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AN28.1-10 | Face & parotid region — Part 1
CLINICAL SCENARIO
A 55-year-old school teacher from Villupuram wakes up one morning unable to close her right eye. The right side of her face droops — she cannot smile, wrinkle her forehead, or purse her lips. Her speech is slurred. She has no limb weakness.
Which nerve is affected? At what level? How does the anatomy explain why she cannot close her eye despite this being a "facial" palsy rather than an eye problem?
The face is where anatomy meets clinical medicine every day — Bell's palsy, parotid tumours, trigeminal neuralgia, facial artery aneurysms. Master the face, master the clinic.
WHY THIS MATTERS
The face and parotid region has extraordinarily high clinical yield:
- Bell's palsy — the most common cause of unilateral facial palsy; understanding CN VII anatomy is essential for localising the lesion level (UMN vs LMN, canal vs stylomastoid).
- Parotid surgery — surgeons must identify and protect the CN VII branches within the parotid gland to avoid permanent facial deformity.
- Trigeminal neuralgia — one of the most severe pain syndromes; understanding the three divisions of CN V explains the trigger zones and treatment targets.
- Lymph node metastasis — head and neck cancers (oral, tongue, parotid) spread in predictable patterns along the lymphatic drainage described here.
- Frey's syndrome — an interesting post-parotidectomy complication caused by aberrant nerve regeneration (a favourite exam question).
- Dangerous area of the face — deep facial vein, angular vein, cavernous sinus communication.
RECALL
Before reading: What are the two types of facial palsy (upper motor neurone vs lower motor neurone)? Where does CN VII exit the skull? What is the difference between CN V (sensory) and CN VII (motor) in their relationship to the face?
Muscles of Facial Expression (AN28.1, AN28.6)
Muscles of facial expression are unique: they are derived from the 2nd pharyngeal arch (mesoderm) and therefore all supplied by the facial nerve (CN VII). They are inserted into the skin (not bone to bone) — hence they move the skin to create facial expressions.
Key muscles and their actions:
| Muscle | Action | Clinical note |
|---|---|---|
| Orbicularis oculi | Closes eye (palpebral part: gentle blink; orbital part: tight closure) | Paralysis → lagophthalmos (eye cannot close) → corneal ulceration |
| Orbicularis oris | Closes/purses lips | Paralysis → drooling, difficulty eating, whistling |
| Buccinator | Compresses cheek against teeth; essential for chewing and blowing | Pierced by parotid duct; "trumpeter's muscle" |
| Zygomaticus major | Draws angle of mouth upward and backward (smiling) | "Dimple muscle" |
| Frontalis | Raises eyebrows; wrinkles forehead | Spared in UMN lesions (bilateral cortical supply) — key clinical clue |
| Corrugator supercilii | Draws eyebrows together and down (frowning) | |
| Platysma | Depresses mandible; tenses neck skin | Superficial neck muscle, 2nd arch origin |
| Nasalis | Compresses/dilates nostrils | |
| Mentalis | Raises chin skin; protrudes lower lip |
All muscles of facial expression = CN VII (facial nerve).
UMN vs LMN facial palsy — key distinction:
In UMN lesion (stroke), the upper face (especially frontalis) is SPARED because it has bilateral cortical representation (both sides of the motor cortex contribute). In LMN lesion (Bell's palsy, parotid tumour), the entire ipsilateral face is involved including the forehead.
Facial Nerve (CN VII) — Course and Branches (AN28.4)
CN VII (facial nerve) carries:
1. Motor fibres → muscles of facial expression (all 2nd arch muscles)
2. Parasympathetic (secretomotor) → lacrimal, submandibular, sublingual glands
3. Special sensory (taste) → anterior 2/3 of tongue via chorda tympani
4. General sensory → small area behind the ear (auricular branch)
Course:
- Nucleus in the lower pons → emerges at the cerebellopontine angle (with CN VIII)
- Enters internal acoustic meatus → travels through the facial canal in the petrous temporal bone
- Makes a sharp bend at the geniculum (geniculate ganglion → greater petrosal nerve exits here to lacrimal gland)
- Exits skull through the stylomastoid foramen
- Enters posterior surface of parotid gland → divides into five terminal branches
Five terminal branches (Temporal → Cervical):
"To Zanzibar By Motor Car" — Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical
| Branch | Muscles supplied | Clinical testing |
|---|---|---|
| Temporal | Frontalis, orbicularis oculi (upper), corrugator supercilii | Raise eyebrows, wrinkle forehead |
| Zygomatic | Orbicularis oculi (lower) | Close eye on command |
| Buccal | Buccinator, orbicularis oris, nasal muscles | Puff cheeks, show teeth |
| Marginal mandibular | Depressor anguli oris, mentalis | Depress lower lip |
| Cervical | Platysma | Tense neck skin |
Clinical localisation of CN VII lesions:
- Before geniculate ganglion: Loss of taste (chorda tympani), lacrimation (greater petrosal), hyperacusis (stapedius) + complete facial palsy
- Between geniculate ganglion and chorda tympani: No lacrimation but loss of taste + complete facial palsy
- After stylomastoid foramen: Pure motor facial palsy only (all secretory and taste fibres already branched off)
Sensory Innervation of the Face (AN28.2)
The face (excluding the scalp) is supplied entirely by the three divisions of the trigeminal nerve (CN V):
| Division | Area supplied | Key foramen |
|---|---|---|
| CN V1 (Ophthalmic) | Forehead, upper eyelid, nose bridge, cornea, conjunctiva | Supraorbital notch (supraorbital nerve); exits superior orbital fissure |
| CN V2 (Maxillary) | Lower eyelid, cheek, upper lip, lateral nose, upper teeth | Infraorbital foramen (infraorbital nerve); exits foramen rotundum → pterygopalatine fossa → inferior orbital fissure → infraorbital canal |
| CN V3 (Mandibular) | Lower lip, chin, anterior ear, lower teeth, anterior 2/3 tongue (general sensation) | Mental foramen (mental nerve); exits foramen ovale |
The ear is a complex zone: supplied by CN V3 (auriculotemporal — anterior), CN VII (auricular branch — concha/posterior), CN X (auricular branch — ear canal), and C2/C3 (greater auricular — lobule/mastoid).
Trigeminal neuralgia (tic douloureux): Severe, paroxysmal, electric shock-like pain triggered by light touch (eating, speaking, wind) in one division — usually V2 or V3. The trigger zone anatomically corresponds to the division's territory. Carbamazepine is first-line treatment; refractory cases undergo microvascular decompression.