Subjective and Objective Taste Change After Cochlear Implantation Systematic Review and Meta-Analysis.

INTRODUCTION: There is a paucity of data reporting the rate of chorda tympani nerve injury during cochlear implantation (CI) surgery. To better provide clarity to patients and surgeons regarding the risk of taste change, we performed a systematic review and meta-analysis of prospective studies examining taste change after CI. DATA SOURCES: PubMed, Embase, and Cochrane Library databases were queried. METHODS: Databases were queried according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "(chorda tympani OR gustatory OR taste OR chemosensory OR dysgeusia OR nervus intermedius) AND (cochlea OR cochlear implant OR cochlear implantation)." Prospective studies were included and further divided into "objective" and "subjective" assessments of taste dysfunction. A systematic review was performed for all studies. A random-effects model was used to compare studies with similar methods and patient demographics. RESULTS: The initial database query yielded 2,437 articles, which were screened according to inclusion and exclusion criteria. Nine appropriate studies were identified, including 442 total patients-254 with subjective assessment and 271 with objective assessment of gustation. Seventeen of 144 patients (11.8%) reported short-term taste change (incidence = 0.09 [0.02-0.16], 95% confidence interval with pooled data). Twenty-six of 265 patients (9.8%) reported long-term taste change (incidence = 0.07 [0.01-0.13]). Objective results were heterogenous and therefore not amenable to pooled meta-analysis. CONCLUSIONS: Taste change from chorda tympani nerve injury is a likely underrecognized complication of CI and may be the most common adverse consequence of CI surgery. Surgeons should counsel prospective patients on this potential complication and that the risk of taste change may persist longer than the immediate postoperative period.

The impact of injury of the chorda tympani nerve during primary stapes surgery or cochlear implantation on taste function, quality of life and food preferences: A study protocol for a double-blind prospective prognostic association study.

BACKGROUND: The chorda tympani nerve (CTN) is a mixed nerve, which carries sensory and parasympathetic fibres. The sensory component supplies the taste sensation of the anterior two-thirds of the ipsilateral side of the tongue. During middle ear surgery the CTN is exposed and frequently stretched or sacrificed, because it lacks a bony covering as it passes through the middle ear. Injury may cause hypogeusia, ageusia or altered taste sensation of the ipsilateral side of the tongue. To date, there is no consensus regarding which type of CTN injury (sacrificing or stretching), during middle ear surgery, leads to the least burden for the patient. METHODS: A double-blind prospective prognostic association study was designed in a single medical centre in the Netherlands to determine the effect of CTN injury on postoperative taste disturbance and quality of life. 154 patients, who will undergo primary stapes surgery or cochlear implantation will be included. The taste sensation, food preferences and quality of life of these patients will be evaluated preoperatively and at one week, six weeks and six months postoperatively using the Taste Strip Test, Electrogustometry, supplementary questionnaire on taste disturbance, Macronutrient and Taste Preference Ranking Task, Appetite, Hunger and Sensory Perception questionnaire and Questionnaire of Olfactory Disorders to assess the association of these outcomes with CTN injury. Evaluation of olfactory function will only take place preoperatively and at one week postoperatively using the Sniffin' Sticks. The patient and outcome assessor are blinded to the presence or absence of CTN injury. DISCUSSION: This study is the first to validate and quantify the effect of chorda tympani nerve injury on taste function. The findings of this study may lead to evidence-based proof of the effect of chorda tympani injury on taste function with consequences for surgical strategies. TRIAL REGISTRATION: Netherlands Trial Register NL9791. Registered on 10 October 2021.

Analysis of the rat chorda tympani nerve response to "super salty" sodium carbonate.

