title: Localized air foci in the lower thorax in the patients with pneumothorax: skip pneumothoraces.
abstract: OBJECTIVE
  To investigate the characteristics and imaging features of localized air foci in the lower thorax in patients with pneumothorax using thin-section multidetector computed tomography.
  
  
  METHODS
  Of 10,547 consecutive CT examinations comprising the chest, the CT scans of 146 patients with ordinary pneumothoraces were identified and retrospectively evaluated. The study group included 110 male and 36 female patients (mean age, 50 years; range, 1-93 years). All examinations were performed at our institution between January 2009 and December 2009. Cause of pneumothorax was classified as traumatic or non-traumatic. Localized air foci in the lower thorax were defined as being localized air collections in the lower thorax that did not appear to be adjacent to the lung. If these criteria were met, the shape, size, location laterality, and number of foci were evaluated. Associations with trauma, sex, severity of the pneumothorax, and laterality were evaluated using the χ(2) test. All P values <0.05 were considered significant.
  
  
  RESULTS
  Localized air foci in the lower thorax presented as slit-like or small ovoid air collections in the lowest part of the pleural space. These foci were observed in 79/146 (54.1%) patients. The traumatic pneumothoraces group showed a higher prevalence of these features than the non-traumatic group. Some foci that were situated in the anterior part mimicked the appearance of free intraperitoneal air.
  
  
  CONCLUSIONS
  Patients with pneumothorax commonly had localized air foci in the lower thorax. Because such foci can mimic pneumoperitoneum, accurate recognition of them is required to avoid confusion with free intraperitoneal air, especially in traumatic cases.
authors.affiliation: Department of Diagnostic Radiology, Niigata City General Hospital, 463-7 Chuo-ku, Shumoku, Niigata 950-1197, Japan. higuchi@hosp.niigata.niigata.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Higuchi
authors.forename: Naoya
authors.initials: N
authors.lastname: Takahashi
authors.forename: Takao
authors.initials: T
authors.lastname: Kiguchi
authors.forename: Motoi
authors.initials: M
authors.lastname: Shiotani
authors.forename: Haruo
authors.initials: H
authors.lastname: Maeda
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000388:Air / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011030:Pneumothorax / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D013902:Radiography, Thoracic / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013909:Thorax / Q000737:chemistry*; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*; D055815:Young Adult