Cranial Dural Vascular Malformations

Vascular malformations or fistulas of the dura are uncommon diseases, but they have the potential to develop severe complications. They account for 10% to 15% of intracranial arteriovenous malformations of all types. They can occur in the brain or spine (Chapter 21) with characteristic patterns of pathophysiology in both locations.

The cranial dura consists of two tightly apposed layers, an outer periosteal layer and an inner meningeal layer, separated by a rich vascular layer of meningeal or dural veins and arterioles. Where the two layers of dura become separated, a larger venous space forms the dural sinuses. Along the cranial dura, any meningeal artery that perforates the dura usually does so in close relationship to surrounding venous plexuses. The artery penetrates the dura through or may run for a while within a venous structure or sinus. Venous thrombosis or other injuries, including surgery (1,2,3), may occasion a process of inflammation, neovascularization, and angiogenesis (4). The adjacent arterioles are thought to become involved with the formation of pathologic shunts to venous channels (5). In some instances, the fistulous connection could be the initiating event, as might happen with acute trauma, and the high-flowing lesion is then hypothesized to recruit additional arterial supply through the angiogenic mediators. In most patients, an acquired etiology is certain, in view of well-documented cases of such lesions soon after surgery, trauma, or mastoid air-cell infection. Metachronous formation of dural arteriovenous malformations (DAVMs) has also been seen, supporting the assumption of an acquired etiology (6). Patients with systemic syndromes involving abnormalities of vascular fragility, such as neurofibromatosis type I, fibromuscular dysplasia, and Ehlers–Danlos syndrome (7,8,9,10), are reported to be slightly more prone to develop these disorders of the cranial dura or spine.

An acquired dural fistula may be single, multifocal, or complex. The terms DAVMs and dural arteriovenous fistulas are interchangeable and synonymous. Fistulous malformations of the dura can be seen in young children as well. In children, long-standing changes suggest that some rare instances of congenital DAVMs occur.

In the cranial dura, the pathophysiology and significance of these lesions derive from their effects on venous flow (Figs. 20-1 and 20-2). Various classification schemes have been proposed to categorize these lesions (11,12,13,14,15,16). The quintessence of all of these schemes is an analysis of the state of disruption of venous outflow from the malformation, and the patency and direction of flow in adjacent dural sinuses, dural veins, and subarachnoid veins. The particular arterial feeders involved with a dural vascular malformation are usually not of primary importance for analysis of risks or treatment options (Figs. 20-3 and 20-4). An interesting classification scheme (16) on the basis of the homologous embryologic origins of segments of dura of the spine and cranium has been proposed with the predictive value that clinical complications are more likely to be seen with certain types, but the process of clinical decision making is not influenced, regardless of the perspective.

Uncomplicated DAVMs are occasionally seen as incidental findings (Fig. 20-5). They may be single or multiple, resulting in arterialization of flow in an orthograde fashion in a major dural sinus. Symptomatic patients present with pulsatile tinnitus, audible bruit, or cranial nerve deficits, depending on location of the lesion. Pulsatile tinnitus may be reported in 20% to 70% of patients, some of whom will volunteer a history of being able to suppress the bruit by manual compression of the neck. Visual symptoms and headache are also common (17). Hydrocephalus due to impaired resorption of CSF in more advanced cases can be seen, progressing in extreme instances to a state of dementia, parkinsonism, seizure, or movement disorders which can be reversible with treatment of the vascular lesion (18,19,20,21,22). Patients with symptomatic DAVMs are reported to have a recurrence rate of hemorrhage or non-hemorrhagic complications of at least 15% to 19% per year, necessitating urgent treatment (23,24). Thus, the presence of cortical reflux of venous flow has been represented as an angiographic

indicator for urgent intervention, but it is likely that such a sense of urgency is not always valid. DAVMs with cortical reflux which are asymptomatic at the time of detection have a much lower rate of complication, <2% (25,26), implying that a more tempered approach should be advocated in advising asymptomatic patients for whom an endovascular treatment may involve significant risk.

