Normal Posterior Tracheal Wall Thickness on Radiography
The posterior tracheal wall, also known as the tracheal stripe, is a thin soft-tissue interface visible on lateral chest radiographs between the tracheal air column and the adjacent retrotracheal space. Accurate measurement of this structure is clinically important because abnormal thickening can be an early or sole radiographic indicator of significant mediastinal or esophageal disease.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | <2.5 mm |
Clinical Significance
On a lateral chest radiograph, the posterior tracheal wall should measure less than 2.5 mm in thickness. Thickening beyond this threshold warrants further evaluation, as it may reflect direct invasion, extrinsic compression, or inflammatory involvement of the retrotracheal tissues.
Common pitfalls include overlying cervical soft tissues, patient rotation, and suboptimal inspiration, all of which can artifactually thicken the apparent tracheal stripe. It is also important to distinguish true wall thickening from a retrotracheal mass displacing the posterior wall anteriorly without intrinsic wall involvement.
- Esophageal carcinoma — posterior mediastinal mass with direct tracheal abutment
- Goiter or thyroid mass — extrinsic retrotracheal extension
- Lymphadenopathy — subcarinal or paratracheal nodal enlargement
- Esophageal foreign body or impaction — retrotracheal soft-tissue prominence
- Retrotracheal abscess or mediastinitis — thickening with or without gas
Reference: Coche EE. Medical Radiology / Diagnostic Imaging, Comparative Interpretation of CT and Standard Radiography of the Chest. Springer Verlag Berlin Heidelberg. p. 113 (2011).
Imaging Notes
The posterior tracheal wall is best assessed on a true lateral chest radiograph obtained in full inspiration. The measurement is taken as the width of the soft-tissue stripe between the posterior margin of the tracheal air column and the anterior wall of the esophagus (or retrotracheal airspace). A well-penetrated, non-rotated lateral projection is essential — even mild patient rotation can superimpose cervical soft tissues and falsely increase apparent wall thickness.
When posterior tracheal wall thickening is identified on radiography, cross-sectional imaging with CT is the recommended next step to characterize the extent, tissue density, and relationship to adjacent mediastinal structures.