Arteriovenous malformations (AVMs)

Normally, blood flows from arteries into a fine mesh of tiny vessels called capillaries, and then into veins. The capillaries slow the blood down and feed the tissue. In an arteriovenous malformation (AVM), some arteries connect directly to veins, skipping the capillaries. High-pressure blood rushes straight into the veins, which stretch and enlarge over time.

The spot where arteries and veins meet is called the nidus (Latin for nest). A simpler AVM with a single direct connection is called an arteriovenous fistula. Most AVMs start before birth, even if they are not noticed until childhood, the teenage years or adulthood. They are not cancer and do not spread.

AVMs belong to a larger family of vascular malformations. Most others, such as venous or lymphatic malformations, have slow flow. AVMs are the fast-flow type, which is why they behave differently and need careful planning.

AVMs in the brain and spinal cord are managed by specialized neurovascular teams. This page focuses on AVMs in the rest of the body: arms, legs, pelvis, lungs, kidneys, face and other organs.

Symptoms depend on where the AVM is, how big it is and how much blood flows through it. Many start quietly and grow slowly over years. Growth often speeds up during puberty, pregnancy, after an injury or after incomplete surgery.

Lung AVMs deserve a special mention. They let blood skip the lung's natural filter, so small clots or bacteria can pass to the brain. Many people with lung AVMs have an inherited condition called hereditary hemorrhagic telangiectasia (HHT), which also causes frequent nosebleeds and red spots on the lips and hands. If you have HHT, your family members should be screened too.

Doctors often describe AVM stages to guide timing. A quiet AVM may be warm and pink but stable. An expanding AVM gets bigger and starts to pulse. A destructive AVM causes pain, sores or bleeding. A very large AVM can strain the heart. Treatment is usually considered once an AVM is growing or causing symptoms.

Our first goal is to confirm the diagnosis, because some tumors can look like vascular malformations. We then map the AVM in detail so we can plan the safest treatment.

What we see

Every AVM is different, so treatment is planned around its location, size, symptoms and your goals. For all but the simplest AVMs, your history, exam and imaging are reviewed by a team that includes interventional radiology and vascular surgery.

Embolization means blocking the abnormal vessels from inside. We guide a catheter through an artery, or place a needle directly into the AVM, and inject materials such as liquid glue-like agents, alcohol or tiny metal coils. The aim is to close the nidus itself, not just the arteries feeding it. Blocking only the feeding arteries tends to make the AVM recruit new ones and come back worse.

For lung AVMs, the feeding artery is usually closed with coils or plugs in a single session. Learn more on our AVM embolization page.

With an AVM, the most important thing I do happens before any treatment: I study the angiogram and MRI until I understand exactly where the nidus is and what surrounds it. I tell patients honestly that large AVMs are often controlled rather than cured, and that we will likely treat in stages. My goal is to make you feel better and keep the AVM from causing harm, while protecting the healthy tissue around it.

Fabio Komlos, MD, interventional radiologist · About Dr. Fabio Komlos

Embolization is usually an outpatient procedure, meaning you go home the same day. We do these procedures at El Camino Hospital in Mountain View, in a specialized procedure room with X-ray, ultrasound and CT imaging. Most are done with local numbing and moderate sedation, which makes you relaxed and drowsy. Some complex AVMs need general anesthesia.

A small tube is placed in the groin, wrist or directly into the malformation. There is no incision and no stitches. Afterward you are watched for at least 2 hours to make sure there is no bleeding before you go home.

1. First few days
   Pain and swelling in the treated area are expected and can be significant. Anti-inflammatory medicine, pain medicine and sometimes a short course of steroids help.
2. 1–2 weeks
   Swelling settles. Keep the area raised if it is an arm or leg. Watch the skin over the AVM.
3. Monthly during treatment
   We usually see you in clinic about once a month while treatment is under way, and plan the next stage if needed.
4. Long term
   Periodic imaging to watch for regrowth. AVMs can recur, and a repeat treatment is sometimes needed.

Outcomes vary a lot because AVMs vary a lot. Small AVMs, especially those with a single draining vein, can often be cured with embolization alone. Large, spread-out AVMs are usually not curable, but most people get meaningful relief of pain, bleeding and swelling with treatment.