Pleural effusion in patients with pulmonary embolism

Background and objective: It has been suggested that pulmonary embolism (PE) is an under-recognized cause of pleural effusion. This study aimed to (i) establish the incidence and clinical relevance of pleural effusion in patients with pulmonary emboli; and (ii) determine if there is a relationship between development of pleural effusions and the location of emboli and number of pulmonary arteries involved. Methods: A retrospective analysis of all CT pulmonary angiograms (CTPA) performed over 12 months on adult patients with clinically suspected PE in a hospital which used CTPA as first-line imaging investigation for PE. Results: Of 285 CTPA, 60 patients (21%) had evidence of pulmonary emboli (38 had both central and peripheral clots and 22 peripheral emboli only). Emboli were bilateral in 39 cases and unilateral in 21 cases. Pleural effusion was present in almost one half (n = 29, 48%) of the patients with pulmonary emboli. Patients with pulmonary emboli were more likely to have a pleural effusion (OR 2.2 (95% CI: 1.1-4.7), P < 0.05) than patients without PE; however, the effusions were generally very small. Most (86%) of the effusions were present on the same side as the emboli. The location of emboli and number of arteries involved did not predict the presence of pleural effusions. Conclusions: Pleural effusion is common in patients with pulmonary emboli demonstrated on CTPA. These effusions are small and seldom alter clinical management. Clinicians should therefore have a high threshold of suspicion in attributing large or contralateral pleural effusions to embolic diseases without excluding alternative diagnoses.