Imaging Diagnosis of Arterial TOS
Venous TOS is quite uncommon. However, the presentation of venous TOS is quite dramatic, and complications can be serious. Venous TOS occurs when a blood clot forms in the main vein draining the arm. Although some treatment questions remain unsettled, doctors treat the blood clot urgently. Following this, doctors undertake diagnosis and treatment of the underlying cause.
Your doctor will examine the thoracic outlet on each side for the presence of a pulsatile mass. This mass may prove a subclavian artery aneurysm, or a normal subclavian artery passing over a cervical rib. With or without an aneurysm, your doctor may hear a bruit in the thoracic outlet with her stethoscope. A bruit is a swooshing sound caused by turbulent arterial blood flow. Narrowing of an artery may cause blood pressure in the two arms to be different.
Because of the risk of permanent damage, your physician will always look for signs of acute arterial insufficiency, including the 5 Ps described above. Your physician will also look for signs of arterial emboli. These signs include skin ulcerations and discoloration, and splinter hemorrhages. Splinter hemorrhages are tiny emboli that travel from the damaged artery to small arteries in the fingers, causing tiny hemorrhages. Splinter hemorrhages are a sign of a proximal blood clot, usually in the arteries or heart. Their presence indicates the need for evaluation of the arteries or heart as a source of emboli. Finally, your physician will look for signs of chronic arterial insufficiency, including trophic skin changes, as described above.
Imaging tests are incredibly valuable tools in modern medicine. They are particularly valuable for a disease in a complex anatomic area like the thoracic outlet.
X-rays show excellent bone detail, but do not show soft tissue detail, and are limited to two dimensions. X-rays do not show arteries or veins. About 1% of the population has cervical ribs, but most of these people do not have arterial TOS. Even in patients with cervical ribs and arterial TOS, they have had cervical ribs their entire life, and only developed arterial TOS when they become symptomatic. X-rays thus have quite limited value in diagnosing arterial TOS and in planning treatment.
A flexible plastic catheter is inserted by a physician directly into an artery, usually in the groin. The physician advances the catheter under live x-ray (fluoroscopy) through the aorta, the main artery of the body, until it reaches the heart. At this point, the physician injects dye into the proximal aorta, after which the dye passes through the subclavian artery. As the dye passes through the arteries, x-rays create images. Direct angiography is an invasive test with a significant radiation dose. For this reason, CT angiography or MR angiography can almost always replace direct angiography.
Ultrasound is performed without any radiation, and can demonstrate blood flow in the arteries in real time, allowing dynamic movement of the arms during the examination. However, bones create severe blind spots, limiting assessment of bony compression of arteries. Ultrasound is also quite limited for viewing fibrous bands and muscle anomalies.
CT angiography is performed by injecting contrast into a peripheral vein, without an arterial catheter. CTA is fast, and shows excellent detail of bones and arteries. CTA requires significant radiation, and is limited in the evaluation of soft tissues, including fibrous bands and muscle anomalies. In cases of pure arterial TOS, CTA is the first-line test for many vascular surgeons.
MR angiography is performed by injecting contrast into a peripheral vein, without an arterial catheter. MRA shows excellent arterial detail while eliminating most other structures, including bones. It requires no radiation. If used in conjunction with MRI, superb soft tissue detail is available. Excellent depiction of fibrous bands, muscle anomalies, bones, and the brachial plexus is possible with MRI.
This interactive media demonstrates magnetic resonance angiography (MRA) images in two different patients. One patient has a normal MRA. The other patient has compression of each subclavian artery. Note that the structures that cause this compression are not visible on MRA alone.
Treatment of Arterial TOS
Critical treatment decisions revolve around the presence or absence of a blood clot causing arterial occlusion. When present, acute arterial occlusion demands urgent treatment. When absent, surgeons can assess and treat patients with arterial TOS less urgently.