2. Zuckerman JD, Skovron ML, Koval KJ, Aharonoff G, Frankel VH. Postoperative complications and mortality associated with operative delay in older patients who have a fracture of the hip. J Bone Joint Surg Am. 1995;77(10):1551-1556.
3. Hakkarinen DK, Banh KV, Hendey GW. Magnetic resonance imaging identifies occult hip fractures missed by 64-slice computed tomography. J Emerg Med. 2012;43(2):303-307.
4. Feldman F, Staron RB. MRI of seemingly isolated greater trochanteric fractures. AJR Am J Roentgenol. 2004;183(2):323-329.
5. Schultz E, Miller TT, Boruchov SD, Schmell EB, Toledano B. Incomplete intertrochanteric fractures: imaging features and clinical management. Radiology. 1999;211(1):237-240.
6. Cannon J, Silvestri S, Munro M. Imaging choices in occult hip fracture. J Emerg Med. 2009;37(2):144-152.
PE or Not PE: That Is the Question
Jessica Fisher, MD
Dr Fisher is an instructor of radiology at Weill Cornell Medical College in New York City.
Pulmonary embolism (PE) represents the third most common cause of death from cardiovascular disease after myocardial infarction and stroke.1 Given the potential for fatal outcome, prompt diagnosis and management are essential. To avoid overdiagnosis of PE and unnecessary treatment with anticoagulation therapy, diagnostic tests with both a high sensitivity and high specificity are essential.
Clinical stratification of patient risk for PE, in combination with D-dimer assays, is typically used to determine the need for imaging. Preliminary studies with chest X-ray are utilized to evaluate alternate causes of clinical symptoms but do not provide a definitive diagnosis. In the ED setting, advanced imaging options to detect PE include computed tomography angiography (CTA), ventilation perfusion scintigraphy (V/Q lung scan), and magnetic resonance angiography (MRA).
Computed Tomography Angiography
 |  | ||
| Figure 1. Coronal (A) and axial (B) contrast-enhanced computed tomography angiography scans reveal pulmonary embolism (white arrows).. | |||
CTA has long been the standard technique for evaluating PE. In addition to reported sensitivities of 96% to 100% and specificities of 97% to 98% with multislice detectors,2 CTA also provides information on disease severity, such as clot burden, evidence of right heart strain, and the presence of pulmonary infarct (Figure 1). It also can reveal alternative etiology and diagnosis in negative cases (Figure 2).
Figure 2. Coronal contrast-enhanced computed tomography angiography scan reveals pneumonia mimicking pulmonary embolism (white arrow).
CTA is readily available in today’s ED and can be performed quickly and efficiently. However, it does require intravenous (IV) contrast and emits a high-dose of radiation, which may be contraindicated in some patient populations (eg, patients with renal failure, allergy to contrast, and pregnant and pediatric patients). Also, to avoid degradation of images and accurately visualize peripheral branches, patient cooperation (ie, suspension of respiratory motion) during the examination is essential.
Ventilation Perfusion Scintigraphy
Before the advent of CTA, V/Q lung scan was the first-line imaging choice to assess for PE.3 This modality continues to have a role in modern practice, especially given its estimated 6-fold lower whole-body effective radiation dose compared to CTA.4 Current applications of this modality include patients with contraindications to IV contrast as well as pregnant and pediatric patients in whom perfusion-only studies should be used to significantly lower the radiation profile.
In patients with a clear chest X-ray, the negative predictive value of V/Q is not significantly different from CT.5 This suggests a growing role for V/Q scans in the younger, healthier patient population where limited/reduced exposure to radiation is particularly desired—eg, pediatric patients and women younger than age 20 years in whom there is an increased risk of malignancy associated with radiation exposure to the breast/chest area.6
The limitations of V/Q lung scan include a higher rate of indeterminate results compared to CTA (particularly in patients with an abnormal chest X-ray). Moreover, V/Q does not provide alternative diagnoses or qualify disease severity. Also, the longer imaging times compared with CTA make this modality impractical in critically ill patients.
Magnetic Resonance Angiography
MRA has emerged in recent years as a potential alternative to CTA. Since this modality does not use ionizing radiation or iodine-based contrast, it is a reasonable and appropriate option for pediatric patients and those with a contrast-dye allergy. Initial meta-analysis of MRA studies demonstrated sensitivity ranging from 77% to 100% and a specificity of 95% to 98%.7-9 However, subsequent studies have found unacceptably high rates of technically inadequate examinations resulting in nondiagnostic results.10 As progress to reduce respiratory and cardiac motion artifacts and improve spatial resolution continues, along with the growing availability of MRA in the ED, this modality may soon emerge as a useful diagnostic option.
Conclusion
New advances in the diagnosis of PE continue to emerge. Evidence suggests improved sensitivity of CTA with the use of dual-energy CT scanners.11 The recent advance of V/Q single photon emission CT has also shown promise in improving detection accuracy.12 Ongoing research will help continue to expand the emergency physician’s range of imaging choices in the diagnosis of PE.