Myth 1: CTPA Is the Incontrovertible Standard for PE

Today’s imaging standard for pulmonary embolism (PE) is CT pulmonary angiogram (CTPA). However, in the context of overinvestigation leading to overdiagnosis, we must recognize the limitations of CTPA. Conventional wisdom and recent evidence have informed us that without proper risk stratification for low-risk patients, PE is pursued when it should not be. Just with shopping, when you look, you find, and when you find, you buy. With CTPA, when we look, we find, and when we find, we treat. Thus, we know we need to be looking less often.

Conventional wisdom has also led us to the practical question of whether all diagnosed PEs (especially isolated subsegmental PEs) are clinically relevant and worthy of anticoagulation. However, Hutchinson et al have taken this discussion to a new level.¹ They set aside the concept of clinical relevance to answer the question of whether such radiographic PEs are truly PEs at all.

The authors performed a retrospective review of 174 patients with CTPAs positive for PE. They performed blinded reviews of these studies by chest radiologists, comparing them to initial readings by general radiologists. The overall discordance rate was 25.9 percent. In other words, one-quarter of the PEs diagnosed on CTPA were overinterpretations and not even radiographic PEs. When the discordance rate was broken down further, the story gets even better. For solitary PEs, the discordance rate was 46.2 percent, but for multiple PEs, it was 13.1 percent. This implies that an interpretation of a solitary PE is more likely to be in error than one reporting multiple PEs. Segmental PEs and subsegmental PEs had respective discordance rates of 26.8 percent and 59.4 percent, and finally, with interpretations of lower-lobe solitary subsegmental PEs, the experts disagreed with the initial interpretations 66.7 percent of the time. The causes cited for overinterpretation were 24 from motion artifact, 10 from beam hardening artifact, and eight from poor contrast opacification.

Overdiagnosis isn’t simply a function of overinvestigation but also of overinterpretation. Based on these data, subsegmental PEs, and in particular lower-lobe solitary subsegmental PEs, are suspect. Caution should be exercised when considering the use of anticoagulation. The interpretation isn’t enough. The patient’s presentation needs to match the disease. Don’t believe everything they read.

Myth 2: Plain Films Are Good Enough for Blunt Pelvic Trauma

What is good for the goose is good for the gander, excluding the elderly trauma patient.

Plain radiographs have been notoriously insensitive for posterior pelvic ring and sacral fractures. In the elderly, there is a high mortality rate associated with prolonged immobilization for pelvic fractures. Furthermore, recent advances in orthopedics have expanded the potential treatment options for sacral fractures, which makes their detection that much more important.

Schicho et al performed a retrospective review of 233 consecutive patients (75 years or older) who presented to a level I trauma center with symptomatic blunt pelvic trauma.² Only six plain films showed a sacral fracture compared to 56 of CTs performed. The sensitivity, specificity, negative predictive value, and positive predictive values of plain films for sacral fractures were 10.5 percent, 99.4 percent, 77.8 percent, and 85.5 percent, respectively, and for pubic bone fractures they were 65.7 percent, 90.3 percent, 76.8 percent, and 84.3 percent, respectively. Sacral fractures were associated with pubic bone fractures in 75 percent of cases and with acetabular fractures in 23.3 percent. The average age for those with sacral fractures was 85 years, and 88 percent were women.

Especially in the elderly with symptomatic blunt pelvic trauma, CT may be high-yield and very useful. Those at greatest risk were women in their 80s. In high-risk symptomatic patients, the insensitivity of plain films questions their use at all. When it comes to the elderly pelvis, CT may be the single most important test to order.

References

1. Hutchinson BD, Navin P, Marom EM, et al. Overdiagnosis of pulmonary embolism by pulmonary CT angiography. Am J Roentgenol. 2015;205(2):271-277.
2. Schicho A, Schmidt SA, Seeber K, et al. Pelvic X-ray misses out on detecting sacral fractures in the elderly – importance of CT imaging in blunt pelvic trauma. Injury. 2016;47(3):707-710.