Background and objective: The aims of this study were to describe the frequency and radiographical characteristics of pleural effusions in a large population of patients with acute pulmonary embolism (PE) and characterize the pleural fluid biochemistry in those patients who underwent diagnostic thoracentesis.
Methods: This was a retrospective observational single-centre study. A total of 230 consecutive patients with a diagnosis of PE over a 9-year period were enrolled. Spiral CT pulmonary angiography (52%) and high-probability ventilation and perfusion scans (42%) were used as the main reference methods.
Results: Pleural effusions were observed in 32% and 47% of patients by CXR and CT, respectively. Typically, pleural effusions were small (90% occupied less than one third of the hemithorax) and unilateral (85%), but occasionally they reached more than a half of the hemithorax. On CT, 21% of pleural effusions showed loculation. In patients with loculated pleural fluid the diagnosis of PE had been delayed for a mean of 12.2 days after symptoms developed. The presence of pleural fluid was not related to infarction. Twenty-six of 93 (28%) patients with effusions on imaging underwent thoracentesis. All the fluids met Light's criteria for exudate, 58% contained erythrocyte counts >10,000/microL and 46% showed neutrophilic predominance.
Conclusions: Small pleural effusions, mostly unsuitable for diagnostic thoracentesis, were present in about one third of patients with PE. All the pleural effusions due to PE were exudates. If PE diagnosis was delayed the pleural effusion tended to become loculated.