A total of 23 cases of DAVFs in the falx cerebri including our cases has been reported (Tables 1 and 2), 21 of which had detailed baseline information and treatment-related information.5–17 The average age of the patients was 52.8 ± 12.9 (range, 24–73), and 81.8% (18/22) were men. Eight patients presented with intracranial hemorrhage or subarachnoid hemorrhage (36.4%, 8/22). All of DAVFs are classified as high-grade types and often accompanied with venous pouch. DAVFs in the falcine sinus/venous plexus can be categorized as lateral epidural DAVFs.12,13,22 They exhibit a severe clinical course, cortical venous reflux, and lack evidence of venous outflow obstruction, resembling anterior cranial base DAVFs.3,22 DAVFs in the falx cerebri often receive arterial supply from the dural or pial branches of the ACA (34.8%, 8/23). Yoshioka et al. reported the only case in which the drainage vein of these DAVFs was identical to the falcine sinus/falcine venous plexus, but some cases could be judged to have falcine sinuses as part of their drainers.12,13,15
Anatomic considerations
The falcine sinus is a vascular structure that forms during embryonic development, connecting the SSS and ISS, typically closing after birth.23 Yoshioka et al. reported a case of DAVF in the falx cerebri associated with the anterior falcine sinus.12 Instances of persistent falcine sinus have been documented, while the persistence of the anterior falcine sinus is rare. The anterior falcine sinus establishes a connection between the SSS and ISS, offering an alternate pathway for venous drainage from the frontal lobes of the brain.24 The falcine sinus may potentially act as a venous plexus.25,26 It plays an important role in the vascular network that surrounds the falx cerebri and eventually transforms into the falcine sinus.12,25–27 In the study by Yoshioka et al., observations during surgery and examination of the surgical sample showed a minor vascular structure within the falx cerebri connecting to the falcine sinus and ISS, likely indicative of a falcine venous plexus.12 Satoh et al. described a rare case of DAVF in flax with a prominent falcine venous plexus that drained into a dilated corticle vein and was successfully treated with TAE.15 However, Yang et al. failed to identify the falcine sinus in both the DSA and the surgical field.16 The venous drainage converged in a venous pouch before entering the left frontoparietal leptomeningeal venous and, finally, the SSS.16 In our case, due to the lack of surgical specimens, we had to rely solely on literature to determine the presence of the falcine sinus/venous plexus from DSA (Figs. 1 and 2).
A persistent falcine sinus is a rare occurrence often observed in pediatric patients, frequently found alongside various anomalies. These anomalies may involve a bifid cranium, vein of Galen aneurysmal malformation, agenesis of the corpus callosum, Apert syndrome, osteogenesis imperfecta, as well as Chiari malformation Type II.23 It is essential to differentiate between the rare persistent fetal falcine sinus and the falcine venous plexus. The sinus originates from mesenchyme in the mesencephalic flexure, where the straight sinus also forms. In cases where the straight sinus is absent or underdeveloped, the persistent falcine sinus may be recanalized.27,28 The presence of a persistent falcine sinus without any accompanying anomalies is exceedingly rare.26 The type of falcine venous plexus/falcine sinus observed in reported DAVF should not be considered a vascular anomaly, but consider that an embryonic vessel structure may become obvious with this abnormal circulation.12,26
Treatment outcomes
Based on literature reviews and our case series, DAVFs in this location are easily treated with a low rate of complications and recurrence (Tables 1 and 2; Figs. 1 and 2).5–17 In contrast to the majority of the literature, all treated patients in our cases received TAE treatment and achieved the same therapeutic effects, resulting in lower trauma for the patients. Almost all DAVFs in the falx cerebri have straight MMA or occipital artery pathways, making TAE with Onyx to completely occlude the venous side a simple cure. Transvenous embolization is not feasible due to the difficulty in accessing and embolizing the venous side. Therefore, contrary to previous literature findings, with the continuous advancement of endovascular treatment, we consider TAE to be the primary treatment option for this type of DAVF, with direct surgery a secondary option.
In the treatment of falx cerebri DAVF with pial arterial supply, common complications are related to intracranial hemorrhage or ischemic stroke.19,21,29–32 The high risk of hemorrhage may be due to the lack of dural covering around the bridging vein fistula extending into the subdural space. The fragile glomus-like structures may rupture due to increased pressure after arterial embolization restricts venous drainage, similar to the principle observed in arteriovenous malformation embolization, in which feeding arteries rupture if the draining vein is completely occluded first.33,34 The causes of ischemic stroke may be related to the reflux of embolic agents into the pial arteries or postoperative retrograde thrombosis of pial arteries, leading to cerebral ischemia.31 These complications are more likely to occur in DAVFs with pure pial arterial supply.32 Despite the controversy surrounding the treatment strategy for DAVFs with pial artery supply, we prefer to embolize the pure pial branches first, followed by the dural branches.
Extensive removal of the falx cerebri, including the falcine sinus, the abnormal falcine venous plexus, and other draining veins, or complete endovascular obliteration of the entire draining system, is an effective strategy for treating them.12,13
Study Limitations
This study, being a single-center, retrospective analysis, is inherently limited. Some of these limitations include potential self-report bias and the lack of core laboratory adjudication. Furthermore, due to the wide time span covered in the literature review, it may not capture the current treatment status of DAVF in this location. Our case series also lacks surgical specimen, preventing confirmation of the existence of the falcine sinus/venous plexus.