Abdominal Aortic Aneurysm Imaging

Overview

This StatPearls review by Gibbons and colleagues, last updated in May 2022, explains how point-of-care ultrasound is used to diagnose abdominal aortic aneurysm (AAA). AAA has a prevalence of about 1.3% in people over 50 and is more common in elderly men. Ruptured aneurysms carry a mortality of 50 to 95%, and nearly 30% are misdiagnosed at first presentation. Physical examination has a sensitivity below 65%, and fewer than 25% of patients show the classic triad of hypotension, abdominal pain and a pulsatile abdominal mass.

Why ultrasound

Bedside ultrasound reaches a sensitivity of 94 to 99%, measures the aorta to within 4 mm of CT, takes under 5 minutes and is reported to have reduced mortality by 20 to 60%. An aorta wider than 3 cm defines an aneurysm. Most are fusiform, and about 90% lie below the renal arteries.

Who to scan

Consider scanning patients over 50 with chest, abdominal, flank, groin or back pain, renal colic, hematuria or hydronephrosis, and those with cardiac arrest, hypotension, syncope, lower-limb thromboembolism or neurologic deficit. For screening without symptoms, the USPSTF and AAFP recommend men over 65 who ever smoked. The Society for Vascular Surgery also recommends all men over 65, men over 55 with a family history, and women over 65 with a family history or smoking history.

Technique and pitfalls

A curvilinear probe is ideal, with the patient supine. The aorta is scanned in transverse and sagittal planes from below the xiphoid to the bifurcation near the umbilicus, and measured at its maximal diameter from outer wall to outer wall, including any thrombus. Bowel gas can be overcome by steady pressure, changes of angle or a left lateral decubitus position. In about 5% of patients the aorta cannot be seen and CT angiography or MR angiography is needed. Distinguish the aorta from the vena cava by its thick, non-compressible, pulsatile wall. An intimal flap is specific for aortic dissection.

Limitations and team care

Body habitus, bowel gas and operator experience limit the exam, and most ruptures occur in the retroperitoneum, where ultrasound cannot assess them routinely. In an unstable patient a right upper quadrant scan looks for free fluid. Ultrasound is the initial test and is also used for monitoring, while CT or MR angiography is recommended for surgical planning in stable patients.