Computed Tomography and Magnetic Resonance

In cases of DAVF without CVR, computed tomography and magnetic resonance imaging (MRI) of the brain parenchyma are typically normal. However, MRI and magnetic resonance angiography may show the stenosis or occlusion of the dural sinuses.⁷ Hydrocephalus may be seen in any DAVF that causes venous hypertension in the superior sagittal sinus. In cases of DAVF with CVR, computed tomography and MRI of the brain may show ICH, engorged pial vessels, and diffuse white matter edema secondary to venous congestion. The ICH is usually intraparenchymal but may also have subdural, subarachnoid, or intraventricular components (see Fig. 80-2). The pattern of hemorrhage is not specific to DAVFs, and a high index of suspicion is required. Dilated pial vessels and white matter edema are more likely to be seen on MRI than on computed tomography.⁷ On T2-weighted MRI, dilated pial vessels are seen as flow voids on the surface of the brain, and diffuse white matter edema is seen as hyperintensity in the cerebral or cerebellar hemispheres, brain stem, or spinal cord (Fig. 80-3). Recent reports have demonstrated improvements in the ability of magnetic resonance angiography to diagnose DAVFs and to detect CVR.²⁷ However, these results have been reported in small selected series and require further study. At present, the diagnosis of DAVFs cannot be excluded with negative computed tomography, MRI, or magnetic resonance angiography. If clinically suspected, catheter angiography is required to confirm or exclude the presence of a DAVF.

FIGURE 80-3 A 67-year-old woman presented with severe headache and subsequent deterioration in conscious level. Computed tomography scan showed a right cerebellar hematoma that was evacuated. A, Axial T2-weighted magnetic resonance imaging (MRI) shows a central area of hyperintensity in the right cerebellar hemisphere. Tortuous dilated vessels appearing as flow voids in the right cerebellar hemisphere indicate the presence of cortical venous reflux. B, Axial gadolinium-enhanced T1-weighted MRI shows peripheral enhancement surrounding the hyperintense region seen on the T2-weighted image. C, Left vertebral artery angiogram, lateral projection DAVF with ectasia (arrowheads) fed by dural branch of vertebral artery (arrow). D, Right external carotid artery (ECA) angiogram, lateral projection, same ectasia (arrowheads) fed by posterior branch of middle meningeal artery (arrow).E, Show a torcular dural arteriovenous fistula (DAVF), fed by branches of the left vertebral artery (arrow), and right and left middle meningeal arteries (arrowheads). The fistula drains into a cortical vein (curved arrows), with a varix (open curved arrow), making this a Borden type III/Cognard type IV DAVF. F, The venous phase of the angiogram demonstrates tortuous, dilated pial veins, referred to as a pseudophlebitic pattern. This fistula was successfully cured by transarterial embolization.

Intra-arterial Catheter Angiography

This is the gold standard method for diagnosis and evaluation of DAVFs. The characteristic angiographic feature of DAVFs is premature visualization of intracranial veins or venous sinuses during the arterial phase (see Fig. 80-3C; Fig. 80-4A).²⁸ This is caused by shunting of arterial blood into the venous system through the fistula. To obtain the necessary information regarding the arterial supply and venous drainage of the DAVF and the venous drainage of the brain, imaging must start in the ultraearly arterial phase and be carried well into the late venous phase. Selective angiography with magnification and subtraction techniques is essential. The study should include injections of both internal carotid arteries (ICAs), both external carotid arteries (ECAs), and both vertebral arteries. This is because a single DAVF may have multiple feeding arteries (see Figs. 80-3 and 80-4) and also because 8% of patients have multiple DAVFs.²⁹ Detailed knowledge of dural arterial anatomy is essential in angiographic evaluation of DAVFs. Meningeal arteries that are invisible or difficult to see on normal angiograms may be dilated and clearly visible when supplying a DAVF. For example, the tentorial branch of the meningohypophyseal trunk of the ICA (the artery of Bernasconi and Cassinari) or the meningeal branch of the posterior cerebral artery (the artery of Davidoff and Schecter) may be dilated and easily seen on the angiograms (see Fig. 80-3C).

FIGURE 80-4 Angiograms of a 52-year-old woman who presented with pulsatile tinnitus and audible bruit behind the right ear. A, Right external carotid artery angiogram, lateral projection shows premature appearance of the sigmoid sinus (arrowheads) in the ultraearly arterial phase of the angiogram. A transverse sinus dural arteriovenous fistula (DAVF) is shown, fed by the posterior branch of the right middle meningeal artery (arrow) and draining antegradely into the transverse/sigmoid sinus (arrowheads) without any cortical venous reflux (CVR) (Borden type I, Cognard type I). The same DAVF is shown in Figure 80-1A being fed also by the right occipital artery. B, Right internal carotid artery angiogram, lateral projection, revealed a hypertrophied artery of Bernasconi and Cassinari, also supplying the DAVF (arrow). As there was no CVR, the patient was managed with observation alone.

The nidus of a DAVF is the site of arteriovenous shunting and refers to that part of the dura where there is convergence of all feeding arteries and the origin of venous draining channels. The best views of the nidus are often obtained during the ultraearly arterial phase of the angiogram and by injections of distant arterial feeders.²⁸ Images obtained when injecting the main arterial feeders, particularly in the later arterial phase or in the venous phase, are often obscured by engorged feeding arteries and draining veins.

