Features and management of a schwannoma of the chorda tympani and review of the literature.

Intrinsic facial nerve tumors are rare lesions. Among the different histology types, schwannomas is the most frequently reported in literature. Other histological types of facial nerve tumors are hemangiomas, meningiomas, and neurofibromas. Chorda tympani schwannomas (CTSs) are extremely rare entities and are considered as an independent subgroup of facial nerve schwannomas because of their clinical characteristics. The aim of this report is to present the clinical and radiological features and the management of a CTS in a 27-year-old male presenting with conductive hearing loss.

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

BACKGROUND: To visualize the course of the tympanic segment of chorda tympani nerve (CTN) using ultra-high-resolution computed tomography. METHODS: A hundred and fourteen ears with no evident otologic pathologies were included. The tympanic segment of CTN was divided into 4 portions as follows: 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 ultra-high-resolution computed tomography. Preoperative evaluation of the tympanic segment of CTN might be helpful in avoiding iatrogenic injury during middle ear surgery.

Classification of the Chorda Tympani: An Endoscopic Study.

OBJECTIVES: To determine the ability of preoperative computed tomography (CT) to predict the variable surgical anatomy of the chorda tympani nerve (CTN) based on endoscopic tympanotomy. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: We identified 192 ears of 162 patients who underwent transcanal endoscopic ear surgery from August 2013 to June 2018. Patients with middle ear malformations, revision surgeries, myringoplasty, and cholesteatoma involving the CTN were excluded. INTERVENTIONS: An intraoperative endoscopic image depicting the chorda tympani was selected for each patient and classified into one of five types. Preoperative CT images were analyzed to match the pictorial classification. MAIN OUTCOME MEASURES: The visible tympanic segment of the chorda tympani was classified into the following five types: external auditory canal (EAC), detached, attached long, attached short, and ultrashort. RESULTS: A total of 128 ears from 101 patients ranging in age from 2 to 81 years were enrolled. The EAC, detached, attached long, attached short, and ultrashort types of CTN were found in 7 (5.5%), 6 (4.7%), 84 (65.6%), 18 (14.0%), and 13 (10.2%) patients, respectively. The presence of the EAC type could be predicted by preoperative CT while the other four types could be predicted by binning into two groups, with a sensitivity of 0.61 and specificity of 0.72. CONCLUSION: The variable anatomy of the chorda tympani nerve can be classified into five major groups based on endoscopic tympanotomy.

Facial nerve and chorda tympani schwannomas: Case series, and advantages of using non-rigid registration of post-enhanced 3D-T1 Turbo Field Echo and CT images (TURFECT) in their diagnosis and surgical treatment.

OBJECTIVE: Facial nerve schwannomas (FNSs) and chorda tympani schwannomas are very rare. Diagnosis of these tumors is sometimes difficult, and treatment consensus has not yet been reached. We report here a series of cases of FNS and chorda tympani schwannoma and highlight the usefulness of our newly developed technique of non-rigid registration of post-enhanced 3D-T1 Turbo Field Echo and CT images (TURFECT) in their diagnosis and treatment. METHODS: MRI images were adjusted with the corresponding CT images in terms of angle and position in order to index the anatomical structures. The well-enhanced T1-Gd+ lesions of tumors having good blood flow show up as bright red after color mapping. RESULTS: Between 2014 and 2018, five patients were diagnosed with schwannomas in the temporal bone: three with FNS and two with chorda tympani schwannoma. Gd-enhanced MRI showed only a high-intensity mass, and we could not detect the relationship between tumor-like mass and bone (including the ossicles) by MRI only. In contrast, TURFECT was very useful for diagnosing the precise location, allowing us to decide on an endoscopic surgical plan in some of our cases. An endoscope enabled visualization of the medial wall of the tympanic cavity and the status of the tumors, thus we could successfully perform transcanal endoscopic biopsy and resections. CONCLUSION: TURFECT can be very useful for diagnosis of FNSs and chorda tympani schwannomas and for deciding surgical treatments such as a transcanal endoscopic approach.

