Saber-Sheath Trachea

Saber-Sheath Trachea

Aqeel A. Chowdhry, MD

Tan-Lucien H. Mohammed, MD, FCCP

Frontal radiograph shows the typical features of tracheal narrowing image from a saber-sheath trachea. The deformity is often overlooked on chest radiographs.

Axial CECT shows a normally shaped extrathoracic trachea image and saber-sheath deformity image of the intrathoracic trachea.


Abbreviations and Synonyms

  • Tracheal narrowing, tracheomalacia, scabbard deformity


  • Trachea in which coronal dimension is ≤ 2/3 of sagittal dimension

    • Extrathoracic trachea normal


General Features

  • Best diagnostic clue

    • Marked decrease in coronal diameter with increase in sagittal diameter

    • Inward bowing of lateral tracheal wall usually worsened with forced expiration

  • Patient position/location

    • Intrathoracic airway

      • Main bronchi and extrathoracic trachea are usually normal

  • Size

    • Normal trachea

      • Sagittal diameter is 13-27 mm in men and 10-23 mm in women

      • Coronal diameter is 13-25 mm in men and 10-21 mm in women

      • Tracheal index (coronal diameter)/(sagittal diameter) usually measured 1 cm above aortic arch

      • Round or horseshoe-shaped

    • Saber-sheath tracheal measurements

      • Tracheal index ≤ 2/3

  • Morphology

    • Saber-sheath deformity

      • Narrowed trachea on frontal view, widened on lateral view

CT Findings

  • Morphology

    • Side-to-side narrowing of trachea at and below thoracic inlet

    • Tracheal index ≤ 2/3

      • Specificity for chronic obstructive pulmonary disease (COPD) (95%)

      • Sensitivity for COPD < 10%

  • Wall

    • No tracheal wall thickening

    • Inner wall of trachea usually smooth

    • Tracheal cartilage usually calcified

  • Lung

    • Hyperinflated, usually from centrilobular emphysema and bullous lung disease

  • Extrathoracic trachea remains normal in configuration

  • Tracheal index may increase following lung reduction surgery

    • Does not return to normal, however

Imaging Recommendations

  • Best imaging tool: HRCT, as tracheal deformity often overlooked on chest radiographs

  • Protocol advice: CT during forced expiration or Valsalva maneuver shows inward bowing of tracheal walls

Radiographic Findings

  • Posteroanterior chest radiograph shows diffuse narrowing of coronal diameter of intrathoracic trachea

  • Extrathoracic trachea is normal in diameter

Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Saber-Sheath Trachea
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