Assessment of the venous drainage pattern of DAVFs is extremely important as this factor determines the natural history of the lesion and aids in selecting the most appropriate management strategy. The presence or absence of CVR, venous sinus occlusion, direction of flow in the venous sinuses, and the venous drainage pattern of the brain must be determined. The exact site of CVR must be determined to allow treatment planning.⁷ At angiography, a delayed circulation time is compatible with venous congestion.³⁰ Focal areas of delayed venous drainage in the brain correspond to the site of CVR.⁷ In some cases, tortuous, dilated pial veins may be seen that develop as a result of venous hypertension (see Fig. 80-3F). Willinsky and colleagues³⁰ have described this finding as the pseudophlebitic pattern, which is a sign of venous congestion of the brain and may be associated with an aggressive natural history.⁷

Dural Arteriovenous Fistulas with Cortical Venous Reflux

Of 236 cranial DAVFs, 119 had CVR (Borden classification type II or III and Cognard classification type IIb, IIa + b, III, or IV). Of these, 96 patients successfully underwent curative treatment, and three patients were lost to follow-up. Van Dijk and colleagues²⁰ followed the remaining 20 patients with persistent CVR (14 patients who refused treatment and 6 who had partial treatment only) for a mean follow-up period of 4.3 years (86.9 patient-years). In these 20 patients, the annual risks of ICH and NHND (disregarding aggressive events at presentation) were found to be 8.1% and 6.9%, respectively, adding up to an annual event rate (i.e., ICH and NHND) of 15%. The annual mortality rate was 10.4%. These results demonstrate that DAVFs with CVR have an aggressive natural history.

Dural Arteriovenous Fistulas without Cortical Venous Reflux

Of the 236 cranial DAVFs, 117 had no CVR (Borden type I, Cognard type I or IIa). Five patients were lost to follow-up. The remaining 112 patients were followed up clinically for a median of 27.9 months (range, 1 month to 17.5 years), amounting to 348 patient-years. Of these, 68 underwent observation alone, and 44 underwent palliative treatment for symptomatic control (43 endovascular, 1 surgery). Palliative treatment, never aimed at cure, was performed if the patient had intolerable symptoms or if there was persistent high intraocular pressure or decreasing visual acuity. Using this conservative management strategy, 98% of patients had a benign and well-tolerated clinical course, without any ICH or NHND.³ Long-term angiographic follow-up in 50 patients showed that DAVFs without CVR have a 2% to 3% risk of developing CVR.³

Observation

DAVFs without CVR usually behave in a benign manner and are rarely associated with hemorrhage or neurologic deficit. Therefore, observation is the most appropriate management option for these patients if they are asymptomatic or are tolerating their symptoms.^4,7 As they have a 2% to 3% chance of developing CVR, all patients should be followed up clinically and radiographically. Any change in symptoms (worsening or improvement) may be a warning signal for development of CVR and should prompt repeat cerebral angiography.^3,7 In patients with a stable clinical condition, serial MRI and magnetic resonance angiography and a conventional angiogram after 3 years is advised.⁷ Observation is not a valid treatment option for DAVFs with CVR.

Compression Therapy

Intermittent manual carotid compression by the patient has been used by Halbach and colleagues,^8,31 to treat DAVFs of the cavernous sinus in patients with no evidence of carotid atherosclerosis. The patient is instructed to compress the carotid-jugular area ipsilateral to the DAVF, with the contralateral hand for as long as 30 minutes per session. The compression should be terminated if any weakness develops.⁸ Halbach and colleagues^8,31 reported a cure rate of 27% with this technique after 4 to 6 weeks. However, this treatment has been the subject of debate because the 27% cure rate in the short term may reflect the natural history of the disease.⁷

Transarterial Embolization

Superselective embolization of the dural feeding vessels to a DAVF can be an effective treatment in some cases.⁸ The ideal goal is to cure the DAVF by occluding the fistula itself. To achieve this from the arterial side, a microcatheter must be navigated into the distal part of a feeding artery and wedged, so that cyanoacrylate glue can be pushed through the nidus and into the most proximal venous outlet. This is essentially a venous treatment performed through the arterial side. Liquid adhesive agents (e.g., n-butyl cyanoacrylate), the rate of polymerization of which can be controlled, are the best agents to permanently occlude a fistula.⁷ Successful occlusion of the fistula using this technique has been reported in a small number of patients.^7,32

In most cases, transarterial embolization involves occlusion of the feeding arteries without occlusion of the fistula. This may decrease flow through the fistula but is rarely curative because most DAVFs have multiple small feeding arteries that are not amenable to transarterial embolization. Furthermore, in most cases, the lesion will continue to recruit feeding arteries from other sources, leading to recurrence.^8,32 Transarterial embolization is commonly used as an adjunct before surgical treatment or transvenous embolization of DAVFs. It is also used as palliative treatment for benign DAVFs with intolerable symptoms. Preoperative embolization of large feeding arteries, particularly in the external carotid territory, carries a relatively low risk and helps to reduce intraoperative blood loss. Particles (e.g., polyvinyl alcohol) may be used for this purpose.⁷

Endovascular therapy is not without risk. Knowledge of the important anastomoses between the external carotid, internal carotid, and vertebrobasilar systems is crucial for safe embolization.³³ Embolic agents can inadvertently travel through these anastomoses and lead to occlusion of important branches. Embolization of feeding arteries that arise directly from the ICA or vertebral artery may lead to reflux of embolic material into the parent artery and result in stroke. In the case of benign DAVFs, it is important to ensure that the embolic material does not flow past the fistula site and obstruct venous outflow. If this occurs, venous drainage may be diverted to cortical veins, thereby converting a benign fistula to an aggressive one.

