Dural arteriovenous fistula is a rare vascular malformation, accounting for 10-15% of all intracranial vascular malformations.
1.Concept.
The so-called dural arteriovenous fistula is actually an arteriovenous fistula that occurs in the dura mater and its accessory structures. To clarify the dural arteriovenous fistula, we must first clarify what is dura mater and what is arteriovenous fistula. The dura is a tough, shiny, double-layered membrane that covers the surface of the brain tissue and the inner side of the skull, acting as both a meningeal and a cranial periosteum. Between the two layers, some parts form conduits for blood flow through veins, called dural venous sinuses; the inner layer of the dura mater forms folds inward, and the part of it that extends between the cerebral hemispheres is called the cerebral falx; and the part that extends between the brain and cerebellum is called the cerebellar curtain. All of these can be accessory structures of the dura mater. The vasculature of the dura mater is rich in arterioles between the two layers of the membrane, in addition to the venous sinuses. Arteriovenous fistulas are direct short-circuits between arterioles and venous vessels and can be congenital or result from a variety of acquired factors. Arteriovenous fistulas can occur in various parts of the body containing the vascular system. When the arteriovenous fistula is located on the dura mater and its above-mentioned accessory structures, we call it a dural arteriovenous fistula.
2. Etiology.
Dural arteriovenous fistula is currently recognized as an acquired disease, often due to pathological changes formed by narrowing or occlusion of the dural venous sinuses due to trauma, inflammation or compression by tumors (e.g. meningioma), but it is also commonly seen in children under 10 years of age with cerebrovascular malformations, and rarely has an obvious cause, so it was once thought to be due to congenital causes.
3. Clinical presentation.
The clinical manifestations of dural arteriovenous fistulas are varied and can present with only mild symptoms or with fatal cerebral hemorrhage. The clinical manifestations of DAVF are closely related to its venous drainage, which is diverse due to the diversity of its venous drainage, and the mode of venous drainage determines the severity of the clinical manifestations and the patient’s prognosis. DAVF draining through the supratrochlear and infratrochlear sinuses and the lateral sinus area usually presents first with tinnitus; DAVF draining through the ophthalmic veins presents with ocular symptoms such as protruding eyes and conjunctival congestion; patients draining through the cortical veins may present with cerebral hemorrhage and neurological dysfunction; those draining through the deep veins with increased intracranial pressure may present with coma or rapid decline in cognitive function. Cerebral hemorrhage and neurological deficits are the most severe. Cerebral hemorrhage can manifest in various forms, the more common ones being intracerebral hematoma and subarachnoid hemorrhage. Patients presenting with intracranial hemorrhage can have up to a 35% risk of rebleeding within two weeks.
The clinical presentation is also related to the site of the fistula, as the venous drainage of DAVF often varies from site to site. The arteriovenous fistula in the spongy sinus area often drains through the ophthalmic veins, so it usually starts with conjunctival congestion, edema and visual disturbances, even pulsating proptosis, and it is often combined with drainage from the superior and inferior petrosal sinuses, as well as with intracranial murmurs or tinnitus. Arteriovenous fistulae in the lateral sinus and jugular foramen: pulsatile tinnitus is common, and in some cases, headache is present. Arteriovenous fistulas in the superior sagittal sinus area often cause impaired limb movement, and in severe cases, impaired consciousness. DAVF in the base of the anterior cranial fossa and the canopy area usually only drains through the cortical veins due to the lack of venous sinuses in the adjacent areas, and mostly manifests as intracranial hemorrhage.
4. Diagnosis.
Similar to the diagnosis and treatment process of any other diseases, the diagnosis of intracranial DAVF requires a combination of clinical symptoms, physical examination and auxiliary examinations and other clinical information.
Because of its relatively low incidence but complex and diverse clinical manifestations, it is often seen in different departments, such as ophthalmology for eye symptoms, otolaryngology for intracranial murmur and tinnitus, neurology for dementia and epilepsy, or orthopedics for spinal cord dysfunction, and neurology for some of the ancillary tests suggesting intracranial abnormalities or new clinical symptoms. Neurosurgery is usually consulted only when some of the ancillary tests suggest intracranial abnormalities or new clinical symptoms appear.
