Spiral Computed Tomography for the Diagnosis of Acute Pulmonary Embolism

The accuracy of computed tomography (CT) imaging for the diagnosis of acute pulmonary embolism (PE) was reviewed. Single detector CT, based on pooled data, showed a sensitivity of 73% and multidetector CT, mostly 4-slice, showed a sensitivity of 83%. Respective specificities were 87% and 96%. Among patients with suspected PE evaluated with single slice CT, 20% of patients found to have venous thromboembolic disease were diagnosed on the basis of a positive CT venous phase venogram. With multislice CT, 14% were diagnosed on the basis of a positive CT venogram. The positive likelihood ratio with single detector CT was 5.7 and with multidetector CT it was 19.6. Respective negative likelihood ratios were 0.31 and 0.18. Calculations of post-test probability using pretest probability and likelihood ratios according to Bayes' theorem showed that even with multidetector CT, false positive and false negative images are not uncommon when clinical assessment is discordant with the CT interpretation. Outcome studies showed recurrent PE in only 1.7% or fewer untreated patients with negative CT pulmonary angiograms.