Lung Azygoesophageal Recess

• What is it?
  • The azygoesophageal recess is a vertical interface formed between the medial right lower lobe of the lung and adjacent structures, including the azygos vein and esophagus.
  • It is created by the apposition of the lung parenchyma with the mediastinal structures.
• Parts:
  • Medial right lower lobe lung interface.
  • Adjacent azygos vein.
  • Esophagus.
  • Posterior mediastinum.
• Size and Shape:
  • Typically, a vertically oriented and concave structure.
  • The degree of concavity can vary with the size of the azygos vein and mediastinal pathology.
• Position:
  • Located on the right side of the posterior mediastinum.
  • Extends vertically from the level of the azygos vein arch superiorly to the diaphragm inferiorly.
• Embryology:
  • Forms during lung development as the right lung expands to meet the mediastinal structures, including the developing azygos vein and esophagus.
• Applied Anatomy:
  • Imaging Application:
    • The azygoesophageal recess is an important radiological landmark on chest imaging.
    • Changes in its contour can indicate pathology, such as:
      • Right lower lobe atelectasis or consolidation.
      • Mediastinal lymphadenopathy.
      • Esophageal masses or dilation.
      • Azygos vein enlargement.
      • Posterior mediastinal masses or abnormalities.
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  • CXR:
  • On chest radiographs, the azygoesophageal recess appears as a thin, smooth, and concave line on the right side of the mediastinum.
  • Distortion, obliteration, or convexity of this line suggests underlying pathology, such as:
    • Right lower lobe consolidation or atelectasis.
    • Mediastinal lymphadenopathy.
    • Posterior mediastinal mass or esophageal abnormalities.
• CT scan:
  • On CT imaging, the azygoesophageal recess is seen as a sharp interface between the medial right lower lobe and adjacent mediastinal structures, specifically the azygos vein and esophagus.
  • Normal appearance: a thin, well-defined curvilinear interface with no masses or distortions.
  • Abnormal findings:
    • Bulging or obliteration due to lymphadenopathy, posterior mediastinal masses, or esophageal pathology.
    • Displacement caused by right lower lobe collapse or consolidation.
    • Thickening of the recess associated with inflammatory or neoplastic conditions.
• Key Points and Pearls:
  • The azygoesophageal recess should normally appear as a smooth, concave interface on imaging.
  • Deviation, obliteration, or bulging of the recess can signal significant mediastinal or pulmonary pathology.
  • Careful evaluation of the recess on chest radiographs and CT is critical for detecting subtle mediastinal abnormalities.
  • When distorted, the recess can provide clues to the underlying condition, such as lymphadenopathy, esophageal disease, or vascular abnormalities.