What are arteriovenous fistulas?
Arteriovenous fistulas (AVFs) are rare abnormalities in which arteries connect directly with veins, bypassing the capillaries. They can occur anywhere in the body. The Cerebrovascular Surgery and Interventions Center treats arteriovenous fistulas and other cerebrovascular conditions.
Brain AVFs are most often found in the dura mater, the protective membrane lining the brain and spinal cord, also called the meninges. These are referred to as dural AVFs (dAVFs). Another, rarer type of AVF involves vessels on the surface of the brain itself; these are known as pial AVFs (pAVFs).
Depending on their location and which blood vessels are involved, AVFs may need to be treated urgently, depending on the risk they pose.
What is an AVF?
How are AVFs treated?
What is surgery like?
What is a follow-up like?
Anatomy of an AVF
AVFs place a strain on the blood vessels. Normally, the arteries that carry high-pressure, fast-flowing blood branch into smaller and smaller vessels, ending in capillaries, where blood flow slows down and the tissues get oxygen. The veins then carry low-pressure, slow-flowing blood from the capillaries back to the heart.
But in AVFs, veins in the brain or spinal cord receive high-pressure blood directly from the arteries, bypassing the capillaries. The extra strain on these veins can cause them to bleed, a potentially life-threatening or permanently disabling event. Even if there is no bleeding, chronically elevated pressure in these veins can eventually damage brain or spinal tissue, leading to progressive neurological dysfunction.
Arteriovenous Fistulas | Symptoms & Causes
In some cases, children develop AVFs before birth. Several gene mutations affecting blood vessel development have been found in children with AVFs.
Children with blood-clotting disorders are also more likely to develop AVFs. However, AVFs can occur in anyone, sometimes as a complication of a head injury, a serious infection, or severe dehydration.
Symptoms of AVFs will vary depending on the child’s age, the location, and the rate of blood flow. Brain AVFs in newborns can cause heart failure. Older children may have any of the following symptoms, depending on the type of AVF, its location and whether it is causing bleeding:
- mild heart failure symptoms (such as shortness of breath)
- very prominent veins in the face and scalp
- bulging, redness, or pain in the eye, or vision problems
- hearing a whooshing or pulsing sound
- enlarged head (in infants)
- stroke-like symptoms
- cognitive impairment
- weakness or sensory loss in the legs, or (for back and spine AVFs) changes in the child’s urinary or bowel movement pattern
Arteriovenous Fistulas | Diagnosis & Treatments
How do we diagnose AVFs?
Arteriovenous fistulas are diagnosed by noninvasive imaging of the brain to determine their location. Usually, diagnosis begins with one of the following imaging studies:
- CT angiography (CTA): This test uses the technology of a conventional CT scan and a special dye (known as contrast) injected into a vein to generate images of the blood vessels. During CTA, the child must lie still on a table that slides slowly through a donut-shaped device (young children may need sedation to keep them still). A computer then constructs three-dimensional images of the blood vessels from the CTA images.
- Magnetic resonance angiography (MRA): These scans, based on MRI technology, generate images of the blood vessels, usually without the need to inject a contrast dye. They also avoid the use of x-rays.
Sometimes a catheter angiogram (also known as a cerebral angiogram or cerebral arteriogram) is needed. This test uses live x-rays to produce detailed images of the arteries and veins. A small needle is inserted into an artery in the groin, and a catheter (a thin, flexible tube) is guided to the area being studied. A special dye, injected through the catheter, allows the radiologist to more clearly see the AVF and the pattern of arteries and veins surrounding it. This test is usually done under general anesthesia. Read more about angiograms.
The treatment team at the Cerebrovascular Surgery and Interventions Center will provide advance instructions on how to prepare for these tests.
In addition to imaging tests, our neurologist colleagues may conduct a variety of specific tests to assess the child’s brain function. In addition, Boston Children’s often recommends that children with AVFs have blood testing for disorders that cause abnormalities of blood clotting, as these can increase their risk for AVF complications. Finally, we often recommend genetic screening for children with AVFs, as they may have a genetic mutation that can potentially cause other medical problems.
