Introduction
Cochlear implantation is a safe and effective method of auditory rehabilitation to partially restore hearing to individuals with severe-to-profound hearing loss, who fail to benefit from a conventional hearing aid. The increasing popularity for and experience with the surgical procedure of implantation has enabled relatively low complication rates.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1 Facial nerve paresis, despite the nerve's close proximity to the site of surgical implantation, is a rare post-operative complication.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1
The timing of facial nerve paresis is commonly referred to as either immediate or delayed.Reference Alzharni, Lenarz and Teschner2 The difference in prognosis between these two groups suggests that the causative mechanisms differ. Patients with delayed-onset facial nerve paresis are more likely to fully recover, and typically do so within months of onset. However, those with an immediate onset weakness, if they do recover, take longer, and this is most often because of intra-operative factors such as direct mechanical and thermal injury.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1 Delayed-onset facial weakness is less well understood and not so commonly addressed in the literature. Several mechanisms have been postulated, and include: an inflammatory process of the nerve or surrounding tissue, direct pressure on the nerve (for instance by the cochlear implant electrode), or reactivation of a herpes virus.Reference Alzharni, Lenarz and Teschner2
The vast majority of delayed-onset facial nerve paresis cases described in the current literature are reported to have occurred within the first month of implantation.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1–Reference Tarkan, Tuncer, Özdemir, Sürmelioğlu, Çetik and Kiroğlu4 A literature review performed for the purposes of this case report identified only two cases of facial nerve paresis occurring many years after cochlear implant insertion. In each of these cases, a cause for the facial nerve paresis was identified, such as bony dehiscence of the facial nerve canalReference Alzharni, Lenarz and Teschner2 and endocochlear inflammation.Reference Benatti, Castiglione, Trevisi, Bovo, Rosignoli and Manara5
We report the case of facial nerve paresis occurring in an adult patient three years after cochlear implantation. Interestingly, there was complete resolution of facial nerve function once the cochlear implant device was explanted. Although this would suggest a causal relationship between the implanted electrode and the facial weakness, despite investigations, no evidence of such a relationship was found. We present this case of delayed-onset facial nerve paresis, along with a brief discussion of other similar cases, and discuss the potential for management of this condition.
Case report
A 60-year-old lady developed a right-sided facial weakness 3 years following right-sided cochlear implantation. Examination at the time of presentation revealed a normal external auditory canal and tympanic membrane bilaterally, with no evidence of infection over the cochlear implant site, yet there was a right-sided lower motor neuron facial nerve paresis (House–Brackmann grade IV). Blood testing revealed normal inflammatory markers. At the time of presentation, the patient had no auditory perception through the cochlear implant.
The cochlear implant electrode array had always functioned extremely well for the patient, until two years post-implantation when the patient developed symptoms of right-sided otalgia, dizziness and decreased auditory perception. The aforementioned symptoms, including sound quality issues, were initially resolved with programming of her cochlear implant. However, four months prior to the onset of her facial weakness, this lady presented to the otolaryngology department on numerous occasions with increasing pain around the cochlear implant site and decreasing speech perception. All testing of the cochlear implant device showed it to be functioning correctly; however, the performance decrement was due to increased impedances causing several channels to go out of compliance. Interestingly, the patient also experienced facial nerve stimulation on the remaining channels; hence, it was not possible to deliver sufficient stimulation for the patient to perceive useful sound.
Clinical examination findings and inflammatory markers at each of these presentations were all normal. A computed tomography (CT) scan of the petrous bones was performed approximately two weeks prior to the onset of the facial nerve paresis. Two consultant otorhinolaryngologists and an experienced neuroradiology consultant retrospectively reviewed the CT scan images; all were in agreement that there was no obvious electrode contact with the facial nerve throughout its course. Imaging also showed no evidence of bony remodelling or destruction of the otic capsule.
Upon presentation with the right facial nerve paresis, the patient was admitted to the otolaryngology ward, and given intravenous antibiotic, antiviral and corticosteroid therapy. The lack of improvement in facial function after 48 hours of treatment, along with the decrement in auditory performance, led to the decision to explant the right cochlear implant. The internal component of the cochlear implant was found to be entirely intact, with the electrode array fully inserted through the round window. The bony covering of the facial nerve was fully intact in the vertical and horizontal portions, and there was no active middle-ear or mastoid disease. The patient was reviewed in the recovery room immediately post-operation and the facial nerve function was documented to have already improved (House–Brackmann grade II).
A magnetic resonance imaging scan of the internal auditory meatus (IAM) was performed on post-operative day 1. This showed abnormal soft tissue signal material in the right cochlea and IAM. However, the nature of this abnormality was uncertain and was thought to possibly represent haemorrhage related to cochlear implant removal, rather than a definite infective or inflammatory process.
