[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Stylomastoid foramen [Skeletal system](https://durgical.com/en/anatomy/system/skeletal-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Stylomastoid foramen The stylomastoid foramen is a small opening behind the ear, between two bony points, where the facial nerve leaves the skull for the muscles of the face. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=stylomastoid_foramen&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A small opening between the styloid and mastoid processes. ## What it does Where the facial nerve leaves the skull, on its way through the parotid gland to the muscles of the face. ## Key points - A lesion at the foramen paralyses all the muscles of facial expression on that side, but tears, taste and the stapedius reflex are spared, because their branches leave higher up - In newborns and small children the mastoid process has not grown, so the foramen sits near the surface: forceps delivery or an incision behind the ear can injure the facial nerve - Necrotising (malignant) otitis externa, mostly in older people with diabetes, spreads along the skull base and the facial nerve is often the first cranial nerve hit, at this foramen ## Key facts **Where** Between the styloid and mastoid processes **Function** Transmits the facial nerve (VII) and stylomastoid artery ## Relations **Contents** [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) leaving the skull, and the stylomastoid artery, usually from the posterior auricular artery, entering to supply the facial canal and middle ear **Course** Just outside the foramen the nerve gives the posterior auricular nerve and twigs to the posterior belly of the [digastric](https://durgical.com/en/anatomy/anterior-belly-of-digastric-muscle/) and the [stylohyoid](https://durgical.com/en/anatomy/stylohyoid-muscle/), then turns forward over the styloid process into the [parotid gland](https://durgical.com/en/anatomy/parotid-gland/) **In front** Styloid process, from which the stylohyoid muscle and the styloglossus arise **Behind** Mastoid process, with the posterior belly of the digastric arising from the mastoid notch just medial to it **Medial** [Jugular foramen](https://durgical.com/en/anatomy/jugular-foramen/) with the [internal jugular vein](https://durgical.com/en/anatomy/internal-jugular-vein/), a short distance inward ## How to find it It cannot be felt. It lies deep, about level with the ear lobe, between the mastoid tip and the back of the mandibular ramus. In parotid surgery it is reached by following the tympanomastoid suture, which leads down to it; the upper border of the posterior belly of the digastric marks the same depth. ## Examination - Topographic testing: normal tear production (Schirmer test), stapedial reflex and taste on the front of the [tongue](https://durgical.com/en/anatomy/tongue/) with complete facial weakness place the lesion at or below the foramen ## On imaging High-resolution [temporal bone](https://durgical.com/en/anatomy/temporal-bone/) CT shows it between the styloid and mastoid processes, where the mastoid segment of the facial canal ends. On axial CT or T1 MRI it is normally filled by a small pad of fat; loss of that fat or a widened foramen suggests a parotid cancer spreading up the facial nerve. In facial palsy after a temporal bone fracture, CT follows the fracture toward the canal. ## Clinical notes - Parotid tumours and surgery, deep cuts behind the angle of the jaw and mastoid surgery can injure the trunk just after it leaves the skull - Electroneurography stimulates the trunk just below the foramen and compares the facial muscle response on the two sides to estimate how many fibres have degenerated - In parotidectomy the trunk is identified as it leaves the foramen and then traced forward to protect its branches ## Development At birth there is almost no mastoid process and the foramen opens on the side of the skull; as the mastoid grows over the first years it comes to lie deeper and lower, shielded by the process. ## Related conditions - [Bell palsy](https://durgical.com/en/conditions/bell-palsy/) ## Test yourself Think of the answer, then tap the question to see it. ## Which nerve leaves the skull through the stylomastoid foramen? The facial nerve (VII), with the stylomastoid artery entering alongside. ## What does a facial nerve lesion at the stylomastoid foramen spare, and why? Tears, taste and the stapedius reflex, because their branches leave higher up; all facial expression muscles on that side are paralysed. ## Why is the facial nerve at the stylomastoid foramen vulnerable in newborns? The mastoid process has not grown, so the foramen is superficial; forceps delivery or an incision behind the ear can injure the nerve. ## Which skull base infection often affects the facial nerve first at the stylomastoid foramen? Necrotising (malignant) otitis externa, mostly in older people with diabetes. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/stylomastoid-foramen/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** foramen stylomastoideum TA2 684 **Official Spanish (DeCS)** Agujero estilomastoideo **English (TA2)** Stylomastoid foramen ## Related - [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) Sources: Terminologia Anatomica (TA2); [Facial Nerve Anatomy and Clinical Applications](https://www.ncbi.nlm.nih.gov/books/NBK554569/); [Anatomy, Head and Neck, Skull Foramen](https://www.ncbi.nlm.nih.gov/books/NBK546621/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/stylomastoid-foramen/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/stylomastoid-foramen/