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title, docid, authors, breadcrumbs, category, cmeTopicId, documentVersionId, imageCount, lastUpdated, pageDescription, pageKeywords, pageTitle, enhancedTitle, type, breadcrumbs
title docid authors breadcrumbs category cmeTopicId documentVersionId imageCount lastUpdated pageDescription pageKeywords pageTitle enhancedTitle type breadcrumbs
Facial Nerve in Temporal Bone 21dccac8-d73d-4ef3-859b-73e013ec15cc
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b2e6dabb-ee1c-42a4-a332-9f0814c1c607 Surjith Vattoth, MD, FRCR
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Head and Neck head-and-neck ed24ed8c-5d57-4629-879b-447b82d2973d
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Anatomy anatomy 678bc99d-d43e-45e6-9c8d-9fa5a7648616
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Head and Neck 16b49f7c-b13a-4957-a456-28bff373fe31 0b11b8a3-7805-4dd7-b7ac-f1db6ef4f9d3 21 11/28/23 Facial Nerve in Temporal Bone Head and Neck, Anatomy, Temporal Bone, Facial Nerve in Temporal Bone Facial Nerve in Temporal Bone | STATdx Facial Nerve in Temporal Bone ANATOMY
Head and Neck
Anatomy
Temporal Bone
Facial Nerve in Temporal Bone

title: "Facial Nerve in Temporal Bone" docid: "21dccac8-d73d-4ef3-859b-73e013ec15cc" authors:

  • key: "b2e6dabb-ee1c-42a4-a332-9f0814c1c607" value: "Surjith Vattoth, MD, FRCR" breadcrumbs:
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  • name: "Facial Nerve in Temporal Bone" slug: "facial-nerve-in-temporal-bone" treeNodeId: null category: "Head and Neck" cmeTopicId: "16b49f7c-b13a-4957-a456-28bff373fe31" documentVersionId: "0b11b8a3-7805-4dd7-b7ac-f1db6ef4f9d3" imageCount: 21 lastUpdated: "11/28/23" pageDescription: "Facial Nerve in Temporal Bone" pageKeywords: "Head and Neck, Anatomy, Temporal Bone, Facial Nerve in Temporal Bone" pageTitle: "Facial Nerve in Temporal Bone | STATdx" enhancedTitle: "Facial Nerve in Temporal Bone" type: "ANATOMY" breadcrumbs:
  • "Head and Neck"
  • "Anatomy"
  • "Temporal Bone"
  • "Facial Nerve in Temporal Bone"

TERMINOLOGY

  • Abbreviations

    • Facial nerve (FN); greater superficial petrosal nerve (GSPN)

  • Definitions

    • FN in temporal bone: Internal auditory canal, labyrinthine, anterior genu, tympanic, posterior genu, & mastoid segments

IMAGING ANATOMY

  • Overview

    • Internal auditory canal (IAC) segment: Porus acusticus to IAC fundus; anterosuperior position above crista falciformis
    • Labyrinthine segment: Connects fundal CNVII to geniculate ganglion (anterior genu)
    • Anterior genu: Geniculate ganglion of FN resides here - GSPNoriginates at geniculate ganglion, where nervus intermedius of Wrisberg (NIW) joins FN
    • Tympanic segment: Connects anterior to posterior genu - On coronal CT/MR, seen under lateral semicircular canal & above oval window in medial wall of middle ear - On more anterior coronal CT/MR, look for snake eyes (snail eyes) appearance of FN labyrinthine segment medially & tympanic segment laterally
    • Posterior genu: Beyond this, FN dips down inferiorly as descending mastoid segment
    • Mastoid segment: Inferiorly directed from posterior genu to exit mastoid temporal bone at stylomastoid foramen - Extracranial FN enters parotid gland - Gives off nerve to stapedius & chorda tympani nerve (CTN) - Runs in posterior wall of ME cavity with air-filled facial recess just anterior to FN upper mastoid segment - Bony pyramidal eminence (PE) with stapedius muscle at it base located just medial to FN upper mastoid segment - Do not confuse stapedius muscle for FN - Air-filled sinus tympanilies further medially in retrotympanum (RT) & connects to air underneath bony round window niche - Mnemonic for this mediolateral orientation of RT: Sinus tympani has "m"; hence medial; & facial recess has an "l"; hencelateral - Sinus tympani can be blindspot at mastoidectomy where cholesteatoma may hide