Figure 20-1. (A–C) Cavernous sinus DAVMs. The arterial and venous anatomy in the region of the cavernous sinus is illustrated (A), as depicted in preceding chapters. Most commonly, DAVMs in this region involve a degree of flow that is easily handled by the multitude of venous connections around the cavernous sinus bilaterally (B) so that exiting arterialized venous flow is seen as opacification of the superior ophthalmic vein (SOV), the superior petrosal sinus, or the IPS (arrows). When the flow is too voluminous or when there are anatomic constrictions on venous connections (C), arterialized flow can be diverted intracranially to the ipsilateral temporal lobe, the deep venous system, the superficial Sylvian vein, or even to the posterior fossa (either via the basal vein of Rosenthal or via the petrosal venous connection between the superior petrosal sinus and the cerebellar veins). The manifestation of these venous fields can be very subtle but of enormous moment to the patient, and therefore, the angiographic images must be examined thoroughly for the possibility of these findings.

Figure 20-2. (A–E) Idealized gradation of a DAVM of the sigmoid–transverse sinus. The several grading schemes referenced in the text for categorizing DAVMs all share the emphasis that the threat to the patient lies in the pattern of venous flow.

(A) represents a simple malformation with antegrade unrestricted flow into the ipsilateral sigmoid sinus, which is also used for antegrade venous drainage of the normal upstream brain.

(B) represents a slightly more advanced situation where—either through elevated sigmoid pressure from the malformation or restriction of caliber of the jugular–sigmoid channel—the normal parenchymal drainage into the transverse sinus is reversed via the torcular to the other side.

(C) shows that the malformation is still more restricted in its outflow, and there is retrograde flow into the ipsilateral superior petrosal sinus and retrograde drainage via the upstream transverse sinus.

(D) shows the additional complication of retrograde flow into the vein of Labbé and other cortical veins. The lateral hemispheric cerebellar veins may opacify in this manner as well.

(E) shows extreme progression of the intraparenchymal complications of venous reversal of flow with variceal distension of a parenchymal or cortical vein, an appearance that can also represent a contained pseudoaneurysm of the vein when the patient has presented with intracerebral hemorrhage.

Figure 20-3. (A–B) DAVM of right sigmoid sinus. An elderly patient presented with a 3-month history of pulsatile tinnitus. Angiography demonstrated a DAVM of the right sigmoid sinus supplied by the ipsilateral occipital (A) and vertebral (B) arteries. All avenues of fistulous flow converge on a single venous channel (arrow), which empties into the sigmoid sinus. Although this DAVM is confined and simple on its arterial side, there is constriction (arrowhead) in the sigmoid sinus (S ) with bidirectional flow to the jugular bulb and transverse sinus (T ). This suggests that the DAVM has passed the early stages of evolution and is developing signs of sinus hypertension.

Figure 20-4. (A–C) Postsurgical DAVM of the cavernous sinus. A middle-aged male presented with left-sided proptosis and an audible bruit after surgery for chronic ethmoidal sinusitis. A contrast-enhanced MRI (A) demonstrates prominent paracavernous vessels and distention of the left SOV (arrows). These findings were not seen on the preoperative MRI. Because of worsening proptosis, endovascular treatment was recommended.

An angiogram of the left internal carotid artery (B) demonstrates a large recurrent meningeal artery (arrow) from the ophthalmic artery opacifying the cavernous sinus and IPS (double arrow). Identification of the IPS on pre-embolization angiography points to the most accessible route of transvenous access to a DAVM in this region. Multiple external carotid artery branches were also involved in the fistulous lesion. The cavernous sinus was embolized (C) via the left IPS with thrombogenic coils (arrowheads), causing an immediate normalization of flow in the previously involved vessels.

Figure 20-5. (A–B) Synchronous DAVMs. An elderly male presented with headaches. Two separate DAVMs were demonstrated on lateral (A) and oblique (B) images of the right internal carotid artery. A DAVM of the tentorium causing the patient’s symptoms opacifies greatly distended veins in the posterior fossa. It is supplied by the marginal tentorial artery (arrows) arising from the ophthalmic artery and tentorial arteries (arrowheads) from the cavernous internal carotid artery. A separate fistula of the superior sagittal sinus is supplied by the anterior artery of the falx cerebri.

