DAVFs are usually solitary, but multiplicity has been reported in about 8 % of cases.

DAVFs occur more common in females (61–66 %).

Usually found adjacent to dural venous sinuses. Most common transverse sinus (63 %) and more in left side (usually at the transverse and sigmoid junction).

The transverse/sigmoid location is the most common and represents more than 50 % of DAVFs.

These fistulas are frequently idiopathic but can be acquired causes like venous thrombosis, trauma, tumor, cranial surgery, sinus infection or meningitis, or association with meningiomas.

Demyelination may be seen around leptomeningeal veins as a result of venous hypertension which can lead to leptomeningeal retrograde drainage and predispose these channels to become varicose and potentially rupture.

DAVFs with retrograde drainage or cortical venous drainage are typically considered to be associated more frequently with ICH, thus warranting more aggressive treatment.

DAVFs located in the posterior fossa are a risk factor for hemorrhage, not the anterior fossa.

Five risk factors for hemorrhage are cortical venous drainage, focal neurological deficits, DAVFs located in the posterior fossa, male sex, and increasing age.

Proptosis (especially pulsatile) is frequent with carotid-cavernous DAVFs.

Pulse-synchronous tinnitus is nearly always exacerbated by a Valsalva maneuver.

Dural sinus hypertension can produce elevated ICP by impeding cerebral venous drainage and by impairing the function of the arachnoid granulations (which can also lead to hydrocephalus).

Change in a bruit (either worsening or disappearance) should prompts restudy.

Pulsatile tinnitus is the most common initial symptom and is frequently associated with high-flow fistulas in the transverse sinus/sigmoid location.

Compression of the carotid artery and jugular vein or occipital artery may result in a reduction in bruit intensity and provide a clue to the diagnosis.

Both MRI and CT can miss DAVF, especially if small or if the DAVF drains into the ipsilateral venous sinus.

Findings on CT are often normal, although it is the most sensitive in evaluating acute subarachnoid, subdural, or intraparenchymal blood.

Injection must include the vertebral and internal and external carotid arteries because DAVF may be overlooked with conventional studies alone.

If conservative treatment is chosen, patients are advised to avoid antiplatelet or anticoagulant agents, if possible, to prevent interference with spontaneous thrombosis of the DAVF.

Borden type I DAVFs have a high rate of spontaneous remission and can be observed, especially since they may spontaneously thrombose, which has been noted with cavernous sinus DAVFs.

Compression therapy is seldom used currently, except in patients with Borden type I fistulas as a possible first step before neuroendovascular therapy.

Compression of the ipsilateral carotid or occipital artery (if the latter vessel is a known feeder to the fistula) is performed for 30 minutes at a time, three times a day. If compression of the carotid artery is chosen, patients are instructed to use the contralateral arm.

In 25 % of simple DAVFs of the transverse/sigmoid sinuses supplied by the occipital artery, compression of the occipital artery results in complete thrombosis of the DAVF within several weeks.

The Borden classification system stratifies lesions on the basis of the site of venous drainage and the presence or absence of cortical venous drainage.

Type I:

Type II:

Type III:

In type III fistulas, the venous sinus may be patent but largely defunctionalized because of high-flow venopathy causing reversal of flow into arterialized leptomeningeal veins.

In type III fistulas, when the sinus is patent, the point of the fistula is located either between the meningeal artery and leptomeningeal vein or between the meningeal artery and a segment of arterialized dural venous sinus that is thrombosed at either end or somehow isolated from the rest of the sinus, thereby causing reversal of drainage into leptomeningeal veins.

Type III with direct cortical venous drainage without venous ectasia

Type II fistulas, in the main sinus, with reflux into the sinus (IIa), cortical veins (IIb), or both (IIa+b)

The Cognard classification is based on angiographic patterns and is generally more applicable to DAVFs involving the transverse sinus.

Extra care is taken to place copious dural tack-up sutures to obliterate the epidural space which is abnormally vascular.

Most DAVFs are better treated endovascularly; however, ethmoidal DAVFs are probably best treated microsurgically.