The thumb is a remarkable appendage. By allowing us to grasp objects, to use tools, to write, the thumb has helped us evolve above and beyond all other animal species. Can the thumb also be useful in helping us detect an enlarged aorta?
The aorta is the main artery of the body. It arises from the heart, courses through the chest and abdomen and ends by splitting into two arteries to supply blood to the lower extremities. Arteries arise from the aorta to supply blood and oxygen to the heart, brain, stomach, kidneys and all of the muscles of the torso and the upper extremities. The aorta is divided into two main parts, the thoracic (chest) aorta and the abdominal aorta. One of the most serious, and deadly, problems with the aorta is an aortic aneurysm. An aneurysm is an enlargement of the aorta. As the aortic diameter increases and balloons out, the wall of the aorta weakens. At some critical size, the wall is so weak that it can burst open. Unfortunately when that happens, the patient most likely will die from bleeding. The keys to managing an aortic aneurysm is to identify an aneurysm, monitor its growth and size and refer the patient to surgery to repair the aorta before it ruptures. Aneurysms of the thoracic and abdominal aorta have different causes and different ways to monitor them.
The exact cause of abdominal aortic aneurysm (AAA) is not known. It does occur in families and those with a first-degree relative with AAA are at two times the risk. AAA can occur in the setting of atherosclerosis. Risk factors for AAA include male sex, older age, smoking, and hypertension. Aneurysms that are greater than 5.0 cm in diameter are at increased risk for rupture and at that level of dilatation patients are referred to surgery for repair. AAA can be detected by physical examination. A pulsatile mass is felt in the area around the umbilicus. Ultrasound is very good for detection and screening of AAA. It is recommended that men over age 65 who have ever smoked or who have a family history of AAA have a one-time screening (the benefits of screening women hasn’t been determined). Once identified, yearly ultrasounds are used to follow patients with AAA. If there is rapid growth, or the AAA reaches 5.0 cm, then a CT scan is done to further delineate the anatomy and help in planning for surgery.
There are many different causes for thoracic aortic aneurysm (TAA). Connective tissue diseases are an important etiology. In these conditions, patients are born with loose muscles and joints. They can perform all kinds of contortions (they are “double jointed”). The aorta has muscle and connective tissue within its walls; this makes it elastic, allowing it to expand when the heart pumps blood through it and to relax when there isn’t blood flow. These elastic properties help the aortic wall handle the high pressure of blood flow, without rupturing. Unfortunately the same connective tissue laxness in these patients also causes weakness within the aortic wall. This leads to TAA and these patients are prone to rupture at smaller aortic diameters than other TAA patients. The most well known connective tissue disease is Marfan’s Syndrome. These patients are tall, skinny and lanky (Abe Lincoln was thought to have it). They may have TAA, their aneurysms can grow rapidly and are at risk for bursting at about 4.5 to 5.0 cm. Athletes with Marfan’s Syndrome are barred from playing sports because extreme physical activity can increase the risk for their aneurysm bursting. Therefore it is very important to identify and follow these patients. Other causes of TAA are bicuspid aortic valve (the aortic valve has two leaflets instead of the normal three leaflets), atherosclerosis, vasculitis (inflammation of the wall of the aorta), infection (for example, syphilis) and trauma. Detection and screening for TAA is more difficult than with AAA. The echocardiogram (ultrasound of the heart) can image parts of the thoracic aorta. It is not an ideal screening tool as it can’t view the entire thoracic aorta and measurement of aortic size is fraught with error. However, it is noninvasive and doesn’t require intravenous contrast. The gold standard for measuring TAA is either CT scan or MRI, both of which require intravenous contrast. Due to the contrast, the cost and the radiation exposure (for CT scan) these tests are not ideal for screening. A good, low cost, low risk screening test for TAA is sorely needed. Enter the thumb test. The thumb test is simple. Hold up one hand and keep the palm flat. Stretch the thumb as far as possible across the palm. If the thumb crosses beyond the edge of the palm, the test is positive. A positive thumb test indicates that the joints are loose, due to a connective tissue disease and that a TAA may be present. The majority of aneurysm patients do not have a positive thumb test, but if the test is positive there is a very high likelihood of having a TAA. A negative test does not exclude the possibility of an aneurysm.
If you are a male, over 65 years old and have ever smoked or have a family history of AAA or if you have a positive thumb sign, talk to your doctor about screening for an aneurysm. It may save your life.
