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Anatomy of the Nasopharynx, Oropharynx, and Tonsils

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THE PHARYNX - Overview

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1. NASOPHARYNX

Boundaries

• Superior/posterior wall (roof): Sloping basisphenoid and basal occipital bone (contiguous due to the slope - collectively the "basisphenoid"). The roof and posterior wall are often described together.
• Anterior: Right and left choanae (posterior nasal apertures), separated by the vomer; also the posterior ends of the inferior and middle conchae project into the choanae.
• Lateral walls: Bear the pharyngotympanic (Eustachian) tube openings and important recesses.
• Floor: Formed by the soft palate (the only mobile wall). When the soft palate is elevated, the nasopharynx is separated from the oropharynx.
• Communicates below with the oropharynx via the pharyngeal isthmus (posterior to soft palate, anterior to the posterior pharyngeal wall).

Key point: Unlike the oro- and laryngopharynx, the walls of the nasopharynx are rigid (except the soft palate), keeping the cavity always patent for airflow.

Key Structures on Lateral Wall

1. Pharyngotympanic (Eustachian) tube orifice - located approximately 1-1.5 cm from the posterior end of the inferior turbinate, at the level of the superior border of the palate (floor of the nose). It connects the middle ear to the nasopharynx and transiently opens and closes to equalize tympanic membrane pressure.
2. Torus tubarius - a cartilaginous projection covering the pharyngotympanic orifice, orientated posterosuperiorly, with a longer posterior extension giving it a comma-shaped appearance on endoscopy. It forms the anterior boundary of the fossa of Rosenmüller.
3. Fossa of Rosenmüller (pharyngeal recess) - a deep recess situated posterosuperior to the torus tubarius. Its floor is the superior constrictor and its superior/posterior border is the skull base. This is the most common site of origin for nasopharyngeal carcinoma (NPC) and should be targeted during biopsies of the nasopharynx when investigating carcinoma of unknown primary.
4. Salpingopharyngeal fold - a mucosal fold projecting inferiorly from the cartilaginous ridge of the pharyngotympanic tube orifice, overlying the salpingopharyngeus muscle and the levator veli palatini, both of which pass inferiorly and laterally to merge with the lateral pharyngeal wall.
5. Torus levatorius - a broad fold/elevation that appears to emerge from below the pharyngotympanic tube opening, continuing medially onto the upper surface of the soft palate, overlying the levator veli palatini.
6. Tubal tonsils (Gerlach's tonsils) - small lymphoid nodules at the lip of the fossa of Rosenmüller, posterior to the torus tubarius. They constitute an additional component of Waldeyer's ring when present.

Epithelium

• Anteriorly (near choanae): Respiratory epithelium - pseudostratified ciliated columnar with goblet cells.
• Posteriorly (towards oro-/laryngopharynx): Non-keratinized stratified squamous epithelium.
• At the transitional zone where the two meet, columnar (not ciliated) epithelium is found instead of cilia - this is the zone of highest carcinogenic risk in NPC.

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2. OROPHARYNX

Boundaries

• Superior: Junction of hard and soft palate / pharyngeal isthmus
• Inferior: Upper margin of epiglottis / plane of hyoid bone / valleculae
• Anterior: Oropharyngeal isthmus (opening between palatoglossal folds), continuous with the oral cavity; base of tongue (posterior 1/3) forms the anterior wall below the isthmus
• Lateral walls: Bear the palatine tonsils between the tonsillar pillars
• Posterior wall: Upper part overlies C2-C3 vertebrae

Subunits (K.J. Lee)

• Soft palate and uvula
• Base of tongue (posterior 1/3, pharyngeal part)
• Palatine arch - includes tonsillar fossae, palatine tonsils, anterior and posterior pillars (palatoglossal and palatopharyngeal arches)
• Lateral and posterior oropharyngeal walls
• Valleculae and pharyngoepiglottic/glossoepiglottic folds

Oropharyngeal Isthmus

• To hold food/liquid in mouth: Isthmus closed by depression of soft palate + elevation of back of tongue + medial movement of palatoglossal/palatopharyngeal folds - allows breathing while chewing.
• On swallowing: Isthmus opens, palate elevates (closing nasopharynx), laryngeal cavity closes - person cannot breathe and swallow simultaneously.

Tonsillar Fossa (Sinus Tonsillaris)

• Superior: Soft palate
• Inferior: Lingual tonsil
• Anterior (anterior pillar): Palatoglossus muscle
• Posterior (posterior pillar): Palatopharyngeus muscle
• Deep/medial wall: Superior constrictor muscle (covered by the pharyngobasilar fascia and tonsillar capsule)

Valleculae

• Midline: glossoepiglottic fold
• Lateral: pharyngoepiglottic folds

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3. TONSILS AND WALDEYER'S RING

Components of Waldeyer's Ring

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3a. Pharyngeal Tonsil (Adenoids)

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3b. Palatine Tonsils

Surgical note: The key to controlling brisk tonsillar bed bleeding is to direct efforts toward the superior or inferior poles first before trying to control every bleeder in the tonsillar bed, as the poles are the vascular points of entry.

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3c. Lingual Tonsils

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4. SOFT PALATE

Muscles (5 muscles)

• Elevation (swallowing) → closes pharyngeal isthmus → seals nasopharynx from oropharynx (prevents reflux of food into nasopharynx).
• Depression → closes oropharyngeal isthmus → seals oral cavity from oropharynx (allows chewing and breathing simultaneously).

• Ascending palatine artery (from facial artery)
• Lesser palatine artery (from maxillary artery)
• Ascending pharyngeal artery

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5. PHARYNGEAL MUSCLES

Outer Layer - Constrictors (3 overlapping constrictor muscles)

Function: narrow the pharyngeal cavity sequentially from top to bottom to move a food bolus into the esophagus. All supplied by CN X (vagus) via pharyngeal plexus.

• Oropharyngeal triangle (Killian's dehiscence above): Gap between superior and middle constrictors and the posterior border of mylohyoid - allows passage of stylopharyngeus, styloglossus, hyoglossus, lingual artery/vein, lingual nerve, CN XII (hypoglossal), CN IX (glossopharyngeal), and lymphatics.
• Between middle and inferior constrictor: Internal laryngeal vessels and nerve pass to the thyrohyoid membrane.
• Below inferior constrictor: Recurrent laryngeal nerves and inferior laryngeal vessels.
• Killian's dehiscence: Triangular gap between the inferior constrictor and cricopharyngeus, through which a Zenker's (pharyngeal) diverticulum can herniate posteriorly.
• Killian-Jamieson space: Lateral dehiscence inferior to cricopharyngeus, through which branches of the inferior thyroid artery pass.

Inner Layer - Longitudinal Muscles (elevate the pharynx)

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6. NERVE SUPPLY OF THE PHARYNX

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7. BLOOD SUPPLY OF THE PHARYNX

• Ascending pharyngeal artery
• Ascending palatine and tonsillar branches of facial artery
• Branches of maxillary and lingual arteries

• Pharyngeal branches of inferior thyroid artery (from thyrocervical trunk of subclavian artery)

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8. LYMPHATIC DRAINAGE OF THE PHARYNX

• Nasopharynx: Retropharyngeal nodes → upper deep cervical nodes. The nasopharynx drains bilaterally, which explains the bilateral neck nodes often seen in NPC.
• Oropharynx/Tonsils: Jugulodigastric (tonsillar) nodes → deep cervical chain.
• Posterior pharyngeal wall: Retropharyngeal and paratracheal nodes → deep cervical nodes.

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Key Clinical Correlates for ENT Posting

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