Does the chorda tympani nerve confer general sensation from the tongue?

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.

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.

Consequences of Stapes Surgery on Tongue Morphological Characteristics in Narrow Band Imaging, Gustatory Function and General Sensation: A Prospective Tertiary Center Study

(1) Background: Chorda tympani (CT) manipulation during stapes surgery affects its functions. We hypothesized that this alters tongue morphology and sensory functions. (2) Methods: Patients undergoing stapes surgery were tested 1 day preoperatively, 1 and 6 months postoperatively. Narrow band imaging contact endoscopy (NBI) was used to determine the number of fungiform papillae (Npapillae) and the total score of blood vessel morphology (NBItotal). The taste was tested with taste strips. General sensation was tested with a static two-point discrimination. Tests were performed on ipsilateral and contralateral side of the tongue. (3) Results: 52 otosclerosis patients were included in the study. There was a statistically significant decrease of NBItotal (p = 0.005), Npapillae (p = 0.009), sensation of sweet (p = 0.003), salty (p = 0.035), sour (p = 0.036), and bitter taste (p = 0.013) within the test side during the follow-up. A statistically significant impact on presence of dysgeusia for sweet was found 1 month postoperatively (p < 0.005). Postoperative decrease in two-point discrimination score did not reach a statistical significance (p = 0.056). (4) Conclusions: CT manipulation affects fungiform papillae density, vascular patterns and taste sensation. The general sensation of the tongue is not influenced by CT manipulation.

Chemical, Electrical and Tactile Sensitivity Changes After Middle Ear Surgery

OBJECTIVE/HYPOTHESIS

Taste disturbances are often seen in patients after middle ear surgery due to the stress received by an unprotected chorda tympani. It has also been reported that loss in tactile sensitivity may accompany this issue. The current study was designed to measure electrical, chemical, and tactile sensitives of several senses involved in oral processing, smell, taste and touch, over time.

STUDY DESIGN

Prospective cohort study.

METHODS

For three time points, one before middle ear surgery and two after operation (about 5 and 23 days), sensitivity thresholds were obtained using electrogustometry (electrical taste), taste strips (chemical taste), Sniffin' Sticks (smell) and Von Frey Hairs (point-pressure tactile sensitivity).

RESULTS

The results show a decline in both chemical and electrical taste responses. Additionally, the electrical taste response showed more sensitivity to deviations and no sign of recovery unlike the chemical taste response. Mechanosensory function of the anterior tongue and olfactory function was not strongly affected by middle ear surgery.

CONCLUSION

Taste responses, but not mechanosensory or olfaction function, are altered after middle ear surgery. Due to the effects that taste loss has on quality of life, gustometry is recommended for this group of patients.

LEVELS OF EVIDENCE

4.

Feasibility of preservation of chorda tympani nerve during noninflammatory ear surgery: A systematic review

OBJECTIVE

The objective of our systematic review is to investigate the postoperative gustatory function of the chorda tympani nerve following noninflammatory ear surgery for which the chorda tympani is at risk for iatrogenic injury (stretching, handling, or sacrificing).

DATA SOURCES

PubMed and EMBASE.

REVIEW METHODS

A PubMed and EMBASE databases search was conducted on November 15, 2016. Study inclusion criteria included: 1) ear surgery performed for noninflammatory ear diseases, and 2) gustatory function of the chorda tympani reported as an outcome. The quality of eligible studies was assessed using the risk of bias assessment tool for nonrandomized studies. Study characteristics and outcome data of the included studies were extracted.

RESULTS

In total 1,094 articles were retrieved. Fourteen studies encompassing 1,062 operated ears were included after quality assessment. Stapedectomy was the most frequent surgical procedure performed in 398 ears. The follow-up time varied between 6 weeks and 99 months. Patients with a preserved chorda tympani were less symptomatic (24% was symptomatic) compared to patients with a stretched (53% was symptomatic) or sacrificed chorda tympani (47% was symptomatic). The recovery rate varied from 61% to 79%. The results of the electrogustometry and strip test showed a discrepancy with the subjective complaints of the patients.

