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.

Regenerative Failure Following Rat Neonatal Chorda Tympani Transection is Associated with Geniculate Ganglion Cell Loss and Terminal Field Plasticity in the Nucleus of the Solitary Tract.

Neural insult during development results in recovery outcomes that vary dependent upon the system under investigation. Nerve regeneration does not occur if the rat gustatory chorda tympani nerve is sectioned (CTX) during neonatal (≤P10) development. It is unclear how chorda tympani soma and terminal fields are affected after neonatal CTX. The current study determined the impact of neonatal CTX on chorda tympani neurons and brainstem gustatory terminal fields. To assess terminal field volume in the nucleus of the solitary tract (NTS), rats received CTX at P5 or P10 followed by chorda tympani label, or glossopharyngeal (GL) and greater superficial petrosal (GSP) label as adults. In another group of animals, terminal field volumes and numbers of chorda tympani neurons in the geniculate ganglion (GG) were determined by labeling the chorda tympani with DiI at the time of CTX in neonatal (P5) and adult (P50) rats. There was a greater loss of chorda tympani neurons following P5 CTX compared to adult denervation. Chorda tympani terminal field volume was dramatically reduced 50 days after P5 or P10 CTX. Lack of nerve regeneration after neonatal CTX is not caused by ganglion cell death alone, as approximately 30% of chorda tympani neurons survived into adulthood. Although the total field volume of intact gustatory nerves was not altered, the GSP volume and GSP-GL overlap increased in the dorsal NTS after CTX at P5, but not P10, demonstrating age-dependent plasticity. Our findings indicate that the developing gustatory system is highly plastic and simultaneously vulnerable to injury.

Bilateral taste disorders in patients with Ramsay Hunt syndrome and Bell palsy.

OBJECTIVE: Ramsay Hunt syndrome (RHS) and Bell palsy (BP) are typically known as facial nerve motor syndromes and are primarily unilateral. The aim of this study was to challenge this assertion, because both conditions are also known to be associated with viruses that typically affect several nerves. METHODS: Ten participants with RHS, 12 with BP, all clinically unilateral, and 12 healthy controls were prospectively enrolled. Electrogustometric thresholds were measured bilaterally in the areas of the chorda tympani, the glossopharyngeal, and the major petrosal nerve. Also bilaterally, the taste function was tested using chemogustometry with different tastant concentrations. Again bilaterally, the morphology of the mucosa and the vessels of the anterior fungiform papillae were examined by contact endoscopy. Statistically, RHS and BP participants were compared with the healthy controls, and the paretic sides of RHS and BP were compared pairwise with their mobile sides. RESULTS: Electrogustometrically, perception was reduced bilaterally in RHS (10-19dB, p < 0.001) and BP (3-5dB, p = 0.011-0.030) in all 3 innervation areas. Chemogustometrically, it was also reduced bilaterally in RHS (20-70%) and BP (8-50%). Papillary atrophies were increased 100% in RHS (p = 0.001) and BP (p < 0.001). They were more increased on the paretic side in RHS (30%, p = 0.078) and BP (83%, p < 0.001). INTERPRETATION: In these 2 clinically unilateral conditions, the gustatory perception and morphology are bilaterally affected, more in RHS and more on the paretic side. BP, known as an isolated motor condition, appears to be a cranial polyneuritis. A bilateral examination and therapeutic gustatory monitoring might follow these observations in evidence-based practice. Ann Neurol 2018;83:807-815.

Salivary glands regenerate after radiation injury through SOX2-mediated secretory cell replacement.

