Preliminary study on the hemodynamics of Cognard type IV dural arteriovenous fistulas with venous aneurysm

Objective To explore the hemodynamic features of venous aneurysms in Cognard type Ⅳ dural arteriovenous fistulas (DAVF). Methods Computational fluid dynamics analysis was conducted in 7 venous aneurysms of 4 patients who received endovascular treatment at Department of Neurosurgery, Beijing Tsinghua Changgung Hospital between July 2017 and December 2017. All 4 patients experienced no intracranial bleeding before intervention. Results Average flow velocity was 0.030 (0.002-1.567) m/s in the 7 aneurysms and 0.092 (0.050-2.235) m/s in drainage veins. The difference was not statistically significant (P=0.248). Average pressures in fistula area, venous aneurysm and drainage veins were 7 394.9(6 087.3-7 977.0) Pa, 4 882.2 (3 697.8-7 004.7) Pa and 3 439.1 (3 337.2-5 612.9) Pa, respectively. Median values of average wall shear stress (WSS) were 10.22 (4.07-13.58) Pa in fistula area, 4.11 (0.24-13.95) Pa in venous aneurysms and 7.61 (5.16-12.90) Pa in drainage veins. On the draining system, average pressure in venous aneurysms were higher when compared with drainage veins, but the difference was not significant in statistics (W=39, P=0.072), however, average WSS were significantly lower in venous aneurysms (W=8, P=0.040). For the 2 cases with multiple venous aneurysms, high WSS area was identified in the inflow area of subsequent venous aneurysms. Conclusion Preliminary results have indicated that WSS of venous aneurysms is lower compared with drainage veins, and high WSS area is present on drainage veins distal to the venous aneurysm. The relationship between WSS and venous aneurysm rupture requires further validation in future studies. Key words: Arteriovenous fistula; Hemodynamics; Dural; Venous aneurysms