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title, docid, authors, breadcrumbs, category, cmeTopicId, documentVersionId, imageCount, lastUpdated, pageDescription, pageKeywords, pageTitle, enhancedTitle, type, references, breadcrumbs
title docid authors breadcrumbs category cmeTopicId documentVersionId imageCount lastUpdated pageDescription pageKeywords pageTitle enhancedTitle type references breadcrumbs
Middle Ear Prolapsing Facial Nerve 61f6bcaa-f073-4385-b895-dc420ddc8a1e
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94f835c8-fa13-4e8a-995b-53048e6b0605 Philip R. Chapman, MD
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33151213-01b2-4542-9105-342e006b3915 H. Ric Harnsberger, MD
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Temporal Bone temporal-bone 9ad7d7b2-b2e4-4de2-be04-55ce607560c9
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Intratemporal Facial Nerve intratemporal-facial-nerve 35b77f60-796d-460f-8bac-4a187a150171
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Pseudolesions pseudolesions eb1df224-339c-469f-857b-200d08f330df
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Middle Ear Prolapsing Facial Nerve middle-ear-prolapsing-facial-nerve null
Head and Neck 7ffe7dc8-0323-438d-bbae-8f3437dd8a25 04cce8da-a9ae-4396-92b3-02bf6fc2ca6b 7 08/26/21 Middle Ear Prolapsing Facial Nerve Head and Neck, Diagnosis, Temporal Bone, Intratemporal Facial Nerve, Pseudolesions, Middle Ear Prolapsing Facial Nerve Middle Ear Prolapsing Facial Nerve | STATdx Middle Ear Prolapsing Facial Nerve DX true
Head and Neck
Diagnosis
Temporal Bone
Intratemporal Facial Nerve
Pseudolesions
Middle Ear Prolapsing Facial Nerve

title: "Middle Ear Prolapsing Facial Nerve" docid: "61f6bcaa-f073-4385-b895-dc420ddc8a1e" authors:

  • key: "94f835c8-fa13-4e8a-995b-53048e6b0605" value: "Philip R. Chapman, MD"
  • key: "33151213-01b2-4542-9105-342e006b3915" value: "H. Ric Harnsberger, MD" breadcrumbs:
  • name: "Head and Neck" slug: "head-and-neck" treeNodeId: "ed24ed8c-5d57-4629-879b-447b82d2973d"
  • name: "Diagnosis" slug: "diagnosis" treeNodeId: "19b6b986-97d0-40e7-b317-00f0c5cd8fa2"
  • name: "Temporal Bone" slug: "temporal-bone" treeNodeId: "9ad7d7b2-b2e4-4de2-be04-55ce607560c9"
  • name: "Intratemporal Facial Nerve" slug: "intratemporal-facial-nerve" treeNodeId: "35b77f60-796d-460f-8bac-4a187a150171"
  • name: "Pseudolesions" slug: "pseudolesions" treeNodeId: "eb1df224-339c-469f-857b-200d08f330df"
  • name: "Middle Ear Prolapsing Facial Nerve" slug: "middle-ear-prolapsing-facial-nerve" treeNodeId: null category: "Head and Neck" cmeTopicId: "7ffe7dc8-0323-438d-bbae-8f3437dd8a25" documentVersionId: "04cce8da-a9ae-4396-92b3-02bf6fc2ca6b" imageCount: 7 lastUpdated: "08/26/21" pageDescription: "Middle Ear Prolapsing Facial Nerve" pageKeywords: "Head and Neck, Diagnosis, Temporal Bone, Intratemporal Facial Nerve, Pseudolesions, Middle Ear Prolapsing Facial Nerve" pageTitle: "Middle Ear Prolapsing Facial Nerve | STATdx" enhancedTitle: "Middle Ear Prolapsing Facial Nerve" type: "DX" references: true breadcrumbs:
  • "Head and Neck"
  • "Diagnosis"
  • "Temporal Bone"
  • "Intratemporal Facial Nerve"
  • "Pseudolesions"
  • "Middle Ear Prolapsing Facial Nerve"

KEY FACTS

  • Terminology

    • Definition: Midtympanic facial nerve (CNVII) segment protrudes through bony dehiscence - CNVII dehiscencerefers only to segmental absence of bony covering of CNVII - Prolapsing CNVII: CNVII protrudes through dehiscence in tympanic CNVII canal

  • Imaging

    • Incidental finding on temporal bone CT - Tubular soft tissue extends from midtympanic CNVII into oval window niche
    • Coronal bone CT - Soft tissue mass in oval widow niche - Along undersurface of lateral semicircular canal - Contiguous with midtympanic segment of CNVII
    • Axial bone CT - Hammock-like CNVII spanning middle ear cavity under lateral semicircular canal

  • Top Differential Diagnoses

    • Intratemporal facial nerve schwannoma
    • Oval window atresia
    • Persistent stapedial artery
    • Congenital cholesteatoma in facial nerve canal