Transvenous Embolization

Transvenous embolization is increasingly used in the management of cranial DAVFs.^34,35 This involves a retrograde approach through the veins with deposition of materials such as coils into the venous compartment at the fistula site. Usually the transfemoral route is employed. In the majority of cases, transvenous embolization involves sacrificing the involved dural venous sinus. This can only be performed if detailed study of the venous phase of the cerebral angiogram has shown that the involved dural sinus is not being used by the brain and that alternate pathways for venous drainage of the brain have developed.⁷ In some cases it may be possible to use a retrograde transvenous approach to disconnect CVR without sacrificing the dural sinus. However, in most cases this is not possible because of the difficulty in access to the refluxing cortical veins and the tortuosity of these veins.

In some cases of transverse/sigmoid sinus DAVFs, the lesion may be draining into a venous pouch, parallel to and separate from the transverse sinus. The University of California-San Francisco interventional neuroradiology group have reported 10 such cases and named this entity the parallel venous channel. In their series, transvenous embolization was used to occlude the parallel venous channel and cure the fistula in all 10 cases while preserving the transverse/sigmoid sinus.³⁶ Identification of this separate venous channel is important as it may allow curative treatment of the fistula without sacrificing the transverse sinus. However, this type of channel has been identified in a small number of cases only.

The mainstay of transvenous embolization is occlusion of the affected venous sinus. Neurologic complications after embolization occur if outflow to normally draining veins is obstructed, resulting in venous hypertension and venous infarction. After embolization of cavernous sinus DAVFs, paradoxical worsening of ophthalmologic symptoms may develop secondary to excessive thrombosis and venous hypertension involving the ophthalmic veins. Other complications include guidewire injury to the wall of dural sinuses resulting in subarachnoid hemorrhage and injury to cranial nerves.³⁴

Surgery

Although endovascular therapy is increasingly used to treat intracranial DAVFs, surgery still plays an important role in the management of these lesions. We recommend surgery for DAVFs with CVR when endovascular therapy fails or is technically not feasible. Three different surgical strategies exist for treatment of intracranial DAVFs. The first is to obtain venous access for direct packing of the involved dural venous sinus. The second is complete excision of the DAVF. The third is to disconnect the arterialized leptomeningeal veins (CVR) only, without attempting to excise the entire lesion. These strategies are discussed in the following sections.

Disconnection of Cortical Venous Reflux Alone

The goal of treatment for aggressive DAVFs is to eliminate the risk of ICH and neurologic deficit. Because CVR is the predisposing factor for aggressive natural history, it has been suggested that a procedure limited to disconnection of arterialized leptomeningeal veins (CVR) is sufficient in the treatment of aggressive lesions and that complete excision of the involved dural leaflet and the venous sinus is not necessary.^7,40–42 Disconnection of CVR is a simpler procedure with less morbidity and changes the natural history of the lesion from aggressive to benign. There are now several reports showing that this technique is effective, and we now use it in preference to complete excision in most cases.⁴³

The surgical procedure involves exposure of the pathologic dural leaflet as explained previously. Any dural feeding arteries are coagulated or occluded with hemostatic clips. The dura is then opened, and with careful dissection, the arterialized leptomeningeal veins are exposed. These veins are then coagulated or clipped and divided at their entrance into the dural venous sinus or as close to the fistula site as possible. It is important to ensure that the vein is adequately coagulated before division. The adjacent dural areas should be examined to ensure that all arterialized leptomeningeal veins have been disconnected. “Blue” nonarterialized cortical veins should be preserved. The dura is then closed, the bone flap replaced, and the wound closed in the usual manner.

Stereotactic Radiosurgery

There is a limited number of reports on the radiosurgical treatment of intracranial DAVFs.^44–49 Pan and colleagues⁴⁷ reported complete angiographic resolution of the nidus in 47% of 19 transverse/sigmoid sinus DAVFs, after a median follow-up of 19 months. Pollock and colleagues^45,46 have used a combination of stereotactic radiosurgery and transarterial embolization. Although radiosurgery is effective in obliterating some DAVFs, its main disadvantage is the long interval between treatment and the expected therapeutic effects. In patients with CVR, this delay is not acceptable because of the high risk of ICH and neurologic deficit (15% per year) while waiting for obliteration of the lesion.^7,20,42 In patients without CVR, curative treatment is not required because of the benign natural history of these lesions. Most of these patients can be managed by observation alone or by palliative transarterial embolization. The risk of radiosurgery in these patients may not be acceptable, especially in view of the limited data available on the efficacy of this treatment.^3,7 Therefore, the role of radiosurgery in the management of intracranial DAVFs is currently unclear.

Dural Arteriovenous Fistulas without Cortical Venous Reflux (Benign Fistulas: Borden Type I, Cognard Types I and IIa)

For patients with DAVFs without CVR who are asymptomatic or have tolerable symptoms, observation is the most appropriate treatment option.^4,7 If the patient has intolerable symptoms, such as tinnitus or ophthalmologic symptoms, treatment may be indicated. In these cases, curative treatment is not necessary as the patient is not at risk of ICH or neurologic deficit. Palliative treatment in the form of transarterial embolization of the feeding arteries is usually effective in symptom control and is associated with fewer complications compared with curative transvenous embolization or surgery. All patients should be followed up clinically and radiographically, and any change in symptoms (deterioration or improvement) should prompt repeat conventional angiography to look for development of CVR (Fig. 80-5).

FIGURE 80-5 Management strategy for dural arteriovenous fistulas without cortical venous reflux (CVR) (benign dural arteriovenous fistulas, Borden type I and Cognard types I and IIa). MRA, magnetic resonance angiography; MRI, magnetic resonance imaging.

