Arteriovenous Fistula (AVF)
An arteriovenous fistula, or AVF, is an abnormal connection of vessels in the tissues around the brain or spinal cord. It happens when one or more arteries are directly connected to one or more veins or venous spaces called sinuses.
- Arteries carry blood from the heart to the tissues, and veins take blood back from the tissues to the heart. In an AVF, there is a direct connection between one or more arteries and veins or sinuses, which gives rise to many problems.
- AVFs differ from arteriovenous malformations (AVMs) in that AVMs are found within the tissue of the brain or spinal cord, but AVFs are found in the coverings of the brain or spinal cord, such as the dura mater or arachnoid.
- The most serious problem associated with AVFs is that they transfer high-pressure arterial blood into the veins or venous sinuses that drain blood from the brain or spinal cord. This results in an increase in the pressure of the venous system around the brain or spinal cord.
Symptoms of AVF
There are two major types of AVFs: dural AVFs and carotid-cavernous fistulas (CCFs). These are acquired lesions, which means that patients are not born with them, but instead develop them later in life. They can be a result of infection or traumatic injuries, but most develop without any specific cause.
Patients with dural AVFs typically experience a rumbling noise in one ear that follows the heartbeat, which is called a bruit. Patients with CCFs typically note swelling and redness of one or both eyes in addition to a bruit.
Diagnosis of AVF
AVFs are most commonly diagnosed with an angiogram (also called an arteriogram), a test in which a neuroradiologist injects dye into the blood vessels in the brain and obtains images of the blood vessels.
At present, the angiogram is the test that most accurately shows the AVF and its relationship to the surrounding arteries and veins. In the case of most AVFs, the CT and MRI scans are often read as normal.
The goal of treatment is to close the AVFs before the increased pressure in the venous system causes irreversible damage to the brain and spinal cord.
The cerebrovascular team at Johns Hopkins evaluates each AVF patient to decide the best treatment for the patient's specific situation, using one or both of two methods, depending on the type of AVF:
Minimally invasive endovascular embolization — This technique is typically sufficient to repair the majority of AVFs. During this procedure, the surgeon passes a catheter through the groin up into the arteries in the brain that lead to the AVF and inject a glue-like liquid into these arteries. This injection shuts off that artery and reduces the flow of blood through the AVF.
Microsurgical resection — For AVFs that cannot be closed with endovascular embolization, the surgeon may perform a microsurgical resection and craniotomy, using the microscope to isolate the AVF from the tissues around the brain or spinal cord.