Dural arteriovenous fistulas are most commonly seen in the cavernous, sigmoid, and transverse sinuses (Figs. 20-6–20-10). Dural arteriovenous fistulas in the early stages may undergo spontaneous remission, although the likelihood of this in a well-established lesion is low (14,27,28). The dural sinus in early or uncomplicated cases may be completely normal in appearance or may show evidence of only partial thrombosis at the time of presentation. Depending on the patient’s tolerance of symptoms, expectant management of patients with uncomplicated DAVMs may be reasonable (Fig. 20-11). Training the patient to perform manual contralateral carotid compression at home has been advocated to eliminate smaller lesions over a few weeks, but the efficacy of this home remedy is dubious.

The venous pattern changes as the pressure in the venous system increases due to intimal flow-related changes in the main venous channels or recruitment of arterial feeders. Diversion of flow away from the involved sinus is seen angiographically with retrograde flow in the dural sinuses. It can be difficult to identify the presence of incipient cortical venous hypertension unless a careful examination of the entire angiogram is performed. For example, an internal carotid arteriogram in which opacification of the DAVM is not seen may still demonstrate very ominous signs in the patterns of flow in the venous stages.

Figure 20-6. DAVM of the cavernous sinus. A lateral view of a left internal maxillary artery injection demonstrates opacification of a distended and tense cavernous sinus (arrow) via the accessory meningeal artery (ama) and artery of the foramen rotundum (fr ). The cavernous sinus drains anteriorly to the SOV and subsequently to the facial vein (fv ). In contrast to the patient in Figure 20-4, the IPS is not seen in this patient, which implies that transvenous access to the lesion through that route may not be possible. In a patient with a lesion such as this, urgency of treatment is guided primarily by concerns for the patient’s vision. An ophthalmologist’s involvement to monitor the intraocular pressure and visual acuity is imperative. The likelihood of such complications depends in part on the anastomoses of the ophthalmic veins with other drainage routes.

Figure 20-7. (A–D) A “simple” DAVM of the cavernous sinus. A lateral common carotid arteriogram (A) shows an apparently straightforward malformation of the cavernous sinus (arrow) with drainage via the ipsilateral IPS (double arrowheads) to the jugular vein (double arrows). There is no evidence of sinister intracranial complications. Treatment was undertaken because of the patient’s presentation with orbital chemosis and III and VI nerve palsies. The described route of venous drainage was used to access the cavernous sinus retrogradely with a microcatheter through which an angiographic run was performed (B). This image shows the connection to the ophthalmic vein responsible for the appearance of chemosis and also how this straightforward lesion has nevertheless the potential to develop serious complications through small, previously unseen connections to the basal vein of Rosenthal. A misadventurous endovascular treatment could end up diverting flow from the cavernous sinus to these deep channels and induce deep venous cerebral hypertension. The cavernous sinus was occluded with coils (C, D) to eliminate the fistulous flow, but with care taken to include the junction between the cavernous sinus and the SOV (arrow) so as to prevent diversion of flow into this channel with induction of complications in the eye.

Figure 20-8. (A–B) DAVM of the transverse and sigmoid sinuses. A: Lateral view of a distal external carotid artery injection. B: Lateral view of the proximal external carotid artery. A DAVM in a prolonged segment of the transverse and sigmoid sinuses is opacified by squamous (s) and petrosal (p) branches of the middle meningeal artery and transosseous branches of the occipital artery (O). Flow is antegrade into the internal jugular vein (ijv). The transverse sinus is occluded between the DAVM and the torcular.

Figure 20.9. (A–B) Venous hypertension due to a DAVM. An elderly male presented with sudden loss of consciousness and seizure. A CT scan (not shown) demonstrated a small intraparenchymal bleed of the left occipital lobe. An axial image from a T1-weighted contrast-enhanced MRI sequence (A) shows a profusion of enhancing vessel-like structures (arrowheads) through the left hemisphere. A DAVM of the left transverse sinus was found by angiography. A lateral view of the left occipital artery injection (B) shows that the involved segment of transverse sinus (arrowheads) is isolated from the remainder of the sinus. Therefore, this segment of transverse sinus decompresses via cortical veins to the occipital and temporal lobes (curved arrows indicating direction of flow). This causes an extreme elevation of venous pressure throughout the left cerebral hemisphere, which resulted in the patient’s condition of venous infarction and hemorrhage (ss, straight sinus).

