Posterior wall of bronchus intermedius

The posterior wall of bronchus intermedius, also known as the intermediate stem line, is a stripe formed by the interface of the posterior wall of bronchus intermedius and the air within the azygo-esophageal recess .

It normally measures between 0.5-2 mm in thickness but is not considered abnormally thickened until it measures greater than 3 mm . An increased thickness is non-specific but may represent :

• pulmonary edema (most common)
• primary lung malignancy
• lymphadenopathy (from a variety of causes)
  • lymphoma
  • metastases
  • tuberculosis
  • sarcoidosis

Radiolographic features

Plain radiograph

• present on 90-95% of lateral chest x-rays but is only well seen in ~55% of patients
• appears as a vertical or nearly vertical stripe that projects over the lucency created by the left main bronchus and the azygo-esophageal recess

CT

• posterior wall of bronchus intermedius is well seen in almost every patient
• it appears as a sharp, well-defined line from the origin of the right upper lobe bronchus