Head, Neck & Facial Anatomy

🧠 Head, Neck & Facial Anatomy

Cranial nerve exit foramina, triangles of the neck, deep cervical fascia and the danger space — the anatomical foundation for all ENT surgery.

Cranial Nerve Exit Foramina

For MRCS ENT, you must know the exit foramina of the skull base, the entire course of CN VII through the petrous bone, and the clinical consequences of each nerve’s injury. The trigeminal divisions and facial nerve are the highest-yield topics.

🧠 CN V — “Standing Room Only” (SOF, FR, FO)

V1 (Ophthalmic) → Superior Orbital Fissure
V2 (Maxillary) → Foramen Rotundum
V3 (Mandibular) → Foramen Ovale

Also through the SOF: CN III, IV, VI, and the sympathetic fibres — all supply the orbit

CN V — Trigeminal Nerve Divisions

Ophthalmic

ExitSuperior Orbital Fissure

BranchesLacrimal, Frontal (supraorbital, supratrochlear), Nasociliary

SuppliesForehead, scalp to vertex, upper eyelid, cornea (afferent limb of corneal reflex), nose bridge, frontal/ethmoid/sphenoid sinuses

ClinicalHerpes Zoster ophthalmicus (V1 distribution) — vesicles on forehead + tip of nose (Hutchinson’s sign) = nasociliary involvement → risk of keratitis

Maxillary

ExitForamen Rotundum → pterygopalatine fossa → infraorbital foramen

BranchesInfraorbital, zygomatic, posterior superior alveolar, palatine nerves, nasal branches

SuppliesCheek, lower eyelid, lateral nose, upper lip, upper teeth and gum, hard/soft palate, maxillary sinus

ClinicalLe Fort II/III fractures → infraorbital nerve injury → cheek numbness. Maxillary sinusitis can cause V2 pain (toothache-like).

Mandibular

ExitForamen Ovale

BranchesAuriculotemporal, lingual, inferior alveolar (→ mental nerve), buccal nerve; motor to muscles of mastication

SuppliesLower lip/chin (mental), lower teeth/gum, anterior 2/3 tongue (general sensation via lingual), ear (auriculotemporal), TMJ. Motor: temporalis, masseter, pterygoids, anterior digastric, mylohyoid

ClinicalMandibular fracture → mental nerve injury → numb chin (numb chin sign also: malignancy of mandible). Auriculotemporal nerve → Frey’s syndrome after parotidectomy. Chorda tympani joins lingual nerve in infratemporal fossa.

CN VII — The Facial Nerve

The facial nerve has the most complex intracranial and extracranial course of any cranial nerve — you must know every branch it gives off and the clinical consequence of injury at each point.

Course of CN VII Through the Petrous Bone

Segment	Location	Branch Given Off	Function of Branch
Meatal segment	Internal acoustic meatus (with CN VIII)	None	—
Labyrinthine segment	Petrous bone; site of Geniculate Ganglion	Greater Petrosal Nerve	Parasympathetic to lacrimal gland (via pterygopalatine ganglion) — lacrimation. Injury here → dry eye.
Tympanic (horizontal) segment	Medial wall of middle ear (above oval window)	Nerve to Stapedius	Stapedius reflex — dampens loud sounds. Injury → hyperacusis.
Mastoid (vertical) segment	Descends in mastoid	Chorda Tympani	Taste anterior 2/3 tongue (via lingual nerve, V3) + parasympathetic to submandibular/sublingual glands. Injury → loss of taste anterior tongue + dry mouth.
Stylomastoid foramen	Exit point from skull base	Posterior auricular nerve, nerve to posterior digastric and stylohyoid	Motor to posterior auricular muscles
Parotid gland	Divides into superior (temporofacial) and inferior (cervicofacial) divisions	5 terminal branches	See below — motor to muscles of facial expression

🧠 CN VII Terminal Branches — “Ten Zebras Bit My Cat”

Temporal — frontalis, orbicularis oculi (upper), corrugator
Zygomatic — orbicularis oculi (lower), zygomaticus
Buccal — buccinator, orbicularis oris, upper lip
Marginal Mandibular — depressors of lower lip and chin. Most commonly injured in surgery (thin, unprotected, often single branch)
Cervical — platysma

Localising a Facial Nerve Lesion

Dry eye (lacrimation lost) + hyperacusis + taste loss + facial palsy → lesion at or proximal to geniculate ganglion (e.g., Ramsay Hunt, acoustic neuroma, petrous fracture)
Hyperacusis + taste loss + facial palsy, but lacrimation intact → lesion between geniculate ganglion and nerve to stapedius
Taste loss + facial palsy, lacrimation and stapedius reflex intact → lesion between stapedius branch and chorda tympani (mid-mastoid)
Facial palsy only → distal to stylomastoid foramen (e.g., parotid tumour, surgery, Bell’s palsy at stylomastoid)
Bell’s Palsy: LMN (lower motor neuron) — entire face affected including forehead. UMN lesion spares forehead (bilateral cortical representation).

Other High-Yield Cranial Nerves for ENT

Spinal Accessory

ExitJugular foramen (with IX, X)

CourseEnters posterior triangle of neck — very superficial, vulnerable

SupplySternocleidomastoid (SCM) + Trapezius

Injury“Coat hanger” shoulder droop. Inability to shrug shoulder (trapezius) and inability to abduct arm past 90° (trapezius required for final 90° abduction). Winging of scapula (inferior angle). Classic: lymph node biopsy in posterior triangle.

XII

Hypoglossal

ExitHypoglossal canal

SupplyAll intrinsic + extrinsic muscles of tongue EXCEPT palatoglossus (CN X)

CourseLoops around occipital artery, passes over external carotid, runs lateral to hyoglossus alongside lingual artery

InjuryTongue deviates to SAME (ipsilateral) side as lesion — genioglossus on intact side pushes tongue towards lesion side. At risk in submandibular gland excision and carotid endarterectomy.

Complete Skull Base Foramina Table

Foramen	Contents
Cribriform plate	CN I (Olfactory) filaments. Fracture → anosmia + CSF rhinorrhoea (dural tears).
Optic canal	CN II (Optic nerve) + Ophthalmic artery
Superior Orbital Fissure	CN III, IV, V1, VI + sympathetics + ophthalmic veins
Foramen Rotundum	CN V2 (Maxillary)
Foramen Ovale	CN V3 (Mandibular) + accessory meningeal artery + lesser petrosal nerve
Foramen Spinosum	Middle meningeal artery + vein (epidural haematoma)
Carotid canal	Internal carotid artery + sympathetic plexus
Internal Acoustic Meatus	CN VII + CN VIII + labyrinthine artery
Jugular Foramen	CN IX (Glossopharyngeal), CN X (Vagus), CN XI (Accessory) + Internal Jugular Vein
Hypoglossal Canal	CN XII
Foramen Magnum	Medulla oblongata, CN XI (spinal roots), vertebral arteries, anterior/posterior spinal arteries

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