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

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.

Unexpected Branch Malformation of the Facial Nerve during Stapes Surgery: Comparison between Intraoperative and Radiographic Findings

The aim of this study was to determine the prevalence of facial nerve (FN) bifurcation in patients who undergo stapes surgery, and to ascertain the correlation between the intraoperative and radiographic findings in cases where an unexpected branch malformation for patients undergoing stapes surgery. Patients who underwent stapes surgery were retroactively examined for confirmed FN bifurcation. Among the 887 patients, 10 had a bifurcated FN confirmed during surgery and had a preoperative high-resolution computed tomography (HRCT) scan. The HRCT scans were examined by two radiologists who were blinded to the operational findings. The diagnostic accuracy of HRCT imaging was examined along with their preoperative audiometry. In total, 887 patients underwent stapes surgery and among them the prevalence of FN bifurcation was 1.13%. These 10 patients had a 1:1 male-female ratio with a mean age of 17.9 ± 7.0 years. From a surgical review, all cases had bifurcation at the horizontal segment of FN, including 1 case of FN trifurcation. The diagnostic difference between HRCT imaging and intraoperation observations for malformations in the middle ear varies widely depending on the location, ranging from 0% to 90%. The prevalence of incus and stapes malformations was high in both imaging and operation findings (≥60%). The detection rate of abnormal positioning and bifurcation of the FN during HRCT imaging was 30% and 0%, respectively. The mean air-bone gap hearing threshold for patients was significantly improved from 42.3 dB preoperatively to 15.6 dB postoperatively without any complications. These results showed that it is extremely difficult to predict the FN bifurcation prior to surgery with a detection rate of 0%. The diagnostic difference between HRCT imaging and intraoperation observations for malformations of different parts of the middle ear varies widely. These results highlight the importance of being vigilant in regard to FN anatomical variation during stapes surgery for any unexpected malformations that are not detected during HRCT evaluation. In addition, the surgical outcomes for these patients were optimal when treatment was performed by senior surgeons.

Whether cochlea involvement on CT in otosclerosis patients impacts the effect of stapedotomy

BACKGROUND

The success rate of stapedotomy in otosclerosis patients with cochlea involvement was unknown.

AIMS/OBJECTIVES

To determine the difference of surgical outcomes and symptomatology in otosclerosis patients with or without cochlea involvement on CT.

MATERIAL AND METHODS

79 otosclerosis patients were included and grouped by HRCT, including cochlear-involved otosclerosis (C-group) or non-cochlear-involved otosclerosis (NC-group, control group). Patients were defined as NC-group in the presence of normal or solely fenestral involvement, or C-group if the hypodensities involve other parts of the labyrinthine bone Patients in the control group were collected at a 2:1 ratio to the C-group with similar follow-up times. Detailed complaints and surgical outcomes were compared between these groups.

RESULTS

Chief complaints were similar in the C-group and NC-group. Although postoperative AC, BC, and ABG decreased significantly in both groups, the success rate was significantly higher in C-group regarding the postoperative ABG ≤10 dB. Furthermore, diffuse lesions may indicate a more severe disease and a poorer prognosis.

CONCLUSIONS AND SIGNIFICANCE

Stapedotomy was effective for clinical otosclerosis. The surgical outcome was inferior favorable for cochlea involvement patients, especially for cases with widely involvement. There was no difference in chief complaints among patients with different CT degree of otosclerosis.

Microtomographic morphometry of the stapedius muscle and its tendon

The aim of this study was to evaluate the morphology of the stapedius muscle and its tendon with the use of microCT and to describe their anatomic relationship with facial nerve and incudostapedial joint. The study was performed on 16 fresh cadaveric temporal bones scanned in microtomography (microCT). Stapedius muscle and its tendon were identified in each set of images. The length of the medial and lateral border of the stapedius tendon (STL-med, STL-lat), width at the insertion to stapes (STW-s), at the point it emerges from the pyramidal eminence (STW-p) and in the half way from the pyramidal eminence to stapes (STW-m), and the length and the width of the belly of stapedius muscle (BSML and BSMW) were measured in modified axial plane. The shortest distance between the facial canal and incudostapedial joint (FN-isj), and between the facial canal and stapedius tendon (FN-st) were measured in the Pöschl plane. The average values of all distances measured were: STL-lat 1.29 ± 0.50 mm, STL-med 1.27 ± 0.44 mm, BSML 2.98 ± 0.51 mm, STW-s 0.47 ± 0.10 mm, STW-p 0.46 ± 0.12 mm, STW-m 0.35 ± 0.12 mm, BSMW 1.26 ± 0.29 mm, FN-isj 1.72 ± 0.33 mm, FN-st 1.35 ± 0.30 mm. The stapedius muscle complex consists of the tendon and the belly, and the border between them in microCT scans is not always evident. The distance between the facial nerve and the incudostapedial joint is greater than the distance between the facial nerve and the stapedius muscle tendon.

Imaging innovations in temporal bone disorders

The development of new imaging techniques coupled with new treatment algorithms has created new possibilities in treating temporal bone diseases. This article provides an overview of recent imaging innovations that can be applied to temporal bone diseases. Topics covered include the role of magnetic resonance (MR) diffusion-weighted imaging in cholesteatomas and skull base epidermoids, whole-body molecular imaging in paragangliomas of the jugular foramen, and MR arterial spin labeling perfusion for dural arteriovenous fistulas and arteriovenous malformations.