Imaging tests, CT scans in particular, may occasionally reveal positive findings unrelated to the patient’s symptoms. These incidentalomas are often small nodules or cysts in the thyroid, lung, liver, kidneys, or adrenal glands. Like freckles, bumps, and moles on the outside of the body, these internal nodules tend to be more common with increasing age and can be found in up to 15% to 30% of CT scans.8
Fortunately, the vast majority are benign, but because a small percentage eventually turn out to be malignant, surveillance imaging is often recommended. Unfortunately, this leads to added medical costs and, in many cases, additional radiation exposure and increased patient stress and anxiety. Most of this is all for naught, as the number of cancer “saves” from this process is quite low.
Given the scope of the problem, how can clinicians reduce the use of diagnostic imaging without seeing an increase in missed diagnoses? What follows is a top-down approach for minimizing unnecessary use of CT scanning. This discussion will cover the evaluation of head injury; chest pain; and abdominal, flank, and pelvic pain. Additional topics that should warrant your attention but are beyond the scope of this article include nontraumatic headache, neck injury, and abdominal pain in pregnancy.
Head injuries are a common reason for patients to present for medical evaluation. Fortunately, most patients with a normal neurologic exam will not have a brain injury that requires any significant intervention. However, some will. Such clinical factors as the age of the patient, the mechanism of injury, the presence of vomiting, and the use of blood thinners help to risk-stratify these head-injured patients with a normal neurologic exam.
Although clinical information can help providers minimize the use of CT scan without missing any significant injuries, there is no simple rule that can be used to do this effectively. A variety of clinical information, along with provider judgment, must come into play.
A number of large clinical studies have addressed the minimization of CT in patients with head injury, the best known of which have led to the development of the New Orleans Criteria, the Canadian Head CT Rule, and NEXUS-2.9,10,11 All of these are useful, but none is perfect. The issue is too complex to be encompassed by a simple rule. The NEXUS-2 researchers concluded that providers must know the red flags for brain injury and integrate these warning signs with other clinical information to decide whether CT-scanning of the brain is warranted. The authors use the mnemonic BEAN BASH to identify predictors of significant intracranial injury (Table 2).11
Table 2. Predictors of significant intracranialinjury (BEAN BASH)
|Age >65 years|
|Altered mental status|
|Source: Mower WR et al. Developing a decision instrument to guide computed tomographic imaging of blunt head injury patients. J Trauma. 2005;59:954-959.|
Other factors to consider are the presence of a headache, its severity, and whether it is improving or worsening, or aggravated by the Valsalva maneuver. What was the mechanism of injury, and is the trauma confined to the front of the head or does it extend to other areas that are higher risk, such as the occiput? Was there loss of consciousness, and if so, how long did it last? Is short-term memory intact? Does the patient have a reliable person who can wake him or her every two to three hours overnight and in the morning for status checks?
More red flags indicate higher risk of a significant brain injury. Patients with normal exams and no red flags probably do not need any imaging at all. Patients who only have a mild or improving headache or who report a loss of consciousness of fewer than 60 seconds and have no other red flags likely do not need imaging.
On the other hand, patients who are on blood thinners but have normal brain imaging may still not be safe for discharge home. The issues involved are complex, but clinicians should not order indiscriminant CT scanning on all head-injured patients. The clinical information provided by the previously cited head-injury studies provides a viable plan for selective imaging and a reduction in the radiation exposure in adults.9,10,11
Although the risks of radiation are significantly higher in children with head trauma, the clinical issues are somewhat simpler. In general, young children do not drink alcohol, do not have brain atrophy, and do not use blood thinners. Separate studies have addressed the issue of CT scanning after head trauma in children, the most important of which is the PECARN study.12 Researchers looked at more than 42,000 children younger than age 18 years with Glasgow Coma Scale scores of 14-15. Patients were excluded if they presented more than 24 hours after injury, had a prior neurologic injury, or had a nonsevere injury mechanism (e.g., a ground-level fall or walking into an object).
For children younger than age 2 years, red flags for brain injury included changed mental status, concerning or unknown mechanism of injury, loss of consciousness for more than five seconds, palpable skull fracture, or a nonfrontal hematoma.
For children aged 2 to 18 years, red flags for brain injury included changed mental status, concerning or unknown mechanism of injury, loss of consciousness, signs of a basilar skull fracture, vomiting, or a severe headache. Concerning mechanisms were considered to be bike accidents with no helmet, a fall greater than five stairs or 3 ft (>5 ft if older than age 2 years), or being hit with a projectile. Recommendation was for no CT scan in cases without any red flags, CT in all cases with abnormalities on neurologic assessment or signs of a fracture, and selective scanning in cases where there was only one red flag. In the selective scanning cases, the decision to use CT was based on whether symptoms were getting better or worse, clinician experience, and parental preference.12
When suspicion of intracranial injury is low with only a single red flag present, the clinician should discuss the risks and benefits of CT with radiation vs. home observation with return precautions. Advise the parent or patient that it is always safer for the clinician to order more testing, but that the clinician has a duty to recommend what is safest for the patient. This will help create a therapeutic alliance rather than a confrontation. Letting the patient or parent decide in equivocal cases may take a little more time, but it is the right thing to do.
