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AN36.1-7 | Mouth, Pharynx & Palate — Part 1
CLINICAL SCENARIO
A 7-year-old girl from a rural area near Vellore is brought to the ENT outpatient with 2 months of snoring, open-mouth breathing at night, and recurrent ear infections. On examination, her tonsils are grade III (nearly meeting in the midline) and there is a mass visible above the soft palate on nasopharyngoscopy. She also has a 30 dB conductive hearing loss bilaterally.
Why does enlargement of the adenoids cause ear infections and hearing loss? What structures does the pharynx share with the middle ear? How does Waldeyer's ring protect — and how can it harm?
This child's presentation connects the anatomy of the pharynx, the Eustachian tube, and the lymphoid ring into a single clinical story. Master this anatomy and ENT emergencies like peritonsillar abscess and Zenker's diverticulum become anatomically predictable.
WHY THIS MATTERS
The oral cavity and pharynx are central to India's ENT disease burden and several national public health concerns:
- Oral cancer — India has the highest incidence of oral cancer globally (tobacco + betel nut); oral cavity anatomy is essential for staging and surgical planning
- Tonsillectomy/adenoidectomy — among the most common surgical procedures in paediatric ENT
- Peritonsillar abscess (quinsy) — a common ENT emergency; requires immediate incision and drainage
- Nasopharyngeal carcinoma — higher incidence in South and Southeast Asia; spreads via pharyngeal spaces
- Zenker's diverticulum — pharyngeal pouch at Killian's dehiscence; presents with regurgitation of undigested food
- Dysphagia and aspiration — understanding the pharyngeal constrictors and Waldeyer's ring is essential in swallowing rehabilitation
- Adenoid hypertrophy — causes otitis media with effusion (glue ear) by blocking the pharyngeal opening of the Eustachian tube
RECALL
Before we begin, recall:
- The oral cavity is divided into the vestibule (between lips/cheeks and teeth/gums) and the oral cavity proper (between the dental arches and the oropharyngeal isthmus)
- The pharynx is a muscular tube connecting the nasal, oral, and laryngeal cavities to the oesophagus
- The glossopharyngeal nerve (CN IX) is the main sensory nerve of the pharynx — the gag reflex is mediated by CN IX (afferent) and CN X (efferent)
- The vagus nerve (CN X) provides the motor supply to the pharyngeal constrictors and the soft palate (via the pharyngeal plexus)
Oral Cavity — Vestibule and Oral Cavity Proper (AN36.1)
Sensory Innervation of the Tongue
| Region | Nerve | Type of Fibres |
|---|---|---|
| Anterior 2/3 (body) | Lingual nerve (CN V3) | General sensation |
| Anterior 2/3 | Chorda tympani (CN VII via lingual nerve) | Taste |
| Posterior 1/3 | CN IX (glossopharyngeal) | General sensation + taste |
| Epiglottic region | Internal laryngeal nerve (CN X) | Sensation |
Vestibule of the mouth:
- Space between the lips/cheeks externally and the teeth/gums internally
- Parotid duct (Stensen's duct) opens into the vestibule opposite the upper 2nd molar tooth (important for parotid stone diagnosis)
- Labial frenula: median fold connecting lip to gum
Figure: Oral Cavity — Vestibule and Oral Cavity Proper (AN36.1)
Oral cavity proper:
- Bounded: anteriorly/laterally by teeth and gums; superiorly by hard and soft palate; floor = mylohyoid muscle (muscular diaphragm)
- Floor of mouth structures: sublingual gland (opens via multiple ducts on sublingual fold), submandibular duct (Wharton's duct, opens at sublingual papilla beside the frenulum of tongue)
- Tongue: intrinsic muscles — 3 pairs (superior/inferior longitudinal, transverse, vertical) all supplied by CN XII; extrinsic muscles — genioglossus (primary protrusor, CN XII), hyoglossus, styloglossus, palatoglossus (CN X)
Sensory innervation of tongue:
| Part | Nerve | Fibres |
|---|---|---|
| Anterior 2/3 (body) | Lingual nerve (CN V3) | General sensation |
| Anterior 2/3 | Chorda tympani (CN VII via lingual) | Taste |
| Posterior 1/3 | CN IX | General sensation + taste |
| Posterior 1/3 (circumvallate papillae) | CN IX | Taste |
| Epiglottic region | Internal laryngeal nerve (CN X) | Sensation |
Palate:
- Hard palate: bony (palatine processes of maxilla + horizontal plates of palatine bones); mucosa firmly bound to bone (no submucosa)
- Soft palate: mobile; contains 5 muscles:
Figure: Sensory innervation of tongue:
| Muscle | Nerve | Action |
|---|---|---|
| Tensor veli palatini | CN V3 (medial pterygoid nerve) | Tenses soft palate; opens Eustachian tube |
| Levator veli palatini | CN X (pharyngeal plexus) | Elevates soft palate (main muscle for velopharyngeal closure) |
| Palatoglossus | CN X | Depresses soft palate; raises back of tongue; forms anterior pillar |
| Palatopharyngeus | CN X | Pulls pharynx upward/forward; forms posterior pillar |
| Musculus uvulae | CN X | Shortens uvula |
Uvular deviation in unilateral CN X palsy: the uvula deviates to the normal (intact) side when the patient says 'Aah' (the intact levator pulls the uvula toward itself).