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.

Inflammatory stimuli acutely modulate peripheral taste function.

Inflammation-mediated changes in taste perception can affect health outcomes in patients, but little is known about the underlying mechanisms. In the present work, we hypothesized that proinflammatory cytokines directly modulate Na(+) transport in taste buds. To test this, we measured acute changes in Na(+) flux in polarized fungiform taste buds loaded with a Na(+) indicator dye. IL-1ß elicited an amiloride-sensitive increase in Na(+) transport in taste buds. In contrast, TNF-α dramatically and reversibly decreased Na(+) flux in polarized taste buds via amiloride-sensitive and amiloride-insensitive Na(+) transport systems. The speed and partial amiloride sensitivity of these changes in Na(+) flux indicate that IL-1ß and TNF-α modulate epithelial Na(+) channel (ENaC) function. A portion of the TNF-mediated decrease in Na(+) flux is also blocked by the TRPV1 antagonist capsazepine, although TNF-α further reduced Na(+) transport independently of both amiloride and capsazepine. We also assessed taste function in vivo in a model of infection and inflammation that elevates these and additional cytokines. In rats administered systemic lipopolysaccharide (LPS), CT responses to Na(+) were significantly elevated between 1 and 2 h after LPS treatment. Low, normally preferred concentrations of NaCl and sodium acetate elicited high response magnitudes. Consistent with this outcome, codelivery of IL-1ß and TNF-α enhanced Na(+) flux in polarized taste buds. These results demonstrate that inflammation elicits swift changes in Na(+) taste function, which may limit salt consumption during illness.

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

The facial recess approach through posterior tympanotomy is the standard approach in cochlear implantation surgery. The size of the facial recess is highly variable, depending on the course of the chorda tympani. Despite their clinical importance, little is known about the sensitivity and accuracy of imaging studies in the detection of the chorda tympani. A total of 13 human temporal bones were included in this study. All of the temporal bones were submitted to a cone beam CT (Accuitomo, Morita, Japan). The multi-planar reconstruction images were rotated around the mastoid portion of the facial nerve to locate the branches of the facial nerve. A branch was diagnosed as the chorda tympani when it entered the tympanic cavity near the notch of Rivinus. The distance between the bifurcation and the tip of the short crus of the incus was measured. In all temporal bones, the canal of the chorda tympani or the posterior canaliculus was detected. In the CT-based evaluation, the average distance from the bifurcation to the incus short crus was 12.6 mm (8.3-15.8 mm). The actual distance after dissection was 12.4 mm (8.2-16.4 mm). The largest difference between the distances evaluated with the two procedures was 1.1 mm. Cone beam CT is very useful in detecting the course of the chorda tympani within the temporal bone. The measured distance is accurate.

High resolution CT study of the chorda tympani nerve and normal anatomical variation.

OBJECTIVE: The aim of this study was to define the normal anatomical variation of the course of the CTN through the mastoid temporal bone on high resolution CT (HRCT). MATERIALS AND METHODS: Retrospective review of 27 consecutive normal HRCT bilateral temporal bones (n = 54, 14 males and 13 females, mean age 41 years) reconstructed at 0.4-mm slice thickness specifically measuring (1) origin of CTN from the posterior genu of the facial nerve (CNVII) and (2) the lateral-most position of the CTN from the mastoid segment of CNVII. RESULTS: The mean distance of the CTN origin from the mastoid segment of CNVII was 11.5 mm (standard deviation, SD = 3.2, 95% CI 10.7-12.3) with no statistically significant difference between the left and right side observed (p = 0.08). The most lateral distance of the CTN from CNVII was a mean of 1.3 mm (SD = 0.6, 95% CI 1.2-1.7), range 0-2.5 mm and again no statistical significance between contralateral sides was observed (p = 0.11). These measurements demonstrated an excellent level of agreement between observers as assessed by intraclass correlation calculation. CONCLUSIONS: Reproducible measurements demonstrate variability of the CTN in both its origin from the mastoid segment of CNVII and its lateral-most course. Precise description of the course of the CTN with HRCT may be useful for planning of otologic surgery and limiting inadvertent nerve injury.

