Ultrasound of Cerebral - Right Left Shunt Tcd

What Is a Right-Left Shunt Transcranial Doppler (TCD)?

A right-left shunt TCD is a specialized ultrasound exam that uses harmless high-frequency sound waves to measure the speed and direction of blood flow through the cerebral arteries that supply your brain. The test is designed to identify abnormal right-to-left shunts: unwanted connections that allow deoxygenated blood from the right side of the heart or pulmonary circulation to flow directly to the left side of the heart and then to the brain, bypassing the lungs where it would normally be oxygenated. Common causes of these shunts include patent foramen ovale (a small hole in the heart wall that failed to close after birth), pulmonary arteriovenous malformations (abnormal tangle of blood vessels in the lungs), or other rare vascular abnormalities.

Clinical Uses for the Nervous System

This exam is most commonly ordered to evaluate the cause of unexplained ischemic stroke or transient ischemic attack (TIA, or mini-stroke) in people under age 55, as right-to-left shunts are a common cause of paradoxical embolism (a blood clot that bypasses the lungs and travels directly to the brain). It is also used to screen for shunts in people with recurrent migraines with aura, unexplained hypoxemia (low blood oxygen), decompression sickness in scuba divers, or suspected pulmonary arteriovenous malformations in people with hereditary hemorrhagic telangiectasia (HHT, a genetic condition that causes abnormal blood vessel growth).

What to Expect During the Exam

The 30-minute exam is performed while you lie flat on an exam table, and no enclosed imaging machine is used, so there is no claustrophobia risk. A small, handheld ultrasound transducer coated with gel will be placed on your scalp over thin areas of your temporal bone (called temporal bone windows) to send and receive sound waves that measure blood flow in your cerebral arteries. You may be asked to perform a Valsalva maneuver (hold your breath and bear down as if having a bowel movement) during the test, as this increases chest pressure and can open a latent shunt that is not active at rest. The procedure is completely painless, and you can return to your normal activities immediately after it is completed.

Preparation and Aftercare

No special preparation is required for this exam: you can eat, drink, and take your regular medications as normal before your appointment. Avoid applying heavy hair products such as gel, hairspray, or pomade to your hair on the day of the test, as these can create a barrier between the transducer and your scalp and interfere with image quality. Wear loose, comfortable clothing that is easy to remove if needed to access your scalp.

Understanding Your Results

Normal results show no abnormal blood flow patterns that indicate a right-to-left shunt. An abnormal result means a shunt was detected, and your healthcare provider will discuss next steps, which may include a confirmatory bubble study echocardiogram (an ultrasound of the heart) to locate the exact source of the shunt. If the shunt is causing symptoms or increasing your risk of stroke, treatment options may include blood thinners, or a minor catheter-based procedure to close the shunt.