thoracic outlet (anatomy)

Last reviewed 01/2018

The thoracic outlet, also termed the inferior thoracic aperture, is the inferior margin of the thoracic cavity. Its bony margins are:

  • posteriorly: twelfth thoracic vertebra
  • posterolaterally: twelfth and eleventh ribs
  • anterolaterally: the cartilages of the tenth to the seventh ribs forming the costal margin
  • anteriorly: xiphisternum

As with the thoracic inlet, the transverse diameter is greater than the anteroposterior diameter. However, unlike its superior counterpart, the thoracic outlet slopes obliquely anterosuperiorly from the twelfth thoracic vertebra. Also, the thoracic outlet is larger than the thoracic inlet.

The thoracic outlet is bridged by the diaphragm.

The anatomical thoracic outlet described above is not the site of clinical 'thoracic outlet syndrome'.