visualized IPSs bilaterally) according to our classification occurred in 267 of 300 (89.0%) patients. Conclusions In this study, the IPS–IJV junction was located far from the JB (types II and III), with a higher probability (69.6%). This distance and the four-type classification demonstrated high degrees of homology with the contralateral side. These results would be useful for identifying the non-visualized IPS orifice.