As with most vascular lesions, DAVFs are not typically visible by non-contrasted computed tomography (CT). In patients with a high clinical suspicion, the following features might be noted:

Due to the high-flow nature of DAVF and the fact that they are commonly located near bone, the location of the fistulous connection is not generally visualized by CT angiography. Nevertheless, CT angiography can often identify some of the associated findings of the fistula including:

DAVFs are typically not well seen on magnetic resonance imaging (MRI). As with CT/CT angiography, MRI may identify dilated veins resulting from venous hypertension. In some cases, venous hypertension may cause focal areas of hyperintensity on T2 and FLAIR sequences. Dilated cortical veins may appear as flow voids within the cortical sulci but lack a true nidus within the brain parenchyma as would be found in a cortical AVM.

Time-of-flight MR angiography, unlike CT angiography, is sensitive to the direction of blood flow. In some cases this will allow visualization of flow reversal in a dural sinus. As with other noninvasive imaging techniques, however, MR angiography often does not provide enough detail to aid in treatment planning.

Catheter Angiography is the gold standard for the identification and staging of DAVF. In most cases, selective, bilateral injections the ECAs and ICAs as well as the VA should be performed to identify all of the arterial feeders. Often the fistula will have multiple feeders that supply a relatively short segment of the involved dural sinus. Retrograde flow from the arterialized sinus into the cortical veins (cortical venous reflux) is evidence of a hemodynamically significant change in local parenchymal venous drainage and has been associated with a more malignant natural history, including a higher rate of intracranial hemorrhage. The goals of catheter angiography include:

Various classification methods have been adopted that attempt to explain the significance of the angiographic anatomy, namely, the pattern of venous drainage. The commonly used classifications are the Borden and Cognard classifications.

The Borden classification system is used to classify DAVF according to the patency of the affected dural sinus and the presence or absence of cortical venous reflux [4]. This classification system was initially proposed as a guide to help describe DAVF according to anatomical and physiological parameters and by doing so help in selecting the best surgical and/or endovascular approach. Later case series [5] confirmed that the Borden grade also correlates with the risk of intracranial hemorrhage or nonvisual neurological deficit. A summary of this classification system is presented in Table 13.2.

The Cognard classification system is more detailed (Table 13.3) and elaborates on the direction of flow, whether normal (antegrade) or retrograde, and the presence or absence of cortical venous retrograde drainage. In addition, spinal perimedullary venous drainage is recognized [6].

Pial AVFs (PAVFs) arise from the arterial supply to the pia or cortex, and the abnormality does not lie with the dural leaflets. These rare lesions disproportionately affect pediatric patients and young adults. They present with similar symptoms and signs to DVAF, but intraparenchymal hemorrhage may be more common than subdural hemorrhages. The venous drainage is also cortical, and there may be an associate varix. Treatment modalities are similar to DAVF, but the more simple angioarchitecture makes transarterial embolization or surgical disconnection more feasible [7].

Arteriovenous malformations (AVMs) are distinguished from DAVF by the cobweb of fragile connecting blood vessels between the arterial input and the venous output present in the AVM. This network is known as the nidus (see Chap. 12).

The transverse-sigmoid sinus is the most common location for cranial DAVF. These lesions are often Borden type 1 and therefore have a benign natural history. Treatment is only to alleviate symptoms such as pulsatile tinnitus. Lesions with high-risk features such as cortical venous reflux, however, should be treated.

Selection of the treatment strategy involves weighing several different factors including the significance of the patient’s symptoms and their demand for treatment, as well as careful analysis of the angiogram. The angiogram may show that the affected sinus does not participate in normal venous drainage. In such cases venous occlusion has been shown to be effective and safe. Compartments of a sinus may be involved by the fistula, while others are free so that selective occlusion can be achieved while keeping the normal venous pathway patent [11]. When the targeted sinus is participating in normal cerebral drainage, cure by endovascular means is difficult, because in such cases the patent dural sinus is still a normal pathway for venous drainage, and its occlusion may risk a venous infarction. Palliative arterial embolization may thus be used for symptomatic relief. Arterial supply to fistulae of this region typically includes the petrous and petrosquamosal divisions of the middle meningeal artery, lateral division of the meningohypophyseal trunk off the ICA, transosseous branches of the posterior auricular artery, ascending pharyngeal artery, transosseous branches of the occipital artery, posterior meningeal arteries, and artery of the falx cerebelli.

In a large series of DAVFs of the transverse and sigmoid sinuses in 150 patients [12], the occlusion rate of transarterial embolization alone was 30 %, and multiple procedures were often required. Ideally, transarterial embolization with permanent liquid material (as Onyx) that closes only the AV shunts within the wall of the sinus is desirable. Some have proposed the use of transvenous balloon protection within the dural sinus to facilitate closure of the DAVF with preservation of the sinus [13]. Treatment of a transverse sinus DAVF by sinus recanalization by angioplasty and stenting together with transarterial embolization has also been reported [14].