Surgical anatomy of the chorda tympani: a micro-CT study.

PURPOSE: Iatrogenic injury of the chorda tympani is a well-known complication of middle ear surgery, yet few studies have investigated the intraosseous course of the nerve. The aim of this study was to accurately delineate the posterior canaliculus in the temporal bone, particularly its relationship to the tympanic annulus, which is critical during the insertion of subannular ventilation tubes. METHODS: Forty temporal bones from 27 cadavers (15 male, mean age 75 years, 13 bilateral) were scanned using a micro-CT scanner, and standardised 3-D multiplanar reconstructions were generated using a software platform. The posterior canaliculus was measured in relation to reproducible bony landmarks. RESULTS: In 6 (15%) specimens, the chorda tympani originated from the facial nerve outside the skull and in 34 (85%) from within the facial canal at a mean of 3.2 ± 1.8 mm above the stylomastoid foramen. The posterior canaliculus was 12.3 ± 3.8 mm long and converged on the tympanic sulcus cranially. It entered the middle ear at 62 ± 10% of the height of the tympanic membrane. CONCLUSIONS: This novel micro-CT study defines the precise anatomy of the posterior canaliculus housing the chorda tympani and provides data that may help the otologic surgeon protect the nerve from iatrogenic injury.

Automatic segmentation of the facial nerve and chorda tympani in pediatric CT scans.

PURPOSE: Cochlear implant surgery is used to implant an electrode array in the cochlea to treat hearing loss. The authors recently introduced a minimally invasive image-guided technique termed percutaneous cochlear implantation. This approach achieves access to the cochlea by drilling a single linear channel from the outer skull into the cochlea via the facial recess, a region bounded by the facial nerve and chorda tympani. To exploit existing methods for computing automatically safe drilling trajectories, the facial nerve and chorda tympani need to be segmented. The goal of this work is to automatically segment the facial nerve and chorda tympani in pediatric CT scans. METHODS: The authors have proposed an automatic technique to achieve the segmentation task in adult patients that relies on statistical models of the structures. These models contain intensity and shape information along the central axes of both structures. In this work, the authors attempted to use the same method to segment the structures in pediatric scans. However, the authors learned that substantial differences exist between the anatomy of children and that of adults, which led to poor segmentation results when an adult model is used to segment a pediatric volume. Therefore, the authors built a new model for pediatric cases and used it to segment pediatric scans. Once this new model was built, the authors employed the same segmentation method used for adults with algorithm parameters that were optimized for pediatric anatomy. RESULTS: A validation experiment was conducted on 10 CT scans in which manually segmented structures were compared to automatically segmented structures. The mean, standard deviation, median, and maximum segmentation errors were 0.23, 0.17, 0.18, and 1.27 mm, respectively. CONCLUSIONS: The results indicate that accurate segmentation of the facial nerve and chorda tympani in pediatric scans is achievable, thus suggesting that safe drilling trajectories can also be computed automatically.

CT-scan imaging of iron marked chorda tympani nerve: anatomical study and educational perspectives.

The chorda tympani nerve (CTN) is the last collateral branch of the facial nerve in its third intraosseous portion just over the stylomastoid foramen. After a curved course against the medial aspect of the tympanum where it is likely to be injured in middle ear surgery, CTN reaches the lingual nerve in the infratemporal fossa. Knowledge of CTN topographic anatomy is not easily achieved by the students because of the deep location of this thin structure. The aim of this study was to assess the spatial relationships of the CTN in the infratemporal fossa. Therefore, ten nerves were dissected in five fresh cadavers. All the nerves were catheterized with a 3/0 wire. After a meticulous repositioning of surrounding structures, standard X-ray and CT scan examinations were performed with multiplanar acquisitions and three-dimensional surface rendering reconstructions. Ventral projection of the CTN corresponded to the middle of the maxillary sinus. Lateral landmark was the mandibular condyle. The CTN was present and unique in all the dissections. The average length of the nerve, as measured on CT scans, was 31.8 mm (29-34, standard deviation of 1.62); the anastomosis of the CTN to the lingual nerve was located at a mean 24.9 mm below the skull base (24-27, standard deviation of 0.99), approximately in the same horizontal plane as the lower part of the mandibular notch. The acute angle opened dorsally and cranially between CTN and LN measured mean 63.2° (60-65, standard deviation of 1.67). Three-dimensional volumetric reconstructions using surface rendering technique provided realistic educational support at the students' disposal.