  • Clinical Issues

    • Clinical presentation - Most commonly asymptomatic - Rarely conductive hearing loss present from impingement on stapes - Prolapsed facial nerve can be injured during surgical exposure of stapes or oval window

  • Diagnostic Checklist

    • Warning to radiologist - Prolapsed CNVII in peril during stapedectomy - Report & call this finding to ear surgeon

TERMINOLOGY

  • Definitions

    • Midtympanic facial nerve (CNVII) segment protrudes through bony dehiscence
    • CNVII dehiscencerefers only to segmental absence of bony covering of CNVII
    • Prolapsing CNVII: CNVII protrudes through dehiscence

IMAGING

  • General Features

    • Best diagnostic clue

      - Tubular soft tissue extends from midtympanic CNVII into oval window niche (CT)

    • Location

      - Undersurface of lateral semicircular canal (LSCC) → oval window niche

    • Size

      - Variable; may be subtle or appear mass-like (2-3 mm) within oval window niche

    • Morphology

      - Smooth, tubular appearance

  • CT Findings

    • Bone CT

      - Coronal: Soft tissue mass in oval widow niche
        - Along undersurface of LSCC
        - Contiguous with midtympanic segment of CNVII
- Axial: Hammock-like CNVII spanning middle ear cavity under LSCC
- Simple dehiscence (uncovered CNVII) poorly seen unless CNVII prolapsed through dehiscence

  • MR Findings

    • No abnormality identified
    • T1 C+ is normal, excluding facial nerve schwannoma

  • Imaging Recommendations

    • Best imaging tool

      - Axial & coronal thin-section temporal bone CT
        - Best seen on **coronal** at level of oval window
        - Contrast not necessary or recommended

    • Protocol advice

      - When protruding CNVII is mass-like, use contrast-enhanced MR to exclude CNVII schwannoma
        - Facial nerve schwannoma enhances

DIFFERENTIAL DIAGNOSIS

  • Intratemporal Facial Nerve Schwannoma

    • Clinical: Hearing loss > > facial nerve palsy
    • CT: Tubular enlargement of CNVII canal - Geniculate fossa > tympanic > mastoid segments
    • MR: Enhancing tubular mass enlarges CNVII canal

  • Oval Window Atresia

    • Clinical: Conductive hearing loss
    • ± external auditory canal (EAC) atresia
    • CT: Facial nerve tympanic segment ectopic - Tympanic CNVII in oval window niche

  • Persistent Stapedial Artery

    • Asymptomatic vascular variant
    • CT: Absent foramen spinosum - Tubular lesion on cochlear promontory - Large anterior tympanic segment CNVII

  • Congenital Cholesteatoma in Facial Nerve Canal

    • Rare congenital cholesteatoma type
    • CT: Enlargement of CNVII bony canal - Most commonly geniculate ganglion area

PATHOLOGY

  • General Features

    • Etiology

      - Congenital/developmental; can be acquired from cholesteatoma

  • Gross Pathologic & Surgical Features

    • Protrusion: Identified in oval window niche during middle ear surgery
    • Dehiscence: Tympanic > > mastoid segment CNVII

CLINICAL ISSUES

  • Presentation

    • Most common signs/symptoms

      - **Asymptomatic** most commonly
- Rarely, conductive hearing loss: Impingement on stapes

    • Clinical profile

      - **Incidental finding** on temporal bone CT
        - Critical to communicate its presence to surgeon prior to middle ear exploration
        - Easy to injure facial nerve during stapedectomy if CNVII prolapse is present

  • Demographics

    • Age

      - All ages; congenital lesion

    • Epidemiology

      - Simple dehiscence without protrusion ~ 50% of cases
- Prolapsing facial nerve is rare (~ 1% of cases)

  • Natural History & Prognosis

    • Excellent if left alone

  • Treatment

    • Careful avoidance at time of middle ear surgery

DIAGNOSTIC CHECKLIST

  • Image Interpretation Pearls

    • Prolapse often associated with absence of notch defect along undersurface of LSCC
    • If notch is seen, consider alternative explanation

  • Reporting Tips

    • Caveat: Prolapsed CNVII in peril during stapedectomy
    • Report & call this finding to ear surgeon

