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Acta Oto-Laryngologica Case Reports

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Bifurcation of the intratemporal facial nerve: Arare anatomical anomaly

Constantina Christou, Johan Wikström & Karin Strömbäck

To cite this article: Constantina Christou, Johan Wikström & Karin Strömbäck (2018) Bifurcation ofthe intratemporal facial nerve: A rare anatomical anomaly, Acta Oto-Laryngologica Case Reports,3:1, 15-18, DOI: 10.1080/23772484.2018.1436405

To link to this article: https://doi.org/10.1080/23772484.2018.1436405

© 2018 The Author(s). Published by InformaUK Limited, trading as Taylor & FrancisGroup.

Published online: 08 Feb 2018.

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CASE REPORT

Bifurcation of the intratemporal facial nerve: A rare anatomical anomaly

Constantina Christoua, Johan Wikstr€omb and Karin Str€omb€acka

aDepartment of Surgical Sciences, Section of Otorhinolaryngology and Head and Neck Surgery, Uppsala University Hospital, Uppsala,Sweden; bDepartment of Surgical Sciences, Unit of Radiology, Uppsala University Hospital, Uppsala, Sweden

ABSTRACTThe anatomical position of the facial nerve is a critical factor in determining surgical candidacyin patients with congenital aural atresia (CAA). All patients with CAA must preoperatively beevaluated using a grading score based on information gained from a high resolution CT scan. Inpatients not suitable for surgical reconstruction, implantation of novel hearing implants isincreasingly used for hearing rehabilitation. We, here, describe a bifurcation of the intratemporalpart of the facial nerve in a 5-year old boy with CAA undergoing implantation with a boneconductive hearing device.

ARTICLE HISTORYReceived 22 November 2017Revised 30 January 2018Accepted 31 January 2018

KEYWORDSCongenital aural atresia;facial nerve; anomaly

Introduction

Congenital aural atresia (CAA) is caused by theabnormal development of the first and second bran-chial arches [1]. As the absence of an external earcanal precludes fitting of conventional hearing aids,the hearing rehabilitation must be provided throughsurgical reconstruction of the ear canal and middleear or implantation of a hearing implant. Since theatresiaplasty is associated with an abundance of com-plications such as restenosis and recurrent granula-tions of the reconstructed ear canal, different hearingimplants such as bone conduction or active middleear devices are used for hearing rehabilitation. One ofthe most important anatomical prerequisites for surgi-cal repair is the position of the facial nerve, whichmay also influence on the application of hearingimplants [2].

Case report

A 3-year-old boy with bilateral CAA and microtia wasreferred to the ENT clinic. Since birth, he was fittedwith bilateral BAHA on soft band. CT examination(Figure 1) revealed on the right side a narrowed mid-dle ear space, a sclerotic oval window and an atreticround window. The tympanic segment of the facialnerve was positioned lateral to the posterior semicir-cular canal and a bony canal, interpreted as chorda

tympani, was identified inferior of the lateral semicir-cular canal. This canal appeared to communicate withthe tympanic segment of the facial nerve. The pneu-matization of the mastoid was poor and the middleear was opaque. The right external ear canal was nar-rowed and filled with soft tissue. The external ear wasvalued as Microtia grade II.

On the left side, the external ear was normal. Onthe CT scan, the left middle ear space was evaluatedas narrow and the oval window was partially sclerotic.Although the tympanic portion of the facial nerve wascovering the oval window and the mastoid portionwas slightly anterior positioned, the course of thefacial nerve on this side was considered as less aber-rant than on the right side. Moreover, the size of theround window was normal and the external auditoryear canal was very narrow. Consequently, the patientwas not eligible for surgical reconstruction. At the ageof four he was implanted with a fixture appliedBAHA. The fitting was limited through severe skinproblems and pain and he was therefore planned foran implantation with a semi-implantable BonebridgeR

device on the right side. A renewed CT scan at theage of five years showed unchanged anatomicalconditions.

At the mastoidectomy, a thin string of soft tissuein a bony canal was detected in the middle part of themastoid. The canal was positioned posterior of theremnant of the external bony canal wall running

CONTACT Karin Str€omb€ack [email protected] Departments of Surgical Sciences, Section of Otorhinolaryngology and Head andNeck Surgery, Uppsala University, Uppsala, Sweden� 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unre-stricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ACTA OTO-LARYNGOLOGICA CASE REPORTS2018, VOL. 3, NO. 1, 15–18https://doi.org/10.1080/23772484.2018.1436405

superficially to the posterior part of the microticexternal ear. The nerve was monitored during thewhole operation with a Nerve monitor (Neurosign).The structure was directly stimulated with 0.8mVwithout response. To avoid contact with the unknownstructure, the implant was therefore placed furtherposteriorly than initially planned.

After discharge on the day of the operation hecomplained about a numb feeling on the right side ofthe face. A facial nerve dysfunction graded HouseBrackman (HB) IV was observable at the first postop-erative day, more evident in the ramus zygomaticusand ramus marginalis mandibulae. The patient wasimmediately explanted and the structure was identi-fied as a portion of the facial nerve.

The electrophysiological examination one monthafter explantation revealed an axonal blockage in 50%and a conductive blockage in 50%. Several activemotoric units were measured in the frontal muscle atthe EMG, less activity documented in the orbicularisand oculi muscles. The function of the facial nervewas completely restored after 4 months.

