Imaging techniques in treatment algorithms of pulmonary embolism

Pulmonary embolism (PE) is more often diagnosed post mortem by pathologists than in vivo by clinicians. The identification of practical diagnostic algorithms could reduce the rate of diagnoses first made at autopsy. The literature was reviewed for evidence-based approaches to PE diagnosis. Since the PE mortality rate greatly exceeds that of deep vein thrombosis (DVT), more emphasis was given to reports specifically dealing with PE diagnosis by objective pulmonary vascular imaging techniques than to those aimed at DVT detection. Several studies have shown that standardized clinical estimates can be effectively used to give a pretest probability to calculate, after appropriate objective testing, the post-test probability of PE. A prospective trial has shown that perfusion scanning, rather than ventilation/perfusion scanning, should be the imaging technique of first choice for the management of patients suspected of having PE. The clinical usefulness of spiral computed tomography has not as yet been firmly established. However, ongoing technological developments would probably render the technique accurate enough to replace conventional angiography. The authors propose a noninvasive diagnostic algorithm with high predictive accuracy (positive predictive value 96%; negative predictive value 98%) starting with a standardized assessment of clinical likelihood, followed by a perfusion scan and, eventually, spiral computed tomography in only a minority of patients (< 20%) with discordant clinical and scintigraphic findings.