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.

ENT Anatomy - Pharynx Part I

The Pharynx is subdivided into three sites:
1. The Nasopharynx
2. The Oropharynx
3. The Hypopharynx





1. The Nasopharynx

The Nasopharynx is located posterior to the nasal cavity choanae (anterior border). It is bounded superiorly by the sphenoid sinus and inferiorly by the soft palate. The posterior wall overlies the base of skull including the clivus and atlas. The lateral walls are the nasopharyngeal mucosa. Located on the lateral walls is the Taurus Tubarius, which is the opening of the Eustachian Tube. Posterior to this is Rosenmueller's Fossa, which is a common site of origin for nasopharyngeal cancers. The roof of the nasopharynx is lined with adenoid lymphatics, which are a component of Waldeyer's ring.


The nasopharynx is innervated by the Glossopharyngeal Nerve (CN IX) and the Maxillary Nerve (CN V2).

Multiple foramen in this region act as potential points of entry for nasopharyngeal cancers. Notably the Foramen Lacerum, which allows entrance into the middle cranial fossa. Other foramen include Foramen Jugulare, Foramen Ovale, Foramen Spinosum, the Carotid Canals and the hypoglossal canals




2. The Oropharynx

The oropharynx is bounded superiorly by the soft palate and inferiorly by the superior aspect of the hyoid bone. The mucosa overlying the C2 and C3 verterbral bodies form the posterior wall. The anterior aspect consists of the anterior palatine pillar and the anterior edge of the soft palate.

The oropharynx consists of 4 subsites:
The soft palate, the tonsillar region, the base of tongue and the pharyngeal walls.

The soft palate includes the uvula. The tonsils are found between the anterior and posterior tonsillar pillars. The base of tongue encompasses the tongue found between the vallecula and the circumvallate papilla.


Lymphatic drainage of this region is primarily to the jugulodigastric lymph node or Level II lymph nodes. Pharyngeal walls are drained by the retropharyngeal. The retropharyngeal nodes consist of a medial and lateral component. The lateral component is also known as Rouviere Nodes. Drainage is primarily unilateral, unless a tumor invades midline structures where it may drain the bilateral cervical chains.

Innervation of this area is primarily via CN IX & X.


3. The Hypopharynx or Laryngopharynx

See next post...

ENT Anatomy: Temporal & Infratemporal Fossas

Temporal Fossa

This oval shaped fossa is bounded superiorly and posteriorly by the temporal lines. The frontal and zygomatic bones form the anterior boundary. Laterally, the fossa is covered by the temporal fascia. Inferiorly the floor is formed by portions of the sphenoid, frontal, temporal and parietal bones. The area where these four bones meet is the pterion. This is also the area where the temporalis muscle originates. Temporal muscle divides into a superficial and deep layer. The superficial layer attaches to the superior aspect of zygomatic arch. The deep layer extends inferiorly to become the masseter muscle.



Infratemporal Fossa

This space is bounded superiorly by the greater wing of the sphenoid and anteriorly by the infratemporal surface of the maxillary bone. The posterior wall is formed by the condyle of the mandible and the styloid process of the temporal bone. The lateral wall is the medial aspect of the ramus of the mandible. The medial wall is lateral pterygoid plate.



The Maxillary Artery originates from the external carotid and enters medially to the ramus of the mandible. The branches of the maxillary artery include the deep auricular artery, middle meningeal, inferior alveolar, deep temporal, buccal, infraorbital and posterior superior alveolar.

The Pterygoid Venous Plexus is also contained within the infratemporal fossa. This plexus of veins and nerves is located between the temporalis and lateral pterygoid muscles. The key structure is the Mandibular Nerve (CN V3). This enters the infratemporal fossa by the Foramen Ovale. This nerve is responsible for innervation of the muscles of mastication (temporalis, masseter, medial & lateral pterygoids). This nerve also divides into the auriculotemporal, inferior alveolar, lingual and buccal nerves.

One branch of the Maxillary nerve (CN V2) enters the infratemporal fossa, the Posterior Superior Alveolar Nerve.

The Otic Ganglion is a parasympathetic component of the glossopharyngeal nerve (CN IX). It is found medially to the foramen ovale. It is the secretory innervation for the parotid gland.

The Foramen Spinosum also opens into this fossa. It contains the middle meningeal artery and vein and the nervus spinosum, a branch of the mandibular nerve

ENT Anatomy: Parotid Gland

The parotid gland is a salivary gland overlying the masseter and posterior belly of digastric muscle. Saliva is delivered to the mouth via the parotid duct. The parotid bed is bounded by the ramus of the mandible anteriorly and the mastoid process posteriorly. Superiorly it is bounded by the external acoustic meatus. Medially, it is bounded by the styloid process of the temporal bone. Laterally it is covered by the overlying skin.

Traversing through the parotid gland is the facial nerve (CN VII). Within the gland, this nerve divides into a superior and inferior division innervating the temporal/zygomatic/buccal and mandibular/cervical branches respectively. This is particularly important in adenoid cystic carcinomas arising in the parotid gland. In these tumors, they will infiltrate peri-neurally and can track up to the stylohyoid foramen.


Venous drainage of the parotid gland is via the retromandibular vein. This vein joins the posterior auricular vein to form the external jugular vein.

Arterial supply of the parotid gland is via the external carotid artery, which enters the medial aspect of the gland. The external carotid artery then divides into the superficial temporal artery and the maxillary artery.

Innervation of the parotid gland is via the secretoy fibres of the otic ganglion, a parasympathetic component of the glossopharyngeal nerve (CN IX).

Lymphatic drainage is to the superficial and deep cervical chains.