Trent Lee Wei
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1. For which of the following patients is ultrasound screening recommended for abdominal aortic aneurysm (AAA)?
A. A 75-year-old man with a 30 pack-year smoking history
B. A 60-year-old woman with a 30 pack-year smoking history
C. A 65-year-old man with a 30 pack-year smoking history
D. A 60-year-old Hispanic man with diabetes
1. Correct Answer: C. A 65-year-old man with a 30 pack-year smoking history
Rationale: AAA is an abdominal aortic dilation of 3.0 cm or greater. The prevalence of AAA increases with age and is uncommon in persons younger than 50 years. The U.S. Preventive Services Task Force (USPSTF) updated guidelines recommend one-time screening with ultrasonography for men 65 to 75 years of age with a history of smoking, defined as at least 100 cigarettes over the individual’s lifetime. Risk factors associated with a higher likelihood of AAA include first-degree relatives with AAA, history of other aneurysms, coronary artery disease, cerebrovascular disease, atherosclerosis, hypercholesterolemia, obesity, and hypertension. Factors associated with a decreased risk of AAA include black race, Hispanic ethnicity, and diabetes. The Society for Vascular Surgery recommends screening in all men and women 65 to 75 years of age.
1. Chaikof EL, Dalman RL, Eskandari MK, et al. The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm. J Vasc Surg. 2018;67:2-77.e2.
2. U.S. Preventive Services Task Force. Screening for abdominal aortic aneurysm: recommendation statement. Ann Intern Med. 2014;161(4):281-290.
2. When analyzing AAAs with ultrasound in the transverse plane, which two landmarks should be identified to ensure complete visualization of the entire aorta?
A. Superior mesenteric artery and inferior mesenteric artery
B. Celiac trunk and the iliac bifurcation
C. Celiac trunk and the inferior mesenteric artery
D. The renal arteries and the iliac bifurcation
2. Correct Answer: B. Celiac trunk and the iliac bifurcation
Rationale: To fully evaluate the aorta, one must visualize the vessel in the transverse plane from the celiac trunk to the iliac bifurcation. The celiac trunk is the first major vessel to arise from the aorta immediately below the diaphragm. When visualized in the transverse plane, the celiac artery will appear as a “wide Y.” At the level of the umbilicus the aorta will bifurcate into the iliac arteries, which can also be evaluated for aneurysmal disease if warranted.
In unstable patients, a right upper quadrant ultrasound or a focused assessment with sonography for trauma (FAST) to evaluate for pathologic fluid should be included. While the majority of AAAs rupture in the retroperitoneum, free rupture into the abdomen is rapidly fatal unless identified immediately. Lastly, assessing for the occurrence of an undulating intimal flap is important as this pathognomonic finding is 99%-100% specific for aortic dissections.
1. Fojtik JP, Costantino TG, Dean AJ. The diagnosis of aortic dissection by emergency medicine ultrasound. J Emerg Med. 2007;32:191-196.
2. Penny, SM. Examination Review for Ultrasound: Abdomen and Obstetrics & Gynecology. 1st ed. LWW; 2010.
3. Zucker EJ, Prabhakar AM. Abdominal aortic aneurysm screening: concepts and controversies. Cardiovasc Diagn Ther. 2018;8(suppl 1):S108-S117.
3. Which of the following helps differentiate the aorta from the inferior vena cava (IVC)?
A. The aorta is on the patient’s left, is noncompressible, and has no respiratory variation.
B. The aorta is on the patient’s right, is noncompressible, and has no respiratory variation.
C. The aorta is on the patient’s left, is compressible, and has respiratory variation.
D. The aorta is on the patient’s right, is compressible, and has respiratory variation.
3. Correct Answer: A. The aorta is on the patient’s left, is noncompressible, and has no respiratory variation.
Rationale: The aorta passes through the diaphragm at the level of the 12th thoracic vertebral body. It lies slightly to the left of the midline and bifurcates at the level of the 4th lumbar vertebral body. The anatomic landmark corresponding to the entry of the aorta through the diaphragm is the xiphoid process, and the landmark corresponding to the iliac bifurcation is the umbilicus. The aorta is to the left of the IVC, noncompressible, and lacks respiratory variation due to its thick arterial wall.
4. Which of the following is most likely to obscure ultrasound visualization of the aorta?
C. Dilated loops of bowel with gas
4. Correct Answer: C. Dilated loops of bowel with gas
Rationale: Ultrasound waves do not propagate well through gas, which appears as a bright reflective surface with shadowing that obscures the underlying anatomy. The interface with gas/air often causes long-path reverberation artifacts (for large gas collections) or short-path “ringdown” artifacts (for small gas collections). A gas-filled transverse colon often obscures visualization of the aorta. To remedy the situation, move the probe until an adequate sonographic window is visualized between loops of bowel or provide continuous compression with the probe until the gas moves out of the field of view.
1. Hermsen K, Chong WK. Ultrasound evaluation of abdominal aortic and iliac aneurysms and mesenteric ischemia. Radiol Clin North Am. 2004;42:365-381.
2. Kuhn M, Bonnin RL, Davey MJ, Rowland JL, Langlois SL. Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med. 2000;36(3):219-223.
5. Which of the following is most likely to cause underestimation of the size of an AAA?
A. Measuring during inspiration
B. Body positioning
C. Intraluminal thrombus
D. Perpendicular imaging plane
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