Most patients with CSDAVFs present with intolerable neuro-ophthalmic symptoms, such as diplopia, severe cosmetic disfigurement, or severe headache. Endovascular treatment is usually required to occlude the abnormal arteriovenous shunts, especially in patients with higher risk CSDAVFs with cortical venous drainage or hemorrhage.1–3 TVE has been accepted as the first-line treatment, including the petrosal sinuses1, the superior ophthalmic vein2, the sylvian vein7 or the pterygoid plexus7. These veins are accessable by transfemoral or transjugular approach, by direct puncture or surgical exposure. The IPS approach is the simplest and safest transvenous route to reach the CS and represents the first choice for TVE of CSDAVF. Even the IPS does not serve as a venous outflow on angiograms due to thrombosis, this does not exclude it as a reasonable choice for reaching the fistula site with a microcatheter.
Successful catheterization of angiographically invisible IPS has been reported by some authors with successful rate varying 50–80%6–9,14. In previous studies, operators generally rely only on anatomical knowledge and expereince to identify the IPS. According to 3D rotational venography studies15,16, the drainage patterns of the IPS can be classified into the following 6 types based on the level of the IPS-IJV junction: The IPS drains into the jugular bulb (type A, 1.2%); the IPS drains into the IJV at the level of the extracranial opening of the hypoglossal canal (type B, 34.9%); the IPS drains into the lower extracranial IJV (type C, 37.3%); the IPS forms a plexus and has multiple junctions to the IJV around the jugular foramen (type D, 6.0%); the IPS drains into the vertebral venous plexus with no connection to the IJV (type E, 3.6%); and the IPS is absent (type F, 16.9%). Thus, types B and C are most common and should be considered first. With these types, detecting the orifice of the occluded IPS is impossible or uncertain due to its invisibility and anatomical variations and is time consuming due to multiple attempts.
Some alternative strategies have been promoted in such complex situations. Srivatanakul et al used 3D venography of the IJV to identify the remnant of the IPS.9 The catheterization of the occluded IPS was performed under the best working angle by analyzing the 3D image. Some authors suggested 0.035-inch guidewire as a frontier-wire for probing the occluded IPS and gave a 70% technical success rates.12 Yamauchi et al reported the use of intravascular ultrasonography(IVUS) to detect the remnant of occult IPSs in patients with CSDAVFs.17 The low-orifice IPS could be detected by the IVUS, but detecting an intracranial origin of the IPS was difficult with this technique. Up to date, it is yet possible to predict if a catheter can successfully be navigated through the IPS in a case. We therefore considered this new method for detecting the invisible origin of the IPS.
To perform TVE via a thrombosed IPS, initially, the orifice of the angiographically invisible IPS must be located. In the current study, when the microguidewire showed an angle of about 117° on the lateral projection, we determined that this was the orifice of the IPS. The microcatheter was inserted into the orifice of the IPS, and then continue to open the IPS in this direction. The angle of microguide wire is useful for confirming the thrombosed IPS to save time and avoid unnecessary irradiation. To avoid any risk of perforation, we do not use a 0.0350 wire with stiffer properties. If there is substantial resistance when advancing the microcatheter, switching to a Transend14 or an Avigo14 microguidewires is also a sensible alternative for their higher support. The use of a loop at the tip while advancing the wire within the thrombosed IPS was found to be helpful. The softness of the 0.014 loop allows it to conform to the specific anatomy of the IPS and to avoid getting stuck in the irregular, trabeculated venous walls. Further, advancing a loop of a 0.014 hydrophilic wire is much less traumatic than the tip, particularly if the catheter is already wedged. Microguidewires and microcatheters minimize the risk of perforation of the IPS and of subarachnoid hemorrhage. The angulate theory was found to be useful and associated with a higher technical success rate of reaching the CS with the microcatheter. The thrombosed IPS approach avoids the necessity of more aggressive procedures in so-called intractable dural cavernous sinus fistulas. The IPS approach is a low risk procedure, allowing treatment regardless of the patient’s age if symptoms are progressive, vision loss is imminent, or cortical drainage is evident.
Limitation of this study
Despite the high technical success rate, we may have failed to encounter some difficult cases due to anatomic variations (such as no connection between the IPS and the IJV or an extremely low IPS orifice). In the angle measurement, the image we take is 90° laterally. Due to the position of the patient's head, it may not be the standard lateral position. But, we operated in a 90° lateral position and succeeded in all patients. In future applications, we will continue to use this method to operate and measure on the standard lateral position, and more accurate angle measurement will be obtained. As this report involves only a small number of cases, and represents only a preliminary experience, accumulation of more cases will clarify whether this technique is useful.