Anatomical Features of Intratemporal Course of Facial Nerve and its Variations

An evaluation of morphometry and dehiscence of facial canal: a systematic review and meta-analysis of observational studies

INTRODUCTION

The facial canal (FC) is an extensive bony canal that houses the facial nerve and occupies a central position in the petrous part of temporal bone. It is of utmost significance to otologists due to its dehiscence and relationship to the inner or middle ear components. The main objectives of current investigation are to detect variations in the reported values ​​of FC anatomy that may occur due to different methodology and to elucidate the influence of age and ethnic factors on the morphological features of FC.

METHODS

The methodology is adapted to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Pooled weighted estimation was performed to calculate the mean length, angle, and prevalence of dehiscence.

RESULTS

The cross-sectional shape of FC varied from circular to ellipsoid index and is 1.45 [95% CI, 0.86-2.6]. The mean length of the FC is 34.42 mm [95% CI, 27.62-40.13 mm] and the mean width or diameter is 1.35 mm [95% CI, 1.013-1.63 mm]. The length of the FC in fetuses and children is 21.79 mm [95% CI, 18.44-25.15 mm], and 26.92 mm [95% CI, 23.3-28.3 mm], respectively. In meta-regression, age is observed as a predictor and accounts for 36% of the heterogeneity. The prevalence of FC dehiscence in healthy temporal bones is 29% [95% CI, 20-40%].

CONCLUSION

The different segments of the FC exhibit significant variability and an unusually high incidence of dehiscence, which could potentially have clinical implications for the etiopathogenesis of facial nerve dysfunction.

Endoscopic Findings on Facial Nerve Anatomy During Exclusive Endoscopic Stapedotomy: Clinical Considerations and Impact on Surgical Results

BACKGROUND

Variations along the facial nerve (FN) course present considerable challenges in the surgical treatment of otosclerosis, often complicating the procedure. Existing knowledge of its tympanic tract and its implications primarily comes from microscopical procedures. This study aims to assess endoscopic findings of FN anatomy in a healthy tympanic cavity and its impact on the stapedotomy procedure, focusing on the risk of complications and functional hearing outcomes.

METHODS

A retrospective study on exclusive endoscopic stapedotoplasties between October 2014 and October 2021 at our Otorhinolaryngology University Department was carried out. An evaluation of intraoperative endoscopic findings reviewed in surgical descriptive and/or video records was conducted to assess their potential negative impact on the surgery. Demographic data, preoperative and postoperative hearing thresholds, as well as intraoperative and postoperative complications were analyzed.

RESULTS

One hundred fifty-seven subjects were included. A FN partially overhanging the oval window was observed in 7.3% (n=12): 10 prolapsing with bony canal dehiscence and 2 without any detected dehiscence. Each procedure was successfully completed without any issues related to the anomalous anatomy, and in no case, switching to the microscope for the handling of the prosthesis near the dehiscent nerve was required. No facial paralysis occurred, with an early- or long-term postoperative House-Brackman grade of 1 (n=157, 100%). Only 3/157 patients (1.9%) showed a sensorineural threshold reduction of ≥20 dB HL, but a significant air-bone gap improvement was observed (mean closure of 18.36 dB HL, P -lt; .0001).

CONCLUSION

The endoscope promotes a concrete description of tympanic FN anatomy, and endoscopic stapes surgery appears to be a safe and viable option when dehiscent or prolapsed FNs reduce the footplate's exposure.

Facial canal dehiscence, dural exposure, and labyrinthine fistula in middle ear cholesteatoma and mastoiditis

PURPOSE

To analyze the prevalence and associations of facial canal dehiscence (FCD), dural exposure, and labyrinthine fistula in chronic otitis media (COM) with and without cholesteatoma.

METHODS

This was a retrospective study performed in an academic medical center. Patients who received tympanoplasty with mastoidectomy for COM with and without cholesteatoma were included. The prevalence of FCD, dural exposure, and labyrinthine fistula in COM with and without cholesteatoma (mastoiditis) and their relationships were analyzed.