Dural Arteriovenous Fistulas with Cortical Venous Reflux (Aggressive Fistulas: Borden Types II and III, Cognard Types IIb through V)

These lesions must be treated aggressively because they are associated with a 15% annual risk of hemorrhage and neurologic deficit.²⁰ Treatment should be performed soon after the diagnosis has been made.⁴ There is evidence that rebleeding may occur early after an initial hemorrhagic presentation. In one series, 35% of patients had a rebleed within 2 weeks after the first hemorrhage.⁵⁰ Complete obliteration of the fistula is ideal but not critical because there is increasing evidence that disconnection of CVR alone results in long-term protection against hemorrhage and neurologic deficit.^4,40–43,51

Treatment of cranial DAVFs with CVR requires a multidisciplinary approach. A combination of transarterial embolization, transvenous embolization, and surgery may be required in some cases. The primary goal of treatment, whether endovascular or surgical, is to eliminate CVR. Endovascular embolization is usually the primary treatment modality and often begins with transarterial embolization. This is rarely curative and is usually followed by transvenous embolization. If endovascular therapy is not feasible or fails, then surgery is indicated.

For lesions with CVR only without any sinusal drainage (Borden type III and Cognard types III, IV, and V), CVR disconnection alone is all that is required. Transvenous embolization is rarely successful in these cases because the adjacent venous sinus cannot be used for access to the refluxing cortical vein. Most of these cases therefore require surgical disconnection of CVR. Before disconnection, it must be decided whether it is safe to interrupt the veins involved in CVR. This is particularly important when the vein to be disconnected is a major cortical draining vein, such as the vein of Labbé. The venous phase of the cerebral angiograms must be studied in detail to ensure that normal brain is not draining into the concerned veins and that other venous routes are being used by the brain (Fig. 80-6).

FIGURE 80-6 Management strategy for dural arteriovenous fistulas with cortical venous reflux (CVR) only (aggressive dural arteriovenous fistulas, Borden type III and Cognard types III, IV and V).

The management of DAVFs that have both CVR and sinusal drainage (Borden type II and Cognard types IIb and IIa + b) is more complex. The management strategy for these lesions requires a detailed knowledge of the venous drainage of the brain as well as that of the fistula. If the involved dural sinus is being used only by the DAVF and is not being used for venous drainage of the brain, then it may be sacrificed. This can be achieved by transvenous embolization or by surgical packing or excision of the sinus. The decision regarding the safety of sinus sacrifice is based on preoperative clinical and angiographic assessment of the patient. If the patient is neurologically intact, and the venous phase of the cerebral angiogram shows that the involved venous sinus is not used for drainage of the brain and that other pathways have developed for venous drainage of the brain, the sinus may be sacrificed. However, if angiography shows that the sinus is used for venous drainage of the brain, treatment must be limited to CVR disconnection alone without obliteration or excision of the sinus. This converts Borden type II (Cognard types IIb and IIa + b) lesions to Borden type I (Cognard types I and IIa) lesions, which have a benign natural history.

The most difficult situation arises in patients with preoperative neurologic deficit. In these patients, an assumption that the sinus can be sacrificed, based solely on angiographic findings may be incorrect. In other words, the patient’s neurologic deficit may be a consequence of the retrograde flow in the sinus and the resulting venous hypertension, which may improve if normal flow in the sinus can be reestablished. Occlusion of the sinus or the refluxing cortical veins in these cases would eliminate the chance of recovery of neurologic function and may lead to venous infarction. In these patients, the safest option may be to limit the procedure to the arterial side of the lesion. This can be achieved by extensive transarterial embolization of the feeding arteries or by surgical skeletonization of the sinus. All cortical veins and the venous sinuses should be left intact. Fortunately, this situation arises rarely (Fig. 80-7).

FIGURE 80-7 Management strategy for dural arteriovenous fistulas with cortical venous reflux (CVR) and sinusal drainage (aggressive dural arteriovenous fistulas, Borden type II and Cognard types IIb and IIa + b).

In all patients with DAVFs and CVR, treatment should continue until all CVR has been eliminated. Simply reducing the size of the nidus without eliminating CVR does not eradicate the risk of future hemorrhage or neurologic deficit. All patients, particularly those in whom complete obliteration of the fistula has not been achieved, require lifelong follow-up, with a routine delayed angiogram at 3 years to check for recurrence of CVR. Patients would also require an angiogram if there is any change (deterioration or improvement) in their symptoms.

Anatomic Considerations for Dural Arteriovenous Fistulas in Specific Locations

In itself, anatomic location of a DAVF has no direct correlation with aggressive clinical events, although this has been suggested in the past.^3,19 DAVFs in any location can develop CVR (Table 80-4).^1,19 However, DAVFs in particular locations such as the anterior cranial fossa and the tentorium are more often associated with CVR and are therefore more likely to behave aggressively than are lesions in other locations. This reflects the pattern of regional venous anatomy in these locations. For example, anterior cranial fossa DAVFs cannot drain into any venous sinuses and can only drain into cortical veins and are therefore always associated with CVR.¹⁹ Table 80-4 shows the anatomic location of intracranial DAVFs. They are named according to the dural sinus with which they are associated.⁵² This section deals with the anatomy and surgical management of DAVFs in specific locations.

Table 80-4 Anatomic Location of 236 DAVFs Managed by University of Toronto Brain Vascular Malformation Study Group

CVR, cortical venous reflux; DAVFs, dural arteriovenous fistulas.