  • Branches of Facial Nerve in Temporal Bone

    • GSPN: Origin from geniculate ganglion (anterior genu) - Travels anteromedially through small hiatus in petrous temporal bone, then in middle cranial fossa floor between layers of dura mater underneath temporal lobe → foramen lacerum; at foramen lacerum, GSPN (parasympathetic via NIW) joined by deep petrosal nerve (DPN) (sympathetic fibers from internal carotid plexus) to form vidian nerve - Evaluate for GSPN schwannoma or perineural tumor spread in these locations
    • Nerve to stapedius: Origin from upper aspect of descending mastoid segment of FN near PE - Motor innervation to stapedius muscle
    • CTN: Origin from mastoid FN - From proximal, mid, or distal mastoid segment, or, rarely, even after exiting stylomastoid foramen - Ascends through posterior canaliculus of CTNin posterior wall of middle ear - Courses in middle ear cavity from posterior to anterior in substance of tympanic membrane between mucous & fibrous layers - Then between upper aspect of handle (manubrium) of malleus & long process of incus, on medialside of upperpart of handle of malleus - Then travels through anterior canaliculus of CTN & exits temporal bone into masticator space (MS) through petrotympanic fissure (Glaserian fissure) posteromedial to TMJ; in MS, CTN joins lingual nerve (LN) 2 cm below skull base - Chordal eminence: Bony prominence on posterior wall of tympanic cavity formed by CTN posterior canaliculus - Lateral RT divided by chordal eminence into facial recess medially & lateral tympanic sinus laterally - Styloid eminence separates lateral RT superiorly from hypotympanum inferiorly - Chordiculus: Bony crest between chordal eminence inferolaterally & PE superomedially; origin of tympanic segment of CTN at lateral end of chordiculus

  • Anatomy Relationships

    • NIW exits brainstem at pontomedullary junction between pons & inferior cerebellar peduncle lateral to motor root of FN & medial to CNVIII
    • NIW then courses along with motor root of FN through cerebellopontine angle into anterosuperior IAC quadrant
    • NIW joins motor root of FN near geniculate ganglion
    • NIW: Somatic sensory, special sensory, & visceral motor (secretomotor) fibers from various brainstem nuclei
    • Superior salivatory nucleus (SSN) in pons: Parasympathetic root through NIW → FN → GSPN (+ DPN, sympathetic) → vidian nerve → pterygopalatine ganglion in pterygopalatine fossa → lacrimal gland & nasal glands
    • SSN in pons: Parasympathetic root through NIW → FN → CTN → LN (CNV3 branch) → submandibular ganglion suspended by roots from LN in sublingual space → submandibular & sublingual salivary glands
    • CTNalso carries afferent taste sensation from anterior 2/3rd of tongue via LN - LN: Branch of mandibular nerve [V3, trigeminal (CNV) branch]
    • Nucleus of tractus solitarius (NTS) in medulla/lower pons: Geniculate ganglion at anterior genu of CNVII in temporal bone contains pseudounipolar cell bodies - Central processes of cell bodies enter gustatory part of NTS, forming special visceral afferent root - Peripheral processes receive taste sensation from anterior 2/3rd of tongue(CTN) & palate (GSPN)
    • Main sensory nucleus of CNV in pons: General somatic afferents sensation from lateral pinna, posterior external auditory auditory canal & mastoid via geniculate ganglion
    • Mastoid canaliculuswithArnold nerve [auricular branch of vagus (CNX)] extending laterally from lateral aspect of pars vascularis of jugular foramen toward tympanomastoid fissure first connects to descending mastoid segment FN canal several millimeters above stylomastoid foramen - Then dips inferolaterally toward tympanomastoid fissure (suture) at posterior aspect of external auditory canal - Arnold nerve supplies part of tympanic membrane & external auditory canal - Arnold nerve cough reflex on ear stimulation - When mechanically stimulating ear with finger or ear bud