In behavioral experiments, rats perceive sodium carbonate (Na2CO3) as super salty. In fact, when the dissociated Na+ ions are accounted for, rats perceive Na2CO3 as 5× saltier than equinormal concentrations of NaCl. The chorda tympani nerve (CT) responds to salts through at least two receptor mechanisms and is a model system for understanding how salt taste is transmitted to the brain. Here, we recorded CT nerve activity to a broad range of NaCl (3-300 mM) and Na2CO3 (3-300 mN) to investigate why Na2CO3 tastes so salty to rats. Benzamil, a specific epithelial sodium channel (ENaC) antagonist, was used to determine the relative contribution of apical ENaCs in Na2CO3 transduction. The benzamil-insensitive component of CT nerve responses was enhanced by increasing the adapted tongue temperature from 23°C to 30°C. Na2CO3 solutions are alkaline, so we compared neural responses (with and without benzamil) to 100 mM NaCl alone (6.2 pH) and at a pH (11.2 pH) that matched 100 mN Na2CO3. As expected, NaCl responses increased progressively with increasing concentration and temperature. Responses to 3 mN Na2CO3 were greater than 3 mM NaCl with and without benzamil, but the shape of the first log-fold range of was relatively flat. Adjusting the pH of NaCl to 11.2 abolished the thermal enhancement of 100 mN NaCl through the benzamil-insensitive pathway. Rinsing Na2CO3 off the tongue resulted in robust aftertaste that was concentration dependent, thermally sensitive, and benzamil-insensitive. Responses to alkaline NaCl did not recapitulate Na2CO3 responses or aftertaste, suggesting multiple transduction mechanisms for the cations (2Na+) and anion (CO3-2).

Interleukin (IL)-1 Receptor Signaling Is Required for Complete Taste Bud Regeneration and the Recovery of Neural Taste Responses following Axotomy.

Experimental or traumatic nerve injury causes the degeneration of associated taste buds. Unlike most sensory systems, the sectioned nerve and associated taste buds can then regenerate, restoring neural responses to tastants. It was previously unknown whether injury-induced immune factors mediate this process. The proinflammatory cytokines, interleukin (IL)-1α and IL-1ß, and their requisite receptor are strongly expressed by anterior taste buds innervated by the chorda tympani nerve. We tested taste bud regeneration and functional recovery in mice lacking the IL-1 receptor. After axotomy, the chorda tympani nerve regenerated but was initially unresponsive to tastants in both WT and Il1r KO mice. In the absence of Il1r signaling, however, neural taste responses remained minimal even >8 weeks after injury in both male and female mice, whereas normal taste function recovered by 3 weeks in WT mice. Failed recovery was because of a 57.8% decrease in regenerated taste buds in Il1r KO compared with WT axotomized mice. Il1a gene expression was chronically dysregulated, and the subset of regenerated taste buds were reinnervated more slowly and never reached full volume as progenitor cell proliferation lagged in KO mice. Il1r signaling is thus required for complete taste bud regeneration and the recovery of normal taste transmission, likely by impairing taste progenitor cell proliferation. This is the first identification of a cytokine response that promotes taste recovery. The remarkable plasticity of the taste system makes it ideal for identifying injury-induced mechanisms mediating successful regeneration and recovery.SIGNIFICANCE STATEMENT Taste plays a critical role in nutrition and quality of life. The adult taste system is highly plastic and able to regenerate following the disappearance of most taste buds after experimental nerve injury. Several growth factors needed for taste bud regeneration have been identified, but we demonstrate the first cytokine pathway required for the recovery of taste function. In the absence of IL-1 cytokine signaling, taste bud regeneration is incomplete, preventing the transmission of taste activity to the brain. These results open a new direction in revealing injury-specific mechanisms that could be harnessed to promote the recovery of taste perception after trauma or disease.

Unilateral Increase of Gustatory Thresholds in Acute Otitis Media: A Pilot Study.

