Dural arteriovenous fistula (DAVF)
What’s that?
Dural arteriovenous fistulas are direct connections between arteries and veins without capillary circulation. Unlike arteriovenous malformations, they are located in the thickness of the cerebral membranes, connecting with cerebral veins (venous sinuses of the dura mater).
The lack of capillary circulation, which usually lowers the pressure between arteries and veins, creates very high pressure in the cerebral veins, making it difficult for blood to flow away from the brain.
It may also develop in the spinal cord. Spinal dural arteriovenous fistula is the most common type of spinal cord vascular malformation, accounting for ~70% of all lesions. The peak incidence is between 50 and 60 years of age, with men more often affected than women.
Causes and risk factors
It is a relatively rare disease. It accounts for about 10-15% of cerebral arteriovenous malformations.
Unlike congenital arteriovenous malformations, dural fistulas are mainly acquired as a result of cerebral vein thrombosis due to infections, trauma, or surgery. However, the exact cause cannot always be determined.
What are the symptoms of the disease?
Spinal dural arteriovenous fistulas can cause symptoms of venous hypertension and stasis with spinal cord edema. The most common clinical manifestations are progressive pain, weakness in the lower extremities, or sensory disturbances. Sphincter dysfunction may occur. The onset of the disease is gradual, with the clinic progression over several years. A long time may elapse between onset and diagnosis. Hemorrhage is very rare, and dural fistulas may cause subarachnoid hemorrhage.
Increased arterial flow, resulting from the lack of capillaries, can manifest as a sensation of “noise” in the ears, synchronous with the heartbeat.
Increased venous pressure, if it affects a limited brain area, can cause cerebral hemorrhage or focal neurological deficits. If venous outflow obstruction affects the entire brain, there may be a progressive deterioration of all brain functions (dementia).
Increased pressure can also manifest as decreased vision due to damage to the optic nerves.
Finally, if fistulas involve the spinal cord, they can manifest as progressive mobility impairment, sensory impairment, and sphincter control.
Pathology
Spinal dural arteriovenous fistulas are a type of arterio-venous malformations and are characterized by the formation of abnormal access between the arteries and veins of the dura mater. In 85% of spinal fistulas, there is a single feeding artery.
Direct arterial flow into the venous system increases pressures in the venous plexus, which has no valves. The coronal venous plexus dilates, and venous drainage from the spinal cord decreases, leading to venous stasis and intramedullary edema. As a result, spinal cord ischemia and, eventually, infarction can develop. About 60% of spinal dural arteriovenous fistulas are spontaneous; the remainder are the result of trauma.
Diagnosis
MRI of the spinal cord
Spinal cord enlargement in the lower thoracic and conus region is typical, and MR signal changes at many levels are noted. Propagation levels and signal characteristics do not correlate with the level of the fistula.
CT angiography
It is used when there is a contraindication to MRI:
- CT angiography: allows localization of the fistula in 75% of cases;
- CT myelography: allows visualization of tortuous filling defects due to dilated veins.
Selective angiography
Selective X-ray angiography is considered the gold standard in the diagnosis of spinal dural arteriovenous malformations, but one must be aware of the potential risk of iatrogenic vessel dissection, which may lead to spinal cord ischemia. Not only may the location of the fistula not coincide topically with the level, but it may be several levels above or below. Complete angiography includes bilateral catheterization:
- intercostal arteries
- lumbar arteries
- of the medial and lateral sacral arteries.
- vertebral arteries
- of the ascending cervical arteries
- In the case of negative results from previous basin surveys, it may be necessary to consider the need for an assessment
- of the ascending pharyngeal artery
- meningeal-pituitary (posterior carotid-femoral) trunk
- of the middle meningeal artery
- occipital artery
Differential diagnosis
The differential diagnosis of dural arteriovenous malformations is performed according to the following diseases:
- intramedullary tumor;
- an artifact of cerebrospinal fluid movement;
- arteriovenous malformation – unlike DAVF, they are often combined with hemorrhage, have an acute onset, are equally common in men and women, and are detected at an earlier age.
What’s the treatment?
Some types do not require surgical treatment because there is no risk of cerebral hemorrhage. Others require treatment, which may be surgical, endovascular, or a combination of both.
The optimal treatment is chosen based on the fistula and its location, and surgeons and neuroradiologists evaluate it jointly.
All these treatment options are available in more than 180 hospitals worldwide (https://doctor.global/results/diseases/dural-arteriovenous-fistula-davf). For example, Radiosurgery can be done in 6 clinics across Israel for an approximate price of $11.8 K – 38.7 K (https://doctor.global/results/asia/israel/all-cities/all-specializations/procedures/radiosurgery).
Conclusion
Dural arteriovenous fistula is a potentially serious vascular disorder that can have diverse clinical presentations and requires prompt and accurate diagnosis to prevent complications. Advances in diagnostic imaging and interventional treatments have greatly improved the management and prognosis of DAVF, allowing for more precise targeting of the vascular abnormalities and better outcomes for patients. Continued research and awareness are key to enhancing treatment strategies and minimizing the impact of this condition on individuals’ quality of life.
