In most cases, recognition of a pulmonary embolism requires a high index of suspicion that prompts objective evaluation. Exposure of the mother and fetus to ionizing radiation is a concern when investigating a suspected pulmonary embolism during pregnancy. However, this concern is largely overruled by the hazards of missing a potentially fatal diagnosis. Moveover, erroneously assigning a diagnosis of pulmonary embolism to a pregnant woman is also fraught with problems. It unnecessarily exposes the mother and fetus to the risks of anticoagulation treatment and will impact delivery plans, future contraception, and thromboprophylaxis during subsequent pregnancies. herefore, investigations should aim at diagnostic certainty (Konstantinides, 2014).
In 2011a, the American horacic Society and the Society of Thoracic Radiology developed an algorithm-shown in Figure 52-5 for the diagnosis of pulmonary embolism during pregnancy (Leung, 201l). In addition to compression ultrasonography, which was previously discussed (p. 1010), the algorithm includes computed-tomographic pulmonary angiography (CTPA) and ventilation-perfusion scintigraphy.
Multidetector computed tomography with pulmonary angiography is currently the most commonly employed technique used for pulmonary embolism diagnosis in nonpregnant patients (Bourjeily, 2012; Pollack, 2011). he technique is described further in Chapter 46 (p. 907), and an imaging example is
Dia. 1.5 cm each; total area 9 cm2
Dia. 8 mm each; total area 1 3 cm2 arteries Dia. 6 mm each; = arteries Dia. 4 mm each;
FIGURE 52-4 Schematic of pulmonary arterial circulation. Note that the cross-sectional area of the pulmonary trunk and the combined 2 pulmonary arteries is 9 cmo. A large saddle embolism could occlude 50 to 90 percent of the pulmonary tree, causing hemodynamic instability. As the arteries give of distal branches, the total surface area rapidly increases, that is, 13 cm2 for the combined five lobar arteries, 36 cm2 for the combined 19 segmental arteries, and more than 800 cm2 for the total 65 subsegmental arterial branches. Thus, hemodynamic instability is less likely with emboli past the lobar arteries. (Data from Singhal S, Henderson R, Horsfield K, et al: Morphometry of the human pulmonary arterial tree, Circ Res. 1973 Aug;33(2):190-197.)
Stop CUS, CTPA Treat Stop
FIGURE 52-5 The American Thoracic Society and Society of Thoracic Radiology diagnostic algorithm for suspected pulmonary embolism during pregnancy. CTPA = computed tomographic pulmonary angiography; CUS = compression ultrasonography; CXR = chest x-ray; PE = pulmonary embolism; V/O = ventilation/perfusion scintigraphy. (Modified with permission from Leung AN, Bull TM, jaeschke R, et al: An oficial American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline: Evaluation of suspected pulmonary embolism in pregnancy, Am j Respir Crit Care Med. 2011 Nov 15;184(10):1200-1208.)