title: Pleural effusion and ventilation/perfusion scan interpretation for acute pulmonary embolus.
abstract: This study was conducted to determine if pleural effusion size affects ventilation/perfusion (V/Q) scan interpretation algorithms for acute pulmonary embolus (PE).
  
  
  METHODS
  Retrospective analysis identified 163 consecutive patients undergoing angiography for PE with radiographic evidence for pleural effusion. V/Q scanning was performed in 94 (58%) of cases and reported using original Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) criteria. Effusions were classified as small, large and/or bilateral. Radiographic and scintigraphic results were compared with regard to size and location of abnormalities.
  
  
  RESULTS
  Of the 163 patients, 57 (35%) had angiographically-proven PE, 77 (47%) had at least one large pleural effusion and 86 (53%) had a small effusion; 33 (43%) with large effusions and 24 (28%) with small effusions had emboli at angiography. Thirty-six of 119 patients (30%) with clear chest radiographs (a control group) had PE. Thus, large effusions were associated with a higher incidence of PE than those with small effusions or clear lungs (p < 0.05). Of those with V/Q scanning, 26 of 94 (28%) had a solitary large effusion, with 12 (46%) positive for emboli. V/Q-matched abnormalities limited to effusion size were found in 16 with a solitary large effusion and 10 with a solitary small effusion. In both groups, 50% were angiographically positive for emboli. Twenty-three (66%) of 35 with bilateral effusions had corresponding V/Q-matched defects at one (n = 11) or both (n = 12) lung bases, and 9 (39%) were positive for emboli. In total, 45% with a V/Q-matched defect of equivalent size to the effusion were angiographically positive for PE.
  
  
  CONCLUSIONS
  Pulmonary emboli are associated with pleural effusions of all sizes. Matched V/Q defects corresponding to radiographically-evident pleural effusions are of intermediate probability for PE. Thus, revision of the traditional lung scan interpretive criteria based upon pleural effusion size is not warranted.
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston 02114, USA.
authors.forename: S N
authors.initials: SN
authors.lastname: Goldberg
authors.forename: D D
authors.initials: DD
authors.lastname: Richardson
authors.forename: E L
authors.initials: EL
authors.lastname: Palmer
authors.forename: J A
authors.initials: JA
authors.lastname: Scott
mesh_terms: D000208:Acute Disease; D000465:Algorithms; D006801:Humans; D015994:Incidence; D008168:Lung / Q000000981:diagnostic imaging*; D010996:Pleural Effusion / Q000150:complications / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011336:Probability; D011651:Pulmonary Artery / Q000000981:diagnostic imaging; D011655:Pulmonary Embolism / Q000150:complications / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011859:Radiography; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D014692:Ventilation-Perfusion Ratio