Imaging options for patients with acute abdominal pain
CT scan shows an abdominal aortic aneurysm above the aortoiliac junction.
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At a glance
- Plain films are rapid, universally available, and have a much lower radiation dose than that of CT scan.
- Ultrasound is portable, radiation-free, and can provide preliminary results more quickly than other modalities.
- CT scan is considered the test of choice for most causes of acute abdominal pain.
- Consider no imaging for nonemergency abdominal pain.
Diagnostic imaging plays a key role in the evaluation and management of acute abdominal pain. Serious consequences may result from incorrect or delayed diagnosis of a number of medical and surgical diseases that may present with GI symptoms. Imaging tests are often vital to confirming the diagnosis for many of these conditions.
The three main modalities of medical imaging used to evaluate abdominal complaints in the emergency department (ED) are plain films, diagnostic ultrasound, and CT scan. Each has its own unique set of strengths and weaknesses with regard to providing optimal medical care. For example, CT scans generally yield more information than other imaging tests but also have the highest risk of adverse events (attributable to higher doses of radiation and the use of IV and/or oral contrast). Another factor to bear in mind when choosing the most appropriate initial test is the associated delay in care. Plain films and bedside ultrasound tend to be rapid, whereas CT scanning may be associated with hours of delay due to queuing (which can be highly variable among different EDs or even within the same ED at different times of the day), waiting for serum creatinine levels, or the use of oral contrast.
Plain films—such as the kidney, ureter, bladder (KUB); upright chest x-ray; and abdominal series—have the advantage of being rapid and, for the most part, universally available. In addition, the radiation dose tends to be much lower than that for CT scan. However, the sensitivity of plain radiography for most intra-abdominal diseases is quite low.1 Generally accepted indications for plain films in the evaluation of abdominal pain are bowel obstruction, perforated viscus, and pneumonia.1 Although CT scan is still significantly more sensitive for even these three conditions, plain films are especially worth considering in specific situations.
The first such situation is any potentially high-risk disease in which a delay of an hour or two may lead to a worse outcome (e.g., perforated viscus or a closed-loop bowel obstruction such as a volvulus). For such conditions, plain radiography should be the initial study of choice. Reserve CT scan for cases in which plain films are negative but suspicion remains.
At the opposite end of the sensitivity spectrum, plain films are often preferable to CT scan. If the condition seems low-risk and/or the patient is young or has received multiple CT scans in the past, consider plain films to minimize radiation exposure and save time. A patient with a potential (but doubtful) bowel obstruction or someone who has had multiple low-grade obstructions that rarely or never required surgery are prime candidates. In such a case reassuring plain films might be all that is necessary to create an initial treatment plan, with advanced imaging reserved only for select cases.
Plain radiography is not indicated for generalized abdominal pain, kidney stones, appendicitis, or most other conditions not mentioned above. The sensitivity and specificity for most causes of abdominal pain other than bowel obstruction, perforation, or pneumonia is too low to be clinically useful. Ordering plain films in these situations only adds to radiation exposure, delays in care, and medical costs.