What Is a Carotid-Cavernous Fistula?

Medically Reviewed by Whitney Seltman, OD on July 10, 2023
Written by WebMD Editorial Contributors
4 min read

Carotid cavernous fistula is a condition that affects your eye. It can come on suddenly after a head injury or slowly over time. 

A carotid-cavernous fistula is an irregular connection between your carotid artery and a vein called the cavernous sinus. The cavernous sinus is behind your eyes and drains blood from your facial veins.‌

There are two main types of carotid-cavernous fistulas:

Direct. This type is sometimes also called trauma carotid cavernous fistula. It is a hole or tear in a branch of your carotid artery inside the cavernous sinus. This tear is called a fistula, and it is usually caused by accident or injury, including:

  • Being hit in the head
  • Car accident
  • Fall 
  • Penetrating head injury like a stabbing
  • It can also be iatrogenic, which means it happens as a complication from surgery or treatment.‌

Indirect. This occurs when there is an irregular connection between the carotid artery and the cavernous sinus. ‌

It’s not exactly clear why it happens, but sometimes the artery, or a branch of the artery, will reroute and the blood flow changes. This rerouting is called a shunt. 

A spontaneous carotid fistula can happen because of a blockage in the artery or other conditions, including:

When a fistula happens, high blood flow from the artery is pushed into a low pressure cavernous vein. This causes problems with blood drainage from your eye socket and can cause your eye to bulge.‌

It can sometimes be confused for thyroid eye disease where an overactive thyroid causes your eyes to bulge.

Direct carotid fistulas usually happen within a few days or weeks of having a head injury. Symptoms can include:

Indirect carotid fistulas usually come on slowly over time. Symptoms can include:

  • Mild eye bulging
  • Eye congestion
  • Headache
  • Pulsing eyeball‌

Sometimes it’s also hard to close your eyes, which can cause dryness. If your eyelid is drooping, it might be hard to see, too. 

Your doctor will take your personal history and do a physical examination. They will also order some imaging tests to see what’s happening inside your head and eye. These can include:‌

Cerebral angiogram. A cerebral angiogram is an X-ray of your head and neck. It looks for any blockages or other irregularities in your blood vessels.‌

Pneumotonometry. This test measures the pressure inside your eyes by exposing it to a sudden puff of air.

Doppler ultrasonography. Your doctor will use a Doppler ultrasound to listen to the blood flow in your eye socket.‌

Magnetic resonance imagery. Also called an MRI, this imaging test will help your doctor see your veins, arteries, and your brain.

Sometimes a spontaneous fistula and a low flow fistula will get better and close on its own, but it’s unlikely that a direct fistula will. ‌

Treatment for a fistula depends on the blood flow rate. ‌

Compression therapy. If the flow rate is low, your doctor might use compression therapy. This is the least invasive treatment and involves putting pressure on your carotid artery in your neck with your hand several times a day for 4 to 6 weeks. This technique is about 30% effective.‌

Clipping the fistula. Surgery is an option for some fistulas. Clipping a fistula involves placing a clip on the opening in the artery to stop blood flow.‌

Fistula ligation. This procedure uses a stitch to tie off the artery and stop the blood flow.

Radiosurgery. This treatment is surgery that uses radiation to close the fistula. Radiosurgery is less invasive, but it can’t be used for emergency treatment.‌

Endovascular embolization. In this procedure, a catheter is pushed through your groin into the arteries in your brain. Glue is injected into the artery to block it off and lower blood flow to the area. 

The prognosis for a carotid cavernous fistula is generally good. It isn’t considered life-threatening, but you should have your eye treated right away to protect your eyesight and eye health. ‌

It can take a few weeks to months for the fistula to fully close and for blood flow to change. Once it is closed, symptoms improve within hours to days. 

Most people with indirect fistulas are better within 6 months of treatment. Sometimes people who have a direct fistula have lasting side effects, including:

If you’re experiencing changes in your eye or eyesight, talk to your doctor.