BACKGROUND: To evaluate chorda tympani nerve function as measured by unilateral increases of gustatory thresholds in the presence of ipsilateral acute otitis media. METHODS: Prospective clinical study comparing electrogustometric measurements was conducted to evaluate the taste thresholds of each side of the tongue in a patient during an acute episode of unilateral acute otitis media. Included were patients aged 12-40 who presented to the emergency department and outpatient ear, nose, and throat clinic of a university-affiliate tertiary medical center with unilateral acute otitis media between January 2019 and January 2020 and consented to the study. RESULTS: Eleven patients were initially recruited into the study, and 10 patients aged (mean ± standard deviation) 26.1 ± 11.2 years comprised the final study group. Taste thresholds were significantly elevated on the side ipsilateral to the ear affected by acute otitis media (P < .05). CONCLUSION: Chorda tympani nerve conductance is impaired during the acute stage of acute otitis media. This may have implications in the understanding of peripheral neural properties during acute middle ear inflammatory conditions and on the diagnosis of acute otitis media.

Vitamin C deficiency in osteogenic disorder Shionogi/Shi Jcl-od/od rats: effects on sour taste preferences, lick rates, chorda tympani nerve responses, and taste transduction elements.

Animals use sour taste to avoid spoiled food and to choose foods containing vitamins and minerals. To investigate the response to sour taste substances during vitamin C (ascorbic acid; AA) deficiency, we conducted behavioral, neural, anatomical, and molecular biological experiments with osteogenic disorder Shionogi/Shi Jcl-od/od rats, which lack the ability to synthesize AA. Rats had higher 3 mM citric acid and 10 mM AA preference scores when AA-deficient than when replete. Licking rates for sour taste solutions [AA, citric acid, acetic acid, tartaric acid, and HCl] were significantly increased during AA deficiency relative to pre- and postdeficiency. Chorda tympani nerve recordings were conducted to evaluate organic acid taste responses in the AA-deficient and replete rats. Nerve responses to citric acid, acetic acid, and tartaric acid were significantly diminished in AA-deficient rats relative to replete controls. There was no significant difference in the number of fungiform papillae taste buds per unit area in the AA-deficient rats relative to the replete rats. However, mRNA expression levels of Gnat3 (NM_173139.1), Trpm5 (NM_001191896.1), Tas1r1 (NM_053305.1), Car4 (NM_019174.3), and Gad1 (NM_017007.1) in fungiform papillae taste bud cells from AA-deficient rats were significantly lower than those in replete rats. Our data suggest that AA deficiency decreases avoidance of acids and reduces chorda tympani nerve responses to acids. AA deficiency downregulates some taste-related genes in fungiform papillae taste bud cells. However, the results also reveal that the mRNA expression of some putative sour taste receptors in fungiform papillae taste bud cells is not affected by AA deficiency.

Taste Changes after Atresioplasty in Patients with Congenital Aural Atresia.

OBJECTIVE: We evaluated chorda tympani nerve (CTN) and postoperative taste dysfunction according to anomaly severity and intraoperative CTN status. STUDY DESIGN: Prospective observational study. SETTING: Tertiary referral center, Samsung medical center hospital. PATIENTS: Thirty-one patients who underwent atresioplasty by a single surgeon in a tertiary referral center were enrolled. INTERVENTIONS: Therapeutic surgery. MAIN OUTCOME MEASURES: Preoperative Schuknecht type and Jahrsdoerfer score and intraoperative CTN status were recorded, and a postoperative questionnaire was administered to evaluate taste function. RESULTS: A significant difference was found among intact, cut, and unidentified groups in terms of Schuknecht type ( p = 0.000) and Jahrsdoerfer score (9.28 ± 1.11, 8.80 ± 0.83, 8.10 ± 0.93, p = 0.028). CTN was observed in Schuknecht type B, and not in type C ( p = 0.000), and was more likely to be observed as Jahrsdoerfer score increased ( p = 0.012). Taste disturbance tended to last longer in adult patients than in children. A significant difference was observed in the incidence of taste change between cut and intact CTN groups ( p = 0.018). CONCLUSION: CTN was not identified during surgery in patients with Schuknecht type C anomalies, and there was no change in taste after surgery. Meanwhile, CTN was observed in all patients with Schuknecht type B anomalies, and CTN injury occurred in 41.67%. Therefore, CTN presence can be predicted by severity of anomaly, and patients with type B anomalies should be informed of the risk of CTN injury before surgery.