CLINICAL IMPLICATIONS

  • Clinical Importance

    • Enhancement of geniculate ganglion, tympanic & mastoid segments of CNVII normal on postcontrast T1W MR; can be asymmetric intensity of enhancement on right & left - Secondary to circumneural arteriovenous plexus
    • Cisternal, IAC, labyrinthine& parotid segments do notnormally enhance on MR - Faint enhancement may be seen depending on MR scanner, sequence, & type of contrast used - Be familiar with normal images in different institutions
    • Always check parotid in peripheral CNVII paralysis
    • Focal dehiscence of undersurface of tympanic segment FN canal normal variant occurring in as much as 20- 25% of adults, most commonly just above oval window - Important to mention in presurgical temporal bone CT reports to avoid nerve injury during middle ear surgery

73481e07-60c3-4a54-b1aa-e4adc388db30

Images

Graphics: Sagittal, Coronal, & Axial

Sagittal graphic shows the medial wall of the middle ear. Note craniocaudal orientation of the lateral semicircular canal (LSCC), facial nerve (tympanic segment), oval window (stapes footplate attaches to oval window), and cochlear promontory (bony bulge covering the basal turn of cochlea). Greater superficial petrosal nerve (GSPN) originates at geniculate ganglion in the anterior genu of the facial nerve, where the nervus intermedius of Wrisberg [(NIW) not shown] joins the facial nerve. Posteroinferiorly, the descending mastoid segment of the facial nerve exits the temporal bone at the stylomastoid foramen on its way to the parotid gland. Sagittal graphic shows the medial wall of the middle ear. Note craniocaudal orientation of the lateral semicircular canal (LSCC), facial nerve (tympanic segment), oval window (stapes footplate attaches to oval window), and cochlear promontory (bony bulge covering the basal turn of cochlea). Greater superficial petrosal nerve (GSPN) originates at geniculate ganglion in the anterior genu of the facial nerve, where the nervus intermedius of Wrisberg [(NIW) not shown] joins the facial nerve. Posteroinferiorly, the descending mastoid segment of the facial nerve exits the temporal bone at the stylomastoid foramen on its way to the parotid gland.

Sagittal graphic shows the medial wall of the middle ear. Note craniocaudal orientation of the lateral semicircular canal (LSCC), facial nerve (tympanic segment), oval window (stapes footplate attaches to oval window), and cochlear promontory (bony bulge covering the basal turn of cochlea). Greater superficial petrosal nerve (GSPN) originates at geniculate ganglion in the anterior genu of the facial nerve, where the nervus intermedius of Wrisberg [(NIW) not shown] joins the facial nerve. Posteroinferiorly, the descending mastoid segment of the facial nerve exits the temporal bone at the stylomastoid foramen on its way to the parotid gland. Sagittal graphic shows the medial wall of the middle ear. Note craniocaudal orientation of the lateral semicircular canal (LSCC), facial nerve (tympanic segment), oval window (stapes footplate attaches to oval window), and cochlear promontory (bony bulge covering the basal turn of cochlea). Greater superficial petrosal nerve (GSPN) originates at geniculate ganglion in the anterior genu of the facial nerve, where the nervus intermedius of Wrisberg [(NIW) not shown] joins the facial nerve. Posteroinferiorly, the descending mastoid segment of the facial nerve exits the temporal bone at the stylomastoid foramen on its way to the parotid gland.

Coronal graphic shows craniocaudal orientation of LSCC, facial nerve canal (tympanic segment), oval window, & cochlear promontory, a very useful anatomic landmark for evaluating a coronal temporal bone CT. Superior & LSCCs, vestibule, & basal turn of cochlea together form a goose/duck-like appearance on coronal images. Coronal graphic shows craniocaudal orientation of LSCC, facial nerve canal (tympanic segment), oval window, & cochlear promontory, a very useful anatomic landmark for evaluating a coronal temporal bone CT. Superior & LSCCs, vestibule, & basal turn of cochlea together form a goose/duck-like appearance on coronal images.

Axial graphic shows the posterior wall of the mesotympanum with small, air-filled areas (called sinus tympani) medially & facial (CNVII) recess laterally with the bony pyramidal eminence in between. Axial graphic shows the posterior wall of the mesotympanum with small, air-filled areas (called sinus tympani) medially & facial (CNVII) recess laterally with the bony pyramidal eminence in between.