How do we treat arteriovenous fistulas?
The goal in treating AVFs is to close off the fistula before the abnormal blood flow can damage the brain or spinal cord. The treatment team at the Cerebrovascular Surgery and Interventions Center customizes the approach to each child, depending on the type of AVF, where it is located, and the pattern of surrounding vessels.
For pial AVFs, we almost always recommend treatment as soon as possible. In about half of the children we see, we are able to use a minimally invasive, catheter-based treatment known as endovascular embolization. Dural AVFs are sometimes less urgent, and can almost always be treated with endovascular techniques.
When the AVF cannot be closed with the endovascular approach, we treat it with neurosurgery, or through a combined surgical/endovascular approach. In our experience, most children have an excellent prognosis.
Endovascular embolization uses a catheter (a thin, flexible tube) to inject various glue-like compounds into the vessel or insert tiny devices to close off the fistula.
The procedure is performed under general anesthesia. A guide catheter is inserted into an artery in the child’s groin through a tiny incision and, guided by live x-ray pictures, advanced to the vessels in the neck. The neuro-interventional radiologist then injects a contrast solution (a dye) through the catheter to visualize the blood vessels.
Multiple images may be taken to determine which vessels need embolization. Once these have been identified, a thinner microcatheter is inserted through the first catheter and advanced directly into the vessels in the diseased brain area to inject the embolic agent or device.
Most children have no pain or other symptoms with embolization, and recovery is usually rapid. In some instances, a child will be admitted to the ICU for several days of observation. Patients usually leave the hospital within a few days and return for a follow-up office visit within a few weeks. Follow up may be in part through video teleconference for patients who live outside the Boston area.
Though there are some serious risks, complications from embolization are rare. Because it uses x-rays, the procedure does require exposing patients to ionizing radiation. Because children are more sensitive to radiation than adults, we have established protocols that enable us to deliver the lowest possible dose.
In addition to treating the AVF itself, children with blood-clotting abnormalities can be treated with medications to reduce their risk for AVF complications. In children who have mutations identified on genetic testing, follow-up with a genetic counselor and other medical specialists may be recommended.
How we care for AVF at Boston Children’s Hospital
Our goal is always to close off the AVF before the abnormal blood flow can damage the brain or spinal cord. The Cerebrovascular Surgery and Interventions Center team will recommend the best technique or combination of techniques for each child, based on the type of AVF and its location, and guided by detailed imaging studies. In our experience, most children have an excellent prognosis.
Arteriovenous Fistulas | Research & Innovation
The Cerebrovascular Surgery and Interventions Center continually adopts, enhances and pioneers new minimally invasive strategies and devices to treat arteriovenous fistulas (AVF) safely in the youngest children. Our extensive experience with AVFs, captured in a comprehensive database, allows us to track long-term outcomes, compare the results of different procedures and improve our quality of care. Some of our initiatives in research include the following:
- 3D printing to model brain and vascular anatomy: Working with the Simulations group at Boston Children’s Hospital, Edward Smith, MD, and Darren Orbach, MD, PhD, are pioneering the creation of precision 3D models of individual patients’ brains and blood vessels, using the data from brain scans. These models, created with special digitally guided printers that lay down different types of molten plastic, are helping our physicians plan neurosurgical and embolization procedures in advance.
- A variety of novel techniques developed and tested here have allowed safe use of catheters and endovascular devices in infants’ tiny vessels.
- New techniques have dramatically improved safety and reduced children’s radiation exposure during endovascular embolization. Working closely with fluoroscopy equipment vendors to adjust and optimize technical factors, we have demonstrated that it is possible to achieve high-quality imaging at low radiation doses. Read more.
- We successfully adopted Onyx, an improved material used for endovascular embolization in adults, to treat dural AVFs and other cerebrovascular malformations in children. We have more experience using Onyx in children than any other center, and our safety record is unparalleled.
- We have conducted research implicating mutations in the gene RASA1 as one potential cause of spinal AVF in children.