CONCLUSION

Patients with a stretched chorda tympani were slightly more symptomatic compared to patients with a sacrificed chorda tympani. Therefore, in cases for which the chorda tympani greatly hinders a proper view of the surgical field, sacrificing the nerve could be considered to maximize surgical performance and have a satisfactory postoperative result. Laryngoscope, 1904-1913, 2018.

Change of somatosensory function of the tongue caused by chorda tympani nerve disorder after stapes surgery

OBJECTIVES

Patients after middle ear surgery often complain of taste disturbance and a lingual numbness. The purpose of this study was to objectively assess changes in the somatosensation of the tongue and taste function in patients undergoing stapes surgery.

STUDY DESIGN

Prospective study.

METHODS

Symptoms of taste disturbance and tongue numbness after surgery were investigated before and after surgery in 41 patients (13 males, 28 females; mean age 41.8 years) who underwent stapes surgery. Twenty-eight patients (9 males, 19 females; mean age 43.1 years) underwent sensory and taste function tests before and after surgery. Sensory function of the tongue was measured at the operated side and the nonoperated side using the 2-point discrimination test and an electrostimulator test. Taste function was assessed with electrogustometry (EGM).

RESULTS

The chorda tympani nerve (CTN) was gently touched or stretched in all patients. Postoperative thresholds on the operated side were significantly higher than preoperative thresholds in all tests in the patients who underwent all three kinds of tests. Tongue somatosensory symptoms improved significantly earlier than the taste disturbance postoperatively, and the sensory thresholds returned to the baseline along with recovery of symptoms.

CONCLUSION

These findings suggest that dysfunction of the CTN occurred following surgery even when the CTN was preserved, and that the sensory nerve threshold of the tongue correlated with the symptom of lingual numbness. The CTN may play a role not only in taste function but also in the somatosensory function of the tongue.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:701-706, 2018.

Surgical complications following cochlear implantation in adults based on a proposed reporting consensus

CONCLUSION

The rate of severe complications was low and cochlear implantation is a relatively safe procedure. Standardization is crucial when reporting on cochlear implant complications to ensure comparability between studies. A consensus on the reporting of complications proposed by a Danish team of researchers was applied, evaluated and found beneficial.

OBJECTIVES

To report the surgical complications following cochlear implantation at our centre, applying and evaluating a proposed reporting consensus.

METHODS

A retrospective file review of 308 consecutive adult implantations in 269 patients between 1994 and 2010 at Odense University Hospital was performed.

RESULTS

The three most common major complications were wound infection (1.6%), permanent chorda tympani syndrome (1.6%) and electrode migration/misplacement/accidental removal (1.3%). Permanent facial nerve paresis occurred following one implantation (0.3%). Transient chorda tympani syndrome (30.8%), vertigo/dizziness (29.5%) and tinnitus (4.9%) were the most frequent minor complications.

Postnatal development of chorda tympani axons in the rat nucleus of the solitary tract

The chorda tympani nerve (CT), one of three nerves that convey gustatory information to the nucleus of the solitary tract (NTS), displays terminal field reorganization after postnatal day 15 in the rat. Aiming to gain insight into mechanisms of this phenomenon, CT axon projection field and terminal morphology in NTS subdivisions were examined using tract tracing, light microscopy, and immunoelectron microscopy at four postnatal ages: P15, P25, P35, and adult. The CT axons that innervated NTS rostrolateral subdivision both in the adult and in P15 rats were morphologically distinct from those that innervated the rostrocentral, gustatory subdivision. In both subdivisions, CT terminals reached morphological maturity before P15. Rostrolateral, but not rostrocentral axons, went through substantial axonal branch elimination after P15. Rostrocentral CT synapses, however, redistribute onto postsynaptic targets in the following weeks. CT terminal preference for GABAergic postsynaptic targets was drastically reduced after P15. Furthermore, CT synapses became a smaller component of the total synaptic input to the rostrocentral NTS after P35. The results underlined that CT axons in rostrocentral and rostrolateral subdivisions represent two distinct populations of CT input, displaying different morphological properties and structural reorganization mechanisms during postnatal development.