Effects of the chorda tympani damage on submandibular glands: scintigraphic changes.

The aim of this study is to compare the scintigraphic results of a denervated submandibular gland with the contralateral normal side in patients with unilateral chorda tympani damage. Sixteen patients (11 women and five men with a mean age of 27) with unilateral proven chorda tympani damage during their previous ear surgery were included in the study. The perfusion ratio (PR), concentration ratio (CR) and stimulated excretion ratio (SER) were calculated scintigraphically and the results from the salivary glands on opposite sides were compared. For submandibular glands, the perfusion ratio (PR), concentration ratio (CR) and stimulated excretion ratio (SER) were found to be 0.65 +/- 0.21, 0.70 +/- 0.21, 0.79 +/- 0.37, respectively. All ratios resulted from statistically decreased radioactivity accumulation on the affected side (p<0.05). Chorda tympani damage negatively affects the function of the ipsilateral submandibular glands despite the absence of atrophy. Dynamic salivary gland scintigraphy is a practical and valuable method of disclosing the decreased capacity of perfusion, concentration and secretion function in unilateral neurological deprivation.

Chorda tympani neuroma masquerading as cholesteatoma.

Facial nerve neuromas occur throughout the course of the facial nerve and its branches, however lesions occurring on the chorda tympani branch are exceptionally rare. We present a case where the diagnosis was made intra-operatively; the patient was pre-operatively thought to have had a cholesteatoma. Total resection is the treatment of choice for these cases. Early diagnosis, aided by high resolution computed tomography (CT) scanning, will facilitate complete excision without damage to the facial nerve itself or the ossicular chain. The slow growing nature of the neuroma is likely to allow compensatory mechanisms to occur without the patient experiencing dysgeusia. As with any rarity the diagnosis can only be made with a high index of suspicion.

A functional imaging guide to the bony landmarks of the seventh nerve.

This article links the imaging anatomy of the skull base with the seventh cranial nerve's pathway. The specific landmarks are illustrated, and the clinical presentations of lesions are defined. Unifying the anatomic and clinical features of the seventh nerve will improve detection of small lesions, assist in communication between clinicians, and aid in teaching this complex subject.

High-resolution computed tomography of the canals of the temporal bone: anatomic correlations.

The aim of this study was to define precisely the imaging of the canals of the temporal bone by means of high-resolution computed tomography (HR CT). Based on 24 temporal bones removed from embalmed cadavers and investigated with HR CT, several canals were studied: the canal of the chorda tympani (CdT), the canal of the auricular branch of the vagus nerve (ABV), the canal of the tympanic nerve, the canal of the carotico-tympanic nerve and that of the lesser petrosal nerve. Anatomic correlations for six temporal bones were made to confirm the validity of our radiologic hypotheses. In CT, in axial sections OM 0 degree, the posterior canal of the CdT was visualized in 71% of cases, the ABV canal in 4%, the inferior tympanic canal in 12.5%, the carotico-tympanic canal in no cases and the canal of the lesser petrosal nerve in 50% (and in 75% with an incidence of OM + 10 degrees). In coronal incidence, the posterior canal of the CdT was seen in 20% of cases, the ABV canal in 25%, the inferior tympanic canal in 85%, the caroticotympanic canal in 65% and that of the lesser petrosal nerve in 15%. The six anatomic comparisons confirmed the radiologic hypotheses in every case. These different structures are easy to identify in HR CT and are important to define so that any lesion (tumoral or vascular) developing in their vicinity may not be overlooked.