Parotid Region & Facial Nerve

Parotid region boundaries

Anterior: ramus; Superior: zygomatic arch; Posterior: mastoid process; Inferior: posterior belly of digastric; Medial: styloid plane; Lateral: superficial parotid fascia

Parotid region: anterior boundary

Anterior border of the ramus of the mandible

Parotid region: superior boundary

Zygomatic arch

Parotid region: posterior boundary

Mastoid process

Parotid region: inferior boundary

Posterior belly of digastric

Parotid region: medial boundary

Sagittal plane through the styloid process

Parotid region: lateral boundary

Sagittal plane through the superficial layer of parotid fascia (sheath)

Parotid fascia (sheath)

Extension of deep investing cervical fascia; anchored to zygomatic arch (sup), SCM fascia (inf), masseteric fascia (ant); thick superficial lamina, thin deep lamina

Septa of the parotid sheath

Penetrate the gland; lots of fat allows flexibility for mandibular movement

Mumps

Viral infection of salivary glands; parotid swelling with severe pain (sheath limits swelling); especially painful to chew

Facial nerve and parotid gland relationship

CN VII emerges from stylomastoid foramen and travels THROUGH the parotid but does NOT innervate it

Parotidectomy

Surgical removal of parotid gland for tumors; puts the facial nerve in jeopardy

Parotid tumors

80% of salivary tumors are benign; malignant cancers are rare and often treated with parotidectomy

Parotid gland location

Lateral to masseter; anterior & inferior to auricle; anterior & superior to SCM

Parotid gland superficial shape

Triangular, apex inferiorly

Parotid gland medial extension

Into the lateral pharyngeal (parapharyngeal) space; posterior to ramus, anterior to mastoid, lateral to styloid

Superficial vs deep lobe of parotid

Bilobate shape defined by CN VII: superficial lobe superficial to CN VII, deep lobe deep to it

Structures traveling through the parotid gland

Facial nerve (CN VII), external carotid artery (and superficial temporal and maxillary branches), retromandibular vein

Parotid plexus

Branching of the facial nerve as it travels within the parotid gland

Course of the parotid duct

Emerges from anterior border of gland; runs superficial to masseter, inferior to zygomatic arch; turns at anterior masseter through buccal fat pad; pierces buccinator

Parotid duct opening

Parotid papilla, opposite the maxillary 2nd molar

Arterial supply of the parotid gland

External carotid artery and its branches in the gland: maxillary, superficial temporal, transverse facial

Venous drainage of the parotid gland

Retromandibular vein

Retromandibular vein formation

Superficial temporal vein + maxillary vein (transverse facial v. drains into superficial temporal v.)

Anterior division of retromandibular vein

Joins facial vein to form common facial vein, which drains into the internal jugular vein

Posterior division of retromandibular vein

Joins posterior auricular vein to form external jugular vein, which drains into the subclavian vein

Lymphatic drainage of the parotid gland

Parotid nodes, then superficial cervical nodes (around EJV) and superior deep cervical nodes (around IJV)

Somatic sensory innervation of parotid

Auriculotemporal n. (V3; cell bodies in trigeminal ganglion) and great auricular n. (C2-C3; cell bodies in DRG)

Parasympathetic effect on parotid

Increases salivation and thins the saliva

Parotid preganglionic parasympathetic cell bodies

Inferior salivatory nucleus in the medulla (CN IX)

Parasympathetic pathway to parotid

Inferior salivatory nucleus, CN IX (jugular foramen), tympanic n., lesser petrosal n., foramen ovale, otic ganglion, auriculotemporal n. (V3), parotid

Lesser petrosal nerve

Carries preganglionic parasympathetics (from CN IX via tympanic plexus) to the otic ganglion through foramen ovale

Otic ganglion

Parasympathetic ganglion where fibers to the parotid synapse

Nerve postganglionic parasympathetics 'hitch a ride' on to parotid

Auriculotemporal nerve (V3)

Sympathetic pathway to parotid

IML cell column T1-T2, white ramus, sympathetic trunk, superior cervical ganglion, external carotid plexus, parotid