Chorda tympani injury during endoscopic versus microscopic stapes surgery: a randomized controlled clinical trial.

OBJECTIVES: The aim of this study was to compare the incidence of chorda tympani nerve (CTN) injury between endoscopic and microscopic stapes surgery. METHODS: This randomized controlled clinical trial included 88 patients who were randomly divided into two groups: endoscopic stapedotomy group (n = 44) and microscopic stapedotomy group (n = 44). The incidence of chorda tympani nerve (CTN) injury after surgery was determined by both subjective taste testing and chemical taste tests, before and after surgery. The results were compared between the two groups. RESULTS: The total number of patients who were identified as having CTN affection (based on the chemical testing) was 16 out of 88 (18.2%). The incidence was significantly lower in the endoscopic group (n = 2) than the microscopic group (n = 14) (p = 0.019). CONCLUSION: Altered taste as a result of iatrogenic CTN injury can affect the patients' quality of life. Endoscopic ear surgery offers better visualization, less need for extensive manipulation of the chorda tympani, and consequently decreased incidence of CTN injury.

The Sensory Auricular Branch of the Facial Nerve and its Relationship to Landmarks of the Facial Recess.

OBJECTIVE: Delineate the anatomic relationship of the sensory auricular branch (SAB) of the facial nerve to other structures of the facial recess. METHODS: Ten adult cadaveric temporal bones were randomly selected and dissected under operative microscopy. Linear and angular measurements were obtained for the following parameters: (1) the distance from the tip of the short process of the incus to the point of convergence of the SAB and the main trunk of the facial nerve; (2) the distance from the point of convergence of the SAB and the main trunk of the facial nerve to the chorda tympani (CT) division from the main trunk; (3) the distance from the bifurcation of the CT and facial nerve to the crossover point of the SAB/CT; (4) the angle at which the SAB merges with the main trunk (Y°), and (5) the angle at which the CT divides off the main trunk (X°). RESULTS: The mean distance from the tip of the short process of the incus to the SAB takeoff was 8.7 ± 1.83 mm (range 6-13 mm). The mean distance from the SAB to the CT division from the main trunk was 5.9 ± 2.41 mm (range 3-10 mm). The mean angle at which the SAB merged with the main trunk of the facial nerve was 38.5 ± 12.63° (range 25°-68°). The mean CT-main trunk angle was 16 ± 4.24° (range 8°-21°). The branching point of the SAB from the facial nerve approximately bisected the facial recess. CONCLUSION: Recognizing the SAB and knowing its relationships to surrounding anatomy provides a useful adjunctive landmark for the identification of the main trunk of the facial nerve's mastoid segment. LEVEL OF EVIDENCE: 4.

Validation of the radiological detection of the chorda-facial angle: impact on the round window accessibility during pediatric cochlear implantation.

