What is expected of the facial nerve in michel aplasia? Anatomic variation

A Novel Classification: Anomalous Routes of the Facial Nerve in Relation to Inner Ear Malformations

OBJECTIVES/HYPOTHESIS

The objective of this study was to classify anomalous facial nerve (FN) routes and to determine their association with inner ear malformations (IEMs).

STUDY DESIGN

Retrospective cross sectional study.

METHODS

The computed tomography images of 519 patients (796 ears) with IEMs were retrospectively evaluated, and the abnormal routes of the FN were classified as: Meatal segment: type 1, normal internal auditory canal (IAC); type 2, narrow IAC; type 3, facial canal (FC) only; type 4: separate FC/duplicated IAC. Labyrinthine segment (LS): type 1, normal; type 2a/b/c, mild/moderate/severe anterior displacement; type 3, superior displacement; type 4: straight LS. Tympanic segment (TS): type 1, normal; type 2, superiorly displaced TS; type 3, TS at the oval window; type 4: TS inferior to the oval window; type 5: unclassified. Mastoid segment: type 1, normal facial recess (FR)/normal mastoid segment; type 2: narrow FR; type 3, unclassified.

RESULTS

In meatal segment classification, a narrow IAC was common in ears with cochlear hypoplasia (CH) (76.1%), and only FC was common in ears with severe IEMs (62.7%) such as Michel deformity, common cavity, and cochlear aplasia. Incomplete partition-III has its unique superiorly displaced LS (100%). CH-IV also has its unique mild anterosuperior displacement. Ears with a superiorly displaced TS usually (93.1%) had aplastic or hypoplastic semicircular canals. The FR is likely to be narrow in CH and severe IEMs.

CONCLUSIONS

The FN route is affected in IEMs, which must be kept in mind when operating on ears with IEMs. Especially in CH cases, all segments of the FN can be abnormal.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:E696-E703, 2020.

Facial nerve anomalies in paediatric cochlear implant candidates: radiological evaluation

Background:

Pre-operative radiological identification of facial nerve anomalies can help prevent intra-operative facial nerve injury during cochlear implantation. This study aimed to evaluate the incidence and configuration of facial nerve anomalies and their concurrence with inner-ear anomalies in cochlear implant candidates.

Methods:

Inner-ear and concomitant facial nerve anomalies were evaluated by magnetic resonance imaging and temporal high-resolution computed tomography in 48 children with congenital sensorineural hearing loss who were cochlear implant candidates.

Results:

Inner-ear anomalies were present in 11 out of 48 patients (23 per cent) and concomitant facial nerve anomalies were present on 7 sides in 4 patients (7 per cent of the total). Facial nerve anomalies were accompanied by cochlear or vestibular malformation.

Conclusion:

Potential facial nerve abnormalities should always be considered in patients with inner-ear anomalies. Pre-operative facial nerve imaging can increase the surgeon's confidence to plan and perform cochlear implantation. Magnetic resonance imaging should be used to detect inner-ear anomalies; if these are identified, temporal high-resolution computed tomography should be used to evaluate the facial nerve.