Total Transcanal Endoscopic Approach for Selective Facial Nerve Decompression in Traumatic Facial Nerve Palsy

Abstract

Facial nerve palsy is one of the complications of temporal bone fracture. Several approaches can be used for facial nerve decompression which include the middle cranial fossa approach, transmastoid approach and translabyrinthine approach. When the site of injury is identified at the tympanic segment and perigeniculate area, total transcanal endoscopic approach (TTEA) is an excellent surgical option. This approach is safe and less invasive avoiding external incision and mastoid drilling. Our patient showed recovery to House-Brackmann grade II facial function and reduction of the air–bone gap 6 months after the surgery.

Introduction

Head trauma results in approximately 4–30% of skull base fracture with 18–40% involving the temporal bone. Temporal bone fracture can be classified generally into longitudinal, transverse or mixed fracture. Facial nerve palsy is a known complication with the overall rate of 7% [1]. The most common segment involved in post-traumatic facial nerve palsy is considered to be the perigeniculate ganglion and tympanic segment [2]. Management of traumatic facial paralysis varies in the literature in regards of the role, the timing and the type of surgery. The decision mainly depends on the clinical progression, site of injury, electrophysiological tests and imaging findings. A few surgical approaches have been described for facial nerve decompression, these include the middle cranial fossa approach, transmastoid approach and translabyrinthine approach [3]. In the recent years, due to the improvement of knowledge and technique of the use of endoscopy in the field of otology, it is feasible to perform total transcanal endoscopic approach for injury involving the tympanic segment of the facial nerve, which is minimally invasive [4].

Case Report

A 45-year-old man presented with delayed worsening facial nerve palsy following a motor vehicle accident. Post trauma, he also noticed reduced left ear hearing, intermittent tinnitus and left ear bleeding which stopped spontaneously. Upon examination, he was found to have left facial palsy with House-Brackmann grade V. Otoscopy showed a small perforation at the anterior superior part of the tympanic membrane (Fig. 1). Pure tone audiometry (PTA) showed left moderate to profound mixed hearing loss. High resolution computed tomography (HRCT) temporal bone revealed a transverse fracture crossing the tympanic segment of facial nerve and first genu, with soft tissue density in the epitympanum and minimal disruption of incudomalleolar complex (Fig. 2b, c). He was treated conservatively with tapering dose of corticosteroid for 2 weeks and facial physiotherapy. However, there was no improvement of his facial palsy (Fig. 3a, b). The patient subsequently underwent facial nerve decompression via total transcanal endoscopic approach (TTEA).

Fig. 1.

Preoperative left ear otoendoscopy shows perforation at the anterior superior quadrant (blue arrow)

Fig. 2.

HRCT temporal findings. a Fracture line crossing the tympanic segment (red arrow: fracture line, blue arrow: tympanic segment, asterisk: soft tissue density) b Fracture line involving first genu (red arrow: fracture line, blue arrow: first genu)

Fig. 3.

Facial nerve function. a and b Preoperative facial nerve function House-Brackmann grade V c and d Postoperative facial nerve function House-Brackmann grade II

The surgery was performed using 0° and 30° rigid endoscope (Karl Storz) 3 mm in diameter and 15 cm in length. Infiltration using adrenaline 1:10 000 was given at the posterior superior part of the ear canal to reduce bleeding. Curvilinear incision was made from 11 o’clock to 6 o’clock on the external auditory canal and the tympanomeatal flap was elevated and transposed anterior inferiorly. Then, atticotomy was performed using 2 mm cutting and diamond burr to allow access to the epitympanic space. The incudostapedial joint was disarticulated and the incus was removed to expose the entire tympanic segment of facial nerve, from the geniculate ganglion anteriorly up to the second genu posteriorly. Processus cochleariformis served as an important landmark in which the geniculate ganglion lies anterior and superior to it. The lateral semicircular canal was also identified as the posterior limit where the second genu lies inferior to it. Intraoperatively, a fracture line was noticed along the posterior superior part of the external auditory canal, the incudo-malleolar joint was minimally dislocated with a hematoma found overlying the tympanic segment of facial nerve (Fig. 4a). The facial nerve was decompressed by delicate drilling of the bony canal with 1 mm diamond burr followed by neurolysis from the geniculate ganglion to just posterior to the lateral semicircular canal (Fig. 4b). The tympanic segment of the facial nerve was oedematous and non-stimulable up to 3.0 mA. Gelfoam soaked with dexamethasone was placed on top of the exposed part of the facial nerve after the decompression. Ossicular chain reconstruction was performed using autologous graft, by placing a small tragal cartilage plate in between the handle of malleus and head of stapes. Tragal cartilage with attached perichondrium on one side was used for attic reconstruction. The tympanomeatal flap was repositioned and the external auditory canal was filled with Gelfoam and BIPP ribbon gauze.

Fig. 4.