A renewed evaluation of the CT scan including 3Doblique reformats showed the duplication of the facialnerve at the transition between the tympanic and mas-toid portion with one lateral component displaying anaberrant course laterally in the mastoid cavity(Figure 2). The second component of the duplicatednerve had a slight abnormal ventral position in themastoid and covered the oval window. The duplication

was located directly below the lateral semi-circularcanal (Figures 3 and 4).

One year after explantation, the boy was aided witha bone-aided hearing aid, ADHEARR (Med-El,Innsbruck, Austria)

Discussion

The development of the facial nerve is closely relatedwith the development of the middle ear and the mas-toid process as these structures derive from the firstand second branchial arches and the facial nervederives from the second branchial arch [2]. The orien-tation of the facial nerve is established in the 8thweek of gestation but the ultimate position and cover-ing of the facial nerve are determined by furtherdevelopment of structures like the stapes, labyrinthinecapsule, mastoid bone and tympanic bone. The finalposition of the nerve in the temporal bone is estab-lished during the second year of life.

The most common abnormalities of the facial nervein CAA are displacement of the nerve and bonydehiscence in the tympanic segment [3]. The bonydehiscence can also be seen in normal temporal bonesup to 53% and it is considered as a normal anatom-ical variation [4]. An aberrant course of the nerveappears in 0.3% of normal ears. Goldsztein andRoberson presented the anatomical findings in 209atresia cases and found that in 39% of the cases, thefacial nerve had an abnormal course, located more

Figure 1. Oblique high-resolution CT. This oblique slice attempts to follow the mastoid portion of the right facial nerve. Anaberrant duplicated third portion of the facial nerve is seen, crossing laterally in the mastoid bone.

16 C. CHRISTOU ET AL.

lateral and anterior, not identified in 1% and dehis-cent in 57% [5].

Bifurcation of the facial nerve was described in theliterature but is a very rare anomaly. Marquetreported bifurcation of the intratemporal part of thefacial nerve in 0.7% from anatomical specimens [6]. Itwas also described in a series of 972 patients under-going cochlear implantation were seven patients hadan abnormal facial course and two of those hade aduplication of the facial nerve [7].

We found only two previous case reports of congeni-tal duplication of the facial nerve. In one of these reports,a duplicated mastoid segment of the facial nerve in ayoung female with middle ear anomalies was described[8] and another author reported three cases [9].

Facial nerve injury is a well-recognized risk of atre-siaplasty. Its incidence has been quoted in the litera-ture to range from 0% to 11% [10]. Since theintroduction of perioperative facial nerve monitoring,the risk probably has decreased.

We conclude that although the course of the facialnerve in atretic ears is almost normal in most cases themeticulous evaluation of the preoperative CT scan ismandatory in the surgical planning. In present casestudy, the bifurcation of the nerve was overseen despiterepeated imaging. The mechanical pressure of the skinretractor used at the surgery was considered as thecause of the postoperative facial nerve dysfunction.

Summary

Surgery of CAA remains one of the most challengingprocedures in otology. As facial nerve anomalies,

Figure 2. Placement of the Bonebridge in the mastoid.

Figure 3. Transverse high-resolution CT of the temporal boneat the level of the facial nerve bifurcation. Aberrant portion isdirected laterally (white arrow). Normal portion is depicted byblack arrow.

Figure 4. Transverse high-resolution CT of the temporal bone,slightly inferior to Figure 3, where the two portions of thefacial nerve are seen separated (white arrow: aberrant portion,black arrow: normal portion).

ACTA OTO-LARYNGOLOGICA CASE REPORTS 17

often, are associated with middle- and inner earanomalies the careful evaluation of the preoperativeCT scan in different projections is essential before asurgical intervention and a prerequisite for a success-ful surgery.

Disclosure statement

A written consent for publication was obtained by thepatient’s parents.

The authors report no conflict of interests.

References

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[2] Jahrsdoerfer RA. Embryology of the facial nerve. AmJ Otol. 1988;9:423–426.

[3] Di Martino E, Sellhaus B, Haensel J, et al. Fallopiancanal dehiscences: a survey of clinical and

anatomical findings. Eur Arch Otorhinolaryngol.2005;262:120–126.

[4] Jahrsdoerfer RA. The facial nerve in congenitalmiddle ear malformations. Laryngoscope. 1981;91:1217–1225.

[5] Goldsztein H, Roberson JB Jr. Anatomical facialnerve findings in 209 consecutive atresia cases.Otolaryngol Head Neck Surg. 2013;148:648–652.

[6] Marquet J. Congenital malformations and middle earsurgery. J Roy Soc Med. 1981;74:119–128.

[7] Song JJ, Park JH, Jang JH, et al. Facial nerve aberra-tions encountered during cochlear implantation.Acta Otolaryngol. 2012;132:788–794.

[8] Jakkani RK, Ki R, Karnawat A, et al. Congenitalduplication of mastoid segment of facial nerve: arare case report. Indian J Radiol Imaging.2013;23:35–37.

[9] Glastonbury CM, Fischbein NJ, Harnsberger HR,et al. Congenital bifurcation of theintratemporal facial nerve. Am J Neuroradiol. 2003;24:1334–1337.

[10] Lambert PR. Congenital aural atresia: stability ofsurgical results. Laryngoscope. 1998;108:1801–1805.

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