Dural arteriovenous fistula (DAVF) is a rare intracranial vascular disease, which is an abnormal traffic between dural sinuses such as cavernous sinus, lateral sinus, sagittal sinus and other nearby arterioles, accounting for 10%-15% of intracranial arteriovenous malformations. It can occur in any part of the dura, with the highest incidence in the transverse sinus-sigmoid sinus area, followed by the cavernous sinus area and the superior sagittal sinus area. The disease is more common in adults, especially in the age group of 40-60 years, and most scholars believe that it is an acquired disease. The disease is more common as a single occurrence, and multiple DAVFs have also been reported.
1.Pathogenesis and etiology
(1) Venous sinusitis or embolism Under normal circumstances, part of the meningeal arterioles terminate near the sinus wall and send out many tiny branches to nourish the dura of the sinus wall. In addition, Hamada et al. found that the lesion is based on the existence of direct traffic between the dural arteries and the dilated small veins, and named them crack-like vessale, with a diameter of about 30 μm and a layer of endothelial cells and smooth muscle cell layer, while the capillary network that usually exists between the arterioles is not found in the above structure. It is suggested that there is a direct arteriovenous pathway in the dura mater, which is completely closed under normal conditions, while under certain pathological conditions, such as venous sinusitis or embolism, the venous return is blocked and the venous sinus pressure is increased, which opens this channel and forms DAVF.
(2) Imbalance of estrogen levels in the body. the effect of estrogen on DAVF is based on clinical observations. lsajaunias found that women during pregnancy develop clinical symptoms of DAVF, which improve significantly with hormonal treatment, and found that the incidence of DAVF is higher in postmenopausal and pregnant women than in the general population. Although the specific site of estrogen action is not known and no different features of the imaging presentation of DAVF have been found in this group of patients, such cases do show a specific relationship between hormonal changes and clinical symptoms, and some patients can be cured with hormonal treatment without the need for aggressive therapeutic measures. Therefore, it is believed that estrogen plays an important role in the development of DAVF. When the estrogen level is imbalanced in the body, the meningeal artery wall becomes less elastic, more brittle, and dilated and tortuous, and with the impact of blood flow, it is easy to form fistulas with veins.
(3) DAVF can be induced by craniocerebral trauma and surgery, which is caused by venous sinus hypertension or occlusion:Terada et al. induced DAVF in rats by causing venous sinus hypertension by anastomosing the common carotid artery and external jugular vein in vivo.Sakaki found progressive development of DAVF in the posterior cranial fossa after surgical ligation of the sigmoid sinus.Chung et al. suggested that embolization of intracranial venous sinuses, previous intracranial (4) congenital factors.
(4) Congenital factors, some scholars believe that dural arteriovenous fistulas are formed due to an increase in “physiological arteriovenous traffic” in the dura mater as a result of abnormal cerebral vascular development during embryonic development, or due to abnormal proliferation of blood vessels near the venous sinuses. Dural arteriovenous fistulas are also found to occur in infancy and can coexist with congenital disorders such as cerebrovascular malformations, suggesting that dural arteriovenous fistulas may be related to congenital factors.
2. Classification
Currently, fistulas are classified according to the location of the fistula and the draining vein, especially the latter is useful for understanding the clinical manifestations, developing treatment plans, and improving the prognosis. Depending on the location of the fistula, there are many types of fistulas, such as transverse sinus, sigmoid sinus, and cavernous sinus, and also according to the region to which the lesion belongs. This classification has been gradually replaced by drainage vein typing because of its limited role in guiding clinical management. Dindiian type I, where blood drains into a patent venous sinus, is characterized by intracranial murmurs and rarely causes intracranial hypertension and neurological symptoms; type II, where blood drains into the venous sinus and returns to the cortical vein, is characterized by chronic intracranial pressure; type III, where blood drains directly into the cortical vein, causing Grisoli et al. concluded that almost all of this type have SAH; type IV, drainage into the venous lake, significant occupational effect, significantly increased intracranial pressure, high bleeding rate, and often neurological deficits.
