<prompt> Answer this question truthfullyWhat are some distinguishing features of dural arteriovenous fistula AVF?  <response>: <reason> Dural arteriovenous fistula AVF is an abnormal connection between an artery and a vein in the dura mater, the outermost layer of the brain and spinal cord. Some characteristics of dural AVF include:- It can be either high flow or low flow, with high flow AVMs being more common.- It is thought to be acquired secondary to dural sinus thrombosis, unlike AVMs which are usually congenital.- Unlike AVMs, there is no nidus or central point of abnormal connection.- It typically presents in the 50s to 60s, while AVMs tend to present in the 20s to 30s.- The classic symptom is pulsatile tinnitus when it involves the sigmoid sinus. It can also cause vision issues if the cavernous sinus is involved.- There is an increased risk of bleeding due to direct cortical venous drainage.- Dural AVF can be occult on MRIMRA, so catheter angiography may be necessary if suspicion is high.- Interestingly, spinal AVFs are actually the most common type of AVF.- A helpful hint for diagnosis is a clinical history of gradual onset lower extremity weakness. 