On the first day of your fourth year neurology rotation as a medical student, you are asked to see two patients complaining of right facial droop.\xA0 The first patient is found to have a tumor on the cranial floor at the entrance to the internal acoustic meatus.\xA0 The second patient has a tumor at the stylomastoid foramen. Discuss the anatomy, functional components, and distribution of the facial nerve. \xA0 Compare the deficits resulting from a lesion of the facial nerve at the internal auditory meatus to the deficits resulting from a lesion of the facial nerve at the stylomastoid foramen. (12 pts)

Anatomy

• Posterior cranial fossa
• Internal auditory meatus
• Horizontal part
  • Geniculate ganglion and greater superficial petrosal nerve
• Descending part
  • Nerve to stapedius
  • Chorda tympani
• Stylomastoid foramen
• Posterior auricular branch and main trunk
• Nerves to stylohyoid and posterior belly digastric
• Motor nerves to muscles of facial expression including the buccinator
  1. Temporal branch - orbicularis oculi
  2. Zygomatic branch - orbicularis oculi
  3. Buccal branch - buccinator
  4. Mandibular branch - orbicularis oris
  5. Cervical branch - platysma

Distribution and Nerve Injury

1. Stylomastoid Foramen (GSA SVE)
   • Motor and sensory to external ear by posterior auricular nerve - anesthesia within external auditory meatus and posterior pina, limited ear movement
   • Stylohyoid muscle and posterior belly digastric muscle - difficulty with swallowing, depressing the mandible, and raising the larynx
   • Motor to muscles of facial expression by main nerve trunk - facial paralysis, difficulty positioning food in occlusion plane
   • Postganglionic parasympathetic to parotid are spared
2. Distal to nerve to stapedius and proximal to chorda tympani (SVA, GVE)
   • Taste to anterior 2/3 of tongue
   • Preganglionic parasympathetic to submandibular gland - dry mouth
3. Distal to greater superficial petrosal nerve and proximal to stapedial nerve (SVE)
   • Stapedius muscle - hyperacusis
4. Proximal to greater superficial petrosal nerve (GVA, SVA, GVE)
   • Touch, temperature, pain to posterior parts of soft palate
   • Taste to hard and soft palate (excluding immediately posterior to the upper incisors)
   • Mucosal secretion from hard palate, soft palate, nasal cavity, and maxillary sinus - dry mouth and dry mucosa
   • Lacrimation - dry eye

A 12 year old girl is playing Little League baseball when she is struck in the right eye by a batted ball. In the emergency department the soft tissues around her right eye are swollen to the extent that she cannot open her eye.\xA0 Her globe is not ruptured but is displaced inferior, and a CT scan reveals a fractured floor and medial wall of her right orbit. The inferior orbital fissure and its structures are compromised. Review the anatomy of the orbit. Include bones, contents, relationships, fascial specializations, muscles, vasculature, innervation, and lymphatic drainage. Discuss the deficits resulting from injury to the structures passing through the inferior orbital fissure. (12 pts)

Bones and Foramina

• Orbital Walls
  • Superior - orbital plate of frontal bone
  • Inferior - maxilla
  • lateral - zygoma
  • Medial - lacrimal bone, ethmoid bone, palatine bone
  • Posterior - greater wing of sphenoid bone, body of sphenoid bone,
• Foramina
  • Optic foramen - optic nerve, ophthalmic artery, central artery
  • Superior orbital fissure - III, IV, V1, VI, ophthalmic vein
  • Inferior orbital fissure - V2, infraorbital artery and vein, zygomatic nerve and branches
  • Infraorbital groove, canal, and foramen
  • Anterior and posterior ethmoidal foramina
  • Foramina for the zygomaticotemporal and zygomaticofacial nerves
  • Canal for the nasolacrimal duct

Contents

• Periorbita
• Bulbar fat
• CN2,3,4,5 (V1 and V2),6,7
• Sympathetic root of ciliary ganglion
• Extraocular muscles
• Globe - chambers, lens, ciliary body, dilator, sphincter
• Ophthalmic artery and branches
• Opthalmic vein and branches
• Ciliary ganglion
• Annulus tendineus
• Lacrimal gland

Relationships

• Structures passing through annulus tendineus
• Ciliary ganglion
• Trochlea

Fascial specializations

• Annulus tendineus
• Periorbita
• Bulbar fat
• Trochlear
• Orbital septum, palpebral ligaments, tarsal plates
• Conjunctiva

Muscles and movements

• Rectus muscles
• Rotation by the obliques
• Levator palpebrae superioris and superior tarsal muscle
• Orbicularis oculi

Vascularization

• Ophthalmic artery and branches
  • Lacrimal artery
  • Supraorbital artery
  • Supratrochlear artery
  • Infratrochlear artery
  • Anterior ethmoidal artery and clinical significance
  • Posterior ethmoidal artery
• Ophthalmic vein and branches
  • Clinical significance of facial and orbital venous drainages
  • Clinical significance of inferior ophthalmic vein and pterygoid venous plexus