Salivary gland acinar cells are routinely destroyed during radiation treatment for head and neck cancer that results in a lifetime of hyposalivation and co-morbidities. A potential regenerative strategy for replacing injured tissue is the reactivation of endogenous stem cells by targeted therapeutics. However, the identity of these cells, whether they are capable of regenerating the tissue, and the mechanisms by which they are regulated are unknown. Using in vivo and ex vivo models, in combination with genetic lineage tracing and human tissue, we discover a SOX2+ stem cell population essential to acinar cell maintenance that is capable of replenishing acini after radiation. Furthermore, we show that acinar cell replacement is nerve dependent and that addition of a muscarinic mimetic is sufficient to drive regeneration. Moreover, we show that SOX2 is diminished in irradiated human salivary gland, along with parasympathetic nerves, suggesting that tissue degeneration is due to loss of progenitors and their regulators. Thus, we establish a new paradigm that salivary glands can regenerate after genotoxic shock and do so through a SOX2 nerve-dependent mechanism.

Long-term Follow-up Results of Regeneration Process of Fungiform Taste Buds After Severing the Chorda Tympani Nerve During Middle Ear Surgery.

OBJECTIVE: To elucidate the regeneration process of fungiform taste buds after severing the chorda tympani nerve (CTN) by confocal laser scanning microscopy in vivo. METHODS: In 7 consecutive patients whose CTN was severed during tympanoplasty, an average of 10 fungiform papillae in the midlateral region of the tongue were periodically observed, and the number of taste buds was counted until 12 to 24 months after surgery. Gustatory function was assessed by EGM. RESULTS: EGM thresholds showed no response within 1 month after surgery in any patient. All taste buds had disappeared until 13 to 71 days after surgery. Regenerated taste buds were first detected 5 to 8 months after surgery in 5 of the 7 patients. EGM thresholds recovered to their preoperative values in 2 patients. In these 2 patients, the number of regenerated taste buds gradually increased in combination with a recovered taste function. However, a time lag existed between taste bud regeneration and taste function recovery. EGM thresholds did not recover in the other 3 patients with regenerated taste buds, suggesting that these taste buds were immature without gustatory function. CONCLUSION: The long-term regeneration process of fungiform taste buds could be clarified using confocal laser scanning microscopy.

Changes in transient receptor potential channels in the rat geniculate ganglion after chorda tympani nerve injury.

We reported differential expression of the transient receptor potential vanilloid 1 (TRPV1), the transient receptor potential ankyrin 1 (TRPA1), and the (TRPM8) in the geniculate ganglions (GGs) of naive rats. In medical practice, the chorda tympani nerve (CTN) is injured in some patients during middle-ear surgery, and results in tongue numbness and taste disorder. We investigated changes in the expression of these receptors in GGs after CTN injury. In naive-rat GGs, 11.4, 11.8, and 0.5% of neurons were found to express the TRPV1, the TRPA1, the TRPM8, respectively. At 3 days after CTN injury, 5.2 and 4.0% of activating transcription factor 3-immunoreactive neurons, considered as injured neurons, were found to express the TRPV1 and the TRPA1, respectively. Among activating transcription factor 3-immunonegative neurons, considered as uninjured neurons, 3.9 and 3.8% were found to express the TRPV1 and the TRPA1, respectively. The TRPM8 was not detected in GGs after CTN injury. We found decreased mRNA levels of the TRPV1 and the TRPA1 in all neurons, as well as in uninjured neurons of ipsilateral GGs after CTN injury. CTN injury changes the gene expression in GGs and may have effects on the tongue.

Successful treatment of dysgeusia after middle-ear surgery with amitriptyline: Case report.

INTRODUCTION: The chorda tympani branches off of the facial nerve within the petrous portion of the temporal bone, and is responsible for controlling the taste in the anterior two-thirds of the tongue on each side. Due to its location, it is commonly injured during middle-ear surgery resulting in dysgeusia. METHOD: A case of a 59-year-old male had recurrent otitis media resulting in tympanic membrane perforation. Patient subsequently underwent lateral graft tympanoplasty. Shortly after surgery patient reported onset of dysgeusia consisting of metallic taste at the tip of the tongue and salty taste on the left side of the tongue. RESULTS: Treatment with Amitriptyline 50mg each night significantly improved the patient's symptoms of dysgeusia. CONCLUSIONS: Amitriptyline may be an effective treatment for dysgeusia occurring after middle-ear surgery.

