Introduction
In cases of acute traumatic facial nerve injury, exploration of the facial nerve is generally indicated if more than 90 per cent degeneration is indicated on electroneurography within six days of the onset of paralysis, or if there is radiological evidence of a bony spicule penetrating the nerve.Reference Fisch1 Consideration of the type of fracture and the location of the nerve injury are crucial when planning an appropriate surgical approach. Although a post-auricular, extended mastoidectomy approach may allow adequate exposure in some cases, the middle fossa approach is preferred for the evaluation and treatment of facial nerve injury, as the most frequent site of such injury in blunt trauma cases is the labyrinthine segment and the geniculate ganglion region.Reference Fisch1 However, although these approaches provide good exposure of the superior and/or lateral sides of the geniculate ganglion, they do not provide good access to its inferior surface.
We present a case of traumatic facial nerve injury which was surgically managed by decompression via a trans-tensor tympani approach, because of bony spicules penetrating the inferior aspect of the geniculate ganglion.
Case report
A 30-year-old woman was referred to our department for management of her right-sided facial paralysis. Two weeks previously, she had fallen on some stairs, resulting in subarachnoid haemorrhage, right-sided temporal bone fracture and facial paralysis. She had been admitted to the intensive care unit for 10 days but had received no surgical intervention.
At the time of her referral to our hospital, all of her symptoms related to the intracranial haemorrhage had resolved.
Physical examination revealed haemotympanum in the involved ear. A complete facial nerve palsy was noted, graded VI on the House–Brackmann (HB) scale.
Audiometry showed mild conductive hearing loss with an air–bone gap of 10 dB. Electroneurography indicated 91 per cent degeneration of the facial nerve.
High-resolution, temporal bone computed tomography displayed a longitudinal fracture of the right temporal bone, with a bony fragment penetrating the geniculate ganglion in the inferior part (Figure 1). The bony fragment (Figure 2a) was the fractured septal bone located between the tensor tympani tendon and the facial nerve. There was no evidence of involvement of inner ear structures.
Pre-operative and post-operative coronal computed tomography (CT) scans of the temporal bone. (a, b) The fractured bony spicule and fractured septum are seen between the geniculate ganglion and the tensor tympani tendon (red arrows). (c, d) Computed tomography scans of the contralateral, intact ear at the same level, showing the intact facial nerve (arrowheads) and the tensor tympani tendon and muscles (arrow). (e, f) After removal of the fractured segment inferior to the geniculate ganglion, CT scans taken one month after surgery show the successfully decompressed facial nerve (arrowhead).
(a) Surgical photograph and (b) schematic drawing of the operative field. The separated tensor tympani tendon and muscles have been removed from their groove and displaced antero-laterally using alligator forceps. The bony fragment is identified and removed inferiorly without any damage to the facial nerve. SCC = semicircular canal
Although the middle fossa approach provides good exposure of the superior surface of the geniculate ganglion, it was not considered in this case as the main pathology was located beneath the geniculate ganglion. Instead, we used a post-auricular, extended posterior tympanotomy approach to gain access to the geniculate ganglion area, and then a trans-tensor tympani approach to remove the bony spicules from beneath the geniculate ganglion itself. During cortical mastoidectomy, the mastoid air cells were seen to be filled with organised blood clots and granulation tissue accompanied by several bony segments caused by fractures in the mastoid area. After posterior tympanotomy, the incudostapedial joint was separated. The incus was then removed in order to obtain a complete view of the tympanic segment of the facial nerve all the way to the geniculate ganglion. The malleus head was also removed to enable further visualisation of the lateral surface of the geniculate ganglion. A large bony fragment was seen to penetrate the facial nerve inferiorly, but it was too large and dangerously positioned (being located medial and inferior to the facial nerve) to be removed without risking damage to the facial nerve (Figure 2). Therefore, the tendon of the tensor tympani muscles was cut out of the malleus neck, after which the lateral bony sheath of the tensor tympani tendon was thinned out using a diamond drill. The tensor tympani tendon was grasped with alligator forceps, elevated from the groove and displaced antero-laterally. The bony fragment was displaced inferiorly into the newly created space and then successfully removed, without any damage to the facial nerve. The ossicular chain was then reconstructed using a partial ossicular replacement prosthesis to bridge the space between the intact stapes and the malleus.
At one month post-operatively, audiometry showed an air–bone gap of less than 10 dB, and the HB grade was III.
Four months after decompression, the patient's facial expression was nearly normal (HB grade II). Electromyography showed partial axonotmesis with signs of regeneration in the patient's facial muscles.
Discussion
Selection of the surgical approach for facial nerve decompression should be based on the injury sites and the cochlear or vestibular status. It has been reported that a post-auricular, extended mastoidectomy approach can provide exposure of the facial nerve from the geniculate ganglion to the stylomastoid foramen.Reference Fisch and Esslen2, Reference Farrior3 However, a middle fossa approach is generally preferred for longitudinal fractures, as the most frequent facial nerve injury sites following blunt trauma are the labyrinthine segment and the geniculate ganglion region, and the middle fossa approach provides the best exposure for management of the labyrinthine segment.Reference Fisch1, Reference Farrior3, Reference Goin4 On the other hand, when cochlear and vestibular function have been lost, the translabyrinthine approach should be considered as it exposes the entire intratemporal course of the facial nerve, including the labyrinthine and geniculate ganglion areas.Reference Pulec5
• The middle fossa approach is usually preferred for treatment of perigeniculate facial nerve injury, as it exposes the superior and/or lateral sides of the ganglion
• However, it does not sufficiently expose the inferior side of the geniculate ganglion
• When needed, this aspect can be successfully accessed via a trans-tensor tympani approach
In our patient, the only lesion precisely localised by temporal bone computed tomography was the bony fragment penetrating the geniculate ganglion at the base. As previously described, traditional approaches to the geniculate ganglion focus on exposure of its superior and lateral surfaces; we needed an alternative approach enabling transposition of the tensor tympani tendon and muscles from their original canal in order to remove the bony fragment located beneath the geniculate ganglion (Figure 2). The trans-tensor tympani approach consists of exposure of the tensor tympani tendon and muscles by drilling out the lateral bony sheath of the tensor tympani canal, followed by antero-lateral transposition of the tensor tympani tendon and muscles; in the present case, this approach enabled exposure and removal of the bony fragments at the base of the geniculate ganglion.
The trans-tensor tympani approach gives additional inferior access to the geniculate ganglion but none to the labyrinthine segment of the facial nerve. This is a limitation of the presented approach. Injury to the labyrinthine segment should be treated via a middle fossa approach. A possible complication of this approach is conductive hearing loss, which is the most commonly reported complication following extended transmastoid decompression.Reference May and Klein6 May and Klein identified an air–bone gap of 15 dB or greater in 14 per cent of 43 patients undergoing intratemporal facial nerve surgical procedures, and a sensorineural loss (primarily at high frequencies) in 51 per cent.Reference May and Klein6 Using the trans-tensor tympani approach, it is also possible to injure such structures as the chorda tympani nerve, vestibule, cochlea, sigmoid sinus, dura and brain. There were no such complications in our case.