Sweet taste and chorda tympani transection alter capsaicin-induced lingual pain perception in adult human subjects

Sweetness signals the nutritional value of food and may moreover be accompanied by a sensory suppression that leads to higher pain tolerance. This effect is well documented in infant rats and humans. However, it is still debated whether sensory suppression is also present in adult humans. Thus, we investigated the effects of sweet taste on the perception of the painful trigeminal stimulus capsaicin in two groups of healthy adult human subjects. A solution of 100 μM capsaicin was applied to the tip of the subject's tongues in order to stimulate trigeminal Aδ- and C-fiber nociceptors. When swallowed, 1M sucrose reduced the capsaicin-induced burning sensation by 29% (p ≤ 0.05) whereas a solution of similar taste intensity containing 1 μM quinine did not. Similarly, sucrose application to the frontal hemitongue suppressed the perception of the burning sensation induced by contralaterally applied capsaicin by 25% (p ≤ 0.01). We furthermore investigated the effects of documented unilateral transection of the chorda tympani nerve on capsaicin perception. In accordance with the ipsi-to-contralateral effect of sucrose on capsaicin perception in healthy subjects, hemiageusic subjects were more sensitive for capsaicin on the tongue contralateral to the taste nerve lesion (+38%; p ≤ 0.01). Taken together, these results argue I) for the existence of food intake-induced sensory suppression, if not analgesia, in adult humans and II) a centrally mediated suppression of trigeminal sensation by taste inputs that III) becomes disinhibited upon peripheral taste nerve lesion.

A survey of oral cavity afferents to the rat nucleus tractus solitarii

Visualization of myelinated fiber arrangements, cytoarchitecture, and projection fields of afferent fibers in tandem revealed input target selectivity in identified subdivisions of the nucleus tractus solitarii (NTS). The central fibers of the chorda tympani (CT), greater superficial petrosal nerve (GSP), and glossopharyngeal nerve (IX), three nerves that innervate taste buds in the oral cavity, prominently occupy the gustatory-sensitive rostrocentral subdivision. In addition, CT and IX innervate and overlap in the rostrolateral subdivision, which is primarily targeted by the lingual branch of the trigeminal nerve (LV). In the rostrocentral subdivision, compared with the CT terminal field, GSP appeared more rostral and medial, and IX was more dorsal and caudal. Whereas IX and LV filled the rostrolateral subdivision diffusely, CT projected only to the dorsal and medial portions. The intermediate lateral subdivision received input from IX and LV but not CT or GSP. In the caudal NTS, the ventrolateral subdivision received notable innervation from CT, GSP, and LV, but not IX. No caudal subnuclei medial to the solitary tract contained labeled afferent fibers. The data indicate selectivity of fiber populations within each nerve for functionally distinct subdivisions of the NTS, highlighting the possibility of equally distinct functions for CT in the rostrolateral NTS, and CT and GSP in the caudal NTS. Further, this provides a useful anatomical template to study the role of oral cavity afferents in the taste-responsive subdivision of the NTS as well as in subdivisions that regulate ingestion and other oromotor behaviors.

Taste function after stapes surgery

OBJECTIVE

A manipulation of chorda tympani nerve (CTN) is frequently necessary during the surgical therapy of stapedial ankylosis. The aim of this study was to re-assess the taste function before and after stapes surgery in patients with unilateral stapes ankylosis.

METHODS

Eighteen patients (14 female and 4 male) with unilateral stapedial ankylosis were included. Taste and olfactory function were measured preoperatively, 3 days and 3 months after surgery by questionnaire, chemical taste test, electrogustometry, and Sniffin'Sticks. The patients who reported deterioration in taste and revealed pathological taste test results were re-investigated 8-12 months after surgery. Postoperatively 11 patients were treated intravenously for 3 days for inner ear protection with 1g of cortisone. The gustatory and olfactory results were compared with age and sex specific normative data.

