Pleural effusion is the collection of fluid in the pleural space when the production of pleural fluid is in excess of absorption. Analysis of pleural fluid by thoracentesis with imaging guidance helps determine the cause of pleural effusion. Light’s criterion is a traditional method of differentiating transudates and exudates. There has been limited studies with no clear consensus on role of measuring Hounsfield units (HU) in Computed Tomography (CT) Scan to differentiate transudate, exudate or empyema. The purpose of this study was to evaluate the efficacy of CT scans in differentiating pleural effusions as exudate or transudate using attenuation values in HU.
Methods: This retrospective study was performed on 100 patients with pleural effusions admitted to Abington Hospital-Jefferson Health between January 2014 and December 2016. Patients who had a chest CT followed by diagnostic thoracentesis within 48 hours were included. Pleural effusions were classified as exudates or transudates on the basis of Light’s criteria using laboratory biochemical markers. CT attenuation value (CTA) in Hounsfield Unit were taken using a region of interest on the CT chest with the greatest quantity of fluid. Each CT scan was also reviewed for the presence of additional pleural features.
21 of the 100 pleural effusions were transudates and 79 were exudates. The mean attenuation of the exudates (31.9±15.2 HU; 95% CI, 28.4-35.2 HU) was significantly higher than the mean attenuation of the transudates (24.8±9.9 HU; 95% CI, 20.3-29.3 HU), (p = 0.047). When a cutoff value for exudative effusion was accepted as ≥24.50, sensitivity and specificity were 65.0% and 47.6%, respectively. All cases of pleural loculations (14%); irregularity (2%); and thickening (2%) were associated with exudates.
CT attenuation values may be used clinically to characterize pleural fluid. Exudates had significantly higher Hounsfield units in CT Scan. Additional CT features, such as pleural loculation, thickening, and irregularities were predominantly associated with exudates. Accurate characterization of empyema with CT chest with HU may guide to early intervention. Standardization of reporting HU in CT chest for pleural effusion is important. Further studies with larger sample size are needed for accuracy.
M. Naglak, None
M. Rosenberg, None