Dyspnea and/or pleuritic chest pain
Many patients with pleuritic chest pain have only pleurisy or bronchitis, but some have pulmonary embolism (PE), a potentially fatal diagnosis. Again, the goal is to avoid unnecessary testing without missing the diagnosis. Patients with no dyspnea, no pleuritic component to their pain, or no tachypnea have a very low pre-test probability of PE and likely need no testing at all. Low-risk patients that do not fit these criteria should be initially screened using either the PE rule-out criteria (PERC) tool or a highly sensitive D-dimer, as both tools avoid radiation.13
In such cases, it is critical to consider whether there is a more likely diagnosis than PE. Small PEs can be difficult to detect in otherwise healthy patients presenting with pleuritic pain but no dyspnea or alteration in vital signs. If the clinical scenario is classic for bronchitis or a muscle strain, no testing may be required, but the provider should be alert for anything in the clinical picture that does not fit.
When used properly, D-dimer testing can prevent unnecessary advanced imaging and its attendant radiation. When D-dimer is used improperly to screen no-risk patients, the many false-positive results produced can lead to increased imaging. D-dimer testing should not be ordered in a patient with chest symptoms that are not suggestive of PE. D-dimer should only be ordered when the provider would otherwise order a ventilation/perfusion (VQ) or CT scan due to clinical concern. If the D-dimer is negative, the workup can usually be stopped and the patient spared the risks of radiation and/or IV contrast. Up to 50% of D-dimers will be false-positives.
The following conditions can cause an elevated D-dimer; in such cases, it may be advisable to skip directly to imaging.14
Traumatic: postoperative (for up to 10 days), bruise, pregnancy/peripartum period
Thrombotic: myocardial infarction, cerebrovascular accident, dissection, abdominal aortic aneurysm (AAA)
Chronic: liver disease, renal disease, malignancy, collagen vascular disease, sickle-cell disease
Infectious/inflammatory: pericarditis, infection, sepsis, disseminated intravascular coagulation.
Factors that can cause-false negative D-dimer results are even more important to be aware of and require advanced imaging with either VQ or CT angiogram.14 These factors include symptoms lasting longer than one week and current use of heparin (Lipo-Hepin, Liquaemin, Panheparin) or warfarin (Coumadin, Jantoven).
D-dimer can be used to rule out PE in low-risk patients; if combined with a high-sensitivity assay, it can also rule out PE in intermediate-risk patients.15 The better D-dimer tests have sensitivities in the mid- to high-90s, which is comparable to or better than CT angiogram. Another advantage of D-dimer is added sensitivity when VQ or CT gives nondefinitive or suboptimal results. Benefits of D-dimer include rapid turnaround, low cost, and no radiation. The main disadvantage is the test’s low specificity, which is around 50% in most studies.
If a patient is considered high-risk clinically, or if a D-dimer is positive or not an optimal test, a VQ scan or CT angiogram is advised. Although CT has gained popularity, VQ remains the test of choice for most patients when available (Figure 1). Benefits of VQ compared with CT include better sensitivity (96% to 98% for a normal scan),16 less radiation (one-eight to one-fourth the dose), and no need for IV contrast or a large proximal IV.14
Disadvantages of VQ include the need for a normal screening chest x-ray to minimize the chance of an indeterminate study, the tests’s inability to detect such other conditions as pneumonia or dissection, and limited availability.14
One disadvantage of VQ that is more perceived than real is the way that results are reported back to the clinician as normal, low, intermediate, or high probability. This should not prevent its use when the
chest x-ray is normal, as fewer than 10% of VQ scans will be read as indeterminate or intermediate probability in such cases.
Figure 1. VQ scan shows right-sided pulmonary embolism.
Advantages of CT scan for evaluation of PE (Figure 2) include superiority when the chest x-ray is abnormal, rapid scanning time for unstable patients, 24-hour availability in most institutions, high specificity (96%),17 and the ability to find alternate diagnoses.14 Disadvantages of CT include lower sensitivity (77% to 83%),17 much higher radiation exposure (especially to breast tissue), need for IV contrast, and incidental findings that occur in approximately 30% of cases.14
Figure 2. CT shows acute embolism in both pulmonary arteries