RESULTS

A significant transient decrease of gustatory measurement values was found on the ipsilateral two thirds of the anterior tongue. 12 out of 17 patients whose CTN was slightly manipulated during stapes surgery reported tongue sensations, such as numbness or gustatory blindness of the ipsilateral tongue side. The measures of chemical taste test significantly decrease in lateralized taste test on the ipsilateral side and in whole mouth testing. There was no significant increase of the EGM measures at the ipslateral tongue. In 11 of 12 patients with symptoms, complaints recovered within one year after surgery completely. The factor "cortisone" did not have a significant effect on the taste test results after surgery.

CONCLUSION

In conclusion, even after minor CTN manipulation the rate of postoperative taste disorders or tongue symptoms after stapes surgery is high. The symptoms appear to be transient. Therefore CTN should be preserved in stapes surgery after mild trauma of the CTN. Transient taste alteration should be mentioned prior to stapes surgery.

Iatrogenic injury of the chorda tympani: a systematic review

Objective:

To review the currently available literature on iatrogenic injury of the adult chorda tympani.

Design:

Systematic literature review.

Method

Five electronic databases and one search engine were used to access available English language literature on the chorda tympani, focusing on iatrogenic injury.

Results:

The chorda tympani is most often injured during middle-ear surgery, after which at least 15–22 per cent of patients experience symptoms, mostly changes in taste and dryness of the mouth. Numerous factors influence whether injury to the chorda tympani causes symptoms, including the extent of injury, type of surgery, age of the patient, anatomical variables and subjective adaptation. Although most patients experience gradual symptomatic recovery, complaints can be persistent and troublesome.

Conclusion:

Care should be taken to preserve the chorda tympani during middle-ear surgery, and to warn patients pre-operatively about this potential complication. This is particularly important if surgery is bilateral.

Clinical anatomy of the chorda tympani: a systematic review

OBJECTIVE

The chorda tympani is at risk of iatrogenic injury throughout its course. This paper reviews the clinical anatomy of the nerve in adults.

DESIGN

Systematic literature review.

METHOD

Relevant English-language articles were identified using five electronic databases and one search engine. Data from approximately 70 scientific papers were supplemented with information from selected reference texts.

RESULTS

The anatomy of the chorda tympani differs from standard descriptions, particularly regarding its exit from the middle ear and area of lingual innervation. Whilst it is known to convey taste sensation from the anterior two-thirds of the tongue and parasympathetic innervation to the submandibular and sublingual salivary glands, the chorda tympani probably has additional sensory and secretomotor functions.

CONCLUSION

A detailed understanding of the anatomy of the chorda tympani may help to reduce the risk of iatrogenic injury during head, neck and middle-ear surgery, and to explain the variable consequences of such injury.

Clinical Assessment of Gustatory Function before and after Middle Ear Surgery: A Prospective Study with a Two-Year Follow-up Period

Objectives:

Middle ear surgery can affect gustatory function because of the course of the chorda tympani nerve (CTN) close to the tympanic membrane. The aim of the study was to evaluate the sense of taste before and after middle ear surgery with a test suitable for clinical routine. Moreover, subjective complaints were assessed over a relatively long period of time.

Methods:

Forty-seven patients (26 female, 21 male; mean age, 42 years) were investigated before and 4 days after surgery on both sides of the anterior part of the tongue. Self-assessment of taste function was performed by visual analog scales.

Results:

The mean (±SD) taste scores significantly decreased on the side ipsilateral to the operated ear in patients with major manipulation of the CTN (12.0 ± 4.5 before surgery and 6.9 ± 4.5 after surgery; p < 0.001), whereas no significant changes were measured in patients with minor manipulation of the CTN (12.5 ± 3.1 before surgery and 11.2 ± 3.9 after surgery; p = 0.14). Self-assessed ratings of taste function significantly decreased after surgery in all patients (p < 0.001). Reassessment of subjective taste function after 2 years indicated no persisting complaints.

Conclusions:

Depending on the amount of manipulation of the CTN, taste function is decreased after surgery. However, long-lasting changes of gustatory function seem to be rare.

