title: Reappraisal of radiographic signs of pneumoperitoneum at emergency department.
abstract: OBJECTIVE
  This study aimed to evaluate the sensitivities of the reported free air signs on supine chest and abdominal radiographs of hollow organ perforation. We also verified the value of supine radiographic images as compared with erect chest and decubitus abdominal radiographs in detection of pneumoperitoneum.
  
  
  METHODS
  Two hundred fifty cases with surgically proven hollow organ perforation were included. Five hundred twenty-seven radiographs were retrospectively reviewed on the picture archiving and communication system. Medical charts were reviewed for operative findings of upper gastrointestinal tract, small bowel, or colon perforations. The variable free air signs on both supine abdominal radiographs (KUB) and supine chest radiographs (CXR) were evaluated and determined by consensus without knowledge of initial radiographic reports or final diagnosis. Erect CXR and left decubitus abdominal radiographs were evaluated for subphrenic free air or air over nondependent part of the right abdomen.
  
  
  RESULTS
  Upper gastrointestinal tract perforation was proven in 91.2%; small bowel perforation, in 6.8%; and colon perforation, in 2.0%. The positive rate of free air was 80.4% on supine KUB, 78.7% on supine CXR, 85.1% on erect CXR, and 98.0% on left decubitus abdominal radiograph. Anterior superior oval sign was the most common radiographic sign on supine KUB (44.0%) and supine CXR (34.0%). Other free air signs ranged from 0% to 30.4%.
  
  
  CONCLUSIONS
  Most free air signs on supine radiographs are located over the right upper abdomen. Familiarity with free air signs on supine radiographs is very important to emergency physicians and radiologists for detection of hollow organ perforation.
authors.affiliation: Department of Emergency Medicine, Taipei Veterans General Hospital, Taiwan, ROC.
authors.forename: Yu-Hui
authors.initials: YH
authors.lastname: Chiu
authors.forename: Jen-Dar
authors.initials: JD
authors.lastname: Chen
authors.forename: Chui-Mei
authors.initials: CM
authors.lastname: Tiu
authors.forename: Yi-Hong
authors.initials: YH
authors.lastname: Chou
authors.forename: David Hung-Tsang
authors.initials: DH
authors.lastname: Yen
authors.forename: Chun-I
authors.initials: CI
authors.lastname: Huang
authors.forename: Cheng-Yen
authors.initials: CY
authors.lastname: Chang