FACIAL NERVE

CONTENTS

1. Introduction2. Nuclei of origin3. Course & Relations4. Branches of facial nerve5. Ganglia associated with facial nerve6. Testing of facial nerve7. Identification of facial nerve8. Nerve injury

Introduction• The Facial nerve is the 7th of twelve paired

cranial nerves.• It is a mixed nerve with motor and sensory roots.• It also supplies pre-ganglionic parasympathetic fibres to several head and neck ganglia

Nuclei of Origin

1. Motor nucleus2. Superior salivatory nucleus3. Nucleus of tractus solitarius

The facial nerve is formed mainly of two parts:• 1- Facial nerve proper (motor): arising from facial

motor nucleus in pons.

• 2- Nervus intermedius: it is the sensory root of facial lies position between the facial proper and vestibulcochlear nerve in the pontocerebellar angle.

Carrying para-sympathetic fibers (from superior salivary

nucleus) and taste fibers ( to the solitary nucleus).

Course & Relations

• I- Intracranial (intrapetrosal) course

• II- Extracranial course

Branches1. Greater superficial petrosal – arises from the geniculate ganglion.2. Branches within the facial canal:• i) nerve to stapedius• ii) Chorda tympani3. After exit from stylomastoid foramen:• i) Posterior auricular• ii) Nerve to posterior belly of digastric• iii) Nerve to stylohyoid.4. On the face - Five major branches:• i) Temporal• ii) Zygomatic• iii) Buccal• iv) Marginal mandibular• v) Cervical

Ganglia associated with facial nerve• Geniculate ganglion

• Submandibular ganglion

• Pterygopalatine ganglion

Geniculate ganglion

• The geniculate ganglion (from Latin genu, for "knee") is an L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head.

• It receives fibers from the motor, sensory, and parasympathetic components of the facial nerve

Submandibular ganglion

• The submandibular ganglion is small and fusiform in shape. It is situated above the deep portion of the submandibular gland, on the hyoglossus muscle, near the posterior border of the mylohyoid muscle

Pterygopalatine ganglion

• The pterygopalatine ganglion (meckel's ganglion, nasal ganglion or sphenopalatine ganglion) is a parasympathetic ganglion found in the pterygopalatine fossa.

• It's largely innervated by the greater petrosal nerve (a branch of the facial nerve); and its axons project to the lacrimal glands and nasal mucosa

Facial Nerve blood supply

• The facial nerve gets it’s blood supply from 5 vessels:

Anterior inferior cerebellar artery – at the cerebellopontine angle

Labyrinthine artery  (branch of anterior inferior cerebellar artery) – within internal acoustic meatus

Superficial petrosal artery (branch of middle meningeal artery) – geniculate ganglion and nearby parts

Stylomastoid artery (branch of posterior auricular artery) – mastoid segment

Posterior auricular artery supplies the facial nerve at & distal to stylomastoid foramen

• Venous drainage parallels the arterial blood supply

Testing of Facial Nerve Branches

• Temporal branches -patient is asked to frown and wrinkle his or her forehead.

• Zygomatic branches -the patient is asked to close their eyes tightly

• Buccal branches -puff up cheeks (buccinator) smile and show teeth (orbicularis oris) tap with finger over each cheek to detect ease of air expulsion on the affected side

Applied Surgical anatomy of Facial Nerve in Oral & Maxillofacial Surgery

After exiting the stylomastoid foramen, which is situated posterolateral to stylomastoid process, the nerve enters the substance of parotid gland where it divides into its upper and lower divisions just posterior to the mandible

The approximate distance from the lowest point of the external bony auditory meatus to the bifurcation of the facial nerve is 2.3cm

Posterior to the parotid gland,the nerve is atleast 2cm deep into the skin surface,from this point the two branches curve around the posterior mandible,where they form plexus between the parotid gland and the masseter muscle

Temporal branch

• It exits the parotid gland anterior to superficial temporal artery

During an open approach to the TMJ, violation of this branch is possible

Zygomatic Branch :

• Its course is antero superior crossing the zygomatic bone

Inadvertent damage may occur to this nerve during open reduction of zygomatic arch or with the use of a byrd screw or zygomatic hook during closed approaches

The surgeon must be mindful of the facial nerves intimate involvement with the TMJ, specially when performing surgical approaches to the joint.

The temporal and zygomatic branches are at increased risk during pre auricular approach and the marginal mandibular branch during submandibular approach

The intra oral approach to the TMJ has minimal risk to the branches of facial nerve which is its major advantage

Buccal Branch:

• It runs almost horizontally and will often divide into separate branch above and below parotid duct as it runs anteriorly

Injury is possible in association with soft tissue trauma to the cheek region

Marginal mandibular branch:• It extends anteriorly and inferiorly within the substance of parotid gland,

there may be two or three branches of this nerve.

These branches run anteriorly parallel to inferior border of mandible and in some cases the course of the nerve is above the inferior border.

In essentially all cases the nerve is located above the inferior border of mandible beyond the facial artery. The marginal mandibular branch is an important structure encountered at the inferior border of the mandible just beneath the platysma muscle fibres during an open approach to the mandibular angle and body area.

• For this reason, an initial incision made approximately 1 to 1.5cm below the inferior border which prevents direct exposure or trauma to the nerve

Cervical Branch:

• The cervical branch exits the parotid gland above its inferior pole and runs downwards underneath the platysma muscle

Identification of Facial Nerve

3 surgical maneuvers used to identify nerve trunk

A. Blood free plane in front of external acoustic meatus

B. Exposure of anterior border of SCM below insertion into mastoid process

C. Peripheral identification of terminal branch of facial nerve (marginal mandibular branch)

Supra nuclear type:

• Paralysis of lower part of face (opposite side)• Normal taste and saliva secretion• Stapedius not paralysed

Nuclear type:

• Paralysis of facial muscle (same side)

• Paralysis of lateral rectus

• Internal strabismus

Peripheral lesion

At internal acoustic meatusa

Paralysis of secretomotor fibersHyper acusis Loss of corneal reflexTaste fibers unaffected Facial expression and movements paralysed

Injury distal to geniculate ganglion

Complete motor paralysis (same side)No hyper acusis Loss of corneal reflexTaste fibers affected Facial expression and movements paralysedPronounced reaction of degeneration

Injury at stylomastoid foramen Bell’s Palsy

THANK YOU