An abdominal aortic aneurysm (AAA) is a localized enlargement or ballooning in the lower part of the aorta, the body’s largest artery, which runs through the abdomen. This condition can be serious, as an aneurysm has the potential to rupture, leading to severe internal bleeding. Computed tomography (CT) scans play an important role in identifying and managing these aneurysms, helping healthcare providers assess the aneurysm’s characteristics and determine the appropriate course of action.
Understanding Abdominal Aortic Aneurysms
An abdominal aortic aneurysm occurs when a section of the abdominal aorta weakens and expands, much like a balloon. The infrarenal aorta, the section most commonly affected, typically has a normal diameter of 1.43 to 1.96 cm. An aneurysm is generally defined as an outer aortic diameter exceeding 3 cm. These aneurysms often develop slowly over time and frequently produce no symptoms.
The primary cause of AAAs is often atherosclerosis, a condition where plaque builds up inside the arteries, leading to stiffening and weakening of the arterial walls. Other contributing factors include high blood pressure, high cholesterol, a family history of aneurysms, and tobacco use, which significantly reduces structural proteins in the artery wall.
While many AAAs remain asymptomatic, larger aneurysms or those nearing rupture may cause symptoms such as a deep, constant pain in the abdomen or lower back, or a throbbing sensation near the navel. A ruptured aneurysm is a medical emergency, presenting with sudden, severe pain in the abdomen or back, accompanied by signs like low blood pressure, rapid heartbeat, dizziness, or fainting. The risk of rupture increases with aneurysm size, making early detection and monitoring important.
Purpose of a CT Scan for AAA
A CT scan is a preferred imaging method for evaluating abdominal aortic aneurysms due to its ability to provide highly detailed, cross-sectional images of the aorta and surrounding structures. This diagnostic tool is used for initial detection of an aneurysm, especially when other imaging methods like ultrasound are limited. CT scans offer accuracy in depicting the aneurysm’s absolute size, which is a primary indicator of rupture risk.
CT angiography (CTA), a specialized type of CT scan, is often considered the gold standard for comprehensive evaluation and preoperative planning. It accurately delineates the aneurysm’s size, shape, and its relationship to nearby blood vessels. This detailed anatomical information is invaluable for surgeons when planning potential interventions, including both traditional open surgery and less invasive endovascular aneurysm repair (EVAR).
Beyond initial diagnosis, CT scans are also used for ongoing surveillance of known aneurysms not yet large enough for immediate intervention. Regular CT scans allow healthcare providers to monitor the aneurysm’s growth rate and detect any changes in its morphology. This serial imaging helps determine if the aneurysm is growing at a concerning pace, such as more than 5 mm over a six-month period, which may indicate a higher risk of rupture and prompt a decision for intervention.
The Abdominal Aortic Aneurysm CT Scan Procedure
Preparing for an abdominal aortic aneurysm CT scan typically involves specific instructions to ensure clear images. Patients are usually asked to fast for a few hours before the scan to reduce bowel contents that could obscure the view of the aorta. It is also important to remove any metal objects, such as jewelry, eyeglasses, or dentures, as these can interfere with the X-ray beams and distort the images.
During the procedure, an intravenous (IV) contrast dye is frequently administered. This dye, often containing iodine, is injected into a vein in the arm. The contrast material travels through the bloodstream, highlighting the blood vessels, including the aorta, making them appear bright on the CT images. This enhanced visibility allows radiologists to better assess the aneurysm’s size, shape, and the presence of any blood clots or leaks. Patients may experience a warm sensation throughout their body or a metallic taste in their mouth as the dye is injected, which is a normal and temporary reaction.
The scanning process itself is generally quick, often taking only a few minutes, with the entire appointment lasting approximately 30 minutes. The patient lies on a motorized table that slides into the CT scanner. Inside the scanner, an X-ray tube rotates around the body, capturing multiple cross-sectional images. Patients will be asked to remain very still and may receive instructions to hold their breath briefly at specific moments to prevent motion blur, which can affect image quality.
Understanding Your AAA CT Scan Results
After your abdominal aortic aneurysm CT scan, a radiologist, a doctor specializing in interpreting medical images, will analyze the detailed cross-sectional pictures. They examine the aorta to measure the aneurysm’s maximum diameter, a primary factor in assessing rupture risk. Radiologists also evaluate the aneurysm’s shape, looking for irregularities or saccular (pouch-like) formations, and assess the presence and extent of mural thrombus, which are blood clots within the aneurysm wall.
The radiologist also looks for signs of impending or actual rupture. These can include a retroperitoneal hematoma, which is bleeding around the aorta. Active extravasation of contrast material, where the dye is seen leaking outside the aorta, is a direct indication of a rupture.
The measurements and observations from the CT scan guide patient management. For aneurysms smaller than 5.0 cm in women and 5.5 cm in men, watchful waiting and regular monitoring with follow-up scans, typically every 6 to 12 months, are often recommended. Larger aneurysms, or those showing rapid growth (e.g., more than 5 mm in six months), generally warrant discussion of intervention. Your doctor will review the results with you, explain their significance, and discuss potential treatment options.