The patient was subsequently discharged 3 days post-explantation and reviewed 3 weeks later in the otolaryngology out-patient clinic. Examination revealed complete resolution of the right-sided facial nerve paresis. The option of left-sided cochlear implantation was discussed, and the patient is currently undergoing the appropriate investigations and assessments for suitability.
Discussion
Our case report describes a delayed-onset post-operative facial nerve paresis leading to explantation of the cochlear implant due to failure of symptom resolution after 48 hours of conservative treatment in addition to performance decrement of the device. This case is particularly interesting for a number of reasons. For instance, the onset of the facial paresis occurred years after implantation. The literature suggests that delayed-onset facial paresis typically occurs hours to days after implantation.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1–Reference Tarkan, Tuncer, Özdemir, Sürmelioğlu, Çetik and Kiroğlu4 The literature review performed as part of this report identified only two other cases of delayed-onset facial weakness occurring years after implantation, both of which were in children.
The first identified case occurred four years after cochlear implantation.Reference Alzharni, Lenarz and Teschner2 Revision surgery showed that the facial nerve was not protected with bone; hence, chronic pressure of the electrode to the nerve and infection owing to the cochlear implant were both considered potential causes of the facial nerve paresis. In terms of the second identified case, this occurred six years after cochlear implant insertion. Clinical, neuroimaging and surgical findings suggested a secondary inflammation process of unknown origin, with endocochlear and internal auditory canal phlogosis. Granulating formations in the middle and inner ear were thought to have given rise to partial erosion of the cochlea, with fibrosis and ossification of the basal and apical turns. Explantation led to complete resolution of the facial nerve paresis.Reference Benatti, Castiglione, Trevisi, Bovo, Rosignoli and Manara5
Late-onset facial nerve paresis (i.e. occurring after years, rather than hours or days) following cochlear implantation is poorly understood. Several mechanisms have been suggested in the literature, such as an inflammatory process of the nerve or surrounding tissue, direct pressure on the nerve (for instance, by the cochlear implant electrode), or an infection or reactivation of a herpes virus.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1, Reference Fayad, Wanna, Micheletto and Parisier3 This makes our reported case even more interesting, as none of these factors were identified to be a definite cause of the facial nerve paresis. Clinical examination findings, blood test results and appearances at the time of device explantation were all contrary to an infective or inflammatory process. Intracranial imaging did not reveal any convincing evidence of contact of the cochlear implant electrode array with the facial nerve. Immunological testing for the presence of herpes viruses was not carried out; however, as the facial nerve weakness immediately improved following explantation, we do not consider viral infection to be a likely cause of the paresis in our reported case.
• Facial nerve paresis is a rare post-operative complication of cochlear implantation
• The vast majority of delayed-onset facial nerve paresis cases occur within the first month of implantation
• However, ours and limited other reports describe late-onset cases that occurred years after implantation
• Potential causative factors have been identified, but the phenomenon can be idiopathic, as indicated in our case
• Prognosis for recovery of delayed-onset facial nerve paresis seems promising, despite the common requirement for device explantation
Regardless of the aetiology of delayed-onset facial nerve paresis following otological surgery, treatment typically includes observation, corticosteroids, antiviral therapy, and surgical decompression where medical intervention fails.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1–Reference Fayad, Wanna, Micheletto and Parisier3 However, most of the evidence relating to medical intervention therapies is assumed knowledge from the Bell's palsy literature, where corticosteroids have been shown to significantly improve outcomes compared to placebo.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1, Reference Sullivan, Swan, Donnan, Morrison, Smith and McKinstry6–Reference Hato, Yamada, Kohno, Matsumoto, Honda and Gyo8 The benefit of combined corticosteroid and antiviral treatment remains controversial, with most high-level evidence failing to show an advantage over steroids alone.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1, Reference Sullivan, Swan, Donnan, Morrison, Smith and McKinstry6, Reference Engström, Berg, Stjernquist-Desatnik, Axelsson, Pitkäranta and Hultcrantz7, Reference Quant, Jeste, Muni, Cape, Bhussar and Peleg9, Reference Lockhart, Daly, Pitkethly, Comerford and Sullivan10 The expected outcome of delayed-onset facial nerve paresis has been reported as excellent, regardless of treatment.Reference Thom, Carlson, Olson, Neff, Beatty and Facer1 However, the case report and literature review in this study tell us that late-onset facial nerve paresis commonly requires device explantation to resolve symptoms when a trial of conservative treatment fails.
Conclusion
Delayed-onset facial nerve paresis following cochlear implantation most commonly occurs relatively early in the post-operative period, typically within the first month. However, our report and other limited reports describe late-onset cases that occurred many years after implantation. Potential causative factors have been identified; however, the phenomenon can be idiopathic, as indicated in our case. Despite this, prognosis for recovery seems promising, despite the common and unfortunate requirement for device explantation.
Competing interests
None declared