Glial responses after chorda tympani nerve injury.

The chorda tympani (CT) nerve innervates lingual taste buds and is susceptible to damage during dental and inner ear procedures. Interruption of the CT results in a disappearance of taste buds, which can be accompanied by taste disturbances. Because the CT usually regenerates to reinnervate taste buds successfully within a few weeks, a persistence of taste disturbances may indicate alterations in central nervous function. Peripheral injury to other sensory nerves leads to glial responses at central terminals, which actively contribute to abnormal sensations arising from nerve damage. Therefore, the current study examined microglial and astrocytic responses in the first central gustatory relay, the nucleus of the solitary tract (nTS), after transection of the CT. Damage to the CT resulted in significant microglial responses in terms of morphological reactivity and an increased density of microglial cells from 2 to 20 days after injury. This increased microglial population resulted primarily from microglial proliferation from 1.5 to 3 days, which was supplemented by microglial migration within subdivisions of the nTS between days 2 and 3. Unlike other nerve injuries, CT injury did not result in recruitment of bone marrow-derived precursors. Astrocytes also reacted in the nTS with increased levels of glial fibrillary acidic protein (GFAP) by 3 days, although none showed evidence of cell division. GFAP levels remained increased at 30 days, by which time microglial responses had resolved. These results show that nerve damage to the CT results in central glial responses, which may participate in long-lasting taste alterations following CT lesion.

Functional role for interleukin-1 in the injured peripheral taste system.

The peripheral taste system presents an excellent model for studying the consequences of neural injury, for the damaged nerve and sensory cells and the neighboring, intact neural cells. Sectioning a primary afferent nerve, the chorda tympani (CT), rapidly recruits neutrophils to both sides of the tongue. The bilateral neutrophil response induces transient functional deficits in the intact CT. Normal function is subsequently restored as macrophages respond to injury. We hypothesized that macrophages produce the proinflammatory cytokine interleukin (IL)-1, which contributes to the maintenance of normal taste function after nearby injury. We demonstrate that IL-1ß protein levels are significantly increased on the injured side of the tongue at day 2 after injury. Dietary sodium deficiency, a manipulation that prevents macrophage recruitment, inhibits the elevation in IL-1ß. IL-1ß was expressed in several cell populations, including taste receptor cells and infiltrating neutrophils and macrophages. To test whether IL-1 modulates taste function after injury, we blocked signaling with an IL-1 receptor antagonist (IL-1 RA) and recorded taste responses from the intact CT. This treatment inhibited the bilateral macrophage response to injury and impaired taste responses in the intact CT. Cytokine actions in the taste system are largely unstudied. These results demonstrate that IL-1 has a beneficial effect on taste function after nearby injury, in contrast to its detrimental role in the injured central nervous system.

Impact of chorda tympani nerve injury on cell survival, axon maintenance, and morphology of the chorda tympani nerve terminal field in the nucleus of the solitary tract.

Chorda tympani nerve transection (CTX) has been useful to study the relationship between nerve and taste buds in fungiform papillae. This work demonstrated that the morphological integrity of taste buds depends on their innervation. Considerable research focused on the effects of CTX on peripheral gustatory structures, but much less research has focused on the central effects. Here, we explored how CTX affects ganglion cell survival, maintenance of injured peripheral axons, and the chorda tympani nerve terminal field organization in the nucleus of the solitary tract (NTS). After CTX in adult rats, the chorda tympani nerve was labeled with biotinylated dextran amine at 3, 7, 14, 30, and 60 days post-CTX to allow visualization of the terminal field associated with peripheral processes. There was a significant and persistent reduction of the labeled chorda tympani nerve terminal field volume and density in the NTS following CTX. Compared with controls, the volume of the labeled terminal field was not altered at 3 or 7 days post-CTX; however, it was significantly reduced by 44% and by 63% at 30 and 60 days post-CTX, respectively. Changes in the density of labeled terminal field in the NTS paralleled the terminal field volume results. The dramatic decrease in labeled terminal field size post-CTX cannot be explained by a loss of geniculate ganglion neurons or degeneration of central axons. Instead, the function and/or maintenance of the peripheral axonal process appear to be affected. These new results have implications for long-term functional and behavioral alterations.

