Study on inferior petrosal sinus and its confluence pattern with relevant veins by MSCT.

OBJECTIVE: To explore the anatomic route of inferior petrosal sinus (IPS) after going out of the cranium and its confluence patterns with internal jugular vein (IJV), anterior condylar vein (ACV) and lateral condylar vein (LCV), and to supply knowledge about typing of IPS-IJV junction, so as to provide reference evidence for evaluation of transvenous access route in the diagnosis and treatment of skull base and cavernous sinus lesions.
METHODS: In 120 patients, the IPS route and its confluence with IJV, ACV and LCV were shown by multi-planar reconstruction (MPR) and curve multi-planar reconstruction (CMPR). Combining with continuous thin slice, the IPS-IJV junction was further subdivided according to the level of IPS confluence with IJV and whether there is an anastomosis with sigmoid sinus (SS). Furthermore, the IPS length, venous diameter at IPS-IJV junction and IPS-SS communicating branch were determined and compared.
RESULTS: Inferior petrosal sinus directly draining into jugular bulb (JB) or/and draining into JB after communication with SS was found in 28 sides (11.7%, pattern A); IPS draining into IJV at the level of exterior opening of hypoglossal canal in 114 sides (47.5%, pattern B); IPS draining into IJV in a lower extracranial level in 83 sides (34.6%, pattern C); IPS with multiple junctions draining into IJV near the jugular foramen in 12 sides (5.0%, pattern D); IPS directly draining into VVP in 1 side (0.4%, pattern E); IPS being absent in 1 side (0.4%, pattern F). IPS draining into VVP via ACV was seen in 218 sides, IPS draining into VVP via LCV in 100 sides and IPS directly draining into IJV in 14 sides. After going out of the cranium, IPS goes along with IJV for a relatively long distance in some cases. The IPS extracranial length over 40 mm was found in ten sides and the lowest level of IPS route was at the inferior margin of the fourth cervical vertebra. The venous diameter at the IPS-IJV confluence was 0.8-5.7 mm (mean 2.51 mm) and it was significantly larger on the right side than on the left (P = 0.01). However, there was no remarkable difference between male patients and female ones.
CONCLUSION: Continuous thin-slice scanning by multislice spiral computed tomography in combination with MPR and CMPR can clearly show IPS route and its confluence with relevant veins, and determine the feasibility of procedures via IPS. Therefore, it can be used as an effective method for preoperative evaluation of IPS for diagnosis and treatment of skull base and cavernous sinus lesions by IJV access route.