CT of the abdominal aorta

Diagnostics of abdominal aortic aneurysms

Aortic aneurysms are most frequently localized in the abdominal segment. Ultrasonography (US) is traditionally used for screening and dynamic monitoring of aneurysm size, but CT is required for detailed morphological assessment and surgical preparation.

When analyzing tomograms, it is important to pay attention to specific forms of the disease:

• Inflammatory aneurysm: accompanied by pronounced atherosclerotic disease. Contrast-enhanced tomograms visualize a thickened outer wall with well-defined contours that actively enhances with contrast medium (unlike mural thrombi). The inflammatory tissue forms a characteristic periaortic sleeve. The ureters are often involved in the pathologic process, leading to bilateral hydroureter.
• Mycotic (infectious) pseudoaneurysm: in active infection, CT images (including maximum intensity projection [MIP] views) may reveal clusters of gas bubbles in the soft tissues surrounding the vessel. This is a reliable marker of severe infectious involvement of the vessel wall.

Types of CT reconstructions and preoperative planning

Successful endovascular stent graft (stent graft) placement requires careful measurements of anatomical parameters. Standard axial slices are not sufficient; therefore, specialized CT reconstructions are used to provide a comprehensive view (comprehensive view) of even complex anatomical structures:

1. Coronal multiplanar reconstruction (MPR): optimal for visualizing the proximal neck (proximal neck) of the aneurysm. This projection evaluates the segment of the vessel located immediately below the origin of the renal arteries.
2. Curved reformations (curved reformations): demonstrate the aorta along its entire length relative to the anatomical curves of the spine. They allow visualization of the distal necks (distal necks) at the level of the bifurcation and iliac arteries.

Performing accurate measurements on these reconstructions makes it possible to determine the required length of coverage (length of coverage) for the stent graft and to assess the condition of the vascular access routes before surgery.

Abdominal aortic coarctation

Abdominal aortic coarctation (abdominal coarctation) is a relatively rare condition that clinically manifests in young patients with severe arterial hypertension and signs of chronic mesenteric ischemia. Physical examination may reveal a bruit in the abdominal cavity, and femoral pulses are usually diminished.

Characteristic CT findings:

• The abdominal aorta has an extremely small caliber over a long extent.
• The point of maximum stenosis is often localized at the level of the L1-L2 intervertebral disc.
• There is marked ostial stenosis of the celiac trunk and critical stenosis of the superior mesenteric artery (SMA). Distal to the SMA stenosis, a post-stenotic aneurysmal dilation may form.
• An enlarged (hypertrophied) arc of Riolan (arc of Riolan)—a collateral anastomosis between the superior and inferior mesenteric arteries—is frequently visualized. Its enlargement serves as an indicator of prolonged impairment of mesenteric blood flow.
• An accompanying anatomical finding may be a retroaortic left renal vein.

Identification of true and false aneurysms

When interpreting tomograms, it is necessary to clearly distinguish between two pathological conditions:

• True aneurysm: local or diffuse dilation of a vessel exceeding its expected diameter by 1.5 times or more. The key criterion is involvement of all layers of the aortic wall. Atherosclerosis is the most common etiological cause. Matrix metalloproteinases (MMPs), which degrade elastin and collagen of the extracellular matrix and compromise the structural integrity of the vessel, play an important role in the pathogenesis.
• False aneurysm (pseudoaneurysm): occurs as a result of a contained rupture of the vessel wall. In this case, the wall is formed only by the adventitial layer. Pseudoaneurysms are extremely unstable and carry a high risk of further rupture, so they cannot be evaluated and classified according to the criteria for true aneurysms.

Class and exam questions

What else to study on this topic

• CT findings and classification of traumatic aortic injury (Presley scale)
• Visualization of thoracic aortic coarctation and its differences from abdominal lesions
• Causes of false-positive results in CT angiography (ductus arteriosus diverticulum, artifacts)
• Capabilities of 4D-flow MRI in assessing aortic aneurysm rupture risk
• Role of transesophageal echocardiography in the emergency diagnosis of aortic syndromes

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.