Chest CT Angiography for Diagnosing Pulmonary Embolism — Too Much Info?

Abstract & Commentary

By Rahul Gupta, MD, MPH, FACP, Clinical Assistant Professor, West Virginia University, School of Medicine, Charleston, WV. Dr. Gupta reports no financial relationship to this field of study.

Synopsis: When a chest CT angiography (CTA) is ordered to rule out pulmonary embolism (PE) in an emergency room setting, it is much more likely that an incidental finding will be discovered than a PE. This often leads to decision-making challenges and raises questions about the proliferating use of such technology.

Source: Hall WB, et al. The prevalence of clinically relevant incidental findings on chest computed tomographic angio-grams ordered to diagnose pulmonary embolism. Arch Intern Med 2009;169:1961-1965.

Pulmonary embolism (pe) is a common and potentially fatal disease. Timely diagnosis and treatment can reduce mortality. However, the clinical presentation can be variable and nonspecific since many of the signs and symptoms detected in patients with acute PE are also common among patients without PE. Whereas many diagnostic algorithms integrate CTA as a part of the evaluation, most recommend an initial clinical evaluation to determine the clinical probability.1,2 However, in emergency departments (ED) across the nation, most patients quickly undergo a scan when PE is suspected. The busy ED physician attempts to use the available technology not only to provide quality care, but also to work in an efficient manner. The high prevalence of incidental findings of questionable clinical significance is becoming increasingly common in all areas of medicine as more scans are being ordered. Therefore, it is important to understand whether this is a rational approach worth the additional radiation and contrast risk.

In their study, Hall et al conducted a cross-sectional study at an academic tertiary care center of a major university with an annual ED patient load of 50,000. The authors reviewed 589 pulmonary CTAs ordered during their ED evaluation. They found that PE was diagnosed in only 55 of 589 CTAs (9%), whereas 195 (33%) had findings that supported alternative diagnoses. The most common alternative diagnoses were pleural effusion and infiltrates (179/195) and more than half of these were evident even on plain chest radiographs. In another 136 of the 589 patients (23%), new pulmonary nodule, adenopathy, or mass was identified. Overall, 141 patients (24%) had incidental findings requiring further evaluation such as clinical or radiologic follow-up. The likelihood of finding a new incidental nodule or adenopathy was twice that of finding a PE.

Commentary

In my experience, it is not unusual to have an admitted patient with an incidental finding as a result of an initial evaluation that the primary care physician feels compelled to investigate further. With the advent of new technology such as the CTA, most hospitals' EDs have the reassurance of not only precisely diagnosing PE when suspected, but also finding alternative diagnoses when PE does not exist. However, as with any test, when such technology is broadly applied to large populations, a significant number of incidental abnormalities may be found, which in turn compel practitioners to run additional tests. Those tests have their own risks and may often not achieve much in terms of early diagnosis of major diseases.3 Therefore, the net result often may be a greatly higher risk from radiation and contrast exposure in addition to causing unnecessary anxiety and costs for the patient. Consequently, it is essential that any ordering of scans be preceded by a careful clinical assessment and utilization of one of the many available algorithms that would incorporate the modified Wells criteria.4 A diagnostic management strategy such as that in the Christopher study, which utilizes a simple clinical decision rule, D-dimer testing, and CT when needed, is effective in the evaluation and management of patients with clinically suspected pulmonary embolism.4 In addition to limiting radiation exposure and contrast risk, this would substantially reduce the number of significant incidental findings while increasing the yield for PE when CTA is ordered.

References

1. Wells PS, et al. Use of a clinical model for safe management of patients with suspected pulmonary embolism. Ann Intern Med 1998;129:997-1005.

2. Wells PS, et al. Excluding pulmonary embolism at the bedside without diagnostic imaging. Ann Intern Med 2001;135:98-107.

3. Iribarren C, et al. Incidental pulmonary nodules on cardiac computed tomography: Prognosis and use. Am J Med 2008;121:989-996.

4. van Belle A, et al. Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. JAMA 2006;295:172-179.