Diagnostic ultrasound is an excellent modality for many conditions that present with abdominal pain. It has the advantage of being both portable and radiation-free. Although actual scanning time may be greater than that of CT, the queue is often shorter. Moreover, preliminary results from the ultrasound technician may be available more quickly. In many institutions, emergency-medicine practitioners are trained to perform scans at the bedside and can make a diagnosis in minutes. For example, a properly trained provider can confirm the diagnosis of an abdominal aortic aneurysm or a ruptured ectopic pregnancy in under one minute. All that is required is for the ED to have its own dedicated machine.
The absence of ionizing radiation is another benefit of ultrasound. Unlike CT scan, which requires the clinician to weigh risks and benefits of the procedure, ultrasound is virtually risk-free. Neither radiation nor iodinated contrast are a concern.
The most common indications for diagnostic ultrasound in the evaluation of abdominal pain include aortic aneurysm, biliary disease, ascites, kidney stones, pregnancy, and pelvic disease. Ultrasound is being used with increasing frequency to evaluate for appendicitis in children and thinner young adults.1 Finally, ultrasound may be used in infants and toddlers to make the diagnosis of intussusception or pyloric stenosis.1
For most causes of acute abdominal pain, CT scan is considered the test of choice. It has sensitivities in the high 90s for appendicitis, diverticulitis, abdominal aortic aneurysm, renal stones, peritoneal bleeding, bowel obstruction, and other conditions (Table 1).1,2 Even for such conditions as biliary disease and pelvic disease, in which ultrasound is usually preferred, the sensitivity of CT scan makes it a test worthy of consideration (as an added benefit, CT can pick up other mimics that ultrasound may miss).
Because the imaging quality and reformatting technology of CT scan continue to improve, it is used with increasing frequency as a diagnostic test.3 However, since it is so useful and available in many settings, overuse is becoming an issue. In many instances, watchful waiting or a trial of medication (e.g., an antacid) will work equally well. The downside of CT scan overuse is multifaceted. The risks of radiation and IV contrast are not negligible, and both cost and delays in the care of other patients in the queue are issues that require consideration. Nevertheless, the CT scan remains a valuable test for evaluating acute abdominal pain.
CT scanning is the test of choice for such common emergency conditions as appendicitis, diverticulitis, aortic disease, renal stones, bowel obstruction, and trauma.1 In addition, CT scan may make the diagnosis of other, rarer causes of abdominal pain that would likely be missed by other types of imaging. Such conditions include epiploic appendagitis, descending aortic dissection, cancer, colitis, pancreatitis, ischemic bowel, intra-abdominal abscess, and hernias. Although CT can be associated with significant delays due to the use of contrast, there is increasing evidence that neither IV nor oral contrast is essential for most diagnostic considerations mentioned above.4 The main caveat is that in trauma or vascular disease, IV contrast remains essential.
The risks of ionizing radiation
With diagnostic imaging, less is often more—especially when risk is low, good follow-up is likely, and thorough patient education is provided. Moreover, the Hippocratic Oath requires clinicians to put patients’ interests before their own and to consider the risks and benefits in all medical decisions. Exposure to ionizing radiation is an important issue that patients can easily understand. A simple explanation such as, “It’s probably safer to wait and see how you are tomorrow rather than do further testing now. This will save you time and money as well as avoid unnecessary radiation exposure,” should work with even the most demanding patient.
The risks of radiation are dose-dependent and cumulative. These risks include malignancy (which tends to develop years to decades later), effects on cognitive development (mostly a consideration in children), and fetal malformations.5
The patient’s age is of paramount importance in weighing the risks and benefits of imaging. Young patients have a considerably higher risk from radiation because their organs may still be developing and they have a much longer life expectancy during which they might go on to develop cancer.5 In addition, the overall incidence of many diseases, especially serious ones, is much lower in younger patients. Think long and hard about the necessity and indication before ordering a CT scan on a younger patient. In older patients, where risk from radiation is lower and serious pathology more common, a more liberal approach may be applied.
To illustrate the principles outlined here, let’s look at three actual cases.