Figure: Uvular deviation in unilateral CN X palsy
Palatine Tonsil — Morphology, Relations, Blood Supply (AN36.2, AN36.6)
Palatine tonsil:
- Location: tonsillar fossa (between anterior pillar = palatoglossal fold, and posterior pillar = palatopharyngeal fold)
- Size: varies greatly; most prominent in childhood (5–7 years); normally involutes after puberty
- Surface: 10–20 crypts (pits) on the medial surface — site of debris accumulation and infection
- Capsule: derived from the pharyngobasilar fascia; defines the surgical plane for tonsillectomy
Figure: Palatine Tonsil — Morphology, Relations, Blood Supply (AN36.2, AN36.6)
The tonsillar bed (lateral wall, outside the tonsil):
| Layer | Contents |
|---|---|
| Capsule (peritonsillar space) | Fat + loose connective tissue — the dissection plane in tonsillectomy |
| Superior pharyngeal constrictor | Muscle layer |
| Buccopharyngeal fascia | Thin fascia |
| Paratonsillar vein | Runs in the capsule — major source of bleeding in tonsillectomy |
| Glossopharyngeal nerve | Lies on the lateral surface of the constrictor — at risk in difficult tonsillectomy |
| Internal carotid artery | ~2.5 cm lateral to the tonsil — the most dangerous relationship |
Blood supply:
- Tonsillar artery (primary, from facial artery) — enters the lower pole via the inferior aspect of the constrictor
- Dorsal lingual artery (lingual artery)
- Ascending palatine artery (facial artery)
- Ascending pharyngeal artery
- Descending palatine artery (maxillary artery)
Venous drainage: paratonsillar vein → pharyngeal plexus → IJV
Figure: Venous drainage
Lymphatics: jugulodigastric node (Level IIA) = "tonsillar node"
Applied anatomy (AN36.6):
- Tonsillitis: acute bacterial (Group A Streptococcus most common in India); recurrent tonsillitis is the main indication for tonsillectomy
- Peritonsillar abscess (quinsy): pus accumulates in the peritonsillar space (outside the capsule) → medial displacement of the tonsil + uvula deviation to the opposite side + trismus (irritation of medial pterygoid)
- Tonsillectomy: dissection in the peritonsillar (extracapsular) plane; tonsil pulled medially; main bleeding point is the lower pole (tonsillar artery). Post-tonsillectomy haemorrhage: primary (within 24h from a vessel), secondary (5–10 days from slough separation)
- Adenoids (pharyngeal tonsil): lymphoid tissue on the posterior wall of the nasopharynx; hypertrophy → blocks the choana (breathing difficulty) and the pharyngeal opening of the Eustachian tube → otitis media with effusion (glue ear)
Pharynx — Muscles, Nerve Supply, Blood Supply (AN36.3)
Structure of the pharyngeal wall (inside-out):
1. Mucosa (stratified squamous, except nasopharynx which is pseudostratified columnar)
2. Pharyngobasilar fascia — fibrous layer; especially thick in the nasopharynx (no muscle superiorly)
3. Pharyngeal muscles (constrictors and longitudinal muscles)
4. Buccopharyngeal fascia — outer covering
Figure: Pharynx — Muscles, Nerve Supply, Blood Supply (AN36.3)
Pharyngeal Constrictor Muscles
| Muscle | Origin | Insertion | Nerve Supply | Key Clinical Point |
|---|---|---|---|---|
| Superior constrictor | Pterygomandibular raphe, medial pterygoid plate, mylohyoid line | Pharyngeal raphe + pharyngeal tubercle | Pharyngeal plexus (CN X + CN IX) | Forms tonsillar bed laterally |
| Middle constrictor | Hyoid bone (greater and lesser horns) | Pharyngeal raphe | Pharyngeal plexus (CN X) | Overlapped by superior constrictor above |
| Inferior constrictor | Thyroid and cricoid cartilages | Pharyngeal raphe | Pharyngeal plexus (CN X) + external laryngeal nerve + recurrent laryngeal nerve | Thyropharyngeus + cricopharyngeus; gap = Killian's dehiscence |
Pharyngeal constrictors:
| Muscle | Origin | Insertion | Function |
|---|---|---|---|
| Superior constrictor | Pterygoid hamulus, pterygomandibular raphe, mandible, tongue | Posterior pharyngeal raphe | Constricts nasopharynx and oropharynx during swallowing |
| Middle constrictor | Greater + lesser horns of hyoid | Posterior pharyngeal raphe | Constricts oropharynx |
| Inferior constrictor | Oblique line of thyroid cartilage (thyropharyngeal part) + cricoid (cricopharyngeal part) | Posterior pharyngeal raphe | Constricts laryngopharynx; cricopharyngeus = upper oesophageal sphincter |
Longitudinal muscles (elevate the pharynx during swallowing):
- Stylopharyngeus (CN IX): the only muscle supplied by CN IX; elevates pharynx and larynx
- Palatopharyngeus (CN X): elevates pharynx and closes off nasopharynx
- Salpingopharyngeus (CN X): opens pharyngeal end of Eustachian tube during swallowing
Figure: Pharyngeal constrictors:
Nerve supply:
- Motor: CN X via the pharyngeal plexus (all muscles EXCEPT stylopharyngeus = CN IX, and tensor veli palatini = CN V3)
- Sensory: CN IX (oro- and nasopharynx), CN X (laryngopharynx)
Blood supply: ascending pharyngeal artery (from ECA), tonsillar and ascending palatine arteries (from facial), descending palatine artery.
Lymphatics: to retropharyngeal nodes and deep cervical nodes.