Transthoracic ultrasound of lung and pleura in the diagnosis of pulmonary embolism: a novel non-invasive bedside approach

The diagnosis of pulmonary embolism (PE) presents a considerable challenge and requires a high index of clinical suspicion from the attending physician. In addition, diagnosing PE may require the use of one or more direct and indirect diagnostic methods. Here, transthoracic sonography (TS) provides an alternative and attractive bedside approach which is based on (1) detecting alterations in the lung parenchyma, (2) involvement of the pleura and (3) peripheral perfusion characteristics associated with thromboembolism. Using a 5 MHz or 3.5 MHz convex scanner, occasionally supplemented by a 7.5 MHz linear scanner or colour-flow Doppler mode, the intercostal areas are systematically examined by TS. Most of the PE-related lesions are localised in the lower lobes of the lung and are often associated with an area of pleuritic chest pain. The characteristic sonographic findings of TS in PE are multiple, hypoechoic, pleural-based parenchymal lesions which adopt a wedge-shape. In addition, a central echo may occasionally be detectable within the lesion. Another regular sonographic feature is the involvement of the pleura manifesting as either localised effusion, basal effusion or both. However, several differential diagnoses such as pneumonia, bronchogenic carcinoma, metastases of extra-pulmonary malignancies, and simple pleurisy need to be excluded. Since localisation of PE-associated lesions may occasionally escape sonographic detection, an inconspicuous sonographic result does not fully exclude PE. As detection of PE-associated lesions using chest ultrasonography has a high specificity and sensitivity, can be rapidly performed, is widely available, non-invasive, cost-effective, and avoids transport of critically ill patients to the investigation site, the technique may prove a valuable tool in the diagnosis of PE at bedside facilitating immediate treatment decision. Further, because the method focuses on detection of peripheral lesions it complements other diagnostic techniques employed when PE is suspected.