What causes saber sheath trachea in the intrathoracic trachea on cross-sectional imaging?
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Saber sheath trachea is caused by chronic obstructive pulmonary disease (COPD) leading to fixed, acquired narrowing of the coronal (side-to-side) diameter of the intrathoracic trachea with compensatory widening of the sagittal (front-to-back) diameter. This deformity correlates with hyperinflation and emphysema severity in COPD. It represents a structural change of the trachea rather than a dynamic or obstructive lesion. Clinical conditions associated include emphysema-predominant COPD and possibly combined pulmonary fibrosis and emphysema (CPFE).
Why is it called so?:
The term “saber sheath” derives from the resemblance of the trachea’s cross-sectional shape to the narrow, flattened, curved profile of a saber or sword sheath—narrow laterally but widened sagittally—visible on axial imaging or other cross-sectional imaging.
Pathophysiology:
Chronic obstructive pulmonary disease (COPD) causes increased intrathoracic pressure and hyperinflation that distort the tracheal cartilage rings. This leads to inward bowing and fibrosis of the lateral tracheal walls, causing fixed coronal narrowing. The posterior membranous portion expands in the sagittal plane to preserve airway patency, producing the characteristic oval cross-section.
Alternative names: Scabbard trachea
Other associated named signs: None specifically named but often occurs with imaging features of emphysema in COPD such as hyperinflated lungs and flattened diaphragms.
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