Coronal Bone CT

First of 3 coronal reformatted bone CT images from anterior to posterior shows snake eyes (snail eyes) appearance of right facial nerve labyrinthine segment medially lying next to tympanic segment laterally. In the anterior aspect of the internal auditory canal (IAC)/petrous temporal bone, facial nerve (CNVII) lies above with cochlear nerve (CNVIII) lying below (mnemonic: "7-up"/"Coke-down"). The posterior aspect of IAC coronally will have the superior vestibular nerve above with inferior vestibular nerve lying below (both CNVIII); not shown. First of 3 coronal reformatted bone CT images from anterior to posterior shows snake eyes (snail eyes) appearance of right facial nerve labyrinthine segment medially lying next to tympanic segment laterally. In the anterior aspect of the internal auditory canal (IAC)/petrous temporal bone, facial nerve (CNVII) lies above with cochlear nerve (CNVIII) lying below (mnemonic: "7-up"/"Coke-down"). The posterior aspect of IAC coronally will have the superior vestibular nerve above with inferior vestibular nerve lying below (both CNVIII); not shown.

CT shows characteristic craniocaudal orientation of the LSCC, facial nerve canal (tympanic segment), oval window, & cochlear promontory. Superior & LSCCs, vestibule, & basal turn of cochlea together form a goose/duck-like appearance. Focal dehiscence of undersurface of tympanic segment facial nerve canal is a normal variant occurring in as many as 20-25% of adults, most commonly just above oval window, but is important to mention in presurgical temporal bone CT reports to avoid nerve injury during middle ear surgery. CT shows characteristic craniocaudal orientation of the LSCC, facial nerve canal (tympanic segment), oval window, & cochlear promontory. Superior & LSCCs, vestibule, & basal turn of cochlea together form a goose/duck-like appearance. Focal dehiscence of undersurface of tympanic segment facial nerve canal is a normal variant occurring in as many as 20-25% of adults, most commonly just above oval window, but is important to mention in presurgical temporal bone CT reports to avoid nerve injury during middle ear surgery.

CT shows the posterior genu & descending mastoid segment of the facial nerve with branches. CT shows the posterior genu & descending mastoid segment of the facial nerve with branches.

Axial Bone CT

First of 7 axial temporal bone CT images from top to bottom shows the right facial nerve IAC fundal segment continuing as the labyrinthine segment towards the anterior genu. GSPN originates at the geniculate ganglion in the anterior genu, where NIW joins the facial nerve. GSPN carries preganglionic parasympathetic fibers from superior salivatory nucleus (SSN) in lower dorsal pons (via NIW coming from cerebellopontine angle/IAC; then facial nerve geniculate ganglion in anterior genu; and then the vidian nerve) to supply lacrimal gland and nasal glands through the pterygopalatine ganglion in the pterygopalatine fossa. GSPN also carries sensory afferent taste fibers from the soft palate to nucleus of tractus solitarius (NTS) in medulla/lower pons. GSPN passes through a small hiatus in the petrous temporal bone & then in the middle cranial fossa floor between the 2 layers of dura mater underneath the temporal lobe. Also note the superior vestibular nerve. First of 7 axial temporal bone CT images from top to bottom shows the right facial nerve IAC fundal segment continuing as the labyrinthine segment towards the anterior genu. GSPN originates at the geniculate ganglion in the anterior genu, where NIW joins the facial nerve. GSPN carries preganglionic parasympathetic fibers from superior salivatory nucleus (SSN) in lower dorsal pons (via NIW coming from cerebellopontine angle/IAC; then facial nerve geniculate ganglion in anterior genu; and then the vidian nerve) to supply lacrimal gland and nasal glands through the pterygopalatine ganglion in the pterygopalatine fossa. GSPN also carries sensory afferent taste fibers from the soft palate to nucleus of tractus solitarius (NTS) in medulla/lower pons. GSPN passes through a small hiatus in the petrous temporal bone & then in the middle cranial fossa floor between the 2 layers of dura mater underneath the temporal lobe. Also note the superior vestibular nerve.

Second bone CT shows the tympanic segment of the right facial nerve. Note the inferior vestibular nerve & singular nerve. Second bone CT shows the tympanic segment of the right facial nerve. Note the inferior vestibular nerve & singular nerve.

Third bone CT shows the posterior genu of the right facial nerve. Third bone CT shows the posterior genu of the right facial nerve.

