Anatomical Characteristics of Facial Nerve and Cochlea Interaction

Abstract

Objective: The aim was to study the relationship between the labyrinthine portion (LP) of the facial canal and the cochlea in human inner ear molds and temporal bones using micro-CT and 3D rendering. A reduced cochlea-facial distance may spread electric currents from the cochlear implant to the LP and cause facial nerve stimulation. Influencing factors may be the topographic anatomy and otic capsule properties. Methods: An archival collection of human temporal bones underwent micro-CT and 3D reconstruction. In addition, cochlea-facial distance was assessed in silicone and polyester resin molds, and the association between the LP and upper basal turn of the cochlea was analyzed. Results: Local thinning of the otic capsule and local anatomy may explain the development of cochlea-facial dehiscence, which was found in 1.4%. A reduced cochlea-facial distance was noted in 1 bone with a superior semicircular canal dehiscence but not in bones with superior semicircular canal “blue line.” The otic capsule often impinged upon the LP and caused narrowing. Conclusion: Micro-CT with 3D rendering offers new possibilities to study the topographic anatomy of the human temporal bone. The varied shape of the cross-section of the LP could often be explained by an “intruding” cochlea.

Third Window Syndrome: Surgical Management of Cochlea-Facial Nerve Dehiscence

“…The present study identified a fairly high prevalence of otic capsule dehiscence in high resolution temporal images from 401 subjects with TWS symptoms. However, it should be emphasized that all of our patients had TWS symptoms, whereas the status of TWS symptoms was not reported for the subjects in published prevalence studies (32,44,45). We identified 463 temporal bones (57.7% [463/802]) with a single site of dehiscence (SSCD, near-SSCD, CT-TWS, CFD, cochlea-internal auditory canal, wide vestibular aqueduct, lateral semicircular canal, modiolus and posterior semicircular canal, SSCD and superior petrosal sinus, SSCD and subarcuate artery).…”

“…Although Jyung and colleagues were the first to identify CFD resulting in TWS in 2014, neither of their two patients were managed surgically (28). As interest in this clinical entity producing TWS has increased, there have been three recent studies focused on the histologic, cadaveric micro-CT and clinical CT prevalence of CFD (32,44,45). Fang and coworkers at reported that the histologic prevalence of CFD was 0.59% in 1,020 temporal bone specimens (32).…”

“…In 2014, Robert Jyung et al were the first to identify CFD resulting in TWS; however, neither of their two patients were managed surgically (28). Interest in this clinical entity producing TWS has been mounting, as there have been three recent studies focused on the histologic, CT and cadaveric micro-CT prevalence of CFD (32,44,45). The relationship between CFD and facial nerve stimulation in cochlear implant recipients has also been described in a total of 5 patients (46,47).…”

“…For the cochlea-facial nerve dehiscence cohort who had round window reinforcement procedures performed, the pre-operative mean HIT-6 score was 64.9 (SE 1.1, range 52-69). The post-operative mean HIT-6 score was 42.4 (SE 2.7, range[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. This improvement was highly statistically significant (paired t-test, p < 0.001).…”

Peri-operative electrically evoked auditory brainstem response assessment of facial nerve/cochlea interaction at cochlear implantation

“…The LP of the facial nerve runs from the internal acoustic canal to the geniculate ganglion near the upper basal turn of the cochlea (Ge and Spector, 1981;Proctor and Nager, 1982;Wadin and Wilbrand, 1987). Recently, Schart-Morén et al, (2017) used micro-computer tomography (micro-CT) with 3D rendering to show the extensive anatomic variations of the LP of the facial nerve (Schart-Morén et al, 2017). Because of the limited resolution, a clinical CT often denies discernment of the true anatomical relationship between the cochlea and the facial nerve in cases with a suspected spread of currents to the nerve and suspected rare closeness.…”