© Springer Science+Business Media New York 2014
Samir K. Shah and Daniel G. Clair (eds.)Cleveland Clinic Manual of Vascular Surgery10.1007/978-1-4939-1631-3_11. Abdominal Aortic Aneurysm
(1)
Department of Vascular Surgery, Cleveland Clinic, 9500 Euclid Avenue, H32, Cleveland, OH 44195, USA
Introduction
Abdominal aortic aneurysm (AAA) is defined as focal dilation of the juxtarenal or infrarenal aorta having a 50 % increase in diameter compared to the expected normal diameter aorta in question. Normal size range of the abdominal aorta by cadaveric studies, angiography, computed tomography (CT), and duplex studies is 10–24 mm. Etiology is degenerative/atherosclerotic, inflammatory, degeneration after dissection, trauma, infection, or congenital. Degenerative infrarenal aortic aneurysms are the most common type of aneurysm of the aorta.
Demographics and Clinical Presentation
The true incidence of ruptured abdominal aortic aneurysms is difficult to determine but varies anywhere between 2 and 15 admissions per 100,000 patients depending on the population. The prevalence estimate for asymptomatic AAA in patients >50 years old is 3–10 %.
In addition to presenting as acute rupture, AAAs often present as incidental findings on a variety of imaging studies performed for other indications. Atheroembolism and, less commonly, thrombosis occur in <5 % of patients with AAA and such an etiology must be considered as a potential source in patients presenting with distal emboli, which is almost always an indication for AAA repair. Infrequently a patient will present with complaints of a pulsatile mass and, rarely, large AAAs can cause symptomatic compression of surrounding structures, e.g., early satiety from duodenal compression and venous thrombosis from iliocaval compression. Chronic back and abdominal pain may be a presenting symptom of AAA that is ill defined and difficult to attribute directly to the aneurysm itself.
Etiology
Degenerative are the most commonly encountered, noniatrogenic aneurysms.
Inflammatory aneurysms are characterized by a fibrotic process in the retroperitoneum that involves the aneurysm as well as surrounding structures. All aneurysms may lie across a spectrum of inflammation.
Infectious or mycotic aneurysms may be due to primary or secondary infection. Infection resulting in disrupted suture anastomoses can lead to the formation of pseudoaneurysms.
Postdissection dilatation can occur from degeneration of the false lumen of a dissection as well as from any underlying pathology responsible for the dissection itself, e.g., Marfan’s syndrome or Ehlers-Danlos syndromes.
Traumatic
Diagnosis
Physical Exam
Physical exam varies depending upon the AAA size, obesity of the patient, and the skill and focus of the examiner and examination respectively. In general, the larger the AAA, the more likely it will be appreciated on abdominal examination. AAA may be falsely suspected in thin patients, patients with hypertension, tortuous aortas, and in patients with unrelated abdominal masses overlying the aorta.
Laboratory
Laboratory tests outside of vascular lab and other imaging modalities are utilized more in the preoperative work-up of the patient rather than in diagnosis of the aneurysm.
Imaging
1.
Ultrasound is the most frequently used, least expensive, and least invasive modality. It is best utilized to diagnose and monitor AAAs until repair is considered. Ultrasound tends to underestimate diameter, have interobserver variability, and have difficulty visualizing the mesenteric aorta as well as iliac arteries [1]. More advanced imaging is used for preoperative evaluation and planning. Lastly, bedside ultrasound in the emergency department provides a rapid assessment of patients with symptomatic or ruptured AAA. Sensitivity and specificity are high in identification of AAA. Fluid collections are easily identified, but visualization of this is not specific for rupture.
Screening with duplex ultrasound is recommended in males 65–75 years old who have a lifetime consumption of at least 100 cigarettes. The U.S. Preventative Services Task Force provided these recommendations in 1996 with an update in 2005 based upon several randomized and nonrandomized studies. One such was the Multicentre Aneurysm Screening Study (MASS) trial which involved >70,000 men aged 65–74 and most notably demonstrated a 32 % reduction in AAA-related mortality [2].
2.
CT scan provides more accurate AAA measurement but exposes the patient to radiation and IV contrast. There is less interobserver variability but some overestimation of tortuous aneurysms when measured obliquely and without the assistance of centerline postprocessing software. CT angiography (CTA) is essential for preoperative planning of asymptomatic and symptomatic but stable patients alike. Furthermore, CT scan is the most accurate method of diagnosing ruptured AAA.
3.
Magnetic resonance imaging (MRI) also provides more information than ultrasound and avoids the ionizing radiation of CT scan. However, it has issues related to cost, spatial resolution, nephrogenic sclerosis with gadolinium in patients with renal insufficiency, patient claustrophobia, and difficultly identifying calcifications. The continued improvement and accessibility of CTA relegates MRI/MRA to a secondary role in the evaluation of AAA.
4.
Angiography was once standard in the preoperative evaluation of the AAA patient. However, given the quality of CTA and the information obtained with image postprocessing and reconstruction of the entire aorta anatomy, not just the flow lumen, angiography is now used only for specific perioperative needs, e.g., renal artery stenting and selective injections to determine renal mass supply by specific vessels.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