Fourth bone CT shows the right facial nerve descending the mastoid segment, posteroinferior to posterior genu. Note the stapedius muscle; the tiny nerve to the stapedius arises from the proximal upper descending mastoid segment. Posterior mesotympanum (retrotympanum) has small, air-filled areas (called sinus tympani) medially & facial (CNVII) recess laterally with bony pyramidal eminence in between. Mnemonic for this mediolateral orientation is that sinus tympani has an "m," hence medial; & facial recess has an "l," hence lateral. Sinus tympani can be a blindspot at mastoidectomy where cholesteatoma may hide. Do not mistake the tensor tympani muscle for facial nerve tympanic segment. Chorda tympani nerve enters the anterior wall of the middle ear cavity at the anterior canaliculus of chorda tympani & continues into petrotympanic fissure (Glaserian fissure), which is medial to the TMJ. Fourth bone CT shows the right facial nerve descending the mastoid segment, posteroinferior to posterior genu. Note the stapedius muscle; the tiny nerve to the stapedius arises from the proximal upper descending mastoid segment. Posterior mesotympanum (retrotympanum) has small, air-filled areas (called sinus tympani) medially & facial (CNVII) recess laterally with bony pyramidal eminence in between. Mnemonic for this mediolateral orientation is that sinus tympani has an "m," hence medial; & facial recess has an "l," hence lateral. Sinus tympani can be a blindspot at mastoidectomy where cholesteatoma may hide. Do not mistake the tensor tympani muscle for facial nerve tympanic segment. Chorda tympani nerve enters the anterior wall of the middle ear cavity at the anterior canaliculus of chorda tympani & continues into petrotympanic fissure (Glaserian fissure), which is medial to the TMJ.

Image shows descending mastoid segment & posterior canaliculus of the chorda tympani nerve. Note GSPN forming the vidian nerve at the foramen lacerum. Image shows descending mastoid segment & posterior canaliculus of the chorda tympani nerve. Note GSPN forming the vidian nerve at the foramen lacerum.

Chorda tympani nerve origin from the descending mastoid segment of the right facial nerve is shown. Chorda tympani nerve origin from the descending mastoid segment of the right facial nerve is shown.

Axial Bone CT, Photon-Counting Detector CT, & Graphic

Last of 7 axial bone CT images shows the right facial nerve exiting the mastoid temporal bone at the stylomastoid foramen on its way to ramify within the parotid gland. Facial nerve perineural tumor spread from parotid malignancy should always be carefully evaluated. Last of 7 axial bone CT images shows the right facial nerve exiting the mastoid temporal bone at the stylomastoid foramen on its way to ramify within the parotid gland. Facial nerve perineural tumor spread from parotid malignancy should always be carefully evaluated.

Axial photon-counting detector CT shows the mastoid canaliculus with the Arnold nerve (auricular branch of vagus [CNX]) originating from the lateral aspect of pars vascularis of the right jugular foramen. Mastoid canaliculus first connects laterally to the descending mastoid segment facial nerve canal a few millimeters above the stylomastoid foramen, then dips inferolaterally toward the tympanomastoid fissure (suture) at the posterior aspect of the external auditory canal (EAC). The Arnold nerve supplies part of the tympanic membrane & EAC & causes Arnold nerve cough reflex when mechanically stimulating the ear with a finger or ear bud. Axial photon-counting detector CT shows the mastoid canaliculus with the Arnold nerve (auricular branch of vagus [CNX]) originating from the lateral aspect of pars vascularis of the right jugular foramen. Mastoid canaliculus first connects laterally to the descending mastoid segment facial nerve canal a few millimeters above the stylomastoid foramen, then dips inferolaterally toward the tympanomastoid fissure (suture) at the posterior aspect of the external auditory canal (EAC). The Arnold nerve supplies part of the tympanic membrane & EAC & causes Arnold nerve cough reflex when mechanically stimulating the ear with a finger or ear bud.

Axial graphic shows the right mastoid canaliculus with the Arnold nerve [auricular branch of vagus (CNX)] on its way from the lateral aspect of pars vascularis of the jugular foramen toward the descending mastoid segment facial nerve canal. Axial graphic shows the right mastoid canaliculus with the Arnold nerve [auricular branch of vagus (CNX)] on its way from the lateral aspect of pars vascularis of the jugular foramen toward the descending mastoid segment facial nerve canal.