Cognard’s typing is a modification of Djindjian’s typing, in which type I and II have mild symptoms or no obvious symptoms; type III has a bleeding rate of 40% due to cortical venous drainage; type IV has cortical drainage with venous aneurysmal dilatation and a higher bleeding rate of 65%; type V, blood drains into the perimedullary veins of the spinal cord and 50% develop progressive spinal cord lesions. In recent years, domestic scholars Ling Feng combined the site and drainage vein to classify DAVF, and proposed that the treatment of different drainage vein types in the same site is different, and the treatment of different sites in the same drainage vein type is different, and the combined classification of site and drainage vein type can help analyze the clinical risk and develop the treatment plan.
3.Clinical manifestation of DAVF
The clinical manifestation of this disease depends mainly on the site and size of the draining vein, but not on the source of the blood supplying artery. According to the different ways of venous drainage, it can be divided into 4 categories:
①Drainage from the cortex to the venous sinus, known as downflow, symptoms are mainly caused by arteriovenous short-circuiting, which can be manifested as pulsatile tinnitus and intracranial vascular murmur, and DAVFs in the cavernous sinus area can be manifested as proptosis, bulbar conjunctival congestion and edema;
② venous hypertension, blood flow from the venous sinus backflow to the cortex, called reflux, symptoms caused by dilated, tortuous, thin-walled veins, can occur intracranial hemorrhage, headache, neurological dysfunction;
(iii) Direct drainage into the subarachnoid or cortical veins, causing aneurysmal dilatation of these veins, is the main cause of subarachnoid hemorrhage;
(iv) Dural arteriovenous fistula with dural or subdural venous lake, where blood drains directly into the venous lake; this type is severe and often has an occupying effect.
(1) Pulsatile tinnitus and intracranial vascular murmur, about 70% of patients have pulsatile intracranial vascular murmur, the murmur can be at the site of the lesion or throughout the head, the murmur height depends on the arteriovenous short circuit, if the blood flow is high and the fistula opening is small, a high pitched murmur can be heard, on the contrary, the murmur is small or no murmur.
(2) Headache, which may be localized to the lesion or spread throughout the head, may be persistent, pulsating and severe, and may be aggravated by activity, change in position or high blood pressure in about 50% of patients.
(3) Intracranial hemorrhage, which can be manifested as subarachnoid hemorrhage, subdural hemorrhage or hematoma, or intracerebral hemorrhage or hematoma. Most scholars believe that it is caused by rupture of a thick tortuous thin-walled drainage vein and is not related to the fistula itself. Intracranial hemorrhage may be followed by corresponding occupying effects.
(4) Increased intracranial pressure The causes are:
(1) Due to the presence of arteriovenous fistula, arterial blood is perfused directly into the dural venous sinus, which transmits unabated arterial pressure to the venous sinus causing a continuous increase in pressure in the venous sinus, causing obstruction of intracranial venous reflux and impaired absorption of cerebrospinal fluid;
②Venous sinus thrombosis, which affects intracranial venous return and cerebrospinal fluid absorption;
(3) The draining vein is tumor-like dilated, and subdural venous lake may occur, producing occupational effect.
(5) Central nervous system symptoms, may be manifested as mental confusion, dementia, limb weakness, stroke, hydrocephalus and epilepsy, etc. Diplopia, vision loss and walking instability are also common symptoms, which may be due to mechanical compression of dilated veins or sinuses, or intravenous hypertension, obstruction of return flow, causing increased intracranial pressure, and direct return of arterial blood to veins, resulting in local cerebral tissue ischemia and hypoxia.
4.Diagnosis of DAVFs
Magnetic resonance imaging (MRI) shows that the fistula is adjacent to the dural sinus and has the phenomenon of “flowing empty”, which can suggest this disease. Selective cerebral angiography is currently the only reliable means of confirming the diagnosis and studying the disease.
