1.3.2.13 General treatment considerations in DAVFs
In the most frequent dural arteriovenous fistulas—in the transverse sinus and cavernous sinus—treatment considerations are concerned with locating the fistulous segment on the wall of the sinus. Transvenous treatment of the fistula-bearing segment is the most widely used form of endovascular therapy. It is based on the assumption that this sinus segment is no longer required for normal drainage of the brain or eye. This is usually not critical in treatment of the cavernous sinus, but when fistulas of the transverse sinus are being treated, the anatomy of cerebral venous drainage needs to be analyzed carefully. All of the cerebral vessels have to be imaged with a long venous phase in order to delineate the anatomy of the intratentorial and supratentorial veins. Once the decision has been taken that the fistula-bearing segment can be occluded, then the location up to which this is to be carried out also has to be carefully assessed. Sinus segments that take up blood from the brain and are required for drainage must not be closed. Usually, coils are used to occlude the sinus. Recent developments have been based on a different approach: the aim is to preserve the sinus by inflating a balloon at a suitable point and then, via an arterial access route, injecting a liquid embolic agent that is modeled to the shape of the sinus wall by the balloon.
Surgical therapy and treatment of dural fistulas using stereotactic radiotherapy are unusual and are not discussed here in greater detail. Spontaneous healing has only rarely been reported with AVMs, but it does occasionally occur with dural fistulas. For example, manual compression of the occipital artery in patients with lateral dural fistulas and mild symptoms can be carried out in an attempt to reduce the shunt or even occlude the fistula by thrombosis. This procedure can also be used to achieve complete occlusion of fistulas that have already been treated but show a slight degree of residual flow.
1.3.2.14 Endovascular therapy for DAVFs
Tentorial and ethmoidal DAVFs
Tentorial and ethmoidal DAVFs are usually treated with arterial injection of liquid embolic agents in one or several sessions. This diverges from the considerations discussed above, because these fistulas are typically located in a circumscribed site and transvenous access is usually not possible due to the anatomic conditions. A surgical approach should also always be considered for these fistulas, and ethmoidal fistulas in particular are well accessible for surgical treatment.
Fig. 1.3–13a-c Endovascular treatment of a traumatic fistula in the cavernous sinus. (a) DSA of the internal carotid artery, showing a fistula between the internal carotid artery and the cavernous sinus. (b) DSA after occlusion of the fistula with a detachable balloon (arrow). (c) Enlarged image of the balloon after opening at the fistula site in the cavernous sinus outside of the internal carotid artery (arrow).
Cavernous sinus fistulas (spontaneous, indirect, Barrow C-D)
These lie in the domain of endovascular therapy. In most cases, the fistula-bearing segment of the cavernous sinus is probed via the inferior petrosal sinus. If this is not possible, access via the facial vein is possible, with or without surgical exposure. The sinus is occluded with coils after arterial demonstration of the fistula; to secure the eye against any recurrence, the initial segment of the orbital veins should also be occluded.
Cavernous sinus fistulas (trauma or aneurysmal rupture, direct, Barrow A)
The fistulous connection consists of a hole in the internal carotid artery resulting from rupture of an aneurysm at that location, or due to direct injury. Endovascular therapy involves occluding the hole by coiling the aneurysm or using a detachable balloon that is opened at the rupture site outside of the carotid lumen, i.e. in the cavernous sinus, and released. Techniques involving stents and liquid embolic agents have also been described for the treatment of cavernous sinus fistulas, but are not discussed further here.
Fig. 1.3–14a-d Endovascular treatment of a spontaneous fistula in the left cavernous sinus. Angiographic analysis of the fistula using an injection into potentially afferent vessels. The fistula in the left cavernous sinus and intercavernous sinus is primarily supplied by the left external carotid artery. From the right, vessels from the external and internal carotid arteries are also involved (Barrow type D fistula). The vertical images (a) demonstrate the supply of the fistula from the carotid flow area from the right (right column). The image at the top left shows the afferent supply to the fistula from the right external carotid artery. Gaps in the cavernous sinus, which mark the course of the internal carotid artery, are clearly recognizable. The next six images (b) demonstrate the supply to the fistula from the external carotid artery, with the first four in a lateral projection with contrasting of the right superior ophthalmic artery in the first image in the lower row. The two last images in the lower row again show the cavernous sinus with gaps in the internal carotid artery (arrow). The following images (c) show access of the ophthalmic artery with a microcatheter, from top left to bottom right. The last five images (d) illustrate treatment using platinum coils; top row: filling of the ophthalmic vein and of the cavernous sinus; middle left: filling of the intercavernous sinus. The last two images show complete occlusion of the fistula.
Transverse sinus and superior sagittal sinus fistulas
As mentioned above, these are usually treated endovascularly, but there are various techniques (see above) for closing the shunts in the sinus wall (see section 1.3.2.6). In addition to the methods mentioned, there is also a technique in which the fistulas in the sinus wall are probed directly from a transvenous or transarterial access route. Techniques involving releasing stents into the sinus have also been described.
1.3.3 Occult (“low-flow”) cerebral vascular malformations
These are vascular malformations involving slow flow. There is no arteriovenous shunt. It is often not possible to demonstrate these malformations on angiography.
1.3.3.1 Cavernous hemangioma (cavernoma)
Cavernomas are congenital or acquired intracerebral vascular malformations with a cavernous venous structure that lie encapsulated in the cerebral parenchyma. Cavernomas are found as cerebral manifestations in approximately 10% of cases in patients with hereditary hemorrhagic telangiectasia (Rendu–Osler–Weber syndrome). In the familial form, there are usually multiple lesions. Seizures are the most frequent clinical manifestation, followed by neurological deficits due to spontaneous bleeding or space-occupying lesions. The risk of bleeding is approximately 2–3% per year, but it is assessed variously depending on whether or not clinically unremarkable blood deposits in the cavernoma are regarded as bleeding. Cavernomas may occur in combination with other vascular malformations, and are most often associated with venous malformation.
MRI is the examination method of choice, and it shows circumscribed areas with signal changes, which may resemble acute bleeding, fresh thrombosis, older bleeding, or only small punctate hemosiderin deposits, depending on the stage. A typical finding is a “popcorn-like” center with areas of bright and dark signal intensity, surrounded by a dark hemosiderin border (Fig. 1.3-15). CT only reveals larger cavernomas. Angiography is usually negative (cryptic or occult malformation).
There are no options for conservative treatment. Clinically silent cavernomas usually only receive observation. There is no endovascular treatment procedure. There is an indication for neurosurgical removal if the cavernoma increases in size or when there are focal neurological deficits, symptomatic bleeding, or seizures. Depending