295 lines
16 KiB
Markdown
295 lines
16 KiB
Markdown
---
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title: "Middle Ear Prolapsing Facial Nerve"
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docid: "61f6bcaa-f073-4385-b895-dc420ddc8a1e"
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authors:
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- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
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value: "Philip R. Chapman, MD"
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- key: "33151213-01b2-4542-9105-342e006b3915"
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value: "H. Ric Harnsberger, MD"
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breadcrumbs:
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-
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name: "Head and Neck"
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slug: "head-and-neck"
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treeNodeId: "ed24ed8c-5d57-4629-879b-447b82d2973d"
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-
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "19b6b986-97d0-40e7-b317-00f0c5cd8fa2"
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-
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name: "Temporal Bone"
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slug: "temporal-bone"
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treeNodeId: "9ad7d7b2-b2e4-4de2-be04-55ce607560c9"
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-
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name: "Intratemporal Facial Nerve"
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slug: "intratemporal-facial-nerve"
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treeNodeId: "35b77f60-796d-460f-8bac-4a187a150171"
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-
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name: "Pseudolesions"
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slug: "pseudolesions"
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treeNodeId: "eb1df224-339c-469f-857b-200d08f330df"
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-
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name: "Middle Ear Prolapsing Facial Nerve"
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slug: "middle-ear-prolapsing-facial-nerve"
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treeNodeId: null
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category: "Head and Neck"
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cmeTopicId: "7ffe7dc8-0323-438d-bbae-8f3437dd8a25"
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documentVersionId: "04cce8da-a9ae-4396-92b3-02bf6fc2ca6b"
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imageCount: 7
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lastUpdated: "08/26/21"
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pageDescription: "Middle Ear Prolapsing Facial Nerve"
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pageKeywords: "Head and Neck, Diagnosis, Temporal Bone, Intratemporal Facial Nerve, Pseudolesions, Middle Ear Prolapsing Facial Nerve"
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pageTitle: "Middle Ear Prolapsing Facial Nerve | STATdx"
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enhancedTitle: "Middle Ear Prolapsing Facial Nerve"
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type: "DX"
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references: true
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breadcrumbs:
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- "Head and Neck"
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- "Diagnosis"
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- "Temporal Bone"
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- "Intratemporal Facial Nerve"
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- "Pseudolesions"
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- "Middle Ear Prolapsing Facial Nerve"
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---
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# KEY FACTS
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- ## Terminology
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- Definition: Midtympanic facial nerve (CNVII) segment protrudes through bony dehiscence
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- **CNVII dehiscence**refers only to segmental absence of bony covering of CNVII
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- **Prolapsing CNVII**: CNVII protrudes through dehiscence in tympanic CNVII canal
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- ## Imaging
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- **Incidental finding** on temporal bone CT
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- Tubular soft tissue extends from midtympanic CNVII into oval window niche
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- Coronal bone CT
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- Soft tissue mass in oval widow niche
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- Along undersurface of lateral semicircular canal
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- Contiguous with midtympanic segment of CNVII
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- Axial bone CT
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- Hammock-like CNVII spanning middle ear cavity under lateral semicircular canal
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- ## Top Differential Diagnoses
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- Intratemporal facial nerve schwannoma
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- Oval window atresia
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- Persistent stapedial artery
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- Congenital cholesteatoma in facial nerve canal
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- ## Clinical Issues
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- Clinical presentation
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- Most commonly **asymptomatic**
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- Rarely conductive hearing loss present from impingement on stapes
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- Prolapsed facial nerve can be injured during surgical exposure of stapes or oval window