Sympathetic effect on parotid

Reduces saliva flow by increasing viscosity (more glycoproteins)

Facial nerve (CN VII) arch

2nd pharyngeal arch nerve

Fiber types of CN VII

Motor to 2nd arch skeletal muscles, minimal somatic sensory (auricle & EAM), parasympathetics, special sense of taste

Muscles innervated by CN VII motor fibers

Muscles of facial expression, stylohyoid, posterior belly of digastric, stapedius

Facial motor nucleus

Location of cell bodies for CN VII skeletal motor fibers (pons)

Where CN VII exits the brain

Laterally at the pontomedullary junction, medial to CN VIII

Course of CN VII

Internal acoustic meatus (with CN VIII), petrous temporal bone, geniculate ganglion, bends inferiorly into facial canal, exits stylomastoid foramen

Branches of CN VII inside the facial canal

Greater petrosal n., nerve to stapedius, chorda tympani

Foramen where CN VII motor fibers exit the skull

Stylomastoid foramen

Immediate branches after stylomastoid foramen

Posterior auricular n. (occipitalis, posterior auricular mm.); nerves to posterior belly of digastric and stylohyoid

5 terminal branches of CN VII

Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical

Temporofacial division of CN VII

Temporal, zygomatic, and (part of) buccal branches

Cervicofacial division of CN VII

Buccal (part), marginal mandibular, and cervical branches

Temporal branch of CN VII

Superior and anterior auricular, frontalis, superior orbicularis oculi

Zygomatic branch of CN VII

Inferior orbicularis oculi and muscles inferior to the orbit

Buccal branch of CN VII

Buccinator, upper lip muscles, orbicularis oris; receives fibers from both divisions

Marginal mandibular branch of CN VII

Inferior orbicularis oris, depressor anguli oris, depressor labii inferioris, mentalis

Cervical branch of CN VII

Platysma

Why CN VII connects with trigeminal branches

Facial muscles need sensory innervation (proprioception & pain) from CN V

Temporal branch connects with

Supraorbital (V1), zygomaticotemporal (V2), auriculotemporal (V3)

Zygomatic branch connects with

Zygomaticofacial (V2)

Buccal branch connects with

Infraorbital (V2) and long buccal (V3)

Marginal mandibular branch connects with

Mental nerve (V3)

Cervical branch connects with

Transverse cervical nerve (cervical plexus)

Test: raise eyebrows

Frontalis - temporal branch

Test: close eyes tightly

Orbicularis oculi - temporal and zygomatic branches

Test: whistle / puff cheeks

Buccinator and orbicularis oris - buccal and marginal mandibular branches

Test: frown (pull mouth corners down)

Depressor anguli oris - marginal mandibular branch

Test: tense the neck skin

Platysma - cervical branch

Facial motor nucleus organization

Separate regions for the upper face and lower face

Central (supranuclear) lesion of CN VII

Lesion in the brain above the facial motor nucleus (e.g., stroke); contralateral LOWER face paralysis

Peripheral lesion of CN VII

Lesion of the facial nerve itself (e.g., Bell's palsy); ipsilateral paralysis of the ENTIRE half of the face

Why the upper face is spared in a central lesion

Upper face receives bilateral UMN innervation; lower face receives only contralateral

Causes of peripheral CN VII injury

Bell's palsy, idiopathic, surgical, viral infection, trauma, acoustic neuroma, parotid gland tumor

Acoustic neuroma

Benign sheath cell tumor of CN VIII that can compress CN VII

Symptoms of peripheral facial nerve injury

Smoothed wrinkles/folds, drooping eyebrow, sagging lower lid, sagging mouth corner, mouth deviates to unaffected side, impaired movements; possibly taste issues, dry mouth

Treatment of peripheral facial nerve injury

Corticosteroids, antivirals (herpes zoster), surgical tumor removal, eye care (drops, bedtime ointment to prevent corneal abrasion)

Stroke and the face

Interruption of brain blood supply; lower half of the face paralyzed contralateral to the CNS damage

Parotid dissection tip

Find the plane where CN VII runs between superficial and deep lobes; trace branches with backwards scissoring; go deep to find ECA and retromandibular v.