Left superior intercostal vein

The left superior intercostal vein drains the left posterosuperior hemithorax and is considered to be part of the azygos venous system even though it does not directly drain into the azygos vein.

Gross anatomy

Origin and course

The left superior intercostal vein forms by the union of the 2 to 4 left posterior intercostal veins. It courses superiorly to the left of the midline, arches posteriorly lateral to the aortic arch to drain into the left brachiocephalic vein.

It typically communicates with the accessory hemiazygos vein.

Tributaries

• left 2 to 4 posterior intercostal veins

Variant anatomy

• may not communicate with the accessory hemiazygos (25%)
• left azygos (or hemiazygos) lobe may be caused by an aberrant left superior intercostal vein (analogous to the azygos lobe)
• hemiazygos and accessory hemiazygos veins may drain directly into the left brachiocephalic vein via the left superior intercostal vein
• may be enlarged in the presence of congenital azygos, hemiazygos or accessory hemiazygos vein absence (rare)

Radiographic appearance

Plain film

• on ~5% of frontal chest x-rays, it may form an "aortic nipple" next to the aortic arch as it is imaged perpendicular to the x-ray beam
  • this should measure less than 4.5 mm and if larger it may indicate underlying pathology (e.g. SVC obstruction or azygos continuation of the IVC)