Drainage into a main sinus with an anterograde flow.

Drainage into the sinus is mediated by the pial veins.

Drainage into the sinus is mediated by the pial veins, which present a large ectasia.

Drainage involves the spinal perimedullary vein.

DAVFs involving the transverse sinus (TS) and sigmoid sinus (SiS) are the most frequent (Halbach et al. 1987; Awad 1993). In many cases, these belong to type 1 and so can be characterized by a benign course. The only symptom is bruit since the fistula is close to the petrous bone, containing the auditory apparatus. In some cases, the bruit can become very loud and intolerable for the patient, necessitating treatment. Some of these fistulas can change (Piton et al. 1984) and become type 2, with a progressively large reflux in the temporal veins, leading to venous congestion. This is particularly the case when a distal or proximal thrombosis of the sinus occurs. In other less common cases, the sinus can be occluded proximally and distally (isolated sinus). The symptoms in such patients can be very severe, characterized by cognitive disorders, epileptic seizures, and other neurological impairments due to venous congestion or hemorrhage (Naito et al. 2001; Bradac et al. 2002; Kiura et al. 2007). The supplying arteries can vary, but commonly branches of the ECA (occipital, ascending pharyngeal artery, middle meningeal artery) are involved uni- or bilaterally. Meningeal branches of the cavernous portion of the ICA and meningeal branches of the VA can also supply the fistula. Endovascular treatment with an arterial or venous approach is commonly the therapy of choice (Figs. 13.2 and 13.3). Surgery is frequently used in cases of an isolated sinus, even if an endovascular approach has been successfully used in some cases (Fig. 13.1). To this group of DAVFs can be included (Fig. 13.12) also those of the torcular herophili (see also tentorial DAVF). These are very rare fistulas belonging commonly to type 2 or 3. The feeders are the MMA and occipital arteries bilaterally, the meningeal branches of the cavernous portion of the ICA, and meningeal branches from the VA uni- or bilaterally. Pial branches of the cerebellar arteries can also be involved. The torcular herophili is frequently thrombosed, with thrombosis extending to the proximal TS uni- or bilaterally and sometimes to the distal superior sagittal sinus (SSS). The venous drainage is rerouted in the straight sinus, vein of Galen, and then in the basal vein and deep cerebral veins. Venous congestion in the cerebral hemispheres and cerebellar hemispheres is frequent. Intracranial hypertension and hemorrhage are frequent. Surgical excision has been the treatment of choice. Endovascular treatment, with selective catheterization of the feeders, followed by injection of acrylic glue or Onyx, and the venous approach through the SiS–TS when at least one TS is patent, followed by placing of coils, is in many cases a valid and successful alternative (Kirsch et al. 2009; Macdonald et al. 2010).

Considering especially the venous way of treatment, a particular aspect which has progressively become evident is the changes involving the sinuses which appear not rarely divided in two or more compartments (Piske et al. 2005). This finding is frequently recognized in fistulae involving TS and SiS. Why this occurs is not known. It has been suggested (Piske et al. 2005) that this could be related to a partial thrombosis of the sinus followed by its recanalization and formation of two or more separated venous channels. An accessory dural sinus separated but communicating with the main sinus can also develop and become the main venous drainage. These possible patterns should be taken into account since they are important in the endovascular treatment of the fistulae in this area (Figs. 13.2 and 13.3).

DAVFs involving the cavernous sinus (CS) are the second-most frequent fistulas (Awad 1993; Cognard et al. 1995). Women are predominantly affected. The fistula can be uni- or bilateral. Also in cases of a unilateral shunt, a bilateral supply may be present. It is common for many feeders to arise from the distal internal maxillary artery (IMA), APhA, MMA, and cavernous portions of the ICA, uni- or bilaterally. More rarely, only branches of the ECA or ICA can be involved (Figs. 13.4 and 13.5). Considering the venous drainage, this can show different patterns. Indeed, as we have described in Sects. 2.​3 and 9.​3.​10, the involved network of veins running in “the space of the cavernous sinus” can have and develop different connections depending on their location. Since the anterior part is connected with the superior ophthalmic vein (SOV) and inferior ophthalmic vein (IOV), a fistula in this sector will create a drainage to these vessels. It should be noted that the IOV connects with the pterygoid plexus. A fistula posteriorly located will be characterized by a drainage into the inferior petrosal sinus (IPS) and superior petrosal sinus (SPS) since this posterior location communicates with these venous channels (Cheng et al. 1999; Agid et al. 2004). Such a situation can occur when the two compartments do not communicate to each other or the links are minimal. A dominant drainage can also occur when one of the routes (ophthalmic veins or IPS, Fig. 13.4) is occluded by thrombosis, which leads to a rerouting of the drainage. In other cases, the two compartments probably are largely in communication, and so both draining patterns are present. Since the CSs are connected by a large intercavernous anastomotic channel, the contralateral sinus can also be involved.

More infrequently, retrograde injection of the pial veins can occur through the several connections linking the plexus in the CS with the pial veins (Fig. 13.6). The possible involvement of the pial veins is as follows:

A type of fistula, which is very rare, is that developing in the middle cranial fossa with involvement of the venous channels present in this area, but not the CS. The venous pattern can take different aspects, depending on the variants of the drainage of the sphenoparietal sinus (SpS), SMCV, and SOV, as described in Sects. 9.​1.​1.​2, 9.​3.​9, and 9.​3.​11. An example is presented in Fig. 13.7a, b. The fistula involved the paracavernous sinus and further the SpS and the SOV, mimicking clinically a CS fistula. A few cases of this kind of fistula, frequently traumatic, are reported in the literature (Pakarinnen 1965; Theron et al. 1975; Bradac et al. 1981b; Freckmann et al. 1981; Unterhofer et al. 2009; Shi et al. 2013). Another example is shown in Fig. 13.7c–e. This was spontaneous fistula involving the SpS in its course on the floor of the middle cranial fossa continuing in its tentorial drainage which was thrombosed. There was a retrograde injection into a dilated SMCV.

DAVFs of the SSS are less frequent. They can be of type 1, but it is not seldom for them to be of types 2 and 3 (Figs. 13.8 and 13.9). In type 2, the venous reflux can be extensive and involve a large part of the cortical veins of the hemisphere. In type 3, the drainage in the sinus is mediated by dilated cortical veins, which enter the sinus after a fairly long, tortuous course. Branches of the ECA, mainly the MMA, are commonly involved, frequently bilaterally. Transosseous branches of the superficial temporal artery and occipital artery can be present. The anterior meningeal artery, arising from the ophthalmic artery, and the meningeal branches of the VA may sometimes supply the shunt. Epileptic seizures, hemorrhage, and/or signs of intracranial hypertension, such as headache and cognitive disorders, can be present (Halbach et al. 1988; Riva et al. 1991). Surgical disconnection of the shunt or selective embolization with acrylic glue (Collice et al. 2000; Van Dijk et al. 2004; Rodesch et al. 2009) may be effective treatments.