Normal Bronchus Intermedius Posterior Wall Thickness on Radiography
The bronchus intermedius is the segment of the right main bronchus extending from the takeoff of the right upper lobe bronchus to the origin of the middle lobe bronchus. Its posterior wall is directly visible on the lateral chest radiograph as a thin soft-tissue stripe, making it one of the few airway structures reliably assessed on plain film. Accurate measurement of this wall is clinically important because thickening may indicate significant cardiothoracic disease.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | <3 mm |
Clinical Significance
On a properly exposed lateral radiograph, the posterior wall of the bronchus intermedius should measure less than 3 mm. Thickening beyond this threshold is a well-recognized sign of abnormality and should prompt further evaluation, typically with CT.
The posterior wall is contiguous with the subcarinal and right paratracheal lymph node stations, so thickening most commonly reflects lymphadenopathy or peribronchial infiltration rather than intrinsic bronchial disease. Misidentification of overlapping vascular structures as bronchial wall thickening is a recognized pitfall on lateral radiography.
- Lymphadenopathy — subcarinal or right hilar nodal enlargement (e.g., sarcoidosis, lymphoma, metastatic disease)
- Peribronchial edema — pulmonary venous hypertension or fluid overload
- Peribronchial inflammation — pneumonia, bronchiectasis
- Primary bronchial neoplasm — endobronchial or peribronchial tumor
- Mediastinal mass — direct extrinsic compression or infiltration
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
Measurement is performed on the lateral projection of the chest radiograph. The posterior wall of the bronchus intermedius appears as a thin vertical stripe running inferiorly from the carina along the posterior aspect of the right bronchial tree, bordered anteriorly by the airway lumen and posteriorly by the azygoesophageal recess. The wall should be measured perpendicular to its long axis at its thickest visible point.
Adequate exposure and patient positioning are critical — rotation or underexposure can obscure or falsely thicken this stripe. When thickening is detected or the stripe cannot be clearly identified, CT of the chest provides superior cross-sectional delineation of the bronchial wall, adjacent lymph nodes, and mediastinal structures.