Transverse/Sigmoid Sinus Dural Arteriovenous Fistulas

Transverse/sigmoid sinus DAVFs are the most common intracranial DAVFs, accounting for 4% to 60% of cases (see Table 80-4).^28,36,43 Their arterial supply is derived mainly from branches of the ECA, namely, the transmastoid branches of the occipital artery, the posterior auricular artery, the posterior branch of the middle meningeal artery, and the neuromeningeal division of the ascending pharyngeal artery. They may also receive arterial supply from the posterior meningeal branch of the vertebral artery, the tentorial branch of the meningohypophyseal trunk of the ICA, and the petrous bone.^8,28 Venous drainage may be through the ipsilateral transverse/sigmoid sinuses or through the contralateral side if the ipsilateral sinus is occluded. Occasionally, these lesions drain into the diploic veins, which may lead to significant hemorrhage during craniotomy. CVR may occur through temporal, occipital, and cerebellar veins.^4,7

If endovascular therapy fails, surgery should be performed in cases with CVR. Preoperative transarterial embolization is very helpful in reducing intraoperative bleeding and should be used whenever possible. The patient is placed in the park-bench position with the side of the lesion up. It is important to have access to the region between the inion and the mastoid. A lazy “S”-shaped incision is made two fingerbreadths behind the ear. The occipital and posterior auricular arteries, which are usually enlarged, should be doubly ligated and divided. In some cases, this interrupts the main arterial supply to the DAVF. The nuchal muscles are incised using monopolar cautery, leaving a small cuff of fascia at the superior nuchal line. The muscles are then scraped off the bone using subperiosteal dissection. A craniotomy is performed to expose the transverse sinus and the dura superior and inferior to it. Great care must be taken to prevent a dural laceration while performing the craniotomy as this may lead to torrential hemorrhage from enlarged dural feeding arteries. The cutting bit of a high-speed drill may be used for performing the craniotomy. The bone is gradually removed along the margin of the bone plate until the dura can be seen through a thin layer of bone. The dura is gently separated from the bone flap, and the bone flap is elevated using a periosteal elevator.³⁹ Significant hemorrhage from the dura when elevating the bone flap may be controlled by placing a large piece of Gelfoam or Surgicel over the dura and applying pressure with a wet sponge for a few minutes. Dural feeders can be coagulated using bipolar cautery or occluded using hemostatic clips.

The remainder of the procedure depends on the goal of treatment, which should have been decided preoperatively. If the goal of treatment is CVR disconnection only, then the dura is incised above or below the transverse sinus depending on the location of CVR (i.e., temporal/occipital or cerebellar). The dural flap is reflected on a base along the transverse sinus. The arterialized leptomeningeal vein or veins should then be identified, coagulated or clipped, and divided as close to the fistula as possible. It is important to ensure that all arterialized leptomeningeal veins are disconnected. The dura is then closed in the usual manner. If the mastoid air cells have been entered, they should be obliterated using bone wax. The bone flap is then replaced, and muscle, fascia, and scalp are closed as usual.

If the goal of treatment is complete excision of the fistula and the sinus can be sacrificed, then after performing the craniotomy as described previously, the mastoid and posterolateral portion of the petrous bone are removed using a diamond burr on a high-speed drill to expose the dura lateral and anterior to the sigmoid sinus.^38,39 Knowledge of the anatomy of this region or assistance from an otolaryngologist is important to avoid damage to hearing or to the facial nerve during this stage of the procedure.³⁸ At this point, bleeding is mainly from arterial feeders contained within the petrous bone, which should be controlled using bone wax. The dura is incised above and below the transverse sinus and parallel to its long axis. Feeding arteries are coagulated or clipped as they are encountered. The transverse sinus is then occluded medially using two curved hemostats placed approximately 2 cm apart. The sinus is cut between the two hemostats, the ends are closed using 3-0 silk transfixion sutures, and the hemostats are removed. The dural incisions above and below the sinus are then continued laterally. Gentle retraction on the occipital lobe and the cerebellum exposes the tentorium, which should also be cut in a medial to lateral direction to interrupt any tentorial feeding arteries. All arterialized leptomeningeal veins are also coagulated and divided. The dural and tentorial incisions are extended laterally, distal to the junction of the transverse and sigmoid sinuses, which is usually the site of the fistula. The skeletonized sinus is resected distal to this site. The sigmoid sinus is then evaluated for patency. If there is a significant vein of Labbé, the sigmoid sinus should be left patent to drain it. However, if the vein of Labbé is arterialized and is not used for venous drainage of the brain, it can be clipped and divided, and the sigmoid sinus is then packed with Surgicel or Gelfoam and ligated. Duraplasty using fascia lata, pericranium, or synthetic dura is then performed to close the dural defect. The mastoid air cells are completely obliterated using bone wax, and the bone flap is replaced. The nuchal muscles and fascia are closed in multiple layers to prevent cerebrospinal fluid leak. The scalp is closed in the usual manner. Intraoperative angiography is used to ensure complete excision of the nidus.

Cavernous Sinus Dural Arteriovenous Fistulas

These are the second most common intracranial DAVFs, accounting for a third of all lesions in our series (see Table 80-4).^8,28,43 They are supplied by branches from the ICAs, ECAs, or both. Venous drainage is via the cavernous sinus, with subsequent anterior drainage into the superior and inferior ophthalmic veins, posterior drainage into the superior and inferior petrosal sinuses (IPSs), or cortical venous drainage into the sphenoparietal sinus, sylvian, uncal, and anterior pontomesencephalic veins.^7,28 Barrow and colleagues²³ classified carotid cavernous fistulas into four categories based on the type of feeding arteries detected on angiography. Type A fistulas are direct fistulas between the ICA and the cavernous sinus. Types B, C, and D are DAVFs involving the cavernous sinus. Type B are fed by meningeal branches of the ICA, type C by meningeal branches of ECA, and type D by meningeal branches of both ICA and ECA. Type A fistulas are high-flow fistulas and usually result from a traumatic tear in the cavernous ICA or spontaneously from a rupture of an intracavernous ICA aneurysm. These high-flow fistulas rarely resolve spontaneously and require treatment to prevent progressive visual loss, intolerable bruit, or pain.¹⁹ They are almost always treated by endovascular embolization and are not dealt with in this chapter. Most spontaneous carotid cavernous fistulas are of the low-flow types B, C, or D and are referred to as cavernous sinus DAVFs. They are usually idiopathic and occur most commonly in middle-aged women. They may present with proptosis, chemosis, diplopia, visual loss, pulsatile bruit, retro-orbital pain, and facial pain.³⁵ Cavernous sinus DAVFs may present with ophthalmologic symptoms on the contralateral side. Unlike type A fistulas, a significant proportion of these low-flow fistulas undergo spontaneous resolution.