Tactile dysgeusia: a new clinical observation of middle ear and skull base surgery

OBJECTIVE

To describe a new clinical observation of "tactile dysgeusia," a phenomenon associated with otologic and skull base surgery likely caused by injury to the chorda tympani nerve (CTN) or the nervus intermedius (NI) with subsequent aberrant cross-innervation with somatosensory fibers in the surgical field.

STUDY DESIGN

Descriptive case series.

SETTING

Tertiary university referral center.

METHOD

Eight patients described a sensation of touch-evoked dysgeusia after surgery. Seven patients underwent a variety of middle ear procedures including stapedotomies and mastoidectomies. One patient had a large cerebellopontine angle meningioma excised through a translabyrinthine approach. There were no preoperatively sensory symptoms of any kind.

RESULTS

In five of seven patients who had an otologic procedure, the CTN nerve was transected, whereas in the remaining two, the nerve was preserved but stretched. In the meningioma patient, the facial nerve was preserved without clear identification of the NI; the facial nerve function was normal postoperatively. All of the otologic patients experienced symptoms of dysgeusia and sensory alteration triggered by touching various parts of the outer ear. One also has a secondary trigger in the V2 dermatome. In the meningioma patient, taste and sensory alteration was induced by stimulating the ipsilateral V2 and V3 dermatome. In all patients, the symptom was located in the lateral aspect of the ipsilateral hemitongue.

CONCLUSION

Tactile dysgeusia is an unusual complication after otologic and neurotologic procedures. It is likely related to aberrant re-innervation of the special sensory fibers within the CTN nerve or the NI with somatosensory fibers. Postoperative "tactile dysgeusia" may not be so rare; its true incidence could only be ascertained through a more rigorous postoperative assessment.

Changes of oral trigeminal sensitivity in patients after middle ear surgery

OBJECTIVES

The specific aim of this study was to re-investigate the effect of chorda tympani damage on both trigeminal sensitivity and taste ability.

STUDY DESIGN

Prospective study.

METHODS

Capsaicin-impregnated filter paper strips (5 concentrations, 0.0001-1%) were used to measure trigeminal thresholds. The strips were placed on the anterior tongue for 10 seconds. Thresholds were estimated in two ways: 1) thresholds related to sensory perception and 2) intensity-related thresholds. The test was applied to 29 patients who underwent middle ear surgery (mean age, 49 yr; 16 females, 13 males). Results were compared with those of 63 healthy subjects (mean age, 40 yr; 36 females, 29 males). In addition to trigeminal thresholds, measures of gustatory function were also obtained using both the validated "taste strips" test kit and electrogustometry.

RESULTS

For lateralized testing with capsaicin, significant differences were found between preoperative and postoperative thresholds and between the operated and nonoperated side, with thresholds being higher postoperatively on the operated side. The sensation-related thresholds from the operated tongue side exhibited a correlation with the corresponding postoperative electrogustometric thresholds. A higher degree of chorda manipulation was associated with higher postoperative capsaicin thresholds at the operated tongue side.

CONCLUSION

Pain-related sensitivity of the tongue decreases after middle ear surgery, indicating that chorda tympani function also influences intraoral trigeminal sensitivity.

Assessment of oral trigeminal sensitivity in humans

The aim of this prospective study was to establish a clinical test for the assessment of oral trigeminal sensitivity. Capsaicin-impregnated filter paper strips (five concentrations: 0.0001-1%) were used to measure trigeminal thresholds. The strips were placed on the anterior tongue for 10 s. Subjects were asked to report the onset of any sensory perception, quality and duration of sensory perception. Thresholds were estimated in two ways: (1) threshold (THR1) related to sensory perception and (2) intensity related threshold (THR2). The test was applied to 63 healthy subjects (mean age 40 years; 34 women, 29 men). For whole-mouth testing with capsaicin, a small but significant correlation was found between THR1 and THR2 (r (63) = 0.41). Coefficients of correlation between test and re-test were r (30) = 0.60 for THR1 and r (30) = 0.78 THR2. Neither THR1 nor THR2 indicated either side or sex-related differences. Age-related differences were only found in THR2 scores, which were lower in young subjects (<40 years). Reliable assessment of intraoral trigeminal sensitivity appears to be possible using the presently described technique.