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Hemiazygos lobe

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

An azygos (azygous) fissure is seen on approximately 1-2% of chest X-rays

The azygos (azygous) lobe of the lung is an accessory lobe of the right lung

  • produced by an aberrant position of the azygous vein near the hilum of the lung
    • divides the right superior lobe near the apex of the lung down to the hilum in roughly the median plane
    • fissure created, the meso-azygous fissure, is lined by both visceral and parietal pleura
    • lobe lies superomedial to the fissure

  • azygos fissure is a developmental abnormality caused by the right posterior cardinal vein (one of the precursors of the azygos vein) failing to migrate over the right lung apex, and instead penetrating and grooving it. When present, the upper part of the right upper lobe tucks medially behind the azygos arch, and the azygos vein and arch lie at the bottom of the azygos fissure
  • azygos vein, which is lined by visceral and parietal pleura, lies in the base of the fissure
  • the azygos vein is a right-sided structure, this accessory fissure is only ever seen on the right side of the chest
  • medially there is a small connection of the 'azygos lobe' with the rest of the upper lobe
    • azygos lobe (when present) lies above and medial to the azygos fissure

  • azygos fissure has a tadpole shape, the azygos vein itself forming the head of the tadpole

Occasionally a left sided hemiazygos lobe may be seen together with a hemiazygos fissure (1)


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