Its methods are.
(1) Selective internal carotid and vertebral artery angiography to exclude cerebral arteriovenous malformations and to confirm the involvement of the meningeal branches of these arteries in the blood supply;
(2) Super-selective angiography of the external carotid artery to show the arteries and arteriovenous fistulas of the meninges and to find the best treatment and route. In some cases, the secondary blood supply artery can only appear after the primary blood supply artery has been embolized;
(3) Understanding the draining veins and direction, fistula location and cerebral circulation disturbance can help to explain clinical symptoms and judge the prognosis.
According to cerebral angiography, the blood supply arteries of DAVFs include.
(1) lesions located in the anterior cranial fossa, whose blood supply arteries are the dural artery and the anterior septal artery, a branch of the ophthalmic artery, which mainly drains to the sagittal sinus;
(2) lesions located in the middle cranial fossa, the blood supply artery may be from the middle meningeal artery, the ascending pharyngeal artery, the superficial temporal artery, and the anterolateral branch of the meningeal pituitary trunk, with venous drainage to the cavernous sinus;
(3) If the lesion is located near the transverse sinus or sigmoid sinus, the blood supplying artery may come from the meningeal pituitary trunk, dural branch of vertebral artery, occipital artery, middle meningeal artery, ascending pharyngeal artery, posterior auricular artery and posterior cerebral artery. The venous drainage is directed to the transverse or ethmoid sinus.
Cerebral angiography should be noted for the presence of “dangerous anastomoses” to guide treatment. Common “dangerous anastomoses” are.
(1) Anastomosis of the anterior branch of the skull base group of the middle meningeal artery or the anterior group and the meningeal return artery of the ophthalmic artery;
(2) Extensive anastomoses between the myocardial branches of the occipital artery, ascending pharyngeal artery, deep carotid artery, ascending carotid artery and the myocardial branches of the vertebral artery in the cervico-occipital region and upper cervical segment;
(3) The middle meningeal artery can anastomose with the internal carotid artery, and the posterior rocky branch of the middle meningeal artery is involved in the ipsilateral lateral nerve supply.
5.Treatment of DAVFs
The treatment methods for this disease are multiple and complex, including conservative observation, carotid artery compression, endovascular embolization, surgical resection and radiation therapy. The above methods can be used individually or in combination.
(1) Conservative observation or carotid compression can be used for patients with early onset, mild symptoms, and small and slow blood flow to the fistula, which can be observed for a period of time and some can heal spontaneously. The carotid artery compression method can also be tried, using fingers or simple devices to compress the affected carotid artery for 30 minutes at a time for 3 weeks, during the compression period, attention should be paid to observe the presence of cerebral ischemia-induced hemiparesis and changes in consciousness. The mechanism of this method is to compress both the common carotid artery and the internal jugular vein, which reduces the arterial blood supply and increases the venous pressure, reducing the arteriovenous pressure gradient at the fistula and promoting the formation of cavernous sinus thrombosis. Compression of the junction of the superior ophthalmic vein and the scalp vein above the medial canthus has also been advocated to increase the pressure in the superior ophthalmic vein to reduce the arteriovenous pressure gradient at the fistula and promote thrombosis.
(2) Endovascular embolization treatment, intra-arterial embolization With the continuous development of interventional radiological endovascular treatment, endovascular embolization treatment of DAVFs has gradually become the main treatment means. The specific method is to use the Seldinger technique to puncture and cannulate through the femoral artery, perform a whole brain angiography to understand the fistula supply artery, the size and location of the fistula, the number and direction of the draining veins, and then place a microcatheter into the supply artery and embolize it. The available microcatheters are the Magic floating catheter series and the Tracker and Magic3F/2F guidewire introducer catheters. Embolic materials available are: n-butyl alpha-cyanoacrylate (NBCA) gel, hydrogel microspheres, polyvinyl alcohol foam (PVA) pellets, spring coils, dry-frozen dural particles, and balloons. The above embolic materials can be used alone or in combination.