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- ## Diagnostic Checklist
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- Warning to radiologist
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- Prolapsed CNVII in peril during stapedectomy
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- Report & call this finding to ear surgeon
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# TERMINOLOGY
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- ## Definitions
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- Midtympanic facial nerve (CNVII) segment protrudes through bony dehiscence
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- **CNVII dehiscence**refers only to segmental absence of bony covering of CNVII
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- **Prolapsing CNVII**: CNVII protrudes through dehiscence
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Tubular soft tissue extends from midtympanic CNVII into oval window niche (CT)
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- ### Location
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- Undersurface of lateral semicircular canal (LSCC) → oval window niche
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- ### Size
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- Variable; may be subtle or appear mass-like (2-3 mm) within oval window niche
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- ### Morphology
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- Smooth, tubular appearance
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- ## CT Findings
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- ### Bone CT
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- Coronal: Soft tissue mass in oval widow niche
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- Along undersurface of LSCC
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- Contiguous with midtympanic segment of CNVII
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- Axial: Hammock-like CNVII spanning middle ear cavity under LSCC
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- Simple dehiscence (uncovered CNVII) poorly seen unless CNVII prolapsed through dehiscence
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- ## MR Findings
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- No abnormality identified
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- T1 C+ is normal, excluding facial nerve schwannoma
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- ## Imaging Recommendations
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- ### Best imaging tool
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- Axial & coronal thin-section temporal bone CT
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- Best seen on **coronal** at level of oval window
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- Contrast not necessary or recommended
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- ### Protocol advice
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- When protruding CNVII is mass-like, use contrast-enhanced MR to exclude CNVII schwannoma
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- Facial nerve schwannoma enhances
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# DIFFERENTIAL DIAGNOSIS
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- [Intratemporal Facial Nerve Schwannoma](/document/temporal-bone-facial-nerve-schwann-/cf2bcc82-4a1b-4989-adeb-f4e82116111b)
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- Clinical: Hearing loss > > facial nerve palsy
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- CT: Tubular enlargement of CNVII canal
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- Geniculate fossa > tympanic > mastoid segments
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- MR: Enhancing tubular mass enlarges CNVII canal
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- [Oval Window Atresia](/document/oval-window-atresia/35bcc265-c33a-4acf-8e1b-ea5029ae0a74)
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- Clinical: Conductive hearing loss
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- ± external auditory canal (EAC) atresia
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- CT: Facial nerve tympanic segment ectopic
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- Tympanic CNVII in oval window niche
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- [Persistent Stapedial Artery](/document/persistent-stapedial-artery/ca36e22e-2bbc-41c9-a381-ddcf47ed27ca)
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- Asymptomatic vascular variant
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- CT: Absent foramen spinosum
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- Tubular lesion on cochlear promontory
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- Large anterior tympanic segment CNVII
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- ## Congenital Cholesteatoma in Facial Nerve Canal
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- Rare congenital cholesteatoma type
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- CT: Enlargement of CNVII bony canal
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- Most commonly geniculate ganglion area
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Congenital/developmental; can be acquired from cholesteatoma
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- ## Gross Pathologic & Surgical Features
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- Protrusion: Identified in oval window niche during middle ear surgery
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- Dehiscence: Tympanic > > mastoid segment CNVII
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- **Asymptomatic** most commonly
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- Rarely, conductive hearing loss: Impingement on stapes
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- ### Clinical profile
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- **Incidental finding** on temporal bone CT
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- Critical to communicate its presence to surgeon prior to middle ear exploration
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- Easy to injure facial nerve during stapedectomy if CNVII prolapse is present
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- ## Demographics
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- ### Age