Routine cranial CT and MRI examinations usually reveal disturbed vascular flow at the site of the lesion, especially abnormal dilatation of venous sinuses, draining cortical veins, or other manifestations. For example, DAVF in the cavernous sinus area with ocular symptoms is usually associated with dilated supraocular veins, DAVF in the sinus commissure area is often associated with bilateral transverse sinus occlusion or stenosis and extensive tortuous dilatation of cortical veins, and DAVF in the anterior cranial fossa base is often associated with dilated frontal pole veins. These indirect signs suggest the possible presence of DAVF, but CT and MRI examinations cannot be used as an exclusionary screening tool. CTA and MRA examinations based on CT and MRI angiography can partially reconstruct the three-dimensional vascular architecture of the lesion, but still cannot clearly show the lesion structure and low-flow lesions due to spatial and temporal resolution limitations. Therefore, whole-brain vascular DSA examination remains the gold standard for the diagnosis of DAVF.
Cerebral angiography is still the gold standard for the diagnosis of the disease. Once the clinical presentation and general ancillary tests suggest the diagnosis, the physician will usually arrange for a detailed cerebral angiogram to confirm the diagnosis and clarify the staging and develop a treatment plan. Detailed cerebral angiography generally needs to clarify the location of the fistula, the source of the blood supply artery, the characteristics of the draining veins, and the cerebral circulation disorders in order to interpret clinical symptoms and determine the prognosis and develop a treatment plan. Superselective cerebral angiography is the only reliable means of confirming the diagnosis and studying the disease.
5. Clinical staging.
Whether it leads to cerebral hemorrhage, focal neurological deficits, cognitive dysfunction, epilepsy, and vision loss are the main indicators to evaluate the severity of dural arteriovenous fistulae, and whether they produce these malignant manifestations is related to the vascular constitution of the disease, which is mainly venous drainage. With further understanding of the course and structure of the disease, many scholars have proposed different staging methods to evaluate and predict the severity and clinical course of the disease.
6.Treatment.
Currently there are various treatment methods for DAVF, including conservative therapy, endovascular therapy, surgery, stereotactic radiation therapy, and the combination of two or even more of the above methods. As mentioned earlier, conservative treatment is applicable to some Borden type I DAVF, including carotid artery compression and compression of the eye. Endovascular embolization treatment can be divided into transarterial access, venous access and combined arteriovenous access according to the treatment route. Craniotomy can treat some dural arteriovenous fistulas, and stereotactic radiation therapy can be used for small, recurrent or involved fistulas. For different types and locations of DAVF, doctors will choose the appropriate treatment method according to the situation.
7.Prognosis.
With the increasing understanding of the vascular architecture of the disease, the progress of the treatment level especially the progress of embolization technology and various embolization materials, the cure rate of dural arteriovenous fistula has increased significantly, and some complex dural arteriovenous fistulas have also changed from incurable to curable, from only palliative treatment in the past to complete cure. However, there are still very few complex dural arteriovenous fistulas with multiple fistulas that have progressed further despite multiple treatment options. As mentioned earlier, dural arteriovenous fistula is a complex and rare intracranial vascular malformation that requires the surgeon to have a thorough knowledge of the vascular architecture of the disease and to develop a perfect surgical plan with the aim of cure and to select the appropriate embolic material; otherwise, not only will the disease not be cured, but the chance of complications increases and even brings greater obstacles to further treatment.
For the already existing focal neurological deficits, such as blindness and limb deficits, there may be a certain degree of recovery after surgery, but complete recovery is unlikely; for the neurological deficits caused by increased intracranial pressure, such as cognitive decline and acute type coma, there is a possibility of complete recovery after complete embolization of the disease if it does not occur for a long time. Although the treatment of the disease is improving and the cure rate is increasing, the possible complications still cannot be completely avoided and certain complications may remain, which may even be life-threatening in severe cases. The main sequelae may include cranial nerve injury such as facial palsy, blindness, diplopia, facial sensory impairment, focal neurological deficits such as speech dysfunction, limb hemiparesis, etc.
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