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Abdominal Aortic Aneurysm, Diagnosis: Imaging
Updated: Oct 2, 2008
Radiography
Findings
Radiograph shows calcification of the abdominal aorta. The left wall is clearly depicted and appears aneurysmal; however, the right wall overlies the spine.
Calcification of the abdominal aortic wall is frequently evident on plain radiographs of the abdomen. Calcification is best seen on lateral views when the spine does not obscure the opposing walls of the vessel. When calcification can be clearly identified in the opposing aortic walls, abdominal aortic aneurysms (AAAs) can be diagnosed with the plain radiographic findings.
Degree of Confidence
If the classic eggshell appearance is present (see Image below and Image 2 in Multimedia), the degree of confidence is approximately 100%; however, this finding is present only in 50% of patients. Occasionally, only the anteroposterior or lateral abdominal image demonstrates the findings clearly. If abdominal aortic aneurysms (AAAs) are suspected, perform abdominal US or CT for confirmation. As such, negative plain radiographic findings do not exclude the diagnosis in any way.
The lateral view clearly shows calcification of both walls. Abdominal aortic aneurysm can be diagnosed with certainty.
False Positives/Negatives
A tortuous, calcified aorta can mimic abdominal aortic aneurysm (AAA) unless both walls can be seen clearly. If the opposing walls are not calcified, the diagnosis cannot be made with certainty. In these cases, US, CT, or MRI must be performed if AAA is clinically suspected.
Computed Tomography
Findings
CT demonstrates an abdominal aortic aneurysm. The aneurysm was noted during workup for back pain, and CT was ordered after the abdominal aortic aneurysm was identified on radiographs. No evidence of rupture is seen (same patient as in Image 2 in Multimedia).
CT accurately demonstrates dilation of the aorta (see Image above and Image 3 in Multimedia) and involvement of major branch vessels proximally and distally. This information helps in determining the appropriate intervention, which may be either surgical or endovascular repair. CT also shows the other organs in the abdomen and demonstrates involvement or displacement of organs that can confuse the clinical picture. The location and number of the renal arteries, caliber of the aneurysm, degree of calcification, lengths of the neck and iliac artery, and presence of mural thrombus are readily assessed. CTA allows multiplanar assessment of the aneurysm and associated relevant vessels (visceral arteries, iliac and femoral arteries).
Degree of Confidence
CT has emerged as the diagnostic imaging standard for the evaluation of AAA with an accuracy that approaches 100%. A well-performed CT examination can reveal the extent of the aneurysm, as well as the involvement of other organs. Intravenously administered contrast agent is needed to obtain the full benefit of CT; however, a nonenhanced study accurately depicts AAAs. Three-dimensional reconstructions of state-of-the-art, multidetector-row, helical CT scans can help in preoperative planning and may replace the need for preoperative diagnostic angiography.
False Positives/Negatives
The administration of contrast material is essential for detecting dissection or ulceration of a vessel that might be missed without it. In the acute setting (eg, in a patient with back pain or an aneurysm), a false-positive diagnosis of rupture is possible if fluid resulting from another cause is seen in the abdomen. Conversely, an aneurysm or rupture can be missed in a patient who has recently undergone barium study because artifact can obscure the aorta.
Magnetic Resonance Imaging
Findings
MRI of a 77-year-old man with leg pain believed to be secondary to degenerative disk disease. During evaluation, an abdominal aortic aneurysm was discovered.
MRI and MRA can be used to define the extent of abdominal aortic aneurysms (AAAs) (see Image above and Image 8 in Multimedia). The absence of iodinated contrast material and radiation are advantages of this modality. However, MRI is more sensitive to motion than CT because a patient must remain motionless for longer than with current multidetector-row helical CT technology. In addition, the remaining organs in the abdomen are not seen as well on MRIs because of motion.
Degree of Confidence
In technically well performed MRI and MRA, degree of confidence approaches 100%. These examinations clearly reveal the extent of the aneurysm; however, motion can cause artifacts that can render the results nondiagnostic. Patients must be able to remain motionless for longer periods than with CT to enable a diagnostic examination.
False Positives/Negatives
If prior abdominal surgery has been performed and if metal clips or devices were used, MRI may not be possible. If the metal is close to the aneurysm or if branch vessels or heavy calcification is seen, artifacts may obscure the vessel and result in a nondiagnostic study.
Ultrasonography
Findings
Ultrasonogram of a patient with an abdominal aortic aneurysm. This aneurysm was best visualized on a transverse or axial image. This patient underwent a conventional abdominal aortic aneurysm repair.
