Case #3: A woman aged 65 years presented with right upper quadrant pain that had persisted for 12 hours. Examination revealed an obese patient with normal vital signs. The usual initial imaging test of choice for such a patient would be an ultrasound for evaluation of the gallbladder. An ultrasound was performed and showed gallstones without evidence of cholecystitis (Figure 3); there was no gallbladder wall thickening, common bile duct dilatation, sludge, or pericholecystic fluid. Assuming all blood tests (including WBC and liver function tests) were normal, what would be the appropriate management of this patient?
The answer is, it depends. If the patient is still in significant pain or requires narcotics to alleviate pain, the possibility of a false-negative ultrasound for early cholecystitis should be considered. Although ultrasound is very sensitive for gallstones, it is only about 80%-90% sensitive for cholecystitis. The 10%-20% miss rate is presumably attributable to early or mild cases. Biliary colic usually lasts for only a few hours, and significant pain should not persist beyond six hours from onset of symptoms. Any right upper quadrant pain that lasts for more than six hours in a patient with gallstones should be considered cholecystitis or some other condition until proven otherwise.
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Management options for this patient include a hepatobiliary iminodiacetic acid scan (95%-98% sensitive), admission for observation with repeat labs and ultrasound after eight hours, or discharge home with recheck in eight to 12 hours. The last choice is only recommended in an otherwise healthy patient with good follow-up and normal labs. Abnormal labs are only about 65% sensitive for cholecystitis.1
It is also important to note that gallstones are a frequent red herring that may lead the clinican astray. Approximately 15% of adults have asymptomatic gallstones. Be cautious about attributing pain to this condition when the clinical picture is not a perfect fit. The differential diagnosis for right upper quadrant pain and an ultrasound showing only nonimpacted gallstones might include appendicitis, leaking abdominal aortic aneurysm (Figure 4), pneumonia, and pulmonary embolism, all of which might be missed by an ultrasound study. Other deceptive imaging findings to be alert for include small ovarian cysts, compressive or atelectatic changes on chest x-ray, constipation, and any other chronic finding. Before relying on any of these as diagnostic, be sure the entire clinical presentation is consistent.
This patient went on to develop cholecystitis and required surgery, but it could have been worse. If she had suffered a leaking abdominal aortic aneurysm, even a short delay would have been catastrophic.
Ultrasound vs. CT
These cases illustrate the appropriate use of ultrasound in the evaluation of abdominal pain. As previously mentioned, CT is the most accurate test for making or ruling out the majority of important diagnoses in the emergent patient. Since many feel that CT is being overused,3 it may be helpful to highlight cases in which diagnostic ultrasound is a better first-choice imaging test.
Ultrasound’s primary benefit is that it lacks radiation. Even in such conditions as kidney stones, where CT is clearly more accurate, ultrasound should be considered instead, particularly when the patient is young and the suspicion for more sinister conditions (e.g., abdominal aortic aneurysm) is low. Since the majority of kidney stones will pass without intervention, diagnosing hydronephrosis by ultrasound may obviate the need for a more risky test.
Use of IV and/or oral contrast is another risk associated with CT. There has been a gradual trend in emergency medicine to do more unenhanced or noncontrast studies to avoid risks and delays. In one study, 93 patients with abdominal pain had CT scans both with and without contrast. There was no overall diagnostic advantage to the contrast-enhanced studies.4 Oral contrast may aid in the diagnosis of obstruction and help delineate bowel-wall thickness. However, oral contrast is usually not necessary, and avoiding it in a nauseated or vomiting patient is more humane and avoids the risk of aspiration. Most EDs require a one- to two-hour delay after contrast is administered before the scan is obtained. In a very sick patient, such delays have the potential to affect outcomes negatively.
Nevertheless, IV contrast is critical to use in the trauma patient and the patient in whom there is concern for a vascular condition (e.g., dissection, ischemia, or infarction). In other cases (with the exception of the search for a kidney stone), contrast may make the radiologist’s job easier but is rarely essential. Risks of IV contrast include allergic reaction, renal damage, and exacerbation of an underlying chronic medical condition. With the use of low-osmolality contrast, allergic reactions occur in up to 3% of patients (0.04% of which are severe).1 Although some degree of renal damage occurs in up to 20% of patients, it is usually reversible, and less than 0.5% of patients end up on long-term hemodialysis.1 Risk factors for renal damage are common in ED patients and include: creatinine >1.4 mg/dL; glomerular filtration rate <60 mL/min; proteinuria; such medications as nonsteroidal anti-inflammatory drugs, diuretics, ACE inhibitors, metformin, and pressors; multiple myeloma; cirrhosis; hypertension; diabetes; congestive heart failure; age older than 70 years; dehydration; and prior contrast in the past 72 hours.1 Pre-existing conditions that can be worsened by the use of IV contrast include pheochromocytoma, hypertensive crisis, sickle cell disease, thyrotoxicosis, and myasthenia gravis.1
The number of CT scans is increasing rapidly without a correlating increase in the number of accurate diagnoses made. Research shows that as much as one-third of all CT scans are not justified by medical need.3 As a result, other tests or no imaging is preferred in appropriate patients.
Bedside ultrasound should be used in suspected cases of abdominal aortic aneurysm, ectopic pregnancy, or other conditions in which the patient may become unstable. Ultrasound should also be used preferentially in evaluation of the liver, gallbladder, pelvic pain, or in younger patients with concern for kidney stones or appendicitis.
Plain films should be used when speed is a major concern. Plain films are also appropriate when obstruction is suspected so long as the situation is low-risk and the plan of care does not involve emergency surgery. This approach is even more preferable in the younger patient or the patient who has had many CT scans in the past.
CT has the advantage of excellent diagnostic accuracy and should be used more liberally in older patients in whom the incidence of disease may be higher and the dangers of radiation significantly lower. Unless the benefits outweigh the risks, IV contrast should be avoided in patients at risk for its complications.
Consider no imaging at all for nonemergency causes of abdominal pain. Antacids for presumed gastritis or home observation for possible early appendicitis are appropriate. Although a single dose of an analgesic prior to discharge may be appropriate once a clinical decision has been made, avoid sending any patient with undiagnosed abdominal pain home with a prescription for narcotics. Finally, consider immediate surgical consultation without imaging for cases in which the clinical suspicion is high for such conditions as classic appendicitis or abdominal aortic aneurysm. This will minimize radiation exposure and, more importantly, the chance of decompensation while awaiting surgical therapy.
Dr. Pregerson is an emergency physician at Cedars-Sinai Medical Center in Los Angeles. He has no relationship to disclose relating to the content of this article.
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References
- Pregerson, DB. Cornucopia: Emergency Medicine. Carlsbad, Calif.: EMresource.org; 2010:57-79.
- Pregerson, DB. Quick Essentials: Emergency Medicine, 4.0. Carlsbad, Calif.: EMresource.org; 2010:92-104.
- Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-2284.
- Basak S, Nazarian LN, Wechsler RJ, et al. Is unenhanced helical CT sufficient for evaluation of acute abdominal pain? Clin Imaging. 2002;6:405-407.
- Picano E. Informed consent and communication of risk from radiological and nuclear medicine examinations: how to escape from a communication inferno. BMJ. 2004;329:849-851.
All electronic documents accessed July 15, 2010.
