Development of the stapedius muscle canal and its possible clinical consequences

Stapedius muscle: Don't mistake it for a branch of the facial nerve in images

OBJECTIVE

The relationship between the stapedius muscle and the vertical part of the facial nerve is important for surgery. The study aims to understand the spatial relationship between the stapedius muscle and the vertical part of the facial nerve in ultra-high-resolution computed tomography (U-HRCT) images.

METHODS

A total of 105 ears from the heads of 54 human cadavers were analyzed using U-HRCT. The location and direction of the stapedius muscle were evaluated with the facial nerve as the reference. The integrity of the bony septum between the two structures and the distance between the transverse sections were examined. Paired Student's t-test and the nonparametric Wilcoxon test were applied.

RESULTS

The lower end of the stapedius muscle emerged at the upper (45 ears), middle (40 ears), or lower (20 ears) level of the facial nerve and was positioned medial (32 ears), medial posterior (61 ears), posterior (11 ears), or lateral posterior (1 ear) to the facial nerve. The bony septum was not continuous in 99 ears. The distance between the midpoints of the two structures was 1.75 mm (IQR=1.55-2.16 mm).

CONCLUSION

The spatial relationship between the stapedius muscle and the facial nerve was varied. They were close to each other and in most cases the bony septum was not intact. Preoperative familiarity with the relationship between the two structures is helpful for avoiding unwanted injury to the facial nerve in surgery.

Location of the stapedius muscle with reference to the facial nerve in patients with unilateral congenital aural atresia: implication for active middle ear implants surgery

Background: Detailed investigations of the stapedial muscle (SM) in congenital aural atresia (CAA) patients have yet to be adequately conducted.Objectives: To assess image variations in the mastoid segment of the facial nerve (FN) and SM in CAA.Materials and methods: A total of nine patients comprising of 9 ears with unilateral CAA were studied. The courses of the FN and SM were evaluated from the basic point to 1 mm intervals between the mastoid portion of FN, and measured from the mean X and Y values in each group.Results: The atresia side of FN among the Y values showed significant differences compared to the contralateral side. In terms of the SM, there were no significant differences in both the X and Y values. The stapedial muscle of the CAA patients was located medially to the FN. Conversely, the distance from the PSC to the FN revealed no significant differences with regard to the X and Y values for each group.Conclusion: The current observations revealed that the SM is located more posterior to the FN in CAA patients, and this is mainly attributed to the laterally and anteriorly displaced FN.

Does Mastoid Pneumatization Affect Facial Canal Dimensions and Distances of Facial Tympanic Segment-Scutum and Lateral Semicircular Canal-Scutum?

OBJECTIVES

In the present study, we investigated whether mastoid pneumatization affects facial canal dimensions and distances of facial tympanic segment and scutum, and lateral semicircular (LSS) canal and scutum.

METHODS

One hundred sixty-one temporal multidetector computed tomography scans were reviewed. Patients with unilateral sclerotic mastoid pneumatization (no aeration) (group 1, n = 81) and unilateral total mastoid pneumatization (100.0% aeration) (group 2, n = 80) were included. Facial canal dimensions at the labrythine, tympanic, and mastoid segments; facial canal dehiscence and length; and facial tympanic segment-scutum and LSS canal-scutum distances were evaluated.

RESULTS

In the present study, facial canal dimensions of labyrinthine, tympanic, and mastoid segments in total pneumatized mastoid group were significantly lower than sclerotic mastoids on axial and coronal images (P < 0.05). Facial tympanic segment and scutum distance of the sclerotic mastoid group was significantly lower than those of the total pneumatized mastoid group (P < 0.05). However, LSS canal-scutum distance was not different between both groups (P > 0.05). The LSS canal-scutum distance of the females was lower than those of the males (P < 0.05). Facial canal dehiscence ratio was 11.3% and 11.1% in sclerotic and total pneumatized mastoids, respectively. The mean ± SD length of the dehiscence was 2.46 ± 1.29 mm in pneumatized mastoids and 1.92 ± 0.68 mm in sclerotic mastoids.

CONCLUSIONS

In cholesteatoma cases, scutum erosion may occur. Because facial tympanic segment and scutum distance decreased in sclerotic mastoids compared with completely pneumatized ones, maximum care must be taken in the operations for avoiding to damage facial canal and nerve. Revision cases may be more difficult because of distorted anatomy. However, in pneumatized mastoids, the mean length of the facial canal was more than 2 mm, which must be kept in mind during operations.

High-resolution computed tomographic features of the stapedius muscle and facial nerve in chronic otitis media

OBJECTIVE

To improve preoperative recognition of the morphologic features of stapedius muscle and facial nerve in cases of chronic otitis media by providing a systemized description using temporal bone high-resolution computed tomography (HRCT).

STUDY DESIGN

Retrospective review of HRCT scans from 212 patients.

SETTING

Tertiary hospital affiliated to Fudan University.

PATIENTS

Men and women undergoing surgery for chronic otitis media. No preference for demographics or side presenting otitis media.

INTERVENTION

Therapeutic surgery.

MAIN OUTCOME MEASURE

Location and morphology of stapedius muscle and facial nerve.

RESULTS

The stapedius muscle was encountered in 90.5% of axial (n = 181) and 87% of coronal sections (n = 174), and differences between sides and genders were not significant (p > 0.05). Five categories of anomalies or pathologic features were identified in axial layers, and 3 categories were identified in coronal layers. Two axial and 2 coronal CT planes were found to be especially significant in imaging the facial nerve and its morphology (p < 0.001), whereas axial planes were more apt to show stapedius muscle features. Other pathologic features were also observed significantly more from specific CT imaging planes.

CONCLUSION

The presence the stapedius muscle and the morphology between the stapedius muscle and the facial nerve vary between different observation areas, and some CT planes provide more useful information than others. The imaging planes outlined in this study can be used to systematically and correctly identify certain facial nerve and stapedius muscle features and clarify unfamiliar pathologic anatomy in preoperative planning.

Imaging the facial nerve: a contemporary review

Imaging plays a critical role in the evaluation of a number of facial nerve disorders. The facial nerve has a complex anatomical course; thus, a thorough understanding of the course of the facial nerve is essential to localize the sites of pathology. Facial nerve dysfunction can occur from a variety of causes, which can often be identified on imaging. Computed tomography and magnetic resonance imaging are helpful for identifying bony facial canal and soft tissue abnormalities, respectively. Ultrasound of the facial nerve has been used to predict functional outcomes in patients with Bell's palsy. More recently, diffusion tensor tractography has appeared as a new modality which allows three-dimensional display of facial nerve fibers.