What Is a Carotid-Cavernous Sinus Fistula?
A carotid-cavernous sinus fistula (CCF) is an abnormal connection between an artery in your neck and the network of veins at the back of your eye.
These veins at the back of your eye transport blood from your face and brain back to your heart and are located in small spaces behind your eyes called cavernous sinuses. Sometimes an abnormal channel forms between these veins and one of the internal or external carotid arteries that run up each side of your neck.
This formation happens as a result of a small tear that sometimes occurs in one of the carotid arteries. If the tear occurs near the veins in the cavernous sinus, an abnormal channel may form between the artery and the network of veins, through which blood may flow. This is called a fistula.
A fistula can raise the pressure in your cavernous sinuses, which may compress the cranial nerves located around the cavernous sinuses. This compression may damage the nerve function, which is to control your eye movements. These cranial nerves also allow you to experience sensation in parts of your face and head. The increased pressure caused by the fistula can also affect the veins that drain your eye. This can cause symptoms such as eye swelling and abnormal vision.
CCF may be classified as direct or indirect.
Direct CCFs form between part of your internal carotid artery and the veins inside your cavernous sinus. In this type of fistula, there is usually a high blood flow rate. This type is most common.
Indirect CCFs form between the cavernous sinus veins and branches of the carotid artery in the membranes that enclose your brain. The rate of blood flow in these fistulas is usually low.
Indirect CCFs tend to cause fewer, less serious symptoms. This is because of their relatively low rate of blood flow. Direct CCFs usually require more urgent attention. For both types, symptoms may include:
- a bulging eye, which may pulsate
- a red eye
- an eye that protrudes forwards
- double vision
- loss of vision
- an audible swish or buzz coming from your eye
- weak or missing eye movements
- pains in your face
- ringing in your ears
Direct CCFs are most often caused by an accident or injury that tears your carotid artery wall. Causes may include:
- motor vehicle accidents
Indirect CCFs frequently arise without warning. They have no known cause. However, risk is increased with:
- high blood pressure
- hardened arteries (atherosclerosis)
- pregnancy and childbirth
- connective tissue disorders
Younger people are more likely to have a direct CCF.
Indirect CCFs are more commonly found in women from middle age onwards.
Your doctor will ask you questions and carefully examine your eye. You may need scans of your eye, nearby blood vessels, and cavernous sinus. Scans can be done with:
- computed tomography (CT)
- magnetic resonance imaging (MRI)
If the results suggest you have a CCF, you may need angiography. Your doctor can use this procedure to confirm your diagnosis.
For an angiography, contrast medium is injected into your blood vessels. Contrast medium is a special substance that shows up on X-rays. An X-ray of your head and neck is then taken. If you have a CCF, it should show up on the image.
In some cases, an indirect CCF will close without any treatment. However, severe or worsening symptoms may require surgery.
The main type of surgery for CCF is endovascular embolization. This surgery involves inserting a narrow tube into an artery in your groin. The tube is then threaded up to the fistula. Once there, materials such as metal coils can be used to seal off the connection.
There are several other treatments for CCF:
- Lubricating drugs can keep your eye from becoming too dry. You may need these if you can’t close your eye.
- Drugs may also be used to lower the pressure in your eye.
- As a last resort, it may be necessary to close your eyelid with stitches. This protects the surface of your eye. The stitches are removed when your condition resolves.
With treatment, symptoms usually improve within hours or days. Some people who have a direct CCF with severe symptoms won’t recover completely. However, most people return to health within six months.
Direct CCFs do not usually open again after surgery. However, indirect CCFs sometimes recur.