Facial Nerve (CNVII)

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Facial Nerve (CNVII)

Main Text

TERMINOLOGY

Abbreviations

• Facial nerve (CNVII)

Synonyms

• 7th cranial nerve

Definitions

• CNVII: Cranial nerve that carries motor nerves to muscles of facial expression; parasympathetics to lacrimal, submandibular, and sublingual glands; and taste from anterior 2/3 of tongue

IMAGING ANATOMY

Overview

• Mixed nerve: Motor, parasympathetic, and special sensory (taste)
• 2 roots: Motor and sensory (nervus intermedius) roots
- Nervus intermedius exits lateral brainstem between motor root of facial and vestibulocochlear nerves, hence its name
• 3 nuclei and 4 segments: Intraaxial, cisternal, intratemporal, and extracranial (parotid)

Nuclei and Intraaxial Segment

• 3 nuclei (1 motor, 2 sensory)
• Motor nucleus of facial nerve
• Superior salivatory nucleus
- Located lateral to CNVII motor nucleus in pons
- Efferent parasympathetic fibers exit brainstem posterior to CNVII as nervus intermedius
  - – To submandibular, sublingual, and lacrimal glands
• Solitarius tract nucleus

Cisternal Segment

• 2 roots in cisternal CNVII
- Larger motor root anteriorly
- Smaller sensory nervus intermedius posteriorly
• Emerge from lateral brainstem at root exit zone in pontomedullary junction to enter cerebellopontine angle (CPA) cistern
- CNVIII exits brainstem posterior to CNVII
• 2 roots join together and pass anterolaterally through CPA cistern with CNVIII to internal auditory canal (IAC)

Intratemporal Segment

• CNVII further divided in T-bone into 4 segments: IAC, labyrinthine, tympanic, and mastoid
• IAC segment : Porus acusticus to IAC fundus; anterosuperior position above crista falciformis
• Labyrinthine segment : Connects fundal CNVII to geniculate ganglion (anterior genu)
• Tympanic segment : Connects anterior to posterior genu, passing under lateral semicircular canal
• Mastoid segment : Inferiorly directed from posterior genu to stylomastoid foramen

Extracranial Segment

• Main CNVII exits skull base through stylomastoid foramen to enter parotid space
• Parotid CNVII passes lateral to retromandibular vein
• Ramifies within parotid, passes anteriorly to innervate muscles of facial expression

CNVII Branches

• Greater superficial petrosal nerve
- Arises at geniculate ganglion, passes anteromedially, exits temporal bone via facial hiatus
- Carries parasympathetic fibers to lacrimal gland
• Stapedius nerve
- Arises from high mastoid segment of CNVII
- Provides motor innervation to stapedius muscle
• Chorda tympani nerve
• Terminal motor branches to muscles of facial expression
- Superior to inferior: Temporal, zygomatic, buccal, mandibular, cervical
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Mar 13, 2021 | Posted by admin in NUCLEAR MEDICINE | Comments Off

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