Cavernous sinus DAVFs can also be classified according to the pattern of venous drainage based on the Borden or Cognard classification. As with other DAVFs, it is the presence or absence of CVR that determines the natural history of these lesions. CVR occurs in 19% to 37% of patients with cavernous sinus DAVFs (see Table 80-4).^35,53 CVR is more common in patients with bilateral orbital signs but can also occur in those with unilateral signs. In a study of 118 patients with cavernous sinus DAVFs, 43% of patients with bilateral orbital signs and 9% of those with unilateral orbital signs had CVR.⁵³ Cavernous sinus DAVFs without CVR usually have a benign clinical course. Many of these lesions undergo spontaneous involution, with symptom resolution over weeks or months.²⁸ The majority of patients can be managed conservatively but must be followed up closely by a neuro-ophthalmologist. Although these lesions have been referred to as benign, in some cases, spontaneous venous thrombosis and venous hypertension may result in increased intraocular pressure and progressive visual loss.⁷ Medical therapy including topical agents, oral corticosteroids, and systemic anticoagulation may be used to prevent blindness. However, if medical therapy fails to control intraocular pressure and deteriorating vision, prompt endovascular treatment is indicated.⁷ Transarterial embolization using particles may be tried first to slow down the flow through the fistula. If this fails, transvenous embolization is required.

If CVR exists, these DAVFs must be treated with the same aggressiveness as DAVFs in other locations. This is usually done using transvenous embolization. Before this, transarterial embolization may be performed, particularly if there is significant supply through ECA branches. For transvenous embolization, access to the cavernous sinus is usually obtained by the femoral route through the internal jugular vein and the IPS. This venous approach may be difficult or impossible in cases in which the IPS is partially or completely thrombosed. However, with improved materials and experience, some surgeons have successfully navigated an angiographic catheter, even through a thrombosed IPS.⁵⁴ If access through the IPS is not possible or has failed, other routes may be employed. These may involve endovascular and/or surgical techniques. The approach depends on the direction of venous drainage of the fistula and may use the superior ophthalmic vein (SOV), the facial and angular veins, the pterygoid plexus, the superior petrosal sinus, the refluxing cortical veins, or direct surgical puncture of the cavernous sinus.³⁴ The goal of transvenous embolization is to occlude the venous side of the lesion. This is usually achieved by placing coils into the cavernous sinus. Obliteration of the venous side of the lesion can result in the total disappearance of the fistula.²⁸ However, in some cases of successful treatment, thrombosis may extend into the orbital veins, and this may lead to venous hypertension and paradoxical visual deterioration.⁷ This may require treatment with oral corticosteroids, antiplatelet therapy, or anticoagulation.

If endovascular therapy fails, surgery is indicated in cases with persistent CVR or when vision is at risk. The role of surgery in the treatment of cavernous sinus DAVFs is mainly in providing venous access to the cavernous sinus in cases in which access through the femoral route is not possible. Several options are available, including cannulation of the SOV, cannulation of refluxing intracranial veins such as the sylvian veins, or direct exposure of the cavernous sinus.³⁴

The SOV approach is often performed by a team consisting of an ophthalmologist, a neurosurgeon, and a neuroradiologist.⁵⁵ The procedure is performed under general anesthesia and under fluoroscopic guidance. A sheath is placed in a common femoral artery to allow intraoperative angiography. The skin incision is made in the nasal part of the superior sulcus of the upper eyelid, under magnification provided by an operating microscope.⁵⁵ The incision is carried down through the orbicularis oculi muscle. The orbital septum is then opened, exposing the retroseptal orbital fat. The SOV is then identified and cleaned of the surrounding orbital fat to expose a segment of vein 5 to 20 mm in length. Two ligatures (2-0 silk suture) are placed around the vein approximately 1 cm apart. A sheath is then inserted into the vein between the ligatures, and thrombogenic material (such as platinum coils) is injected into the cavernous sinus under fluoroscopy. At the end of the procedure, an intraoperative angiogram is performed through the femoral sheath to ensure complete closure of the fistula. The SOV sheath is then removed, the vein is suture ligated, and the lid incision is closed. Alternatives to surgical exposure of the SOV have been reported and include direct percutaneous puncture of the SOV under angiographic guidance, direct percutaneous puncture of the facial vein under sonographic guidance, and transvenous transfemoral access to the facial vein.^34,35 In cases in which the facial vein is catheterized, the catheter is advanced into the angular vein, then into the SOV, and finally into the cavernous sinus.

