Q.For several weeks I've been hearing this thump, thump, thump in my right ear. It's worse when I lie on my right side, and I've discovered that it keeps time with my heartbeat. Is this a form of tinnitus? Is there any treatment for this condition?

A.You do have a form of tinnitus, but the kind you have can be a clue to a serious condition. You should see your doctor for a complete evaluation of this problem.

Tinnitus means a ringing, buzzing or whirring in the ears. The type you have is known as pulsatile tinnitus. This means that you hear your heart each time it beats.

Pulsatile tinnitus is different from the pounding that everyone may occasionally hear after they've exercised intensely or when they're really excited. The key difference is that they hear this pounding in both ears. But with pulsatile tinnitus, you generally hear it in just one ear. And in some people with pulsatile tinnitus, a doctor can sometimes hear the same sound when listening to their head with a stethoscope.

There are a handful of conditions that can cause pulsatile tinnitus. As you might imagine, most of these involve the blood vessels near the ear. These include:

* Hardening of the arteries going from the heart to the brain.

* An abnormal connection between an artery and vein known as an A-V fistula.

* A tumor of a blood vessel at the base of the skull, known as a glomus jugulare tumor.

* An abnormal bulge in an artery, known as an aneurysm.

* A clot within a large blood vessel in the brain, known as a venous sinus thrombosis.

* A narrowing of arteries from a condition called fibromuscular dysplasia.

* A partial rupture of one of the arteries going to the brain, known as an arterial dissection.

* Abnormal clusters of blood vessels known as an A-V malformation.

* Increased pressure inside the skull, known as intracranial hypertension.

Some of these conditions can lead to serious complications, including stroke, paralysis and even death. But if discovered early enough, most can be successfully treated, usually by surgery.

To see what could be causing your problem, your doctor can order several tests that check the blood vessels in your head. These include ultrasound, CT scan, MRI and MRI angiography. This last test shows the blood flow in your arteries without putting a needle or catheter in one. But the ultimate test is angiography of your blood vessels. This test is done by injecting dye through a catheter inserted in a large artery in your leg and advanced to the carotid artery in your neck.

The treatment of pulsatile tinnitus depends on its cause. In some cases, no treatment is necessary; in this situation, the tinnitus is a sign of an underlying condition, such as hardening of the arteries by plaque, and in itself doesn't need treatment. In other cases, surgery to remove or fix an abnormal blood vessel or tumor will keep the underlying problem from causing serious harm.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.