The sensitivity and accuracy of a cone beam CT in detecting the chorda tympani

Radiological Evaluation of Tympanic Segment of Chorda Tympani Nerve in Normal Ears: An Ultra-High-Resolution CT Study

BACKGROUND

To visualize the course of the tympanic segment of chorda tympani nerve (CTN) using ultra-high-resolution computed tomography (U-HRCT).

METHODS

A hundred and fourteen ears with no evident otologic pathologies were included. The tympanic segment of CTN was divided into four portions: periannular, posteromalleal, malleal, and anteromalleal. The length of the periannular portion running along the tympanic annulus was recorded. Four points of interest (the beginning and end of the posteromalleal and anteromalleal portions) were selected to perform distance measurements relative to the tip of the malleus manubrium. Differences in lengths and distances were compared in terms of ear sides and sexes.

RESULTS

The length of the periannular portion was 2.49 ± 1.16 mm. The beginning of the posteromalleal portion was located more laterally on the right side than on the left side (mean: 4.09 mm vs. 3.92 mm, P = 0.016). The end of the posteromalleal portion was located more inferiorly on the right (mean: 2.11 mm vs. 2.26 mm, P = 0.018). The beginning of the anteromalleal portion on the right was located more laterally than that on the left (mean: 2.60 mm vs. 2.45 mm, P = 0.027). The start and end of the anteromalleal portion were more posteriorly located in women than in men (both Ps < 0.001).

CONCLUSIONS

The course of the tympanic segment of normal CTN was comprehensively visualized by U-HRCT. Preoperative evaluation of the tympanic segment of CTN might be helpful in avoiding iatrogenic injury during middle ear surgery.

[Applications of cone beam computed tomography of the craneofacial structure in medical specialties. A review]

Cone-beam computed tomography (CBCT) of the craniofacial structure has demonstrated its usefulness in the dental area during the last decades, thus it has become a fundamental tool in the diagnosis, planning, and evaluation of treatment, and although it was not developed for the exclusive use in dentistry, as it is commonly considered, it is used in other areas such as medicine. It is specifically used in the head and neck area where different medical specialties interact, and at the same time these interact with dental specialties, so knowing the advantages of CBCT over different imaging technologies in the medical area is necessary. The purpose of this review was to describe the applications of observation, diagnosis, planning, and evolution of treatments using maxillofacial HSCT in different medical specialties. This work highlights the use of TCHC in different medical applications and highlights where it is most useful compared to other technologies.

Endoscopic Anatomy of the Chorda Tympani: Systematic Dissection, Novel Anatomic Classification, and Surgical Implications

HYPOTHESIS

A transcanal endoscopic approach enables visualization of the variable course of the chorda tympani inside the middle ear.

BACKGROUND

The chorda tympani is the longest intrapetrous branch of the facial nerve. Despite having been investigated in several studies, a description of its tympanic tract from an endoscopic point of view is lacking in the literature.

METHODS

We performed transcanal endoscopic dissections of 44 human cadaveric head and ear specimens. The entry point of the chorda tympani into the middle ear was classified into four categories according to its location, and as covered or dehiscent according to its appearance. The chordal eminence (CE) was defined as absent, shallow, intermediate, prominent, or fused, based on its shape and extension. The relationship of the chorda tympani to adjacent bony and ligamental structures was assessed.

RESULTS

The tympanic tract of the chorda tympani was divided into three portions. The periannular segment was dehiscent in 54.5% of specimens, with type II being the most frequent entry point configuration (52.3%). In the interossicular segment, the nerve consistently passed lateral to the incus and medial to the malleus. The course of the intrapetrous segment was independent from the conformation of the tensor fold and supratubal recess.

CONCLUSION

The transcanal endoscopic approach allows a detailed description of tympanic segment of the chorda tympani. Novel anatomic classifications of the chorda tympani and CE are proposed herein to highlight their possible surgical implications during otologic procedures.

'Black Bone' magnetic resonance imaging as a novel technique to aid the pre-operative planning of posterior tympanotomy for cochlear implantation

Purpose: 'Black Bone' magnetic resonance imaging (BB MRI) is a novel sequence developed as an alternative to computed tomography (CT) for osseous imaging. We explored its potential utilisation in the pre-operative surgical planning of posterior tympanotomy for cochlear implantation through depiction of the mastoid facial nerve (mFN) canal and the posterior canaliculus of the chorda tympani (ChT), thus defining the facial recess. Methods: Twenty five adult patients were prospectively imaged with a dedicated BB MRI sequence. A consensus qualitative BB MRI 'visibility score' for the confidence of demonstration of the mFN canal and the posterior canaliculus of the ChT was recorded, as well as a 'corresponding score' to determine whether the neural structures on BB MRI corresponded to the paths of the nerves on a previous CT study. Results/discussion: The BB MRI sequence was able to clearly delineate the course of mFN in 100% of cases and that of ChT in 72%, with their courses corresponding to those depicted on CT in almost all cases. Maximum intensity projections with 7 mm slabs provided the optimal simultaneous demonstration of mFN, ChT and round window along the posterior tympanotomy surgical approach. Conclusion: The proposed BB MRI sequence reliably depicts mFN and ChT in the majority of cases, with a performance comparable to that of CT. It is proposed that it will be a useful adjunct to MRI protocols as part of cochlear implant assessment in those centres where CT is not routinely performed.