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- All ages; congenital lesion
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- ### Epidemiology
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- Simple dehiscence without protrusion ~ 50% of cases
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- Prolapsing facial nerve is rare (~ 1% of cases)
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- ## Natural History & Prognosis
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- Excellent if left alone
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- ## Treatment
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- Careful avoidance at time of middle ear surgery
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# DIAGNOSTIC CHECKLIST
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- ## Image Interpretation Pearls
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- Prolapse often associated with absence of notch defect along undersurface of LSCC
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- If notch is seen, consider alternative explanation
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- ## Reporting Tips
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- Caveat: Prolapsed CNVII in peril during stapedectomy
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- Report & call this finding to ear surgeon
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69aa896c-0d3e-431e-9f74-ded28b2244b6
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## References
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# Selected References
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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](http://www.ncbi.nlm.nih.gov/pubmed/?term=32383094%5Bpmid%5D)
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1. [Amadei EM et al: Revision stapes surgery after stapedotomy: a retrospective evaluation of 75 cases. Ear Nose Throat J. 97(6):E1-4, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=30036415%5Bpmid%5D)
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1. [Gosselin E et al: Predictable prosthesis length on a high-resolution CT scan before a stapedotomy. Eur Arch Otorhinolaryngol. 275(9):2219-26, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=30054728%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=25585185%5Bpmid%5D)
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1. [Yetiser S: The dehiscent facial nerve canal. Int J Otolaryngol. 679708, 2012](http://www.ncbi.nlm.nih.gov/pubmed/?term=22518159%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=21453222%5Bpmid%5D)
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1. [Ozbek C et al: Incidence of fallopian canal dehiscence at surgery for chronic otitis media. Eur Arch Otorhinolaryngol. 266(3):357-62, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=18566822%5Bpmid%5D)
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1. [Di Martino E et al: Fallopian canal dehiscences: a survey of clinical and anatomical findings. Eur Arch Otorhinolaryngol. 262(2):120-6, 2005](http://www.ncbi.nlm.nih.gov/pubmed/?term=15592859%5Bpmid%5D)
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1. [Daniels RL et al: The other ear: findings and results in 1,800 bilateral stapedectomies. Otol Neurotol. 22(5):603-7, 2001](http://www.ncbi.nlm.nih.gov/pubmed/?term=11568665%5Bpmid%5D)
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1. [Park GC et al: Dehiscence of the tympanic segment of the facial nerve. Otolaryngol Head Neck Surg. 123(4):522, 2000](http://www.ncbi.nlm.nih.gov/pubmed/?term=11020202%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=9279867%5Bpmid%5D)
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1. [Swartz JD: The facial nerve canal: CT analysis of the protruding tympanic segment. Radiology. 153(2):443-7, 1984](http://www.ncbi.nlm.nih.gov/pubmed/?term=6484176%5Bpmid%5D)
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## Images
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### Selected Images
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*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 <img src='img/arrows/WS.png'/> with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche.*
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*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 <img src='img/arrows/WS.png'/> with associated mild enlargement and prolapse of tympanic facial nerve into oval window niche.*
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*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 <img src='img/arrows/WS.png'/>. 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 <img src='img/arrows/WC.png'/>.*
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*Axial CT in a patient with conductive hearing loss shows the protruding tympanic segment of CNVII <img src='img/arrows/WS.png'/> is strung across the middle ear cavity. Notice that CNVII is prominent in size and touches the crura <img src='img/arrows/WO.png'/> of the stapes, explaining conductive hearing loss presentation.*
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*Coronal left ear temporal bone CT shows the enlarged, prolapsed tympanic segment of CNVII in cross section <img src='img/arrows/WS.png'/>. Enhanced MR can differentiate protrusion of CNVII (no enhancement) vs. facial nerve schwannoma (enhancement).*
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### Additional Images
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*Coronal left ear temporal bone CT shows the normal tympanic segment of the facial nerve in cross section <img src='img/arrows/WS.png'/> along the undersurface of the lateral semicircular canal. Note subtle bone covering and relationship to the oval window niche <img src='img/arrows/WO.png'/>.*
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*Coronal left ear temporal bone CT reveals a focal mass projecting from the midtympanic facial nerve <img src='img/arrows/WS.png'/>. The lesion is prolapsed facial nerve, not a facial nerve schwannoma. Facial nerve prolapse can create significant surgical difficulties during stapedectomy.*
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*Coronal temporal bone CT of the right ear shows a soft tissue mass in the oval window niche <img src='img/arrows/WS.png'/> 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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