Unlike previous case reports or case series with limited sample sizes, the present study analyzed the largest sample of patients with CS-DAVF treated via the SOV route. All patients presented with ophthalmic venous drainage and their initial symptoms and signs were ophthalmological. It is noteworthy that the venous drainage pattern is closely related to clinical manifestations and potential therapeutic modalities. When venous drainage diverts anteriorly into the SOV, it causes ophthalmological symptoms such as chemosis, proptosis, and intolerable diplopia.2 Alternatively, drainage into the superior petrosal sinus or the IPS can cause pulsatile tinnitus. CS-DAVF may manifest as headache, non-hemorrhagic neurological deficits, subarachnoid hemorrhage, or intracranial hemorrhage due to cortical venous reflux. Moreover, DAVF patients with non-hemorrhagic neurological deficits caused by cortical venous drainage have a higher risk of hemorrhage than asymptomatic DAVF patients.6 Therefore, timely interventional treatment is imperative for patients with CS-DAVF with intractable ocular symptoms.

This study found favorable results for transfemoral vein-SOV embolization in patients with CS-DAVF with IPS occlusion. Choosing the SOV route is appropriate based on the venous drainage characteristics. Our experience indicates that early opacification of the SOV during cerebral angiography inevitably signifies the fistula shunt point at the confluence of the SOV and CS. In this scenario, it is not necessary to fully pack the CS from the posterior section to the junction of the SOV. It is also worth noting that the microcatheter and microguidewire can be advanced into the CS even if the IPS is not visualized during angiography.3 When access to the SOV via the FV fails due to tortuosity or stenosis, direct puncture via a transorbital approach of the SOV can be considered a viable treatment option.4 7

Leveraging this anatomical feature enabled us to achieve precise embolization, thereby preventing CS-related symptoms that may result from overpacking. Cranial nerve palsy is the most common complication associated with CS-DAVF endovascular embolization. Several factors may contribute to cranial nerve palsy, including the mass effect of the coils and Onyx, direct toxic effects of dimethyl sulfoxide, and direct axonometric injury.8–10 In the present study, two patients experienced transient third cranial nerve palsy and one patient had transient sixth cranial nerve palsy, although all symptoms resolved within 1 month following endovascular treatment. The incidence was significantly lower than those observed with complete CS embolization via the IPS route.3 10 Moreover, minimal amounts of coils and Onyx were utilized, averaging 1.2 coils and 1.8 mL Onyx per patient. Similarly, Fujita et al reported that transvenous embolization via the SOV significantly reduces the total number of coils in patients with CS-DAVF.11 We prefer embolization with Onyx and detachable coils together when conditions permit. In our opinion, the detachable coils could provide structural support for Onyx, often referred to as a ‘reinforced concrete structure’. It may also help us to control the Onyx within the intended target range (shunt point), allowing us to achieve precise embolization and avoid complications such as pulmonary embolism caused by Onyx escape. Additionally, we showed an excellent immediate postoperative complete embolization rate compared with other routes,3 12 which benefited from the precise positioning of the shunt point via the SOV route.

Furthermore, the operation time was not significantly increased compared with other approaches. Notably, the junction of the angular vein and SOV often presents a sharp tortuous angulation. Improper manipulation may lead to rupture of the SOV and intraorbital hemorrhage, potentially resulting in vision loss in severe cases. We recommend using the ‘wire-loop’ skill to advance the microcatheter and microguidewire through the abrupt angle. Importantly, none of the patients experienced intraoperative SOV bleeding or embolism. All patients in this study had significant SOV dilation, which facilitated the passage of the microcatheter. It is vital to evaluate the relationship among the SOV, frontal vein, supraorbital vein, and superior temporal vein to choose the most suitable approach based on intraoperative conditions.

In summary, we consider that the transient nerve palsies may be attributed to the mass effect of the embolic materials. This underscores the importance of precise embolization confined to the specific compartment of the CS involved in the fistula rather than the entire CS. Striking a balance between achieving complete obliteration and avoiding fistula overpacking is critical to ensure that the shunting point is adequately sealed without negatively affecting neurological function. This is why we strongly advocate the ‘an eye for an eye’ treatment strategy, focusing on addressing CS-DAVF-associated ophthalmological symptoms through the SOV route.

This study also revealed an anatomical variation quite different from textbook structures, as 76.7% (23/30) of patients had an FV that drained into the EJV. According to classic vascular anatomy, the SOV is connected to the angular vein, which continues as the FV. Typically, the FV descends obliquely in a straight line to maintain the common FV and drains into the IJV. Studies conducted in India by Choudhry et al 13 and Gupta et al 14 reported that 5% and 9% of the FVs drained into the EJV, respectively. Furthermore, Fujita et al found that 20% (2/10) of Japanese patients had FVs that drained into the EJV during CS-DAVF embolization via the transfemoral trans-FV-SOV route.11 Luo et al also indicated that 62% of patients from Taiwan and China had FVs that drained into the EJV.15 Thus, there may be racial/ethnic differences in the anatomical variations of the FV. Unlike in Europe and North America, where cases of transverse-sigmoid sinus DAVF are predominantly detected, a higher number of CS fistulas cases have been detected in Japan, indicating racial differences in the presentation of DAVF.16 Hence, the anatomical variation in the FV is an interesting finding. Whether such variations may partly contribute to the high incidence of CS-DAVF in Asian individuals needs further exploration.