Abstract
Objective
To describe the incidence and management of patients with facial nerve stimulation (FNS) associated with cochlear implant (CI) use in the setting of a prior temporal bone fracture.
Patients
One adult CI recipient is reported who experienced implant associated FNS with a history of a temporal bone fracture. Additionally, a literature search was performed to identify similar patients from previous descriptions of CI related FNS.
Main outcome measures
Presence of FNS after implantation and ability to modify implant programming to avoid FNS.
Results
The patient in the present report experienced FNS for middle and basal electrodes during intraoperative neural response telemetry (NRT) in the absence of any surgical exposure or manipulation of the facial nerve. FNS was absent during device activation, but it recurred during follow-up programming sessions. However, additional programming has prevented further FNS during regular implant use. Four other patients with FNS after temporal bone fracture were identified from the literature, and the present case represents the one of two cases in which reprogramming allowed for implant use without FNS.
Conclusions
CI associated FNS is uncommon in patients with a history of a temporal bone fracture, but it is likely that fracture lines provide a lower impedance pathway to the adjacent facial nerve and thus reduce the threshold for FNS. The present report suggests that, in the setting of a prior temporal bone fracture, NRT is not always a reliable predictor of FNS during implant use, and programming changes can help to mitigate FNS when it occurs.
1
Introduction
Facial nerve stimulation (FNS) associated with cochlear implant (CI) use is an unfortunate occurrence that has been described in as many as 9–14% of implant recipients . Different mechanisms have been proposed to explain implant associated FNS, and a common theme is that reduced impedance pathways within the inner ear can shunt current to the fallopian canal . As such, an increased incidence of FNS has been described in specific patient populations with potential abnormalities in otic capsule impedance. For example, in otosclerosis it is hypothesized that otospongiotic bone has reduced impedance, allowing for stimulation of the facial nerve . In otosyphilis, gummatous periostitis and osteomyelitis as well as periostitis with diffuse endosteal inflammation can similarly lower the threshold for current transfer to the facial nerve . When FNS occurs in these settings, it can often be avoided by changing the CI program strategy. However, FNS cannot always be changed with programming, and in this subset of cases, device explanation may be necessary .
The concept of reduced impedance leading to CI associated FNS has also been applied to patients with prior temporal bone fractures . In such cases, breaks within the otic capsule allow current to propagate beyond the bony confines of the cochlea. Prior literature has suggested that programming changes may not be able to successfully overcome FNS after temporal bone fractures . The present study describes a patient who experienced FNS during intraoperative neural response telemetry (NRT) and subsequent implant use in whom programming modifications over time were used to provide durable avoidance of this stimulation. Additionally, a concurrent literature review provides a simple analysis of cochlear implantation following temporal bone trauma with specific regard to FNS.
2
Materials and methods
In addition to a case report, the present study involved a search of the MEDLINE database in October 2014. Fourteen articles were identified that described cochlear implantation after a temporal bone fracture. Cases in this literature were analyzed if they were presented in the English language and involved placement of a CI for sensorineural hearing loss (SNHL) associated with a temporal bone fracture. Cases were excluded if the trauma that caused SNHL did not involve a temporal bone fracture. Outcome measures included the time that elapsed between injury and implantation and the presence of FNS during NRT or subsequent implant use.
2
Materials and methods
In addition to a case report, the present study involved a search of the MEDLINE database in October 2014. Fourteen articles were identified that described cochlear implantation after a temporal bone fracture. Cases in this literature were analyzed if they were presented in the English language and involved placement of a CI for sensorineural hearing loss (SNHL) associated with a temporal bone fracture. Cases were excluded if the trauma that caused SNHL did not involve a temporal bone fracture. Outcome measures included the time that elapsed between injury and implantation and the presence of FNS during NRT or subsequent implant use.
3
Case report
A 30-year-old man presented with bilateral SNHL approximately 17 months following a fall from a rooftop. The patient noted a bilateral subjective hearing loss immediately following this injury, as well as vertigo, right-sided facial weakness and bilateral tinnitus. At the time of his presentation, physical exam revealed House-Brackmann III facial nerve function on the right side and normal facial function on the left. The external auditory canals were clear bilaterally, and the middle ears appeared well aerated. Audiometric testing revealed profound SNHL bilaterally. Computed tomography (CT) revealed bilateral temporal bone fractures along with focal sclerosis within the lateral semicircular canals. Magnetic resonance imaging (MRI) revealed a decrease in T2 signal within the lateral semicircular canals and confirmed the presence of a cranial nerve VII-VIII bundle within the internal auditory canal (IAC) and cerebellopontine angle (CPA) ( Fig. 1 ). The patient elected to undergo bilateral cochlear implantation with perimodiolar implants. During surgery, a full insertion was achieved bilaterally using standard length electrode arrays. No facial nerve dehiscence was noted. Post-insertion electrophysiologic testing revealed FNS from electrodes 13–22 with the left implant. There was no FNS on the right side. During device activation, approximately three weeks after surgery, FNS was absent. However, stimulation during implant use was subsequently reported by the patient on the left side of his face and throat. Repeat testing confirmed FNS with stimulus of electrodes 15–19 in the left ear. C-levels were decreased until no stimulation was noted. Subsequently, the patient again noted FNS on the left side of his face and throat, and testing confirmed this report with electrode 19 in the left ear. Electrode 19 was deactivated, which provided durable relief from FNS. At approximately 5 months of follow-up, audiometric testing revealed hearing sensitivity in the normal hearing to mild loss range, and HINT sentences (Quiet, in Spanish) scores were 97% in the right ear, 98% in the left ear and 99% bilaterally.
4
Results
With the inclusion of the present case, a total of 50 cochlear implants have been reported in the setting of a prior temporal bone fracture. These cases are summarized in Table 1 . Of this group, five implants (10.0%) were associated with FNS. Of note, the average time between injury and implantation was less in cases where FNS was reported (3.9 versus 1.9 years), but this difference was not statistically significant (p = 0.57). Additionally, in three of the four cases reported in the literature, programming was unable to resolve FNS, leading to device explantation on the affected side and implantation in the contralateral ear .
