QS Study

Thoracic inlet

The narrow upper end of the thorax, that is continuous with the neck is termed as a thoracic inlet. It is the upper boundary of the bony thorax composed of the first thoracic vertebra and the upper margins of the first ribs and manubrium of the sternum. It is the inlet through which the thoracic cavity interacts with the root of the neck.

Fig: Thoracic inlet Boundaries

Boundaries – It is kidney-shaped and lies in an oblique transverse plane, tilted anteroinferiorly to posterosuperiorly.

Anteriorly: Upper border of manubrium stemi.

Posteriorly: a Superior surface of the body of vertebra T1

On each side: First rib with its cartilage.

Shape: Reniform/kidney shaped.

Measurements: Transverse diameter: 4.5 inches. And Anteroposterior diameter: 2.5 inches.

Fig: Thoracic inlet Contents


(a) Viscera:

  • Oesophagus,
  • Apices of lungs (with pleurae),
  • Remains of the thymus.

(b) Large vessels:

  • Brachiocephalic artery.
  • Left common carotid artery.
  • Left subclavian artery.
  • Brachiocephalic (Rt. & Lt.) veins.

(c) Small vessels:

  • Right and left internal thoracic arteries.
  • Right & left superior intercostal arteries,
  • Right & left first posterior intercostal veins.
  • Inferior thyroid veins.

(d) Nerves:

  • Right & left phrenic nerves.
  • Right & left vagus nerves,
  • Right & left sympathetic trunks,
  • Right & left first thoracic nerves.

(e) Muscles:

  • Sternohyoid.
  • Sternothyroid.
  • Longus Colli.