Author
Sarah L. Melendez, MD
Resident Physician
Department of Emergency Medicine
SUNY Downstate Medical Center
Brooklyn, New York
Disclosure: Sarah L. Melendez, MD, has disclosed no relevant financial relationships.
Editor
Mark P. Brady, PA-C
Adjunct Faculty and Preceptor
Physician Assistant Program
University of New England
Physician Assistant
Department of Emergency Medicine
Cambridge Hospital, Cambridge Health Alliance
Cambridge, Massachusetts
Disclosure: Mark P. Brady, PA-C, has disclosed no relevant financial relationships.
Reviewer
Timothy Jang, MD
Assistant Professor of Medicine
David Geffen School of Medicine
University of California, Los Angeles
Director of Emergency Ultrasound
Olive View-UCLA Medical Center
Clinical Faculty, Washington University School of Medicine
Torrance, California
Disclosure: Timothy Jang, MD, has disclosed no relevant financial relationships.
Emergency bedside ultrasound (shown) can quickly and accurately identify an abdominal aortic aneurysm when performed by appropriately trained emergency medicine providers. A focal dilatation in an artery, with at least a 50% increase of its normal diameter, is defined as an aneurysm. An enlargement of >3 cm of the abdominal aorta, even if asymptomatic, is considered to be an abdominal aortic aneurysm. Abdominal aortic aneurysms usually result from degeneration in the media of the arterial wall, leading to a slow and continuous dilatation of the lumen of the vessel.[1]
Abdominal aortic aneurysms (arrow) are relatively common, potentially life-threatening, and usually asymptomatic until they expand or rupture. Predisposing risk factors for abdominal aortic aneurysm include smoking, age (more common after the sixth decade), hypertension, hyperlipidemia, atherosclerosis, moderate alcohol consumption (>2 drinks per day), gender (10 times more likely in men), positive family history, and congenital disorders (eg, Marfan and Ehlers-Danlos syndromes). Approximately 90% occur infrarenally, but they can also occur pararenally or suprarenally. Such aneurysms can extend to include one or both iliac arteries in the pelvis. Image courtesy of Wikimedia Commons.
This ultrasound shows a patient with an abdominal aortic aneurysm. Patients with unruptured abdominal aortic aneurysms may experience unimpressive back, flank, abdominal, or groin pain for some time prior to rupture. At times, abdominal aortic aneurysms may cause symptoms from local compression, including early satiety, nausea, vomiting, urinary symptoms, or venous thrombosis from venous compression. An expanding abdominal aortic aneurysm causes sudden, severe, and constant low back, flank, abdominal, or groin pain. Syncope may be the chief complaint, with pain less prominent.
Computed tomography (CT) showed this ruptured abdominal aortic aneurysm. The blue arrow indicates the aneurysm and the red arrow indicates the free blood in the abdomen. More than 80% of patients with ruptured abdominal aortic aneurysms present without a previous diagnosis of abdominal aortic aneurysm. The most typical manifestation of rupture is abdominal or back pain with a pulsatile abdominal mass. However, the symptoms may be vague, and the abdominal mass may be missed. Symptoms may include groin pain, syncope, paralysis, or flank mass. The diagnosis may be confused with renal calculus, diverticulitis, incarcerated hernia, or lumbar spine disease.[2] Image courtesy of Wikipedia Commons.
This ultrasound shows normal anatomy of the aorta in short axis. Criteria for making the diagnosis of abdominal aortic aneurysm include the following: focal dilatation of the abdominal aorta >3.0 cm; increase in the aortic diameter to 1.5 times the normal expected diameter; and ratio of infrarenal to suprarenal aortic diameter ≥1.2. There may be variations in measurement of the aneurysm size depending on technique. The aneurysmal sac should be measured from outer wall to outer wall with a longitudinal image. The transverse diameter should be measured perpendicular to the long axis of the aorta.
To begin ultrasound evaluation for abdominal aortic aneurysm, start in the transverse plane (pointing to 9 o’clock), high in the epigastrium, using acoustic gel. Use the liver as a sonic window. Identify the vertebral body (a dark rounded shape with dense shadow). Identify the aorta on the patient’s left and the inferior vena cava (IVC) on the patient’s right, above the vertebral body on the ultrasound image. If the patient is hypovolemic, use light pressure to avoid effacement of the IVC. In real time, obtain transverse images of the aorta from the celiac trunk to the iliac bifurcation.
If the gas-filled transverse colon obscures the aorta, move the probe until a sonographic window is found between loops of bowel. Rock the probe up and down (shown) without moving it across the patient’s skin to maximize the information attained through the window.[3] Frequently identifiable sonic windows in the upper abdomen are high in the epigastrium and above or around the umbilicus. Also, the liver margin can be lowered by asking the patient to take a deep breath and hold.
Attempt to obtain at least three transverse views—high, middle, and low—with calipers. One view should show the maximal aortic diameter. Sagittal view(s) should show the celiac trunk to the iliac bifurcation. Obtain views of the iliac arteries if possible. Some abdominal aortic aneurysms may contain thrombi. Careful attention must be made to include the thombus (blue arrow) in the diameter measurement. The yellow arrow indicates the correct diameter measurement. The orange arrow does not include the thrombus and hence is an incorrect measurement.
