ANATOMY OF FACIAL NERVE 7th cranial nerve.pptx

Ent ppt

1. ANATOMY OF FACIAL NERVE Dr.MIDHUN BHASKAR K

2. Facial nerve is the 7 th cranial nerve It is a mixed nerve with both motor and sensory functions Nerve of 2 nd branchial arch Facial nerve contains facial nerve proper & Nervus Intermedius Both facial nv proper & NI emerge from Cerebellopontine angle at the caudal border of Pons between Abducens nerve & Vestibulocochlear nv

3. The large motor fibres control the muscles of facial expression Small sensory nerve (the nerve of Wrisberg, also known as Nervus Intermedius) carries secretomotor fibres to the lacrimal and salivary glands, as well as taste and general sensation fibres The facial nerve has two motor fibre branches and two sensory fibre branches. The motor fibres originate from the facial nerve nucleus and superior salivatory nucleus Sensory fibres branches are related to the nucleus tractus solitarius and the spinal nucleus of the trigeminal complex

4. Facial nerve nucleus - contains motor fibres. Superior salivatory and lacrimatory nucleus - contains motor fibres. Nucleus of tractus solitarus (gustatory nucleus). It contains sensory fibres and brings the taste sensations. Spinal nucleus of trigeminal system - It contains sensory fibres and brings touch , pain, temperature sensation of facial nerve

5. Course of Facial nerve 3 parts – 1) Intracranial course (Cisternal/ Pontine segment ), 2) Intratemporal course – 1)Meatal segment 2) Labyrinthine segment 3) Tympanic segment 4) Mastoid segment 3) Extracranial / infratympanic course

6. INTRACRANIAL COURSE Intracranial course also known as pontine or cisternal segment (24-25 mm). From origin of facial nerve from pons to internal acoustic meatus. Motor fibres of facial nerve nucleus, first move backwards towards nucleus of VIth nerve, moves around or hooks around the nucleus of VIth (abducens) and then move forwards to exit the brainstem through cerebellopontine angle Creates Facial Colliculus

7. Intratemporal course

8. MEATAL SEGMENT (8-10 mm) From medial end to lateral end of internal acoustic meatus. Facial nerve travels through internal meatus in the anterosuperior quadrant of the IAC

9. Labyrinthine segment 4.0 mm - Shortest segment of the Intratemporal course From lateral end of IAM(fundus) to geniculate ganglion (1st genu) Narrowest (0.61-0.68 mm), hence most vulnerable to get compressed by oedema or inflammation leading to paralysis Susceptible to low-flow state and vascular compression as it lacks anastomosing arterial cascades Greater superficial petrosal nerve is the first branch of Facial nerve and carries secretomotor fibres to lacrimal gland and the glands of nasal mucosa and palate

10. Tympanic segment (11 mm) From 1st genu to pyramid Facial nerve traverses medial to incus runs posterior-superior to the processus cochleariformis above the oval window below the lateral semi-circular canal Due to the high incidence of fallopian canal dehiscence in tympanic segment – it is the most common site of injury during middle ear surgery

11. Mastoid or vertical segment (13.0 mm) From pyramid to stylomastoid foramen longest segment of the Intratemporal course Second genu is the most common site of injury during mastoid surgery Nerve to Stapedius arises at the level of 2nd genu and supplies the stapedius muscle

12. CHORDA TYMPANI Chorda tympani arises from the middle of vertical segment, 5-6 mm above the stylomastoid foramen Enters the middle ear through posterior canaliculus at the junction of the lateral and posterior walls of middle ear It runs on the medial surface of the tympanic membrane between its mucosal and fibrous layers

13. Runs medially just below the neck of malleus and above the attachment of tendon of tensor tympani Leave the middle ear through anterior canaliculus Carries taste sensation from anterior two-thirds of tongue Supplies secretomotor fibres to the submaxillary and sublingual salivary glands.

14. Extracranial course From stylomastoid foramen to the termination of its peripheral branches The facial nerve exits from stylomastoid foramen, travels anterior to the posterior belly of digastric and lateral to the styloid process. Enters the parotid gland high up on its posteromedial surface and divides within the gland Divides just behind and superficial to the retromandibular vein and ECA The length from stylomastoid foramen to initial intra-parotid bifurcation ranges between 8 -22 mm.

15. Branches from Stylomastoid foramen Posterior Auricular Nerve After facial nv exits the stylomastoid foramen Supplies auricular muscles (superior & posterior) and occipitalis muscle Communicates with auricular branch of Vagus. Nerve to stylohyoid - innervates the stylohyoid muscle – It elevates the hyoid bone Nerve to posterior belly of digastric innervates the posterior belly of digastric muscle - It elevates the hyoid bone.

16. Peripheral branches Forms two divisions: Upper temporo- facial part (further divided into temporal, zygomatic, upper buccal branch). Lower cervico-facial part (further divided into lower buccal, mandibular and cervical branches). Both divisions together form pes anserinus (goose-foot) Temporal branches: supply the frontalis, orbicularis oculi and corrugator supercilli muscles Zygomatic branches: supply the orbicularis oculi muscle. Buccal branches: supply the orbicularis oris, buccinator and zygomaticus muscles. Marginal mandibular branch: supplies the depressor labii inferioris,depressor anguli oris and mentalis muscles. Cervical branch: supplies the platysma muscle in the neck

17. Blood supply Veins accompany the arteries in the fallopian canal. Lymphatic vessels are located in the epineural layer

18. Landmarks of facial nv For middle ear and mastoid surgery 1. Processus cochleariformis - It demarcates the geniculate ganglion which lies just anterior to it. Tympanic segment of the nerve starts at this level. 2. Oval window and horizontal canal - The facial nerve runs Anteromedial to the oval window (stapes) 3.Lateral S.C.C – Seen Postero – Superior to facial Nv. 4. Short process of incus. Facial nerve lies medial to the short process of incus at the level of aditus. Short process points to facial nv 5. Pyramid. Nerve runs behind the pyramid and the posterior tympanic sulcus. 6. Tympanomastoid suture. In vertical or mastoid segment, nerve runs behind this suture. 7. Digastric ridge. The nerve leaves the mastoid at the anterior end of digastric ridge

19. Surgical landmarks during parotidectomy 1. Tragal pointer. The main trunk of nerve lies 1 cm medial and slightly antero-inferior to the pointer. Tragal pointer is a sharp triangular piece of pinna cartilage and it “points” to the nerve. 2. Posterior belly of digastric. When retrograde dissection of this muscle is done along its upper border up to its attachment with the mastoid process, the facial nerve is seen passing between the mastoid and the styloid process. 3. Tympano-mastoid suture. The trunk of the nerve can be identified 6–8mm below the inferior ‘drop off’ of the tympano-mastoid suture. 4. Styloid process. The nerve passes laterally to the styloid process

20. Topo diagnostic tests

21. UMN vs LMN lesion

22. House-Brackmann grading system For facial palsy The degree of facial weakness should be recorded from the time of onset of facial palsy.