Figure 20-10. (A–D) Angiographically uncomplicated DAVM of the right sigmoid sinus. An elderly patient presented with tinnitus behind the right ear. The right external carotid artery AP (A) and lateral (B) views show a rapidly flowing but otherwise uncomplicated angiographic appearance with antegrade flow down the jugular vein. There is no evidence of intracranial venous hypertension. For the reader’s interest, an image of the right internal carotid artery injection (C) is provided, showing a nice example of basal tentorial artery from the meningohypophyseal trunk also feeding the malformation. The most important information is provided on the venous-phase AP view of the right ICA injection (D), where the normal brain parenchymal flow is preserved through the disease segment of sinus (arrowheads). This implies that a transvenous procedure to occlude this sinus is out of the question.

Figure 20-11. (A–D) The case of the disappearing DAVM. The initial CTA on this patient (A) demonstrates the reason for his right-sided orbital proptosis and chemosis. An unusual state of venous opacification is seen near the right hypoglossal canal (arrow) with a similar appearance in the inferior petrosal sinuses (arrowheads) and right ophthalmic vein (small double arrows). The exact location of the fistula is unclear from this study, but the TOF MRA with a superior saturation band (B) demonstrates that the flow signal within the right IPS (arrowhead) and right cavernous sinus (double white arrows) is flowing from caudad to craniad, that is, the fistula is not likely to be in the cavernous sinus. The first angiogram (C, right common carotid artery) demonstrated no evidence of a fistula, but the patient happened to mention that his symptoms had started improving a few days before the angiogram, about the time that his Coumadin was discontinued in preparation for the study. His symptoms resumed after the angiogram, a few days after his Coumadin had been restarted. His second angiogram (D, AP view of right ascending pharyngeal artery; E, lateral view) demonstrated that the fistula was related to the neuromeningeal trunk of that vessel, likely the hypoglossal branch with opacification of the predicted structures on the basis of the initial non-invasive images. This case illustrates the potential for spontaneous closure of some DAVMs and an explanation for fluctuation of symptoms in some patients depending on extraneous factors such as anticoagulation.

With increasing venous and sinus hypertension, retrograde flow of contrast from the sinuses into leptomeningeal (cortical) veins becomes evident. With elevation of venous pressure in the cortical veins, new symptoms related to seizure, headache, venous hemorrhage, elevated intracranial pressure, and focal neurologic deficits can emerge. Depending on the venous territory involved, patients may present with focal hemispheric symptoms, motor weakness, and brainstem or cerebellar symptoms. Cranial nerve deficits may also be seen, particularly ophthalmoplegia in the setting of a cavernous sinus DAVM. Interestingly, it is during this stage of diversion of flow away from the sinuses into cortical veins, perhaps with progressive occlusion of the main sinus, that patients may experience a subjective improvement in tinnitus. Thus, such a report from a patient with a known DAVM is a concern, as it may bode an ominous turn of events. Immediate treatment is indicated when complications appear imminent. Urgent treatment is required also for patients with DAVMs near the cavernous sinus who are developing complications of exophthalmos, secondary glaucoma, or visual deterioration.

The gravest progression of the disease occurs when venous outflow is completely restricted to cortical veins due to complete occlusion of the sinuses. In these instances, the arterial flow may be directed exclusively into the subarachnoid veins or into an isolated segment of sinus that drains only through
cortical veins. These patients present with severe neurologic deficits, extensive cortical venous hypertension (Fig. 20-12), venous hemorrhages or infarcts, and hydrocephalus. DAVMs of the anterior cranial fossa or of the tentorium represent a particular risk of sudden massive frontal lobe or subarachnoid hemorrhage, which may be the presenting symptom in more than 70% to 80% of cases (Fig. 20-13) (29,30,31,32,33). DAVMs in the anterior cranial fossa are usually close to the cribriform plate and have a propensity to develop venous aneurysms or varices adjacent to the site of fistulous flow from the ethmoidal branches of the ophthalmic arteries (34,35). Prompt surgical clipping of the DAVM is the treatment of choice for this particular subgroup of patients. Embolization usually is not favored for lesions in this location, given the risks and difficulties involved in catheterization and embolization of ophthalmic artery branches.

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