A Computed Tomography Angiogram (CTA) of the abdomen is a specialized medical imaging procedure that provides detailed pictures of the blood vessels within the abdominal cavity. This technique combines a standard CT scan with the injection of an iodine-containing contrast dye into a vein, which travels through the bloodstream and highlights the arteries and veins. By timing the scan to coincide with the contrast material filling the vessels, the CTA produces high-resolution, three-dimensional views of the vascular anatomy. This non-invasive method allows doctors to assess the patency, structure, and flow dynamics of the abdominal circulatory system, which is useful for diagnosing and planning treatment for various vascular diseases.
Major Arterial Systems Visualized
The abdominal CTA visualizes the abdominal aorta and its major branches, which supply blood to the organs and the lower body. The abdominal aorta, the body’s largest artery, is clearly delineated as it descends through the abdomen, eventually dividing into the two common iliac arteries.
The scan focuses on the three major arteries that branch off the aorta to supply the digestive organs: the celiac artery, the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA). The celiac artery branches into the splenic, common hepatic, and left gastric arteries, supplying the liver, spleen, and stomach. The SMA feeds blood to the small intestine and part of the large intestine, while the IMA supplies the rest of the large intestine.
The CTA captures the paired renal arteries, which supply the kidneys. The high-resolution images allow for the precise mapping of these vessels, including accessory renal arteries. While the focus is generally on the arteries, the scan timing can also be adjusted to visualize the major abdominal veins, such as the inferior vena cava and the portal vein system.
Diagnosing Structural Vascular Conditions
A primary function of the abdominal CTA is the detection of structural defects in the abdominal vessels. One common application is the evaluation of abdominal aortic aneurysms (AAA), which are localized bulges or weaknesses in the aortic wall. The CTA accurately measures the diameter, length, and precise location of an aneurysm. A diameter of 3.0 cm or greater in the infrarenal aorta generally defines an aneurysmal dilation.
The imaging technique also reveals aortic dissection, a serious condition where a tear occurs in the inner lining of the aorta, allowing blood to flow between the layers of the wall. This tear creates two channels, a true lumen and a false lumen. The CTA distinguishes between these two spaces and traces the extent of the dissection. Detecting intramural hematoma (bleeding into the aortic wall without a full tear) is also possible, as is the presence of penetrating atherosclerotic ulcers.
The CTA identifies stenosis or occlusion, which is the narrowing or complete blockage of an artery, often caused by the buildup of atherosclerotic plaque. Renal artery stenosis, a common cause of high blood pressure, is clearly visualized, allowing for the precise measurement of the degree of narrowing. CTA is an effective tool for diagnosing mesenteric ischemia by showing blockages in the celiac, superior, or inferior mesenteric arteries, which can lead to insufficient blood flow to the bowel.
The CTA also assesses the patency of prior surgical repairs, such as grafts or stents placed for aneurysms or blockages. For patients who have undergone endovascular repair of an AAA, the scan monitors for endoleaks, which are persistent blood flows into the aneurysm sac outside the graft. Additionally, the procedure can identify vascular malformations, such as arteriovenous malformations (AVMs), which are abnormal connections between arteries and veins.
Assessing Organ Health and Active Bleeding
The abdominal CTA provides information about blood flow, which is important for assessing organ health and identifying emergent issues. In cases of trauma or gastrointestinal hemorrhage, the CTA is a highly sensitive tool for detecting active internal bleeding. Active bleeding is visualized as the extravasation of the contrast dye, which appears as a bright, dense collection outside of a vessel or pooling within the bowel lumen.
This ability to detect the source of hemorrhage is valuable for lower gastrointestinal bleeding, where CTA can identify bleeding rates as low as 0.3 to 0.5 milliliters per minute. Identifying this point of active contrast leakage immediately directs interventional procedures to stop the bleeding. The images also help diagnose ischemia, which is a reduction in blood flow to an organ, such as the kidney or intestine, often indicating potential tissue death, or infarction.
In the context of cancer, the CTA evaluates the vascular supply of tumors, a process known as vascular mapping. This information is essential for pre-surgical planning to understand the tumor’s relationship to major vessels or to assess its hypervascularity, a sign of aggressive growth. The scan shows if a mass is invading or displacing nearby vessels, providing surgeons with a detailed roadmap of the anatomy. This diagnostic information also guides decisions for procedures like liver transplantation or hepatic resection.