Innervation

• Optic nerve
• Superior division oculomotor nerve
• Inferior division oculomotor nerve
• Motor root of ciliary ganglion
• Sympathetic root of ciliary ganglion
• Nasociliary nerve
• Sensory root of ciliary ganglion
• Long and short ciliary nerves
• Anterior and posterior ethmoidal nerves
• Infratrochlear nerve
• Lacrimal nerve and non-native fibers
• Frontal nerve and branches
• Trochlear nerve
• Abducens nerve

Lymphatic Drainage

• Lateral lids and conjunctiva - parotid nodes
• Medial lids and conjunctiva - submandibular nodes
• Orbit proper - mostly unidentified (Gray's)

Injury to structures passing through the inferior orbital fissure

• Infraorbital nerve - paresthesia of face inferior to the orbit extending to angle of nose and including upper lip
• Infraorbital artery and vein - exophthalmia
• Zygomatic nerve and branches
  • Zygomaticofacial nerve - paresthesia of face overlying the zygoma
  • Zygomaticotemporal nerve - paresthesia of face posterior to zygoma and the anterior temporal fossa
    • Postganglionic parasympathetic fibers from pterygopalatine ganglion - reduced lacrimation and dry eye
• Entrapment of inferior rectus muscle - depressed globe

Additional Clinical Notes

• Pulsating exophthalmos - Arteriovenous shunt within cavernous sinus
• Inferior root CN3 and ciliary ganglion
• Abducens and cavernous sinus infection
• Sympathetic root of ciliary ganglion and ptosis
• Horner's syndrome

A 51 year old male presents to the Free Clinic with complaints of neck pain and feeling short of breath.\xA0 He states he had a toothache two weeks ago and had some swelling on his lower left jaw.\xA0 He took some Tylenol with minimal relief.\xA0 Over the last 24 hours, he has had fever and chills, some difficulty swallowing and swelling in his neck.\xA0 On exam, his temperature is 103 F, he is tachycardic, with a blood pressure of 100/60.\xA0 He appears acutely ill and when asked to lay back he refuses since doing so makes him feel like he can't breath.\xA0 Exam of his mouth shows his tongue to be elevated and posteriorly displaced.\xA0 He has multiple deep cavities in his teeth.\xA0 His neck has firm edema, is warm and tender to the touch.\xA0 On auscultation you hear a high pitched noise (stridor) in his neck but not in his lungs. An x-ray of his teeth shows an apical abscess on the lower left second molar. Discuss the spaces defined by the cervical fasciae. Include boundaries, contents, relationships, lymphatic drainage, and significance. (12 pts)

Cervical Investing Fascia Attachments and Specialization

• from posterior cervical spines (nuchal ligament)
• envelopes trapezius and sternocleidomastoid muscles
• envelopes strap muscles
• envelopes parotid gland (parotid fascia) and submandibular gland
• superior limits - mandible anterior, scalp posterior
• inferior limits - sternum, clavicle, acromion, vertebra prominens
• creates a continuous collar (carpet)

Pretracheal Visceral Fascia Attachments and Specialization

• surrounds the cervical viscera - thyroid gland, trachea, esophagus, recurrent laryngeal nerves
• posterior: buccopharyngeal fascia (named part of pretracheal visceral fascia)
• superior limit - thyroid cartilage
• inferior limit - superior/anterior mediastinum

Prevertebral Fascia Attachments and Specialization

• surrounds the intrinsic musculature of the cervical vertebral column
• attached to the spinous processes of the cervical vertebrae
• partly covers splenius capitis, levator scapula, scalene muscles, longus colli, longus capitus, anterior vertebral bodies
• superior limit - base of skull near pharyngeal tubercle
• inferior limit - continuous throughout thorax
• alar layer of prevertebral fascia - second layer of prevertebral fascia attached to transverse processes, border for "danger space"
• diverticulum of prevertebral fascia at interscalene triangle forms the axillary sheath
  • space defined by axillary sheath is continuous with space defined by prevertebral fascia
  • anesthesia of brachial plexus could block phrenic nerve - watch out for bilateral effects!

Spaces Defined by Cervical Fascias

• pretracheal space - defined by the collar of pretracheal fascia
  • from thyroid cartilage to superior mediastinum
• retropharyngeal space - defined by pretracheal visceral fascia (buccopharyngeal fascia part) and prevertebral fascia
  • extends from the pharyngeal tubercle to the posterior mediastinum (where alar fascia blends with visceral fascia)
  • especially important for considerations of spread infection
  • infections can enter this space through compromise of the buccopharyngeal fascia (the "throat")
• danger space (prevertebral space) - between alar layer of prevertebral fascia and prevertebral fascia
  • from base of skull (pharyngeal tubercle) and extending inferiorly throughout the thorax

Lymphatic Drainage

• Submandibular and submental nodes
• Retropharyngeal nodes
• Lateral and medial cervical nodes
• Deep cervical nodes

Significance

• Spread of infection - lower molars, pharynx, tonsils
• Dispersion to superior and posterior mediastinum
• Airway obstruction - Ludwig's angina