In rare instances, a cavernous sinus DAVF may only drain by retrograde flow into cortical veins, and there may be no access through the IPSs, the ophthalmic veins, or the pterygoid plexus. In such cases, access to the cavernous sinus may be achieved via the refluxing cortical vein (e.g., a refluxing sylvian vein). This has been described using the percutaneous transfemoral technique and also by surgical exposure of the cortical vein.³⁴

Direct microsurgery of cavernous sinus DAVFs has also been described,^9,56–58 but with advances in endovascular embolization, these techniques are rarely required. These procedures require surgical experience and detailed knowledge of the anatomy of the cavernous sinus. The cavernous sinus is approached through triangles that are formed by convergence and divergence of the cranial nerves in the region of the cavernous sinus and the middle fossa.²⁵ The selection of approach is determined by the pattern of venous drainage of the fistula, and the degree of familiarity of the surgeon. The two main approaches used are described below.

The anteroinferior extradural approach to the cavernous sinus is suitable for anteriorly draining fistulas and is performed through a standard pterional craniotomy. After administration of intravenous mannitol, the dura is reflected away from the anterior and anteromedial walls of the middle fossa to expose the lateral wall of the cavernous sinus. The posterior aspect of the orbital roof is then drilled all the way to the lateral aspect of the anterior clinoid process. The superior orbital fissure region is exposed, the periorbita is opened, and the cranial nerves are identified. The superior or inferior orbital vein is then identified. An intraoperative Doppler probe may be used to localize the high arterial flow in these veins.⁵⁸ An atraumatic intravenous cannula is then inserted into the vein, and a guidewire is directed posteriorly into the cavernous sinus. A catheter is then introduced over the guidewire into the cavernous sinus and used to introduce thrombogenic material such as coils to obliterate the fistula. An intraoperative angiogram is performed to confirm adequate obliteration of the sinus. It must be noted that it may be difficult to identify the ophthalmic veins in a low-flow fistula.⁹

The posterosuperior approach is appropriate for posteriorly draining fistulas. It is performed through a pterional craniotomy. After opening the dura, the sylvian fissure is split widely to allow gentle retraction of the frontal and temporal lobes. The oculomotor nerve is then identified as a landmark. Underneath the oculomotor nerve, the superior petrosal sinus is identified and followed proximally to its origin from the cavernous sinus. Thrombogenic material is injected through the superior petrosal sinus into the cavernous sinus.⁹ If the superior petrosal sinus cannot be identified, the cavernous sinus can be packed through Parkinson’s triangle, bounded by the lower margin of the trochlear nerve, the upper margin of the ophthalmic division of trigeminal nerve, and a line connecting the point of entry of trochlear nerve into the dura to the point of entry of trigeminal nerve into Meckel’s cave.²⁵ An intraoperative angiogram is performed to confirm complete occlusion of the fistula. The dura is closed as usual, the bone flap is repositioned, and the temporalis muscle, galea, and skin are closed in layers. Combined and more extensive approaches to the cavernous sinus, with opening and packing of all triangles, have been described but are rarely necessary.⁵⁶

Anterior Cranial Fossa Dural Arteriovenous Fistulas

The arterial supply to the anterior cranial fossa dura is derived mainly from the ICA through the ophthalmic artery, which gives off the anterior and posterior ethmoidal arteries within the orbit. The ethmoidal arteries leave the orbit to enter the ethmoidal air cells. The smaller of the two, the posterior ethmoidal artery, supplies the dura in the region of planum sphenoidale. The anterior ethmoidal artery gives origin to the falcine artery and supplies the dura of the medial and inferior portions of the anterior cranial fossa. As well as supply from the ethmoidal arteries, DAVFs in this region may also recruit dural arterial supply via the anterior division of the middle meningeal arteries from both dural convexities and transcranial arterial supply via engorged scalp arteries.²⁸ The venous drainage of anterior cranial fossa DAVFs is always via cortical venous drainage through the frontal and olfactory veins.^4,7 The cortical veins may often be variceal. This constant presence of CVR explains the high incidence of aggressive clinical behavior for lesions in this location. They must therefore be treated aggressively to eliminate CVR. Anterior fossa DAVFs are rarely cured by endovascular means. Transarterial embolization is usually limited to ECA branches. Embolization of ophthalmic artery branches is usually avoided as it carries the risk of central retinal artery occlusion and visual compromise.⁵⁹ Transvenous embolization has been described in case reports⁶⁰ but is not possible for most lesions in this location due to lack of venous access. Surgery is associated with high cure rates and low complication rates and is the treatment of choice for most anterior fossa DAVFs.⁵⁹ This is performed through a low unilateral frontal craniotomy in the supine position with minimal retraction of the frontal lobes. A unilateral craniotomy allows disconnection of leptomeningeal veins on both sides via the transfalcine route. Alternatively, a bifrontal craniotomy may be performed. The next step is to disconnect the arterialized leptomeningeal veins, which should be coagulated and divided. Excision of the dura involved with the fistula is not necessary.⁵⁹

Superior Sagittal Sinus (Convexity) Dural Arteriovenous Fistulas

The arterial supply to these lesions is from the middle meningeal arteries. The venous drainage may be into the superior sagittal sinus, into cortical veins, or both. If CVR exists, the lesion must be treated to prevent future hemorrhage or neurologic deficit. Few cases of successful curative endovascular treatment have been reported.^8,61 Surgical treatment is therefore required in most cases and involves disconnection of CVR. The lesion is usually approached through a unilateral craniotomy on the side of the fistula. Preoperative transarterial embolization is used to reduce the amount of hemorrhage from scalp and dura.

