title: The etiology of pneumoperitoneum in the 21st century.
abstract: BACKGROUND
  We sought to determine the origin of free intraperitoneal air in this era of diminishing prevalence of peptic ulcer disease and imaging studies. In addition, we attempted to stratify the origin of free air by the size of the air collection.
  
  
  METHODS
  We queried our hospital database for "pneumoperitoneum" from 2005 to 2007 and for proven gastrointestinal perforation from 2000 to 2007. Massive amount of free air was defined as any air pocket greater than 10.0 cm.
  
  
  RESULTS
  Among patients with free air, the predominant causes were perforated viscus (41%) and postoperative (<8 days) residual air (37%). For patients with visceral perforation, only 45% had free air on imaging studies, and for these patients, the predominant cause was peptic ulcer (16%), diverticulitis (16%), trauma (14%), malignancy (14%), bowel ischemia (10%), appendicitis (6%), and endoscopy (4%). The likelihood that free air was identified on an imaging study by lesion was 72% for perforated peptic ulcer, 57% for perforated diverticulitis, but only 8% for perforated appendicitis. The origin of massive free air was equally likely to be gastroduodenal, small bowel, or colonic perforation.
  
  
  CONCLUSIONS
  The cause of free air when surgical pathology is the source has substantially changed from previous reports.
  
  
  METHODS
  Epidemiologic study, level IV.
authors.affiliation: Department of Surgery, University of Texas Health Science Center, San Antonio, Texas 78229, USA.
authors.forename: Ashwini
authors.initials: A
authors.lastname: Kumar
authors.forename: Mark T
authors.initials: MT
authors.lastname: Muir
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Cohn
authors.forename: Marc A
authors.initials: MA
authors.lastname: Salhanick
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Lankford
authors.forename: Venkata S
authors.initials: VS
authors.lastname: Katabathina
mesh_terms: D000007:Abdominal Injuries / Q000150:complications; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001064:Appendicitis; D015331:Cohort Studies; D016208:Databases, Factual; D013505:Digestive System Surgical Procedures / Q000009:adverse effects; D004238:Diverticulitis / Q000150:complications; D005260:Female; D005544:Forecasting; D006801:Humans; D015994:Incidence; D007416:Intestinal Perforation / Q000150:complications; D008297:Male; D008875:Middle Aged; D010439:Peptic Ulcer Perforation / Q000150:complications; D011027:Pneumoperitoneum / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000209:etiology*; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D013276:Stomach Ulcer / Q000150:complications; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult