Imaging of Pulmonary Embolism

Publisher Website
Google Scholar
Abstract
Pulmonary embolism is a common and potentially lethal condition and the death rate has not changed significantly during the past 30 years. Autopsy studies indicate both over and under diagnosis of the condition which has a prevalence of between 14 and 26% at post-mortem in patients admitted to hospital. Clinical diagnosis is difficult since individual signs and symptoms are poor predictors of embolism. The importance of accurate diagnosis and effective treatment is therefore obvious, but the multiplicity of imaging techniques and diagnostic algorithms is testimony to the inadequacy of any single diagnostic test. Chest radiographs are routinely obtained when the diagnosis is suspected. Their main role is to exclude diagnoses which may mimic PE and to improve the interpretation of V/Q scintigrams. V/Q scintigraphy is the main stay of imaging in most hospitals. This is because it is non-invasive and readily available. At best it is an indirect assessment for PE and provides a diagnosis in less than 50% of patients examined. A normal examination virtually excludes PE but an abnormal study is only able to provide a probability of PE being present. Concordant chest radiographic interpretation improves accuracy as does the pre-test clinical probability. A high probability V/Q result coupled with a high pre-test clinical probability indicates PE with a greater than 90% probability, but low and intermediate V/Q results are of limited value. Furthermore, the likelihood of indeterminate V/Q results is much greater in patients with pre-existing cardio-respiratory disease, which is all too frequently the case in an increasingly elderly hospital population. Indeterminate results should be followed by further imaging. Hitherto, this has meant pulmonary angiography, which has long been regarded as the most sensitive imaging technique for PE. However, it is remarkably underused and in other than a few centers is performed in only 5-15% of patients following indeterminate V/Q scintigraphy. This is despite the fact that mortality and morbidity have been significantly reduced with newer catheter techniques, faster studies using digital imaging and low osmolar or non-ionic contrast agents.

This publication has 0 references indexed in Scilit: