Anatomy for Tracheostomy

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OVERVIEW

To perfrom a tracheostomy, knowledge of the following is required:

• surface anatomy
• course of the trachea
• structure of the tracheal rings
• layers of dissection
• components of the larynx
• related structures (e.g. nerves, vessels and organs)

SURFACE ANATOMY

• hyoid bone (C3)
• thyroid cartilage
• cricothyroid membrane (ligament)
• cricoid cartilage (C6)
• thyroid gland
• sternohyoid muscle just lateral to the midline structures, overlies sternothyroid and thyrohyoid)

COURSE

• Pathway of the trachea from anterior at the cricoid cartilage (C6)
• to more posterior as it enters the chest behind the sternal notch
• trachea is 10 cm long, stretches to 15cm on inspiration (fibroelastic structure)

TRACHEAL RINGS

• C shaped cartilages (first cartilage is bigger than the others in the cervical trachea)
• joined vertically by fibroelastic tissue
• connected posteriorly by the trachealis muscle

LAYERS OF DISSECTION FOR TRACHEOSTOMY

• skin
• subcutaneous tissue
• fat
• pretracheal fascia (superficial and deep)
• trachea

LARYNX

• valve separating the trachea from the upper aerodigestive tract
• allows vocalisation
• necessary for an effective cough or valsalva manoeuvre
• prevents aspiration during swallowing

LARYNGEAL SKELETON

• Hyoid bone – attachment to epiglottis and strap muscles
• Thyroid cartilage – anterior attachment of vocal folds; posterior articulation with cricoid cartilage
• Cricoid cartilage – complete signet-shaped ring; articulates with thyroid and arytenoid cartilages
• Arytenoids – two cartilages which glide along the posterior cricoid and attach to posterior ends of vocal folds.

Larynx — Cartilages (videos from Anatomy Zone)

Larynx and vocal cords — mucosa

Larynx – muscles (see more here)

DIVISIONS

• Supraglottis – usually covered with respiratory epithelium containing mucous glands
• Epiglottis – leaf-shaped mucosal-covered cartilage, which projects over larynx
• Aryepiglottic folds – extend from the lateral epiglottis to the arytenoids
• False vocal cords – mucosal folds superior to the true glottis. Separated from true vocal folds by the ventricle
• Ventricle – mucosal-lined sac, variable in size, which separates the supraglottis from the glottis
• Glottis – the true vocal folds attach to the thyroid cartilage at the anterior commissure. The posterior commissure is mobile, as the vocal folds attach to the arytenoids. Motion of the arytenoids affects abduction or adduction of the larynx. The bulk of the vocal fold is made up of muscle covered by mucosa. The free edge is characterised by stratified squamous epithelium. The vocal folds abduct for inspiration and adduct for phonation, cough and valsalva.
• Subglottis – below the vocal folds, extending to the inferior border of the cricoid cartilage.

NERVES

Branches of the vagus nerve.

• Superior laryngeal nerve — sensation of the glottis and supraglottis — Motor fibres to the cricothyroid muscle, which tenses the vocal folds — This nerve leaves the vagus high in the neck
• Recurrent laryngeal nerve — sensation of the subglottis — motor fibres to intrinsic muscles of the larynx — This nerve branches from the vagus in the mediastinum, then turns back up into the neck — On the right, it travels inferior to the subclavian artery, and on the left, the aorta

VESSELS

• anterior jugular veins run vertically close to midline
• inferior thyroid vessels and variant thryoidea ima artery run over lower trachea
• other vessels more lateral: internal jugular, carotid, external jugular

THYROID GLAND

• lobes extend to 6th tracheal ring
• isthmus overlies rings 2,3,4
• variant pyramidal lobe may extend over cricothyroid membrane

References and Links

• Instant Anatomy