Stylomastoid foramen
Exit foramen · CN VII
The opening between the styloid and mastoid processes on the base of the skull where the facial nerve leaves the facial canal, having already given off the greater petrosal nerve, the nerve to stapedius and the chorda tympani inside the temporal bone. Just after emerging it gives the posterior auricular nerve and branches to the posterior belly of digastric and stylohyoid, then enters the parotid gland.
Traced from the start
- Pons
- Facial nerve (CN VII)
- Stylomastoid foramen
Detail
- Transmits
- Facial nerve (VII) motor trunk, stylomastoid artery
- Landmark
- Deep between the mastoid tip and the styloid process, medial to the parotid; the mastoid is poorly developed in infants so the nerve lies superficially
- Already given off
- Greater petrosal (lacrimation), nerve to stapedius, chorda tympani (taste and salivation) — so a lesion at or beyond this point affects movement only
When it goes wrong
Forceps delivery or pressure on the undeveloped mastoid of a newborn
Transient lower motor neurone facial palsy that recovers over weeks
Lesion at or distal to the foramen (parotid carcinoma, parotidectomy, facial laceration)
Lower motor neurone facial weakness with taste, lacrimation and hearing all spared, distinguishing it from a lesion inside the facial canal
Mastoid surgery or a postauricular incision placed too low in an infant
Iatrogenic facial nerve injury at its exit
Practise this structure
2 questions in the bank tagged Facial Nerve.
A 52-year-old woman has had two months of numbness over the right forehead, the right upper eyelid and the tip of her nose, with a gritty feeling in the right e…
Foundations · middle twist
A 44-year-old man has had drooping of the right side of his face for three days. He drools from the right corner of his mouth, the right nasolabial fold is flat…
Foundations · common