OBJECTIVES: The facial recess, an essential landmark for the posterior tympanotomy approach, is limited by the facial nerve and the chorda tympani, with a complicated relationship. This study tried to find the most appropriate radiological method to evaluate the chorda-facial angle (CFA). We also checked the effect of this angle on the round window accessibility during cochlear implantation. METHODS: It was a retrospective study that included cochlear implant surgeries of 237 pediatric patients, from September 2016 to April 2021. Two physicians evaluated the CFA in the para-sagittal cut of the preoperative HRCT. The round window accessibility was assessed in the unedited surgery videos. RESULTS: The CFA ranged from 21° to 35° with a mean of 27.14 ± 3.5°. It was detected in all cases with a high agreement between the two CT reviewers' measurements. The CFA differed significantly between the accessible group and the group with difficult accessibility (p value < 0.001). Spearman's correlation coefficient revealed a strong correlation between the CFA and the intraoperative round accessibility. 25.5° was the best cutoff point; below this angle, difficult accessibility into the RW was expected, with high sensitivity, specificity, and accuracy CONCLUSIONS: Our study on a relatively large number of cases provided a precise, valid, reliable, and applicable method to evaluate the CFA in the HRCT scan. We found a significant-close relation between the CFA and the round window accessibility; the difficulty increased with a need for posterior tympanotomy modification when the angle decreased. KEY POINTS: • Radiological detection of the chorda-facial angle was always problematic, without a previous straightforward method in the literature. • We used the para-sagittal cut of the high-resolution CT scans to evaluate the CFA. This cut was beneficial to seeing the chorda tympani nerve in every examined case. There was a high agreement between the two CT reviewers' measurements. • Preoperative evaluation of the CFA in the HRCT accurately predicted the round window accessibility. Patients with CFA less than 25.5° were expected to have difficult accessibility into the round window during cochlear implantation.

Gustatory Function of Patients With and Without Cholesteatoma Undergoing Middle Ear Surgery.

OBJECTIVE: To compare measured and perceived taste function before and after surgery of patients with chronic otitis media with cholesteatoma (OMCC) to patients without cholesteatoma (patients with chronic suppurative otitis media [CSOM] and patients with lateral skull base lesions [LSB]). METHODS: This prospective cohort study included 29 patients undergoing surgery for unilateral OMCC. The chorda tympani nerve (CTN) was resected in 8 of these patients. Fourteen patients undergoing surgery for unilateral CSOM and 5 patients undergoing surgery for unilateral LSB (with CTN resection) served as the comparison group. Taste function was measured using taste strips on both sides of the tongue before surgery, 2 weeks postoperatively and 3 months postoperatively. The affected side of the tongue was compared to the unaffected side. A questionnaire on taste perception was completed at each visit. RESULTS: Preoperatively, cholesteatoma patients showed higher taste strip scores than non-cholesteatoma patients, indicating a larger difference between the healthy and affected sides of the tongue. Despite this difference in measured taste function few cholesteatoma patients reported taste alteration before surgery (3/29 [10.3%]). Postoperatively, patients with CTN resection (OMCC patients with CTN resection and LSB patients) showed a decreased measured taste function. Subjectively, only approximately 20% of these patients reported taste alteration 3 months postoperatively. CONCLUSIONS: Before surgery, cholesteatoma patients displayed an impaired measured taste function compared to patients without cholesteatoma (CSOM, LSB). Subjectively this was often unnoticed. After surgery, despite removal of the CTN and consequent reduction of measured taste function, few patients reported taste alteration and subjective taste perception was seen to be improving. In regards to middle ear surgery, perceived taste function does not seem to reflect measured gustatory function.

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.

Subjective and Objective Taste Change After Stapes Surgery Systematic Review and Meta-Analysis.

INTRODUCTION: Iatrogenic injury to the chorda tympani (CT) is a well recognized, although potentially underestimated, consequence of stapes surgery. This study aims to review the currently available literature to determine the incidence and prognosis of taste disturbances in these patients. DATA SOURCES: PubMed, Embase, and Cochrane Library databases. METHODS: Databases were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Search terms included (chorda tympani OR gustatory OR taste OR chemosensory OR dysgeusia OR nervus intermedius) AND (ear surgery OR middle ear OR stapes OR stapedectomy OR stapedotomy). Patients with prospective data collection including preoperative data were further divided by methodology into "objective" and "subjective" assessments of taste dysfunction. A systematic review was performed for all included studies, with meta-analysis using a random-effects model was used for those with comparable methodology and patient populations. RESULTS: Initial search yielded 2,959 articles that were screened according to inclusion and exclusion criteria. Once duplicates were removed, seven studies were identified, representing 173 patients with subjective testing (all seven studies) and 146 with objective testing (five studies). Eighty of 173 patients (46.2%) noted a disturbance in taste at early follow-up, whereas as 26 of 173 (15.0%) noted long-term problems. Objective methodology and result reporting were heterogenous and not amenable to pooled meta-analysis for all studies included. CONCLUSION: Changes in taste occur relatively frequently after stapedectomy. Surgeons should continue to counsel prospective patients as to the risks of both short- and long-term taste disturbances.