Intraoperative findings. a Endoscopic view shows hematoma on the tympanic segment of the facial nerve (asterisk: hematoma, CT: chorda tympani, TMF: tympanomeatal flap) b Exposed tympanic segment of the facial nerve after decompression and neurolysis (red circle: tympanic segment, blue arrow: head of malleus, FN: facial nerve, S: stapes, TMF: tympanomeatal flap)

Post-operatively, patient had significant recovery of the facial nerve function to House-Brackmann grade II after 6 months (Fig. 3c, d). His hearing was slightly better with no more tinnitus. Repeated PTA showed improvement of the air–bone gap at mid-frequency. Otoscopy showed an intact tympanic membrane with good uptake of the graft to cover the attic defect (Fig. 5).

Fig. 5.

Postoperative view shows intact tympanic membrane and good graft uptake (blue arrow: attic reconstruction, red arrow: cartilage plate used in ossicular chain repair, TM: tympanic membrane)

Discussion

Surgical management of facial nerve palsy secondary to temporal bone fracture consists of several approaches which traditionally include the middle cranial fossa approach, transmastoid approach and translabyrinthine approach. The choice of approach is mainly based on the site of the injury and hearing level. Previously, we commonly performed facial nerve decompression from the tympanic segment up to the mastoid segment of the facial nerve in most of the cases of traumatic facial nerve palsy that did not respond to the conservative treatment [5]. Nowadays, with the advancement of HRCT temporal bone, we are able to precisely locate the course of the fracture line and site of injury of the facial nerve. Therefore, selective facial nerve decompression can be performed at the site of injury, avoiding unnecessary decompression of other part of facial nerve. This case has shown that the selective decompression at the site of injury is adequate with good outcome of facial nerve recovery.

With regards to the injury at the tympanic segment of the facial nerve, transmastoid approach with posterior tympanotomy using microscope is commonly performed. However, it has certain limitation due to the close proximity of the nerve to the dome of lateral semicircular canal and stapes, which results in obstructed view and difficulty in removing the bony shell. This may explain the poor prognosis for the facial nerve recovery in these cases [6]. Other option is by performing endoscopic assisted transmastoid approach, in which the microscope is used first during cortical mastoidectomy, before switching to the endoscope later to visualize the tympanic segment of facial nerve without removing the incus [7]. However, it also involves unnecessary temporal bone drilling, external scar and longer operating time. In order to avoid drilling of the mastoid bone, transcanal microscopic approach to the tympanic segment of facial nerve can be performed as an alternative option. However, it provides limited access to the tympanic segment of facial nerve especially at the precochleariform area and near the second genu resulting in incomplete decompression. Ever since the surgical anatomy of the tympanic facial nerve via the transcanal endoscopic approach was explored and described in details by Marchioni et al., we have an additional and perhaps better surgical option. This approach is less invasive compared to the others and has the advantage of providing direct visualization of the entire tympanic segment from the perigeniculuate area anteriorly up to the second genu posteriorly [4].

Careful selection of the patient for the transcanal endoscopic approach is made by reviewing the HRCT temporal bone imaging and PTA result. The status of the ossicular chain should be assessed. Our patient was a suitable candidate as the fracture line could be seen clearly involving the tympanic segment and the geniculate ganglion. Involvement of the mastoid segment of the facial nerve is a contraindication to this approach. Although transcanal endoscopic approach requires the removal of incus for direct visualization of the entire tympanic segment of facial nerve, the ossicular chain can be reconstructed at the end of the surgery without compromising the current hearing level. For our patient, we used tragal cartilage graft to reconstruct the ossicular chain which also be used later to repair the attic defect. Of course, the preformed prosthesis such as PORP would be a better option for ossicular reconstruction if readily available. This patient sustained left moderate to profound mixed hearing loss from the trauma and post-operatively he showed averagely 30 dB improvement in the air–bone gap. The facial nerve recovery was promising in which House-Brackmann grade I to II was achieved in 83% of the patients treated with transcanal endoscopic approach [8]. Our patient had significant recovery of the facial nerve function to House-Brackmann grade II 6 months after the surgery. So far, no peri-operative and post-operative complications have been reported in the present case series.

But of course the transcanal endoscopic approach has its own limitations. Firstly, adequate dimension of the external ear canal is required to provide smooth access. Moreover, bleeding control maybe difficult in inexperienced hand as this procedure is one-handed where it is not possible to hold a suction instrument with a second hand. There is also a potential risk of stapes injury during the decompression leading to profound hearing loss [4]. However, with the improvement of the endoscopic instrumentation, techniques and knowledge of the endoscopic ear surgery, we believe that the transcanal endoscopic facial nerve decompression will be the choice of treatment for post traumatic facial nerve palsy.

Conclusion

Total transcanal endoscopic approach (TTEA) is an excellent alternative for tympanic segment of facial nerve decompression in post-traumatic facial nerve palsy. This approach is safe, minimally invasive and offers good outcome.

Funding

The authors received no financial support for the research and publication of this article.

Declaration

Conflict of interest

The authors shared no conflicts of interest in regards of the research and publication of this article.

Informed consent

Written informed consent was obtained from the patient to be published in this article.