Dural arteriovenous fistulas (DAVFs) are vascular malformations that can present aggressively. Venous hypertension is the pathophysiologic mechanism thought to be responsible for aggressive presentation. 4D flow MRI has demonstrated success generating pressure maps from velocity data in vessels. In this work we measure relative pressure in the dural sinuses in DAVFs patients using 4D flow MRI. Results support the hypothesis that DAVFs result in venous hypertension which may be the mechanism ultimately leading to aggressive presentation. 4D flow MRI allows blood flow directionality assessment along the dural sinuses, which helps to detect retrograde flow and classify the severity of DAVFs.