Last revised by Joshua Yap on 11 Nov 2022

The trachea, known colloquially as the windpipe, connects the upper respiratory tract to the lungs via the tracheobronchial tree, enabling gas exchange.

The trachea is a tube-shaped structure consisting of 15-20 D-shaped cartilage rings anterolaterally bridged by annular ligaments. The trachealis muscle (smooth muscle) encircles the trachea completely but is most prominent posteriorly due to the lack of cartilage 4.

The trachea extends from the inferior margin of the cricoid cartilage (C6) and branches into the right and left main bronchi at the carina, located at the T4 vertebral body level, in the plane of Ludwig. It is usually situated in a midline position and can be displaced slightly to the right at the arch of the aorta 1. In the lateral view, the trachea slants from an anterior position beneath the larynx to a posterior position at the carina 5. The tracheal length is usually between 10-13 cm with a width of 1.5-2 cm and is wider in men than in women 2,3.

  • to inferior thyroid venous plexus

  • to pretracheal and paratracheal lymph nodes

The trachea has three layers 4:

  • external: loose connective tissue/adventitia: note there is no capsule

  • middle: fibromusculocartilaginous membrane: tracheal cartilage, annular ligaments, connective tissue and trachealis muscle

  • internal: respiratory mucous membrane: tracheal glands with a pseudostratified columnar epithelium

  • tracheal bronchus or "pig bronchus" 6,7

    • development of an extra bronchus that usually develops superior to the carina from the trachea, above the right main bronchus and connecting to the right upper lobe

    • common and can be found in 2% of people

    • may not present with any symptoms and can be an incidental finding usually via bronchoscopy, however, it may cause problems during intubation

    • may be associated with chronic atelectasis, bronchiectasis and recurrent pneumonia 

  • lunate trachea 8

    • coronal-to-sagittal ratio of the trachea is >1 giving rise to a lunate-shaped cross-section rather than round or oval

    • may be associated with COPD and tracheomalacia

  • tracheal diverticulum 9

    • outpouching of the posterolateral tracheal wall, usually on the right side

    • majority of patients are asymptomatic although may present with a recurrent respiratory tract infection

  • esophageal bronchus

  • tracheal buckling in young infants

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Cases and figures

  • Figure 1
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  • Figure 2: right sided bronchi
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  • Figure 3: left sided bronchi
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