In this image, the aorta is visualized in long axis. A large (>7 cm) abdominal aortic aneurysm with mural thrombus (blue arrow) and hyperechoic areas (red arrow) are appreciated outside the aorta, which may represent rupture. Color-flow Doppler (yellow arrow) illustrates turbulent flow within the lumen.
In this image, the aorta is visualized in short axis. A large (>7 cm) abdominal aortic aneurysm with mural thrombus (blue arrow) and hyperechoic areas (red arrow) are shown outside the aorta, which may represent rupture. Ruptured aneurysms need surgical repair. Unruptured aneurysms are managed according to size. Recommended intervals for follow-up are based on the diameter of the aneurysm, as follows: 3-4 cm, every 12 months; 4-4.5 cm, every 6 months; >4.5 cm, consider referral to vascular subspecialist. Patients with an incidentally discovered aneurysm <3 cm require no further follow-up. If an abdominal aortic aneurysm expands by >0.6-0.8 cm/year, the patient should be offered repair.
This image shows an aneurysm with retroperitoneal fibrosis and adhesion of the duodenum and fibrosis. The two primary methods of abdominal aortic aneurysm repair are open and endovascular. Open repair requires direct access to the aorta through an abdominal or retroperitoneal approach. Open thoracic abdominal aortic aneurysm repair has a mortality rate of around 8%, with myocardial infarction being a frequent cause of death.
Common pitfalls in performing bedside ultrasonography to evaluate abdominal aortic aneurysms include failing to compress the overlying bowel adequately with probe pressure; mistaking the IVC for the aorta because of transmitted pulsations; overestimating the aneurysmal width because of the lack of a true transverse measurement (cross-section); confusing an imaging artifact with a thrombus; and failing to measure the external diameter (outer wall to outer wall).
Remember that ultrasonography is not good at detecting rupture (arrow) or leakage. Contrast abdominal CT is the criterion standard. However, contrast-enhanced ultrasonography may be a reasonable alternative if CT is unavailable. Other common pitfalls in performing bedside ultrasonography to evaluate abdominal aortic aneurysms include failing to move the transducer off the sagittal plane while following a tortuous aorta; being reluctant to move the transducer far enough laterally to visualize an aorta that is obscured by overlying bowel gas; and misinterpreting acoustic enhancement distal to the aorta as evidence of leakage.
Although CT can reveal an abdominal aortic aneurysm (shown), ultrasonography can be performed at the bedside immediately. Ultrasound is sensitive, specific, low cost, and easy to perform with no radiation or contrast exposure. Bedside ultrasound is especially useful for an unstable patient who cannot be transported for CT of the abdomen. However, ultrasound should never delay potentially lifesaving abdominal surgery when such surgery is immediately available and the diagnosis is strongly suspected. Limitations of ultrasound include the need to visualize the entire abdominal aorta to exclude the diagnosis, as well as difficulty visualizing due to bowel gas, obesity, or guarding.[4]
Computed tomography (shown) has emerged as the diagnostic imaging standard for the evaluation of abdominal aortic aneurysms, with accuracy that approaches 100%. CT can accurately demonstrate dilation of the aorta and involvement of major branch vessels proximally and distally, which can help determine the appropriate intervention (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. Disadvantages include radiation and intravenous contrast exposure, as well as the need to transport the patient from the emergency department or intensive care unit.[4] Image courtesy of Wikimedia Commons.
Angiography (shown), magnetic resonance imaging (MRI), and radiography can also be used to diagnose abdominal aortic aneurysms, with varying degrees of success. Angiography is often ordered for surgical planning, particularly for endovascular repair. This technique is accurate but invasive with high morbidity. MRI is highly sensitive and uses no contrast or radiation. However, MRI is more sensitive to motion than is CT, provides inadequate evaluation of mesenteric circulation, and is contraindicated in patients with implanted devices. When calcification can be clearly identified in the opposing aortic walls, abdominal aortic aneurysms can be diagnosed by plain radiographs.
Author
Sarah L. Melendez, MD
Resident Physician
Department of Emergency Medicine
SUNY Downstate Medical Center
Brooklyn, New York
Disclosure: Sarah L. Melendez, MD, has disclosed no relevant financial relationships.
Editor
Mark P. Brady, PA-C
Adjunct Faculty and Preceptor
Physician Assistant Program
University of New England
Physician Assistant
Department of Emergency Medicine
Cambridge Hospital, Cambridge Health Alliance
Cambridge, Massachusetts
Disclosure: Mark P. Brady, PA-C, has disclosed no relevant financial relationships.
Reviewer
Timothy Jang, MD
Assistant Professor of Medicine
David Geffen School of Medicine
University of California, Los Angeles
Director of Emergency Ultrasound
Olive View-UCLA Medical Center
Clinical Faculty, Washington University School of Medicine
Torrance, California
Disclosure: Timothy Jang, MD, has disclosed no relevant financial relationships.
Bedside Ultrasonography, Gallbladder Evaluation
Focused Assessment With Sonography for Trauma (FAST)
Therapeutic Applications for Bedside Ultrasonography
Critical Findings on Plain Abdominal Radiographs
Can't-Miss Gastrointestinal Diagnoses
