title: Prevalence and characteristics of paratracheal air cysts and their association with emphysema in a general population.
abstract: BACKGROUND
  To evaluate the prevalence and characteristics of paratracheal air cysts and their association with emphysema and gender in a general population using low-dose computed tomography scanning of the chest.
  
  
  METHODS
  We retrospectively enrolled a total of 924 patients (584 women, 340 men; mean age, 59.73 years; range, 37-89 years) who had received low-dose computed tomography scanning for health examination during the period January 1, 2010 to June 30, 2010. Computed tomographic images were evaluated for the presence of paratracheal air cysts. If paratracheal air cysts were identified, the lungs were reconstructed as a three-dimensional model on a commercial workstation. An emphysema index, an objective quantification of the extent of emphysematous changes on CT imaging, was defined as the percentage area of lung with attenuation values below -950 Hounsfield units.
  
  
  RESULTS
  A total of 60 patients with paratracheal air cysts were included in this study (estimated prevalence, 6.5%; 12 men, 48 women; mean age, 59.85; range 45-89 years). Emphysema index differed significantly between genders (P<0.0001). The prevalence of paratracheal air cysts in men was significantly lower than that in women (P=0.005); however, the emphysema index in patients of both genders showed no evidence of emphysema. The majority (95%) of paratracheal air cysts were at the level of the seventh cervical to the second thoracic vertebrae.
  
  
  CONCLUSIONS
  The presence of paratracheal air cysts is a common condition in general populations and should not be misdiagnosed as abnormal paratracheal free air. Paratracheal air cysts are more common in woman than in man. In our study, there is no patient with paratracheal air cysts has CT evidence of emphysema.
authors.affiliation: Department of Medical Imaging, Chi-Mei Medical Center, No. 901, Chung Hwa Road, Yong-Kang, Tainan 710, Taiwan. moyercheng@gmail.com
authors.forename: Hua-Ming
authors.initials: HM
authors.lastname: Cheng
authors.forename: Pau-Yang
authors.initials: PY
authors.lastname: Chang
authors.forename: Kuo-Hsien
authors.initials: KH
authors.lastname: Chiang
authors.forename: Hsin-Wen
authors.initials: HW
authors.lastname: Huang
authors.forename: Chau-Chin
authors.initials: CC
authors.lastname: Lee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D008476:Mediastinal Cyst / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D008478:Mediastinal Emphysema / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D008875:Middle Aged; D015995:Prevalence; D013902:Radiography, Thoracic / Q000706:statistics & numerical data*; D013624:Taiwan / Q000453:epidemiology; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*