RESULTS

A total of 189 patients, including 107 (56.6%) females and 82 (43.4%) males, with 191 ears were included. There were 149 cases (78.0%) of cholesteatoma and 42 patients (22.0%) with mastoiditis. FCD was noted in 27.5% of patients with cholesteatoma and 9.5% of patients with mastoiditis. Dural exposure was found in 21 patients (14.1%) with cholesteatoma and 4 patients (9.5%) with mastoiditis. Eleven patients (7.4%) with cholesteatoma and 1 patient (2.4%) with mastoiditis had labyrinthine fistula. Patients with a labyrinthine fistula had nearly a fivefold greater chance (OR = 4.924, 95% CI = 1.355-17.896, p = 0.015) of having FCD than those without a fistula. There was a positive correlation between dural exposure and labyrinthine fistula (P = 0.011, Fisher's exact test).

CONCLUSION

FCD, dural exposure, and labyrinthine fistula are common complications in COM. These complications are more frequently observed in patients with cholesteatoma than in patients with mastoiditis. Surgeons should pay more attention to the treatment of COM.

Endoscopic vs microscopic facial nerve decompression for traumatic facial nerve palsy: a randomized controlled trial

PURPOSE

To explore a minimally invasive trans-canal endoscopic facial nerve decompression for traumatic facial nerve palsy and compare it with microscopic facial nerve decompression.

METHODS

35 and 38 patients underwent endoscopic and microscopic facial nerve decompression, respectively, for traumatic facial nerve palsy. Onset of symptoms, type of temporal bone fracture, day of surgical intervention following trauma, ossicular chain status and nature of insult to facial nerve were observed. Time period for recovery (House Brackmann grade ≤ 3), long term recovery rates, pre- and post-operative hearing status, surgical time and post-operative pain were compared between groups.

RESULTS

Maximum patients in endoscopic and microscopic groups (77.1% and 76.3%, respectively) had acute onset of symptoms. 57.1% (20/35) had longitudinal, 17.1% (6/35) had transverse and 25.7% (9/35) had mixed fractures in endoscopic group. In the microscopic group, 57.9% (22/38) had longitudinal, 18.4% (7/38) had transverse and 23.7% (9/38) had mixed fractures. The mean (± S.D.) post-operative air-bone gap in endoscopic and microscopic group were 16.47 ± 4.5 dB and 19.4 ± 5.2 dB, respectively, which was statistically significant. The mean (± S.D.) time period for recovery of endoscopic and microscopic groups were 14.4 ± 5 days and 22.5 ± 7 days, respectively (p value < 0.05). The difference in post-operative pain between the two groups was also statistically significant. The difference in long term recovery rates was not statistically significant (p > 0.05).

CONCLUSIONS

Endoscopic facial nerve decompression results in early recovery, less post-operative pain and better post-operative air-bone gap closure when compared to conventional microscopic technique.

Morphometric properties of the fallopian canal: comparison of two nations with different ethnic origins

PURPOSE

To determine the widths of fallopian canal segments (labyrinthine segment, geniculate ganglion, tympanic segment mastoid segment and stylomastoid foramen), in two nations with different ethnic origins, and to analyze the differences in between.

METHODS

We retrospectively analyzed temporal computerized tomographies of 102 individuals including 38 Turks and 64 Syrians. The widths of right and left labyrinthine (LS), tympanic (TS), mastoid (MS), geniculate ganglion (GG) and stylomastoid foramen (SF) segments of the fallopian canal were measured.

RESULTS

The narrowest segment was LS (right: 1.04 ± 0.23 mm, left: 1.03 ± 0.22 mm) and the widest segment was SF (right: 1.82 ± 0.41 mm, left: 1.85 ± 0.35 mm). From the widest to the narrowest, the widths of the FC segments were sorted as SF > GG > MS > TS > LS. The widths of the fallopian canal segments were similar between right and left sides, and between males and females (p > 0.05). Our results indicated that both right and left GG were significantly wider in Turks (p < 0.001 for both), however right LS (p < 0.001) and left TS (p = 0.005) were significantly wider in Syrian refugees. Two groups did not show any differences for the widths of other FC segments (p > 0.05).

CONCLUSIONS

Nations of different ethnic origins may have differences concerning the widths of some segments of the fallopian canal. Further studies with a larger sample size including clinical data of the patients are needed to clarify our findings, and to determine whether these differences have any clinical implications.