Chorda Tympani Nerve: Sagittal Graphic, Sagittal Bone CT, & Longitudinal Oblique (Stenver) Bone CT Reformation

Sagittal graphic shows an internal view of the lateral wall of the middle ear cavity. The chorda tympani nerve originates from the descending mastoid segment of the facial nerve, ascends through the posterior canaliculus of chorda tympani at the posterior wall of the middle ear, courses in the middle ear cavity from posterior to anterior in the substance of the tympanic membrane between mucous & fibrous layers, & then between the upper aspect of the handle (manubrium) of malleus & long process of incus, on the medial side of the upper part of the handle of malleus. It then travels through the anterior canaliculus of chorda tympani & exits the temporal bone into the masticator space through the petrotympanic fissure (Glaserian fissure), which is posteromedial to the TMJ, & joins the lingual nerve 2 cm below the skull base. Sagittal graphic shows an internal view of the lateral wall of the middle ear cavity. The chorda tympani nerve originates from the descending mastoid segment of the facial nerve, ascends through the posterior canaliculus of chorda tympani at the posterior wall of the middle ear, courses in the middle ear cavity from posterior to anterior in the substance of the tympanic membrane between mucous & fibrous layers, & then between the upper aspect of the handle (manubrium) of malleus & long process of incus, on the medial side of the upper part of the handle of malleus. It then travels through the anterior canaliculus of chorda tympani & exits the temporal bone into the masticator space through the petrotympanic fissure (Glaserian fissure), which is posteromedial to the TMJ, & joins the lingual nerve 2 cm below the skull base.

Straight parasagittal bone CT reconstruction perpendicular to the axial CT without any obliquity shows the course of the chorda tympani nerve. Straight parasagittal bone CT reconstruction perpendicular to the axial CT without any obliquity shows the course of the chorda tympani nerve.

Longitudinal oblique (Stenver) bone CT of the right ear near the anterior margin of the petrous temporal bony pyramid shows the chorda tympani nerve canal & the nerve itself in the middle ear cavity. Longitudinal oblique (Stenver) bone CT of the right ear near the anterior margin of the petrous temporal bony pyramid shows the chorda tympani nerve canal & the nerve itself in the middle ear cavity.

Longitudinal Oblique (Stenver) & Transverse Oblique (Pöschl) Bone CT Reformations

Another longitudinal oblique (Stenver) bone CT more posteriorly shows the entire tympanic segment of the facial nerve. Note the anterior genu, tympanic segment, posterior genu, mastoid segment, & stylomastoid foramen, all seen on this single view. The tympanic segment passes beneath the LSCC. Another longitudinal oblique (Stenver) bone CT more posteriorly shows the entire tympanic segment of the facial nerve. Note the anterior genu, tympanic segment, posterior genu, mastoid segment, & stylomastoid foramen, all seen on this single view. The tympanic segment passes beneath the LSCC.

Further posterior longitudinal oblique (Stenver view) bone CT shows the labyrinthine & tympanic segments of the right facial nerve canal. Note the "2-dot" view of crura of the stapes just before they meet the footplate of the stapes at the oval window. Further posterior longitudinal oblique (Stenver view) bone CT shows the labyrinthine & tympanic segments of the right facial nerve canal. Note the "2-dot" view of crura of the stapes just before they meet the footplate of the stapes at the oval window.

Transverse oblique (Pöschl) bone CT reformation of the right ear parallel to the long axis of the superior SCC is shown. The image toward the medial aspect of the petrous temporal bone shows the axis of the labyrinthine segment of the facial nerve. When CNVII pathology is present, it is very helpful to have multiple different views of its canal. Transverse oblique (Pöschl) view image set is made in a plane parallel to the axis created by a line through superior SCC, whereas the longitudinal oblique (Stenver) view image set is made in a plane perpendicular to the superior SCC axis. Transverse oblique (Pöschl) bone CT reformation of the right ear parallel to the long axis of the superior SCC is shown. The image toward the medial aspect of the petrous temporal bone shows the axis of the labyrinthine segment of the facial nerve. When CNVII pathology is present, it is very helpful to have multiple different views of its canal. Transverse oblique (Pöschl) view image set is made in a plane parallel to the axis created by a line through superior SCC, whereas the longitudinal oblique (Stenver) view image set is made in a plane perpendicular to the superior SCC axis.

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