There are many arteries supplying blood to this disease, mainly the ascending pharyngeal artery, middle meningeal artery, secondary meningeal artery, occipital artery and retroauricular artery, etc. Different embolization materials and catheter techniques should be applied according to different situations. Regardless of the embolization method, care should be taken to avoid “dangerous anastomosis” of intracranial and extracranial vessels. A non-absorbable solid embolus is the most commonly used embolic agent, but the size of the solid embolus is crucial. If the embolus is too small, it may cause accidental embolization of the intracerebral vessels through “dangerous anastomosis”; if the embolus is too large, it may embolize the main trunk of the blood supplying artery, and the newly opened arterial branch may still supply the fistula. Generally, 300-700 μm is appropriate. In cases where there is no clear “dangerous anastomosis”, NBCA glue can be considered. In this case, the catheter should be placed as close to the fistula as possible. For multiple blood supply, embolization should be done one by one, avoiding the injection of NBCA in the main trunk of the blood supply artery, where the fistula is not occluded and the blood is still supplied to the fistula after the establishment of the collateral circulation and the loss of access for re-embolization. Gelatin sponges are generally not used, as they can be absorbed in vivo.
The principles of embolization are.
(1) For fistulae with a single blood supply artery, a removable balloon may be applied if the blood supply artery is thicker, while a non-absorbable solid embolus or NBCA is used if the blood supply artery is thinner;
(2) For several fistulas of different sizes, located in the dural sinus wall, and the blood supply artery is divided into several small branches near the fistula, particles such as PVA or lyophilized dura can be used to deliver emboli to the small branches in front of each fistula by blood flow impact. Regardless of the method used, the closer the embolization material is to the fistula, the better. For internal and external carotid arteries involved in blood supply at the same time, the external carotid artery can be embolized first by the above method, and for internal carotid artery meningeal branch blood supply, the carotid compression method can be used, and most of them can be cured.
If the external carotid artery route or venous route fails, a microcatheter can be placed via femoral artery puncture and guided by a microguide wire into the blood supply branch of the internal carotid artery, which can be embolized with a spring-ring embolus or NBCA. When embolizing with the latter, in order to prevent its reflux into the internal carotid artery, it should be injected slowly at low pressure under DSA surveillance, and it is important not to use too much force to cause accidental embolization of normal vessels. When choosing a treatment method, do not simply ligate the external carotid artery or a branch of the blood supply, because the rapid formation of new multiple collateral blood supply will, on the contrary, complicate the disease and lose valuable access for re-embolization.
If the external carotid artery route fails, a femoral vein can be punctured and placed through the internal jugular vein-sigmoid sinus-superior or inferior rocky sinus to the cavernous or lateral sinus, and the fistula can be occluded by embolization of the cavernous or lateral sinus lumen with a spring-loaded plug. In the case of dilated supraocular veins, a tube can be placed through this vein to the cavernous sinus and the fistula can be occluded with a spring-loaded plug or balloon.
(3) Surgical resection, if endovascular embolization fails or is not indicated, surgical resection is an effective treatment. Indications for surgery are.
(1) Combined intracranial hematoma with occupying effect;
(2) The draining vein is dilated like a phleboma, with the possibility of rupture. Special care should be taken when opening the flap, because the dura is filled with arterialized veins. If the fistula is located in the sinus wall and the intravascular embolization is not good, the sinus wall can be opened and the sinus can be filled with copper wire directly, with positive results.
(4) Radiation therapy, for the fistula is small and complex, radiation therapy can achieve certain results and small side effects, the total dose is 30-50Gy. The mechanism is that radiation therapy causes the inflammatory response such as necrosis, detachment and proliferation of endothelial cells, and gradually occludes the fistula to achieve the treatment purpose.
In conclusion, with the development of interventional neuroradiology, intravascular embolization has gradually become the main treatment for DAVF.
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