In some cases without CVR, there may be a high-flow fistula that shunts into a patent superior sagittal sinus. These lesions may be associated with papilledema.²⁸ These cases may be managed with extensive transarterial embolization or surgical skeletonization of the superior sagittal sinus to reduce the flow through the fistula. Other options include the use of lumboperitoneal shunting or optic nerve sheath decompression for treatment of papilledema.²⁸

Deep-Seated and Posterior Fossa Dural Arteriovenous Fistulas

This group consists of lesions associated with the deep veins (tentorial incisura), superior petrosal sinus, IPS, or the marginal sinus (foramen magnum). As with DAVFs in other locations, deep-seated and posterior fossa lesions without CVR can be observed or treated palliatively by transarterial embolization of the arterial feeders. Lesions with CVR should be treated aggressively until all CVR is disconnected. This may be achieved by endovascular or surgical means.^42,43,52 Extensive resection of the nidus, which was performed in the past, often requires complex skull base approaches, carries significant risk of morbidity, and is unnecessary. If endovascular treatment fails to eliminate CVR, surgical disconnection can be performed with relatively little risk to the patient.^42,43

Deep Venous (Tentorial Incisura) Dural Arteriovenous Fistulas

These lesions are located at the tentorial incisura and involve the deep venous system. They may extend along the straight sinus to involve the falx. Their arterial supply may be bilateral and is derived from the tentorial dural branches of the ECA, ICA, and vertebral and posterior cerebral arteries. Angiography may reveal hypertrophy of embryonic dural arteries, including the artery of Bernasconi and Cassinari (tentorial branch of the meningohypophyseal trunk of the ICA) and the artery of Davidoff and Schecter (dural branch of the posterior cerebral artery).²⁸ Venous drainage is almost always leptomeningeal and involves the basal vein of Rosenthal, the lateral mesencephalic veins, and the vein of Galen.^7,8 Fistulas at this location may have infra- or supra-tentorial cortical venous drainage or drainage into spinal medullary veins.⁴² The presence of CVR explains the high incidence of ICH and neurologic deficit with these lesions. Drainage into the spinal medullary veins may be associated with progressive quadriparesis.⁶² Surgical exposure of these lesions may be performed using a posterior parasagittal craniotomy and interhemispheric approach with the trajectory posterior to the splenium of the corpus callosum.⁶³ Surgical treatment consists of CVR disconnection.

Superior Petrosal Sinus Dural Arteriovenous Fistulas

These lesions are often included in the same group as the deep venous DAVFs and together are referred to as tentorial DAVFs. Other authors have grouped them separately because they are located at the petrous ridge and involve the superior petrosal sinus.^8,52 The arterial supply is from dural branches of the ECA, ICA, and the vertebrobasilar system. Most cases are associated with thrombosis of the superior petrosal sinus on either side of the fistula site, with venous drainage diverted into cortical veins.^8,52 ICH is the most common mode of presentation. In a series of 18 patients reported by Ng and colleagues,⁵² 17 (94%) had CVR and 9 (50%) presented with ICH. Ocular symptoms may occur if there is venous reflux into the cavernous sinus and the SOV. Trigeminal neuralgia may occur secondary to irritation of the trigeminal ganglion in Meckel’s cave by dilated tortuous feeding arteries or compression of the trigeminal nerve at the root entry zone by a dilated petrosal vein. Surgical excision of this type of DAVF may require an extensive skull base approach consisting of subtemporal craniotomy, posterior petrosectomy, and suboccipital craniotomy.⁶³ These extensive procedures are usually unnecessary, and treatment should focus on disconnection of CVR only.

Inferior Petrosal Sinus Dural Arteriovenous Fistulas

The main arterial supply to these lesions is usually from the dural and muscular branches of the vertebral arteries and dural branches from the ascending pharyngeal, middle meningeal, and occipital branches of the ECA. Venous drainage may be retrograde up the IPS and into the cavernous sinus. This may result in presentation with ocular symptoms similar to those of cavernous sinus DAVFs. Alternatively, venous drainage may flow into the ipsilateral jugular bulb, resulting in pulsatile tinnitus.⁸ Retrograde flow up the ipsilateral sigmoid and transverse sinuses and into the contralateral transverse/sigmoid sinuses or into the straight and superior sagittal sinuses may also occur.⁶³ Surgical exposure may be performed using the far lateral suboccipital approach.⁶³ Treatment consists of CVR disconnection.

Marginal Sinus (Foramen Magnum Region) Dural Arteriovenous Fistulas

These lesions are rare. The marginal sinus encircles the foramen magnum and communicates with the basal venous plexus of the clivus anteriorly and with the occipital sinus posteriorly. It normally drains to the sigmoid sinus or jugular bulb through a series of small sinuses.⁶⁴ Fistulas in this area have often been grouped together with posterior fossa DAVFs or referred to as foramen magnum region DAVFs. Their arterial supply is usually from the muscular branches of the vertebral artery, the transmastoid perforators of the occipital artery, the neuromeningeal division of the ascending pharyngeal artery, and the posterior clival dural branches of the meningohypophyseal trunk of the ICA.⁶⁴ Venous drainage may be into the sigmoid sinus/jugular vein, in which case the patient may complain of pulsatile tinnitus, or into the IPS, which may lead to venous engorgement in the ipsilateral cavernous sinus and ocular symptoms.^28,64 CVR may lead to ICH, and reflux into the spinal medullary veins may result in progressive myelopathy and quadriparesis.⁶⁵ These lesions are surgically approached through a posterior paramedian craniocervical exposure, with the patient in the semiprone position. The venous plexus surrounding the vertebral artery may be arterialized and require meticulous hemostasis during exposure. Suboccipital craniotomy and laminectomy at the appropriate levels are then performed. The dura is extensively coagulated and opened. Refluxing leptomeningeal veins communicate with arterialized tortuous posterior and/or anterior medullary veins. The refluxing leptomeningeal veins are coagulated or clipped and divided, whereas the anterior and posterior medullary veins should be left intact.