69aa896c-0d3e-431e-9f74-ded28b2244b6

References

Selected References

  1. Hernandez-Trejo AF et al: Prevalence of facial canal dehiscence and other bone defects by computed tomography. Eur Arch Otorhinolaryngol. 277(10):2681-6, 2020
  2. Amadei EM et al: Revision stapes surgery after stapedotomy: a retrospective evaluation of 75 cases. Ear Nose Throat J. 97(6):E1-4, 2018
  3. Gosselin E et al: Predictable prosthesis length on a high-resolution CT scan before a stapedotomy. Eur Arch Otorhinolaryngol. 275(9):2219-26, 2018
  4. Kim SH et al: A case of a prolapsed facial nerve into the middle ear cavity. Br J Hosp Med (Lond). 76(1):50-1, 2015
  5. Yetiser S: The dehiscent facial nerve canal. Int J Otolaryngol. 679708, 2012
  6. Yu Z et al: The value of preoperative CT scan of tympanic facial nerve canal in tympanomastoid surgery. Acta Otolaryngol. 131(7):774-8, 2011
  7. Ozbek C et al: Incidence of fallopian canal dehiscence at surgery for chronic otitis media. Eur Arch Otorhinolaryngol. 266(3):357-62, 2009
  8. Di Martino E et al: Fallopian canal dehiscences: a survey of clinical and anatomical findings. Eur Arch Otorhinolaryngol. 262(2):120-6, 2005
  9. Daniels RL et al: The other ear: findings and results in 1,800 bilateral stapedectomies. Otol Neurotol. 22(5):603-7, 2001
  10. Park GC et al: Dehiscence of the tympanic segment of the facial nerve. Otolaryngol Head Neck Surg. 123(4):522, 2000
  11. Tange RA et al: Dehiscences of the horizontal segment of the facial canal in otosclerosis. ORL J Otorhinolaryngol Relat Spec. 59(5):277-9, 1997
  12. Swartz JD: The facial nerve canal: CT analysis of the protruding tympanic segment. Radiology. 153(2):443-7, 1984

Images

Selected Images

Graphic of medial wall of the right ear (anterior is to the right) demonstrates loss of bone covering midtympanic segment of the facial nerve canal with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche. Graphic of medial wall of the right ear (anterior is to the right) demonstrates loss of bone covering midtympanic segment of the facial nerve canal with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche.

Graphic of medial wall of the right ear (anterior is to the right) demonstrates loss of bone covering midtympanic segment of the facial nerve canal with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche. Graphic of medial wall of the right ear (anterior is to the right) demonstrates loss of bone covering midtympanic segment of the facial nerve canal with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche.

Coronal bone CT of the right ear in a patient with sensorineural hearing loss (SNHL) shows incidental prolapse of the tympanic portion of the facial nerve . The nerve is slightly larger than normal and devoid of a bony canal. A tiny density just below the facial nerve is a portion of the stapes crus . Coronal bone CT of the right ear in a patient with sensorineural hearing loss (SNHL) shows incidental prolapse of the tympanic portion of the facial nerve . The nerve is slightly larger than normal and devoid of a bony canal. A tiny density just below the facial nerve is a portion of the stapes crus .

Axial CT in a patient with conductive hearing loss shows the protruding tympanic segment of CNVII is strung across the middle ear cavity. Notice that CNVII is prominent in size and touches the crura of the stapes, explaining conductive hearing loss presentation. Axial CT in a patient with conductive hearing loss shows the protruding tympanic segment of CNVII is strung across the middle ear cavity. Notice that CNVII is prominent in size and touches the crura of the stapes, explaining conductive hearing loss presentation.

Coronal left ear temporal bone CT shows the enlarged, prolapsed tympanic segment of CNVII in cross section . Enhanced MR can differentiate protrusion of CNVII (no enhancement) vs. facial nerve schwannoma (enhancement). Coronal left ear temporal bone CT shows the enlarged, prolapsed tympanic segment of CNVII in cross section . Enhanced MR can differentiate protrusion of CNVII (no enhancement) vs. facial nerve schwannoma (enhancement).

Additional Images

Coronal left ear temporal bone CT shows the normal tympanic segment of the facial nerve in cross section along the undersurface of the lateral semicircular canal. Note subtle bone covering and relationship to the oval window niche . Coronal left ear temporal bone CT shows the normal tympanic segment of the facial nerve in cross section along the undersurface of the lateral semicircular canal. Note subtle bone covering and relationship to the oval window niche .

Coronal left ear temporal bone CT reveals a focal mass projecting from the midtympanic facial nerve . The lesion is prolapsed facial nerve, not a facial nerve schwannoma. Facial nerve prolapse can create significant surgical difficulties during stapedectomy. Coronal left ear temporal bone CT reveals a focal mass projecting from the midtympanic facial nerve . The lesion is prolapsed facial nerve, not a facial nerve schwannoma. Facial nerve prolapse can create significant surgical difficulties during stapedectomy.

Coronal temporal bone CT of the right ear shows a soft tissue mass in the oval window niche along the undersurface of the lateral semicircular canal in the location of a normal tympanic facial nerve segment. A prolapsing facial nerve was diagnosed at surgery. Coronal temporal bone CT of the right ear shows a soft tissue mass in the oval window niche along the undersurface of the lateral semicircular canal in the location of a normal tympanic facial nerve segment. A prolapsing facial nerve was diagnosed at surgery.

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