CHEST RADIOLOGY

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Imaging Findings
CT shows a thrombus in the right main pulmonary artery with a cavitating infarct.

Discussion

Imaging Findings

Pulmonary embolism can be diagnosed accurately with pulmonary angiography, which is recognized as the gold standard with a sensitivity and specificity greater than 95%. Nevertheless, pulmonary angiography is invasive and has been shown to have 6% morbidity and a 0.5% mortality rate.

Ventilation-perfusion radionuclide lung scanning is the most frequently performed noninvasive imaging study for the diagnosis of pulmonary embolism. A scan showing a normal or low probability has a high negative predictive value when the clinical suspicion of pulmonary embolism is low, and a high-probability scan has a high positive predictive value when the clinical suspicion is high. Unfortunately, only 34% of cases correspond to these two categories, and large differences in inter-observer reporting especially in the classification of low- or intermediate-probability scan necessitates further investigation to exclude or confirm pulmonary embolism.

Although prior clinical probability and noninvasive tests are currently used as the first-line technique to make the diagnosis of pulmonary embolism, CT angiography might be a better initial imaging technique than ventilation-perfusion radio nuclide lung scanning.

However, when helical CT angiography has negative results and when clinical suspicion of pulmonary embolism remains high, pulmonary angiography is still indicated. Further investigations are necessary to assess the effectiveness of CT angiography compared with that of ventilation-perfusion radionuclide lung scanning in particular, patient populations such as patients with chronic obstructive lung disease or other coexistent morbid conditions.

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