Dehiscent mastoid segment of the facial nerve

A Rajeshwary; MK Goutham; K S. Gangadhara Somayaji

doi:10.4103/amhs.amhs_56_18

TEACHING IMAGES

Year : 2018 | Volume : 6 | Issue : 1 | Page : 187-188

Dehiscent mastoid segment of the facial nerve

A Rajeshwary¹, MK Goutham¹, K S. Gangadhara Somayaji²
¹ Department of ENT, K.S. Hegde Medical Academy, Mangalore, Karnataka, India
² Department of ENT, Yenepoya Medical College, Mangalore, Karnataka, India

Date of Web Publication

11-Jun-2018

Correspondence Address:
Prof. Dr. K S. Gangadhara Somayaji
Department of ENT, Yenepoya Medical College, Mangalore, Karnataka
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/amhs.amhs_56_18

Abstract

Course of the facial nerve through the temporal bone is known for variations, the commonest being dehiscence of the bony fallopian canal. It is common to have dehiscence of the horizontal tympanic segment; however, complete dehiscence of the vertical mastoid segment is very rare. Here is the report of one such case as a teaching image.

Keywords: Dehiscence, facial nerve, mastoid segment

How to cite this article:
Rajeshwary A, Goutham M K, Somayaji K S. Dehiscent mastoid segment of the facial nerve. Arch Med Health Sci 2018;6:187-8

How to cite this URL:
Rajeshwary A, Goutham M K, Somayaji K S. Dehiscent mastoid segment of the facial nerve. Arch Med Health Sci [serial online] 2018 [cited 2023 Jan 28];6:187-8. Available from: https://www.amhsjournal.org/text.asp?2018/6/1/187/234108

Case Report

A 30-year-old female presented to ENT OPD with left-sided intermittent ear discharge for the past 10 years. On examination, she had a dry central perforation of the tympanic membrane on the left side with the mild conductive hearing loss. A diagnosis of the chronic mucosal type of otitis media in the inactive stage was made. The patient was posted for left cortical mastoidectomy and tympanoplasty under general anesthesia. On exploring the mastoid through post-aural route, mastoid antrum was identified, and drilling was continued to complete the cortical mastoidectomy. A pale, soft structure was noted immediately inferior and medial to aditus resembling polypoidal mucosa. However, on tracing the structure further inferiorly, it was found to be the facial nerve which was not covered by the bony Fallopian canal ^{More Details} [Figure 1]. Subsequently, the procedure was completed without causing any damage to the facial nerve. The patient did not have any facial paresis postoperatively.

Figure 1: The dehiscent mastoid segment of the facial nerve. A: Dehiscent vertical segment from the level of aditus to digastric ridge. B: Posterior wall of bony external auditory canal. C: Mastoid antrum. D: Mastoid tip

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Discussion

In the middle ear, the facial nerve is enclosed in the bony fallopian canal.^[1] The fallopian canal has a narrow, labyrinthine segment, horizontal tympanic segment, and a vertical mastoid segment.^[1] Facial canal dehiscence is often associated with the squamosal type of otitis media which occurs secondary to bone erosion caused by cholesteatoma.^[2] In such cases, the patient might present with facial paresis. However, several cadaveric dissections and radiological imaging techniques such as high resolution computed tomography now have revealed many anatomical variations in the course of the facial nerve including displacement, dehiscence of the bony fallopian canal, and reduplication of the nerve in the normal population.^[3] The tympanic segment is found to be dehiscent in 8%–55% of cases in different studies.^[4] However, dehiscence of the mastoid segment is very rare and is mainly associated with other congenital abnormalities involving external and middle ear. In our case, although there was a mucosal type of chronic otitis media, it was neither associated with cholesteatoma nor with any other congenital ossicular abnormalities. Good knowledge of anatomy and possible variations in the course of the facial nerve is required to avoid complications in micro ear surgery.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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