Detectability of minute temporal bone structures with ultra-high resolution CT

OBJECTIVE

Computed tomography (CT) is the imaging tool of choice in the diagnosis of temporal bone lesions. With the recent progress in imaging technology, CT with higher spatial resolution (Ultra-high resolution CT) has become available in the clinical setting. The purpose of this study is to evaluate the visibility of small temporal bone structures using ultra-high resolution CT.

MATERIAL AND METHODS

The visibility of 27 minute temporal bone structures on ultra-high resolution CT images was evaluated. Non-helical axial scans were performed in 18 normal hearing ears without previous otologic diseases. Visibility was scored by an experienced radiologist and otologist.

RESULTS

Minute temporal bone structures including the ossicular chain, the crus of the stapes, the greater superficial petrosal nerve, and the anterior malleolar ligament were clearly visualized on ultra-high resolution CT. The stapedius muscle tendon and the chorda tympani exiting the posterior canaliculus and coursing medial to the malleus could be visualized.

CONCLUSION

Ultra-high resolution CT provides good visualization of small temporal bone structures in normal subjects.

The gray scale value of ear tissues undergoing volume-rendering high-resolution cone-beam computed tomography

OBJECTIVE

When the thresholds for VR reconstruction from multi-slice CT images are changed, problems develop when assessing pathologies in the absence of standardized thresholds. The advantages of CBCT include lower radiation exposure compared with other techniques and better visualization of small ear structures. However, a disadvantage is that the scanner provides unstandardized gray scale values, thus not CT numbers (Hounsfield units, HU).

METHODS

We analyzed 88 sets of volume data obtained from temporal bones. The gray scale values were measured in aerated areas (two sites), along the ossicular chain (four sites) and in a bone area (one site) in the external and middle ears, and in soft tissue areas (five sites) and bone areas (two sites) in the inner ear.

RESULTS

The standard male and female gray scale values were 2448-2970 and 2585-3091 for the aerated areas, 3248-4945 and 3359-5223 for the ossicular chains, 3368-4109 and 3371-4147 for soft tissues, and 4790-5776 and 5044-5959 for bone, respectively. Sex significantly affected the values (p<0.05). Significant differences between aerated areas and ossicular chains, and between soft tissues and bone, were evident (all p<0.0001).

CONCLUSION

Volume-rendering (VR) images obtained by cone-beam computed tomography (CBCT) can be standardized simply by using fixed thresholds.

Possibility of differentiation of cochlear electrodes in radiological measurements of the intracochlear and chorda-facial angle position

Due to an increasing number of cochlear implantations, quality control has become more important. In addition to intraoperative biophysical measurements, radiological imaging is another possibility. An upcoming technique regarding this is Cone Beam CT (CBCT). Sixty-five data sets (35 Nucleus Contour Advance–Cochlear; 30 Flex Soft–MedEl) of postoperative imaging by CBCT (Accu-I-tomo F17, Morita, Kyoto, Japan) underwent further evaluation. Insertion angle, height of the cochlea, distance of the electrode to the medial or lateral wall, angle between chorda tympani and facial nerve and the precise position of the electrode cable in the facial-chordal angle were determined. The typical difference between the perimodiolar and lateral course of the electrodes could also be shown in radiological measurements. This demonstrates the accuracy and advantage of CBCT in visualisation of small structures with fewer metal artifacts. Furthermore, in 75% of patients, the angle of the chorda and facial nerve could be visualised. Significant differences in dependence of the electrode type for the relation of them to the facial nerve could be seen. In conclusion, CBCT achieves reliable visualisation and detailed imaging-based measurements of the intracochlear position of different cochlea electrodes. Additionally, clinically known differences can be reproduced. Even visualisation of the position of the electrode in the chorda-facial angle is possible. Therefore, CBCT is a useful tool in intra- and postoperative control of cochlear implants.

Cochlear implantation in a subject with a narrow facial recess: Importance of preoperative radiological findings

OBJECTIVE

This case report aims to emphasize the importance of preoperative computed tomography to evaluate the anatomy of the facial recess (FR) in order to prevent complications during cochlear implantation (CI) and to discuss alternative surgical approaches for the management of a narrow FR. Failure to notice this anomaly may result in facial nerve (FN) injury or inability to complete CI.

CASE PRESENTATION

A 50-year-old female with bilateral sensorineural hearing loss presented for CI. High-resolution CT (HRCT) demonstrated a narrow FR; specifically the space between the vertical segment of the FN and external auditory canal (EAC) was narrow. A section of the EAC was removed to obtain adequate exposure and was repaired with a cartilage graft following CI.

CONCLUSION

CI surgery may be difficult in patients with a narrow FR. Such surgical difficulty could be avoided if cochlear implant surgeons have adequate preoperative radiological imaging to evaluate the anatomy of the temporal bone. HRCT is the only modality that can detect this abnormality preoperatively. If the surgeon identifies this abnormality on preoperative HRCT, an alternative surgical technique could be used.