The cavernous sinuses are small spaces located behind your eyes. They contain veins that transport blood from your face and brain back to your heart.
A pair of internal and external carotid arteries runs up each side of your neck. These carry blood to your brain. Sometimes a small tear occurs in one of these arteries. If this happens near the veins of the cavernous sinus, a channel may form between them. This is called a fistula. It shunts blood from artery to vein.
The cranial nerves are located around your cavernous sinuses. They are responsible for controlling your eye movements. They also experience sensation in parts of your face and head. A fistula can raise the pressure in the cavernous sinus. This may compress the nerves and damage their function. The increased pressure can also affect the veins that drain your eye. This can cause symptoms such as eye swelling and abnormal vision.
CCF may be classed as direct or indirect.
Direct CCF is a connection 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 CCF form between the cavernous sinus veins and branches of the carotid artery in the membranes that enclose the brain. The rate of blood flow in these fistulas is usually slow.
Direct fistulas are most often caused by an accident or injury that tears the carotid artery wall. Causes may include:
- motor vehicle accidents
Indirect fistulas 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 fistulas are more commonly found in women from middle age onwards.
Indirect carotid-cavernous sinus fistulas tend to cause fewer, less serious symptoms. This is because of their relatively low rate of blood flow. Direct fistulas usually require more urgent attention. For both types, symptoms may include:
- a bulging eye, which may pulsate
- a red eye
- an eye which 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
Your doctor will ask you questions and carefully examine your eye. You may need scans of your eye, nearby blood vessels and the 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. This can confirm the diagnosis.
For an angiography, contrast medium is injected into your blood vessels. This 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 fistula 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. Not everyone who has a direct fistula with severe symptoms will recover completely. However, most people return to health within six months.
Direct carotid-cavernous sinus fistulas do not usually open again after surgery. However, indirect fistulas sometimes recur.