ENT Anatomy - Pharynx Part II: Hypopharynx

Hypopharynx or the Laryngopharynx

The hypopharynx is bounded superiorly by the superior aspect of the hyoid bone and inferiorly by the inferior aspect of the cricoid cartilage. Posteriorly it is bounded by the pharyngeal wall overlying the C4-C6 vertebral bodies. Laterally it is also bounded by the pharyngeal walls.

The hypopharynx encompasses 3 structures: 1) the piriform sinuses; 2) the pharyngeal walls 3) the post-cricoid region. The Piriform Sinuses are found lateral to the aryepiglottic folds and are bounded laterally by the pharyngeal walls. The post-cricoid is found below the aretynoids down to the inferior cricoid cartilage and posteriorly to the cricoid cartilage (obviously).

The larynx is composed of the epiglottis, thyroid cartilage, aretynoid cartilage and the cricoid cartilage. The corniculate cartilage sits on top of the aretynoids. The cuneiform cartilage is
located in the aryepiglottic folds and lateral to the corniculate cartilage. Note that the aretynoid, cricoid and thyroid cartilages can ossify, whereas the corniculate, cuneiform, epiglottis and the tips of the aretynoids will not ossify.

There are three important ligaments within the larynx: 1) Hyoepiglottic; 2) Cricothyroid; 3) Thyrohyoid.



The Larynx itself is divided into 3 sections:
1) Supraglottis - Tip of the epiglottis to the true vocal cords
2) Glottis - True vocal cords to 0.5 cm below the true vocal cords
3) Subglottis - 0.5 cm below the true vocal cords to the inferior cricoid

The False Vocal Cords are ventricular folds and are located superior to the true vocal cords. They do not vibrate, hence their name.


Innervation
The main nerve innervating the hypopharynx and larynx is the Vagus Nerve (CN X).
The Sensory component of CN X is the Internal Superior Laryngeal Nerve. The External Superior Laryngeal nerve branch is the motor component.

• Tumor involving the Piriform Sinus and involving the superior laryngeal can cause referred otalgia via the auricular branch of the vagus nerve.
• The External Superior Laryngeal innervates the cricothyroid muscle. This is responsible for stretching and tensing the vocal cords. Damage to the superior laryngeal can cause changes in phonation.
• Innervates the supraglottis and glottis
  

The motor component of CN X is the Recurrent Laryngeal Nerve.

• Innervates the remaining laryngeal muscles. Damage to the recurrent laryngeal nerve will cause hoarseness
• Innervates subglottis

Damage to both Recurrent and external superior laryngeal nerves results in no audible voice. Breathing is also compromised.



Lymphatics & Patterns of Spread
The true vocal cords have sparse lymphatic drainage. Tumors restricted only to the vocal cords do not have a propensity to spread to regional lymphatics (<5%). Tumor invading local structures surrounding the glottis will spread to Level II, III and IV lymphatics.

Supraglottic lesions will grow anteriorly into the pre-epiglottic space, valeculla or base of tongue. It can also grow circumferentially and invade the aryepiglottic folds and the piriform sinuses. Lymphatic drainage is typically to levels III & IV.

Subglottic lesions will grow and invade locally. That is inferiorly into the trachea, superiorly into the epiglottis and anteriorly into the thyroid or cricoid cartilage. Drainage here is to Levels III, IV and VI depending on the structures invaded.

Hypopharynx lesions can drain to II, III, IV, VI and RP nodal levels. There are no borders to invasion, so many of these tumors present as advanced cases. 20% will have distant mets at presentation compared to 1% for glottic cancers and 10% for supraglottic cancers.