Chest

Pulmonary and Pleura

Discuss the anatomy of the trachea (30 marks)

DESCRIPTION

• The trachea is the distal communication of the larynx and it descends through the neck into the thorax.
  • Begins at C6, attached below the cricoid margin by the cricotracheal membrane.
  • Patency maintained by multiple c-shaped hyaline cartilages joined by a fibroelastic membrane
  • Posteriorly the “ring” is closed with a trachealis muscle
  • Length varies with inspiration 10-15 cm. 2cm in diameter
  • Runs inferiorly and backwards into the thorax
  • Terminates into the bronchial tree as the right and left main bronchi

ARTERY

• Tracheal branches of inferior thyroid artery superiorly. Bronchial arteries at inferiorly.

VEIN

• Into inferior thyroid plexus

NERVE

• Autonomic supply from anterior and posterior pulmonary plexuses
  • Parasympathetic: Vagi and RLN – airway smooth muscle tone – constriction, mucous secretion vasodilation
  • SNS: Sympathetic trunk – tracheobronchial blood vessels

LYMPH

• Cervical trachea drained by supraclavicular peritracheal lymph nodes
• The paired upper and lower peritracheal and subcarinal drain the trachea and are important in cancer staging.

 RELATIONS:

• Cervical trachea (5cm). In midline
  • Anterior:
    • Thyroid isthmus on 2^nd to 4^th ring
    • Strap muscles (sternothyroid, sternohyoid)
    • Inferior thyroid veins and anterior venous arch, thyroidea ima artery.
    • Thymus gland in children
    • Skin and superficial and deep cervical fascia
  • Posterior:
    • Anterior surface of oesophagus;
    • Recurrent laryngeal nerves in groove between oesophagus and trachea
    • Prevertebral fascia and vertebral column
  • Lateral:
    • Paired thyroid lobes (down to 5^th or 6^th ring)
    • Carotid sheath with CCA, IJV, and Vagus (X)
• Thoracic Trachea 
  • From superior thoracic inlet to bifurcation at carina
    • Anterior:
      • Manubrium sterni, with sternohyoid and sternothyroid
      • Inferior thyroid and left brachiocephalic veins
      • Remains of the thymus
      • Arch of aorta
      • Pulmonary trunk bifurcation into left and right pulmonary arteries at carina
      • Deep cardiac plexus and lymph nodes
    • Posterior:
      • Oesophagus
      • Thoracic duct on left side
      • Danger space, and prevertebral space/fascia
      • Vertebral bodies of T1-T4
    • Right side:
      • Pleura, Vagus nerve (X) and Right lung
      • SVC and right brachiocephalic vein anterolateral to trachea.
        • Arch of the azygos vein into SVC
      • Brachiocephalic trunk splitting into R CCA and R subclavian arteries
    • Left side:
      • Left CCA, arch of aorta becoming descending aorta
      • Left recurrent laryngeal nerve curving around ligamentum arteriosum into groove between oesophagus and trachea
      • Pleura and Left lung
    • Inferior:
      • Carina at bifurcation
      • Middle mediastinum with pericardial sac
      • Subcarinal lymph node

VARIANTS

• Tracheal bronchus – usually within 2cm of carina
  • Displaced: abnormal bronchus from lateral wall of trachea above carina. Ventilates upper lobe. Asymptomatic variant.
    • 1-2% for Right
    • 3-1% for Left
    • Can be a displaced segmental/subsegmental/subsubsegmental bronchus
  • Supranumerary: less common
    • Can ventilate normal lung, a communicating cyst or blind pouch (tracheal diverticulum)
  • Short trachea – less than 15 tracheal rings. Normally 17+/- 1.28 rings
  • Complete tracheal ring