Mucoepidermoid carcinoma of the parotid infiltrating the chorda tympani nerve.

We present here the first case report of a mucoepidermoid carcinoma of the parotid infiltrating the chorda tympani nerve and also discuss why an initial diagnosis of Bell palsy may be misleading.

A new approach for tubular structure modeling and segmentation using graph-based techniques.

In this work, a new approach for tubular structure segmentation is presented. This approach consists of two parts: (1) automatic model construction from manually segmented exemplars and (2) segmentation of structures in unknown images using these models. The segmentation problem is solved by finding an optimal path in a high-dimensional graph. The graph is designed with novel structures that permit the incorporation of prior information from the model into the optimization process and account for several weaknesses of traditional graph-based approaches. The generality of the approach is demonstrated by testing it on four challenging segmentation tasks: the optic pathways, the facial nerve, the chorda tympani, and the carotid artery. In all four cases, excellent agreement between automatic and manual segmentations is achieved.

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.

[Anatomical course of the chorda tympani nerve in middle ear surgery: clinical classification and relevance for postoperative gustatory dysfunction]. / Verlauf der Chorda tympani bei Operationen des Mittelohres: Klinische Einteilung und ihre Bedeutung für postoperative Schmeckstörungen.

BACKGROUND: The anatomical course of the Chorda tympani nerve (CTN) in the middle ear is known to be very variable, which becomes most obvious during middle ear operations. As well, postoperative gustatory dysfunction belongs to the most frequent complications after otosurgical interventions. The aim of this study was to develop a clinical classification of the intraoperatively visible course of the CTN and to demonstrate a possible correlation of its anatomic course with the prevalence of actual postoperative taste disorders. METHODS: Only cases of first-time ear surgery all operated by one experienced otosurgeon were assessed. Preoperatively, gustatory testing with standardised chemical solutions (sweet, sour, salty, bitter) was performed. During surgery the course of the CTN was classified at first sight by 3 topografical criteria: The angle (A), the height (H) and the depth (D) of the nerve's emergence from the lateral tympanic wall. In cases of postoperative taste dysfunction the patients were followed-up on a regular basis. RESULTS: 103 patients were included in the study. The angle of the nerve;s emergence from the tympanic bone was below 30 degrees in 59 (A1), between 30 degrees and 60 degrees in 41 (A2) and within 60 degrees and 90 degrees in 3 cases (A3). The height of emergence was 33 times in the superior (H1), 61 times in the middle (H2) and 9 times in the inferior third (H3) of the posterior meatal wall. The depth of emergence lay within the plain of the tympanic sulcus in 26 individuals (D1), 44 times medially to this plain without overlapping bone (D2) and 33 times medially but covered by a bony spur (D3). The CTN was preserved in 92 procedures. Postoperatively, gustatory function was diminished in 7% of the cases. CONCLUSION: This study confirms the high diversity of the surgical anatomy of the CTN. According to the proposed classification the A1-H1-D2/3-situation belongs to the CTN-constellations observed most frequently. It is this very anatomical situation, that apparently tends to be associated with postoperative taste deficits quite regularly due to inevitable intraoperative manipulations. Taking into account the results of this study an otosurgeon might be able to anticipate the potential risk for the CTN by judging the AHD-status intraoperatively and - therefore - reduce taste disorders postoperatively. Additionally, the probability of a postoperative gustatory dysfunction depends upon the kind of underlying middle ear disease as well.