Recovery of sweet taste preference in adult rats following bilateral chorda tympani nerve transection.

Background: Numerous studies have noted the effect of chorda tympani (CT) nerve transection on taste sensitivity yet very few have directly observed its effects on taste receptor and taste signaling protein expressions in the tongue tissue. Methods: In this study, bilateral CT nerve transection was performed in adult Sprague Dawley rats after establishing behavioral taste preference for sweet, bitter, and salty taste via short term two-bottle preference testing using a lickometer setup. Taste preference for all animals were subsequently monitored. The behavioral testing was paired with tissue sampling and protein expression analysis. Paired groups of CT nerve transected animals (CTX) and sham operated animals (SHAM) were sacrificed 7, 14, and 28 days post operation. Results: Immunofluorescence staining of extracted tongue tissues shows that CT nerve transection resulted in micro-anatomical changes akin to previous investigations. Among the three taste qualities tested, only the preference for sweet taste was drastically affected. Subsequent results of the short-term two-bottle preference test indicated recovery of sweet taste preference over the course of 28 days. This recovery could possibly be due to maintenance of T1R3, GNAT3, and TRPM5 proteins allowing adaptable recovery of sweet taste preference despite down-regulation of both T1R2 and Sonic hedgehog proteins in CTX animals. This study is the first known attempt to correlate the disruption in taste preference with the altered expression of taste receptors and taste signaling proteins in the tongue brought about by CT nerve transection.

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.

[Functional and morphological disorders of taste and olfaction in COVID-19 patients]. / Funktionelle und morphologische Geschmacks- und Geruchsstörungen bei COVID-19-Patienten.

OBJECTIVE: This study aimed to test the prevalence and evolution of acute olfactory and gustatory functional impairment and their morphologic correlates in COVID-19 patients who require hospitalization due to COVID-19-related respiratory conditions. METHODS: Included were 53 consecutive hospitalized patients (23 males, 30 females; age 42.54 ± 10.95 years) with an RT-PCR-confirmed COVID-19 diagnosis. Patients were examined twice: just after hospital discharge and 4-6 weeks later. Electrogustometric (EGM) thresholds at the tongue area supplied by the chorda tympani, at the soft palate, and in the region of the vallate papillae were recorded bilaterally. Olfaction was examined by Sniffin' sticks (Burghardt GmbH, Wedel, Germany). The patients' nasal and oral mucosa (fungiform papillae, fpap) were examined by contact endoscopy. Findings were compared to those of 53 healthy individuals matched for sex and age (23 males, 30 females; age 42.90 ± 10.64 years). RESULTS: EGM thresholds in patients were significantly higher than those of healthy subjects at both timepoints. EGM thresholds at the second measurement were significantly lower than those at the first measurement. Accordingly, patient-reported gustatory outcomes were improved at the second measurement. The same pattern was found using Sniffin' sticks. Significant alterations in form and vascularization of fPap were detected in patients, especially at the first instance. Interestingly we did not observe any significant changes in the morphology and vascularization of nasal mucosa. CONCLUSION: COVID-19 affects both gustatory and olfactory functions. In parallel, it also affects the structure and vascularization of both nasal and oral mucosa, albeit the nasal mucosa to a much lesser, non-significant extent. Our findings suggest that COVID-19 may cause a mild to profound neuropathy of multiple cranial nerves.