US is the screening examination of choice as a result of its relative availability, speed, and low cost (see Image above and Image 7 in Multimedia). US is operator dependent, unlike other modalities; therefore, operator experience is important. The abdominal aorta normally tapers as it extends distally. Any increase in its diameter is considered abnormal.
Degree of Confidence
If the abdominal aorta can be seen in its entirety, US provides a reliable, low-cost screening examination. Any increase in the size as the aorta travels distally is abnormal. However, in a patient who is obese or in whom the bowel is distended with gas, a complete examination of the aorta and proximal iliac arteries may not be technically possible. In such instances, another cross sectional imaging study (eg, CT, MRI) should be obtained.
False Positives/Negatives
A technically unsatisfactory examination may result from a large patient body habitus or a large amount of bowel gas, which results in incomplete visualization of the aorta. Thus, a false-negative result is possible if these limitations are not recognized.
Angiography
Findings
Arteriogram demonstrates an infrarenal abdominal aortic aneurysm. This arteriogram was obtained in preparation of an endovascular repair of the aneurysm (same patient as in Image 2 in Multimedia).
Lateral arteriogram demonstrates an infrarenal abdominal aortic aneurysm. Demonstration of the superior mesenteric artery, inferior mesenteric artery, and celiac artery on the lateral arteriogram in important to completely evaluate the extent of the aneurysm.
Angiography is often ordered for preoperative evaluation in patients with manifestations of atherosclerotic vascular disease such as renal artery stenosis or peripheral vascular disease.
Compared with other images, arteriograms currently enable better longitudinal measurements of aneurysms. The reason is that the catheters that are used to make these measurements follow the contour of the vessels and therefore allow better determination of the length of the aneurysm, as opposed to linear measurements obtained with CT. This information is not an issue for open surgical repair; however, it is important in endovascular repair. Catheters with radiopaque graduated markers are used, allowing measurement of the lengths of the aneurysm and the caliber of the vessel. These data are occasionally important for endograft placement, and they may not be clear from CT and CTA. Typically, 7-10 measurements are required to size an endovascular graft to an abdominal aortic graft. Much if not all of the sizing can be accomplished with thin-section contrast-enhanced CTA.
As CT algorithms for measuring aneurysms improve, the need for preoperative angiography will decrease. Angiography may be reserved for the most complex aneurysms in which endovascular repair is contemplated.
Angiography is often linked to embolization of the internal iliac artery in a patient in whom the procedure is necessary prior to endovascular repair. Examples of relevant conditions include an internal iliac artery aneurysm or an ectatic aneurysm ipsilateral to a common iliac artery that requires anchoring of the stent-graft in the ipsilateral external iliac artery.
Degree of Confidence
When abdominal aortic aneurysm (AAA) is suspected, it is unlikely to be missed at angiography. In most cases, the morphology of an aneurysm can be clearly defined. If an aneurysm is suspected on the arteriogram, a cross sectional image should be obtained. Not only will it confirm the existence of an aneurysm, but other pathologic conditions that may affect the surgical intervention can be detected.
False Positives/Negatives
If a large amount of luminal thrombus is present, the true diameter of the aneurysm may be obscured unless the wall of the aneurysm has a substantial amount of calcification. This limitation leads to significant underestimation of the diameter of the aneurysm.
More on Abdominal Aortic Aneurysm, Diagnosis |
| Overview: Abdominal Aortic Aneurysm, Diagnosis |
 Imaging: Abdominal Aortic Aneurysm, Diagnosis |
| Follow-up: Abdominal Aortic Aneurysm, Diagnosis |
| Multimedia: Abdominal Aortic Aneurysm, Diagnosis |
| References |
| Further Reading |
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References
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Further Reading
Screening for abdominal aortic aneurysms: recommendation statement .
United States Preventive Services Task Force. 1996 (revised 2005). 16 pages. NGC:003960
Aortic aneurysm and dissection .
Finnish Medical Society Duodecim. 2004 Feb 26. Various pagings. [NGC Update Pending] NGC:004359
Acute chest pain - suspected aortic dissection .
American College of Radiology. 1995 (revised 2005). 5 pages. NGC:004621
Keywords
abdominal aortic aneurysm, inflammatory aortic aneurysm, aortic aneurysm, AAAs, triple-A, triple A, abdominal aneurysm, noninflammatory aneurysms, inflammatory aneurysms, abdominal aortic dissection, aneurysm, dissection
