title: Saber-sheath trachea as a marker of severe airflow obstruction in chronic obstructive pulmonary disease.
abstract: OBJECTIVE
  Saber-sheath trachea is a specific radiographic parameter for chronic obstructive pulmonary disease (COPD), which consists of marked coronal narrowing associated with sagittal widening (tracheal index <2/3-0.67). The aim of this study was to investigate the correlation between saber-sheath trachea and clinical-radiological findings in a group of patients with COPD of varying severity.
  
  
  METHODS
  We evaluated the chest radiographs of 71 patients with COPD distributed as follows: GOLD class I, 8/71 (11.3 %); class II, 34/71 (47.9 %); class III, 16/71(22.5 %); class IV, 13/71 (18.3 %). In 52/71 (73.2 %) patients we also evaluated chest computed tomography (CT) scans. We analyzed the prevalence of saber-sheath trachea and its correlation with the Tiffenau index, GOLD stage and radiological signs of COPD. Moreover, we evaluated the sensitivity, specificity and accuracy of chest radiography as compared to CT taken as the gold standard, and the correlation between the radiographic and CT tracheal index.
  
  
  RESULTS
  Saber-sheath trachea was found in 18/71 (25.4 %) patients, with a greater prevalence in patients with lower Tiffenau Index (p = 0.02), GOLD stages III-IV and visual severity score 3 (severe) on chest CT. Saber-sheath trachea was not found to be related to other radiological signs of COPD. The sensitivity, specificity and accuracy values of radiography were 72.2, 97.0 and 88.5 %, with perfect concordance between the radiographic and CT tracheal index (p < 0.00001).
  
  
  CONCLUSIONS
  Saber-sheath trachea is linked to the functional severity of airway obstruction, but not to other radiological signs of COPD. Thus, evaluation of the trachea at chest radiography is strongly recommended.
authors.affiliation: Radiologia Cardio-Toracica, Policlinico S. Orsola-Malpighi, Bologna, Italy, ciccarese.f@gmail.com.
authors.forename: Federica
authors.initials: F
authors.lastname: Ciccarese
authors.forename: Antonio
authors.initials: A
authors.lastname: Poerio
authors.forename: Silvia
authors.initials: S
authors.lastname: Stagni
authors.forename: Domenico
authors.initials: D
authors.lastname: Attinà
authors.forename: Luca
authors.initials: L
authors.lastname: Fasano
authors.forename: Paolo
authors.initials: P
authors.lastname: Carbonara
authors.forename: Maria Letizia
authors.initials: ML
authors.lastname: Bacchi Reggiani
authors.forename: Maurizio
authors.initials: M
authors.lastname: Zompatori
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013902:Radiography, Thoracic; D012129:Respiratory Function Tests; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed; D014132:Trachea / Q000000981:diagnostic imaging* / Q000503:physiopathology*