Dural arteriovenous fistulas are caused by direct arteriovenous communication within the dura mater, often supplied by the dural artery of the external carotid artery, the internal carotid artery, or the dural branch of the vertebral artery, which returns to the meningeal veins or venous sinuses.
Most DAVMs are acquired and can be secondary to head trauma, cranial surgery, venous sinus thrombosis, and diseases that cause increased pressure in the venous sinuses, most commonly in adults and most often in the transverse sinus, sigmoid sinus area, anterior skull base, and dura of the cavernous sinus area. A small number of DAVMs are congenital, commonly in children, and may be associated with cerebral AVM or Galen’s vein malformation.
Borden (1995) typed DAVM according to the type of veins draining the lesion.
Type I: are those that return only to the venous sinus and dural veins.
Type II: DAVM veins reflux to the venous sinus and dural veins in addition to the soft meningeal veins.
Type III: DAVM that only drains into the soft meningeal veins.
1.Etiology and pathogenesis
(1) Etiology
There is no uniform understanding of the mechanism of its occurrence, but it can be divided into two categories: congenital factors and acquired factors. Some people believe that dural arteriovenous malformation is related to congenital expansion of small arteriovenous circuits, and Robinson believes that the trophoblastic vessels of intracranial venous sinuses are derived from the external carotid artery system, and if there are developmental abnormalities, it is easy to form external carotid artery-cavernous sinus fistula; while in the early embryonic period, the transverse sinus is closely related to the external carotid artery, so dural arteriovenous malformation mostly occurs in the transverse sinus area. In addition, it is also believed that dural arteriovenous malformation is related to venous sinusitis, and any external factors such as trauma and surgery can cause the opening of reticular traffic between dural arterioles and venous sinuses to form arteriovenous fistulas. Most scholars emphasize that dural arteriovenous malformation and venous sinusitis are closely related, due to the formation of neovascularization after venous sinus embolization.
(2) Pathogenesis
The natural course of the disease is highly variable and unpredictable. Some lesions are found incidentally and may remain unchanged for years; some patients have definite symptoms (such as tinnitus or intracranial murmur), but the lesions do not progress, and even the formed thrombus may resolve spontaneously, especially in DAVM in the cavernous sinus, which often occludes itself. However, some other lesions progressively expand and rupture, causing fatal intracranial hemorrhage or neurological impairment.
2.Epidemiology
Dural arteriovenous malformations account for 5% to 20% of intracranial vascular malformations, with the transverse sinus and sigmoid sinus area being the most common, while supratentorial dural arteriovenous malformations are relatively rare. 35% of typical dural arteriovenous malformations occur in the subscripts, while supratentorial ones account for only 6%. The age of onset is mostly from 32 to 65 years old, with an average of 50 years old. Occasionally, it is seen in children or adolescents. There are more males than females. In recent years, with the development of imaging technology, the detection rate has increased and the incidence has increased.
3.Clinical manifestation
Since dural arteriovenous malformation is located outside the brain, it rarely shows neurological symptoms and signs unless the dural arteriovenous malformation flows back into the venous sinus with sinus cortical venous reflux, dural arteriovenous malformation flows directly into the cortical vein or dural arteriovenous malformation with large venous pool.
Intracranial vascular murmur: This is the most common clinical manifestation of dural arteriovenous malformation, 67% to 79% of patients have subjective or objective vascular murmur. The murmur is consistent with the pulse, is booming and persistent, and becomes the most unbearable symptom for the patient. The degree of intracranial vascular murmur is related to the blood flow and location of the dura. If the vertebral artery is not involved in the blood supply, compression of the affected carotid murmur may diminish or disappear.
Headache: Many patients with dural arteriovenous malformation have headache, the possible causes of which are: dural arteriovenous malformation “steals blood” seriously, resulting in dural ischemia. Increased intracranial pressure. Intracranial hemorrhage. Irritation of the meninges by the dilated malformed vessels. Persistent intracranial vascular murmur can cause patients’ nervousness and poor rest, and headache can also occur.
4.Complications
Some patients with mixed dural arteriovenous malformation may have angry and distorted scalp vessels, or even form vascular masses. When the dural arteriovenous malformation of the posterior cranial fossa drains into the spinal cord, it can cause intravertebral venous hypertension, resulting in spinal cord ischemia and spinal cord damage. High blood flow may also be accompanied by heart enlargement and heart failure.
5.Examination
(1) Laboratory tests: no special performance.
(2) Cerebral angiography: It is the most important tool for diagnosis and typing of DAVM, which can clearly show the manifestations of malformed vessels from arterial to venous stages, and is conducive to the typing of lesions and understanding the relationship between angiographic changes and clinical manifestations and prognosis, especially to observe whether there is embolism in the involved venous sinuses and the direction of venous return, which is decisive for the design of treatment plans.
(3) Precautions for angiography.
(1) Six-vessel angiography should be done, i.e., bilateral internal carotid artery, external carotid artery and vertebral artery should be angiographed separately.
(2) If the lesion is in the occipital foramen, aortic arch angiography should be added.
③The film should be placed in the early arterial phase that is started and maintained to the venous phase appropriately.
④Digital subtraction technique and super-selective cannulation technique should be used to increase the diagnostic value of cerebral angiography.
⑤ Magnetic resonance arteriography/venography: It can show the anatomical structure of dural arteries and veins non-invasively. However, the resolution is poor and cannot meet the clinical diagnostic requirements. At present, it is only used as one of the means to screen and follow up DAVM.
6.Diagnosis
Based on the patient’s history of intracranial hemorrhage, with epilepsy, optic nerve dysfunction, intracranial murmur and eye protrusion, combined with cerebral angiography clearly showing the lesion site, size, blood supply artery and drainage vein, etc., the diagnosis can be confirmed.
7.Differential diagnosis
Attention should be paid to differentiate from cerebral arteriovenous malformation. Sudden subarachnoid hemorrhage under the age of 40 with history of epilepsy or mild hemiparesis, aphasia, headache before hemorrhage without obvious increase of intracranial pressure should be highly suspected of arteriovenous malformation. However, a clear differential diagnosis depends on cerebral angiography, CT and MRI examinations.
8.Treatment
The treatment plan should be selected and formulated according to the patient’s past clinical manifestations, current clinical condition and angiographic manifestations.
Since the chance of rupture and bleeding in DAVM is small and individual patients can even heal spontaneously, only follow-up observation and annual cranial MRI examination are needed, except for the appearance of cortical drainage veins. Cerebral angiography can be repeated within a few years if cortical drainage veins are suspected or if clinical symptoms change. Pain and intracranial murmurs are the most common subjective symptoms that affect the patient’s quality of life. Symptomatic management, such as non-steroidal anti-inflammatory drugs, carbamazepine or short-term hormonal therapy, can be given in mild cases and is effective in relieving pain and pulsatile murmurs. However, for pain in the trigeminal nerve distribution area, percutaneous puncture to destroy the nerve root should not be used, as it may puncture the malformed blood vessels and cause hemorrhage.