CT Scans Detect Blood Clots in the Lungs and Legs

CT scans can be more effective and less invasive in diagnosing certain blood clots than traditional diagnostic procedures, according to studies performed at the Medical College of Wisconsin by a team led by Lawrence R. Goodman, MD, FACR, Professor of Radiology and Chief of Thoracic Imaging at the college.

Blood clots sometimes form in veins of the legs in patients who have been on prolonged bed rest or who have experienced injury or surgery to the pelvis or legs, according to Dr. Goodman, who is also a Froedtert & Medical College Radiologist. If the blood clots in the leg veins break away and pass through the heart to the lungs, the heart must work harder to pump blood. It also becomes difficult for the lungs to make the necessary exchange of oxygen and carbon dioxide – with potentially disastrous effects.

The majority of patients with thromboembolic disease have blood clots in lungs and legs. Symptoms of blood clots in the lungs include shortness of breath, chest pain, coughing up blood or sudden collapse. People with blood clots in the legs may experience swelling, pain or redness. Since these symptoms are non-specific, they can be very difficult to diagnose accurately.

CT scans – also known as computed tomography or “CAT” scans – are effective in diagnosing pulmonary embolism (blood clots in the lungs) and deep venous thrombosis (blood clots in the legs), which indicate thromboembolic disease, a potentially fatal condition. CT scans are also effective in eliminating thromboembolic disease as the cause of symptoms and offering alternative diagnoses.

Fewer Shortcoming Than Traditional Techniques
Traditional diagnostic procedures for thromboembolic disease include ventilation-perfusion scanning (a nuclear medicine technique) and ultrasound. Nuclear scans may not be definitive because certain other lung diseases can masquerade as clots; pulmonary angiography may still be needed to reach a diagnosis. These traditional diagnostic procedures are more invasive than CT scanning. Pulmonary angiography, for example, involves inserting a small plastic tube (a catheter) into a vein in the groin and guiding it through the heart into the lungs. Contrast dye is then injected through the catheter so that X-ray images of suspected clots can be created. A similar procedure is used in venograms of the legs. This has been largely replaced by ultrasound.

CT scans do expose patients to radiation – more than a simple chest X-ray but less than an angiogram, according to Dr. Goodman. Also, a few patients could experience an allergic reaction or kidney problems from the dye that is used for CT scans or angiography.

“The traditional diagnostic workup for thromboembolic disease is typically long and cumbersome and often fails to provide a definitive diagnosis,” Dr. Goodman says. “CT scans show the lungs and legs in the same procedure, are quicker, and provide a definitive diagnosis in more than 90% of patients. Ventilation-perfusion scans are conclusive in less than 50% of patients.”

High-Resolution Helical Scanning Provides Clear Results
When a CT scan for thromboembolic disease is performed, contrast dye is injected into the patient’s bloodstream through the arm while the patient rests on a table in the center of a ring of special X-ray equipment. Today’s CT machines provide “helical” images, as both the table and X-ray equipment housed in the ring move together to provide rapid, high-resolution images. This helical computed tomography can effectively scan the lungs and the veins of the legs for blood clots that are highlighted by the dye. CT scanning itself is simple, painless and relatively quick.

If blood clots are suspected only in the legs, an ultrasound may be performed first because it is less costly than a CT and does not involve dye.

If blood clots in the lungs are suspected, a CT will usually be performed. CT can also show alternative diagnoses such as a collapsed lung or pneumonia. In patients with normal chest X-rays, where the results are not likely to be confused by other lung diseases, a nuclear scan may be preferable.

If blood clots are found, anti-coagulant therapy is administered. If blood clots are found in the lungs, the patient will remain in the hospital for a few days of observation because anticoagulant therapy with heparin is individualized to the patient. On discharge, patients are typically switched to the oral anticoagulant warfarin.

Dr. Goodman’s Medical College of Wisconsin research team included co-investigators W. Dennis Foley, MD, Professor of Radiology, Randolph J. Lipchik, MD, Associate Professor of Medicine, Martin R. Crain, MD, formerly an Associate Professor of Radiology, and Kiran B. Sagar, MD, formerly a Professor of Medicine. Their work provides us with a better way to detect thromboembolic disease, a diagnosis that was more difficult and unreliable in the past. Using newer technologies, diagnostic procedures are safer, less invasive and highly effective.

This article includes information from:
Froedtert & Medical College Radiology Department