Head & Neck Anatomy · Neurology

Cranial Nerve Foramina

Each cranial nerve exits the skull through a specific foramen. Knowing these routes explains syndromes from tumours, fractures, and vascular lesions at the skull base.

✦ The Mnemonic

"Clever Ophthalmologists Seek Rare Openings; Internal Acoustics Judge Heroically"

Cribriform · Optic canal · SOF · Rotundum · Ovale · IAM · Jugular · Hypoglossal canal

Cribriform plate CN I (Olfactory) Multiple small foramina in ethmoid

Optic canal CN II (Optic) Also transmits ophthalmic artery

Superior Orbital Fissure CN III, IV, V1, VI SOF syndrome = ophthalmoplegia + V1 loss

Foramen Rotundum CN V2 (Maxillary) Round foramen in sphenoid

Foramen Ovale CN V3 (Mandibular) Oval foramen; also accessory meningeal artery

Internal Acoustic Meatus CN VII + VIII Also transmits labyrinthine artery

Jugular Foramen CN IX, X, XI Also transmits sigmoid sinus → internal jugular vein

Hypoglossal Canal CN XII Above occipital condyle

📚 Clinical Breakdown

Foramina progress anterior to posterior: cribriform plate (I) → optic canal (II) → SOF (III/IV/V1/VI) → rotundum (V2) → ovale (V3) → IAM (VII, VIII) → jugular (IX, X, XI) → hypoglossal canal (XII). Note: foramen spinosum transmits the middle meningeal artery — NOT a cranial nerve.

SOF syndrome: lesion at the superior orbital fissure affects CN III, IV, V1, and VI — complete ophthalmoplegia, ptosis, upper face numbness. Adding CN II (optic canal involvement) = orbital apex syndrome with visual loss added.

Vernet's syndrome (jugular foramen): CN IX, X, XI affected — dysphagia, hoarseness, absent gag reflex, weakness of SCM and upper trapezius. Causes: glomus jugulare tumour, meningioma, nasopharyngeal carcinoma extension.

V2 foramen Rotundum (round)

V3 foramen Ovale (oval)

SOF contents CN III, IV, V1, VI + superior ophthalmic vein

Jugular foramen CN IX, X, XI + sigmoid sinus

⭐ Clinical Pearl

Cavernous sinus thrombosis — the sinus contains CN III, IV, V1, V2, VI (plus internal carotid artery). CN VI is affected first (runs freely inside the sinus; others run in the lateral wall). Presents with proptosis, chemosis, high fever, multiple CN palsies. Origin: facial infections in the danger triangle.

⚠ Exam Trap

Foramen spinosum transmits the middle meningeal artery — NOT a cranial nerve. Temporal bone fracture tears it → extradural haematoma. Anterior fossa fractures (cribriform plate) → CSF rhinorrhoea and anosmia.

← Cranial Nerves Next: Extraocular Muscles →