A pulmonary embolism (PE) is a serious medical condition involving a blood clot that lodges in one of the pulmonary arteries within the lungs. This blockage can prevent adequate blood flow, impacting the body’s ability to exchange oxygen. Computed Tomography (CT) scans are a primary tool for diagnosing PE.
Understanding Pulmonary Embolism
Most often, these blockages are caused by blood clots that originate in other parts of the body, commonly the deep veins of the legs, a condition known as deep vein thrombosis (DVT). When a piece of this clot breaks off, it travels through the bloodstream to the lungs, where it can become trapped. This condition can restrict blood flow to lung tissue, potentially leading to damage and reducing the oxygen supply to the rest of the body.
Why CT is the Preferred Scan for PE
Computed Tomography Angiography (CTPA) is considered the standard imaging technique for diagnosing a pulmonary embolism. This CT scan uses X-rays to create detailed images of the lungs and their blood vessels. During a CTPA, an intravenous contrast dye is injected, which travels through the bloodstream and highlights the pulmonary arteries. This allows radiologists to clearly visualize the blood vessels and detect filling defects or obstructions caused by blood clots. CTPA is highly accurate and provides quick results, making it an efficient diagnostic tool.
Key Signs of PE on a CT Scan
Radiologists look for both direct and indirect signs of a clot on a CT scan. Direct signs involve visualizing the clot within the pulmonary arteries. A PE typically appears as a “filling defect,” an area within the contrast-filled blood vessel where the contrast material is absent or reduced, indicating an obstruction.
Specific appearances include the “polo mint sign,” a central filling defect surrounded by a ring of contrast when the artery is viewed in its axial plane. When viewed parallel to the vessel’s long axis, a clot may appear as a “railway track sign,” with parallel lines of contrast surrounding the central filling defect. Clots can be centrally located or pressed against the vessel wall, forming an acute angle with the vessel boundary. The affected vessel may also appear enlarged.
Indirect signs can also suggest the presence of a PE, although they do not directly show the clot. These may include dilation of the pulmonary artery proximal to the clot, indicating increased pressure. Signs of right heart strain, such as enlargement of the right ventricle, can occur because the heart works harder to pump blood against the blocked pulmonary arteries. Additionally, areas of lung tissue that are under-perfused or infarcted may appear as wedge-shaped opacities, sometimes called a Hampton hump.
What Happens After a PE is Identified
Once a pulmonary embolism is identified on a CT scan, medical attention is necessary. Treatment typically involves the immediate initiation of anticoagulant medications. These medications help prevent existing clots from growing larger and new clots from forming. Depending on the severity of the PE, more aggressive interventions may be considered, such as catheter-directed thrombolysis or surgical removal of the clot. Rapid diagnosis and treatment significantly improve patient outcomes and reduce the risk of serious complications.