title: A Simple Method for Differentiating Complicated Parapneumonic Effusion/Empyema from Parapneumonic Effusion Using the Split Pleura Sign and the Amount of Pleural Effusion on Thoracic CT.
abstract: BACKGROUND
  Pleural separation, the "split pleura" sign, has been reported in patients with empyema. However, the diagnostic yield of the split pleura sign for complicated parapneumonic effusion (CPPE)/empyema and its utility for differentiating CPPE/empyema from parapneumonic effusion (PPE) remains unclear. This differentiation is important because CPPE/empyema patients need thoracic drainage. In this regard, the aim of this study was to develop a simple method to distinguish CPPE/empyema from PPE using computed tomography (CT) focusing on the split pleura sign, fluid attenuation values (HU: Hounsfield units), and amount of fluid collection measured on thoracic CT prior to diagnostic thoracentesis.
  
  
  METHODS
  A total of 83 consecutive patients who underwent chest CT and were diagnosed with CPPE (n=18)/empyema (n=18) or PPE (n=47) based on the diagnostic thoracentesis were retrospectively analyzed.
  
  
  RESULTS
  On univariate analysis, the split pleura sign (odds ratio (OR), 12.1; p<0.001), total amount of pleural effusion (≥30 mm) (OR, 6.13; p<0.001), HU value≥10 (OR, 5.94; p=0.001), and the presence of septum (OR, 6.43; p=0.018), atelectasis (OR, 6.83; p=0.002), or air (OR, 9.90; p=0.002) in pleural fluid were significantly higher in the CPPE/empyema group than in the PPE group. On multivariate analysis, only the split pleura sign (hazard ratio (HR), 6.70; 95% confidence interval (CI), 1.91-23.5; p=0.003) and total amount of pleural effusion (≥30 mm) on thoracic CT (HR, 7.48; 95%CI, 1.76-31.8; p=0.006) were risk factors for empyema. Sensitivity, specificity, positive predictive value, and negative predictive value of the presence of both split pleura sign and total amount of pleural effusion (≥30 mm) on thoracic CT for CPPE/empyema were 79.4%, 80.9%, 75%, and 84.4%, respectively, with an area under the curve of 0.801 on receiver operating characteristic curve analysis.
  
  
  CONCLUSIONS
  This study showed a high diagnostic yield of the split pleura sign and total amount of pleural fluid (≥30 mm) on thoracic CT that is useful and simple for discriminating between CPPE/empyema and PPE prior to diagnostic thoracentesis.
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Tsujimoto
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Saraya
authors.affiliation: Division of Allergy/Pulmonary/Critical Care, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Light
authors.affiliation: Department of Radiology, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Tsukahara
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Koide
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kurai
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Ishii
authors.affiliation: Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kimura
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Goto
authors.affiliation: Department of Respiratory Medicine, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Takizawa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003937:Diagnosis, Differential; D016724:Empyema, Pleural / Q000150:complications / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010994:Pleura / Q000000981:diagnostic imaging* / Q000473:pathology; D010996:Pleural Effusion / Q000150:complications / Q000000981:diagnostic imaging*; D011014:Pneumonia / Q000000981:diagnostic imaging* / Q000209:etiology; D012372:ROC Curve; D013902:Radiography, Thoracic / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*