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Vestibulocochlear Nerve (CNVIII)

Main Text

TERMINOLOGY

Abbreviations

• Vestibulocochlear nerve (CNVIII)

Synonyms

• 8th cranial nerve

Definitions

• CNVIII: Afferent sensory nerve of hearing & balance

IMAGING ANATOMY

Overview

• Sensory (special sensory afferent) nerve consisting of 2 parts

Vestibular part: Balance

Cochlear part: Hearing
• CNVIII best described from peripheral to central

Cochlear Nerve

• Arises from bipolar neurons located in spiral ganglion within modiolus of cochlea

Peripheral fibers pass to organ of Corti in cochlear duct (scala media) within cochlea

Central fibers coalesce & pass as auditory component of CNVIII (cochlear nerve) to brainstem
• Central fibers pass from modiolus through cochlear aperture into internal auditory canal (IAC)

Cochlear aperture defined as bony opening into anteroinferior quadrant of fundus of IAC

Maximum diameter of cochlear aperture: ~ 2 mm
• Cochlear nerve passes from IAC fundus to porus acusticus within anteroinferior q uadrant of IAC
• Near porus acusticus cochlear nerve joins together with superior & inferior vestibular nerves to form vestibulocochlear nerve (CNVIII)
• CNVIII crosses cerebellopontine angle (CPA) cistern posterior to facial nerve
• CNVIII enters lateral brainstem at pontomedullary junction posterior to facial nerve
• Cochlear nerve fibers bifurcate, ending in dorsal & ventral cochlear nuclei
• Dorsal & ventral cochlear nuclei

Cochlear nuclei found on lateral surface of inferior cerebellar peduncle (restiform body)

Vestibular Nerve

• Arises from bipolar neurons located in vestibular (Scarpa) ganglion located within vestibular nerve in fundal portion of IAC

Vestibular ganglion not visible on imaging

Peripheral fibers pass to sensory epithelium of utricle, saccule, & semicircular canals

– Traverse multiple foramina in cribriform plate in lateral wall of IAC fundus

Central fibers coalesce to form superior & inferior vestibular nerves that pass medially to brainstem
• Fundus of IAC

Superior & inferior vestibular nerves are separated by falciform crest (transverse crest)

Superior vestibular nerve separated from facial nerve anteriorly by vertical bony structure called Bill bar

– Bill bar not visible on imaging (CT or MR)
• Superior & inferior vestibular nerves pass medially from IAC fundus to porus acusticus within posterosuperior & posteroinferior quadrants of IAC
• Near porus acusticus, superior & inferior vestibular nerves join together with cochlear nerve to form vestibulocochlear nerve (CNVIII)
• Vestibulocochlear nerve crosses CPA cistern posterior to facial nerve
• Enters lateral brainstem at junction pons & medulla posterior to facial nerve
• Vestibular nerve fibers divide into ascending & descending branches, which mainly terminate in vestibular nuclear complex
• Vestibular nuclear complex

4 nuclei (lateral, superior, medial, & inferior)

Located beneath lateral recess along floor of 4th ventricle (rhomboid fossa) in lower pons

Complex connections exist between vestibular nuclei, cerebellum, spinal cord (vestibulospinal tract), & nuclei controlling eye movement

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Mar 13, 2021 | Posted by admin in NUCLEAR MEDICINE | Comments Off

Main Text

TERMINOLOGY

Abbreviations

IMAGING ANATOMY

Overview

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Vestibulocochlear Nerve (CNVIII)

Vestibulocochlear Nerve (CNVIII)

Synonyms

Definitions

Cochlear Nerve

Vestibular Nerve

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Vestibulocochlear Nerve (CNVIII)

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