The flow within the draining vein or venous sinus is anterograde. Type Ia – simple dural arteriovenous fistulas have a single meningeal arterial supply
Type Ib – more complex arteriovenous fistulas are supplied by multiple meningeal arteriesThe distinction between Types Ia and Ib is somewhat specious as there is a rich system of meningeal arterial collaterals. Type I dural fistulas are often asymptomatic, do not have a high risk of bleeding and do not necessarily need to be treated. Type II
The high pressure within a Type II dural AV fistula causes blood to flow in a retrograde fashion into subarachnoid veins which normally drain into the sinus. Typically this is because the sinus has outflow obstruction. Such draining veins form venous varices or aneurysms which can bleed. Type II fistulas need to be treated to prevent hemorrhage. The treatment may involve embolization of the draining sinus as well as clipping or embolization of the draining veins. Type III
Type III dural AV fistulas drain directly into subarachnoid veins. These veins can form aneurysms and bleed. Type III dural fistulas need to be treated to prevent hemorrhage. Treatment can be as simple as clipping the draining vein at the site of the dural sinus. If treatment involves embolization, it will only typically be effective if the glue traverses the actual fistula and enters, at least slightly, the draining vein.The Cognard et al. Classification correlates venous drainage patterns with increasingly aggressive neurological clinical course.
To simplify the above systems of DAVF classification, the two main factors that should be considered to determine aggressiveness of these lesions are: 

DAVF that have bleed (as opposed to those that have not before)
DAVF resulting in cortical venous refluxTreatment decisions are more complicated and require consultation with a neurosurgeon and team familiar with these lesions. Treatment
Indications
Hemorrhage
Neurologic dysfunction or refractory symptoms

Interventions
Embolization
One approach used for treatment is embolization. A six-vessel angiogram is employed to determine the vascular supply to the fistula. Detachable coils, liquid embolic agents like NBCA, and onyx, or combinations of both are injected into the blood vessel to occlude the DAVF. Preoperative embolization can also be used to supplement surgery. Surgery
DAVFs are also managed surgically. The operative approach varies depending on the location of the lesion. Stereotactic radiosurgery
Stereotactic radiosurgery is used for obliterating DAVFs sometimes in conjunction with embolization or surgery, and is considered an important adjunct and sometimes a primary treatment method for non-aggressive DAVFs. Use of this method, however, is limited as obliteration occurs over the course of up to 2–3 years after the delivery of radiation. Epidemiology
10–15% of intracranial AV malformations are DAVFs. There is a higher preponderance in females (61–66%), and typically patients are in their fourth or fifth generation of life. DAVFs are rarer in children. Research
External Manual Carotid Compression is Effective in Patients with Cavernous Sinus Dural Arteriovenous Fistulaetreatment.