Late sequelae of iatrogenic damage to chorda tympani nerve

The Parasympathetic Root of the Submandibular Ganglion: A Review

The submandibular ganglion is a small fusiform-shaped cluster of cell bodies of the parasympathetic nervous system. Parasympathetic innervation of the submandibular gland is not only responsible for the secretion of saliva, but it also plays a main role in the development and regeneration of the gland. The parasympathetic root of the submandibular ganglion or the posterior branch of the lingual nerve to the submandibular ganglion is one of three roots of the submandibular ganglion. Using standard search engines (PubMed, Google), papers in English discussing the anatomy, embryology, variations, and clinical significance of the parasympathetic root of the submandibular ganglion were reviewed.

Blood supply to the chorda tympani: A review and clinical applications

The chorda tympani (CT) is important in gustatory sensation from the anterior two-thirds of the tongue and in secretomotor innervation to the submandibular and sublingual glands. Although the blood supply to the CT is not well delineated in the literature, some studies have shown that a posterior tympanic branch of the stylomastoid artery supplies CT at its origin from the mastoid segment of the facial nerve. We review the blood supply to the CT comprehensively. A better understanding of the vasculature involved is required to prevent iatrogenic injury during middle ear surgery and complications secondary to ischemia.

Taste Changes in Patients With Middle Ear Surgery by Intraoperative Manipulation of Chorda Tympani Nerve

OBJECTIVES

The aim of study was to evaluate the subjective changes of taste and salivation after middle ear surgery according to chorda tympani nerve (CTN) injury.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

We enrolled 180 patients older than 13 years old who received middle ear surgery.

INTERVENTIONS

The patients were classified into cut, manipulated, and intact groups according to intraoperative assessments of the CTN. The patients responded taste and salivation surveys preoperatively, and 1, 3, and 6 months postoperatively.

MAIN OUTCOME MEASURES

We analyzed results of questionnaires including disturbance rates, severity and character to evaluate taste and salivation functions.

RESULTS

Taste disturbance rate was significantly improved in all groups during follow-up (p < 0.05). The incidence of taste disturbance did not differ significantly between the three groups at each follow-up (p > 0.05). The taste disturbance score improved gradually in the cut and intact groups (p < 0.001), but not in the manipulated group (p = 0.067). Among the patients with taste disturbance, hypoguesia was most common symptom. Incidence of salivation disturbance did not differ between the three groups (p = 0.298). However, this symptom improved significantly only in the intact group (p < 0.001). The taste and salivation disturbance rate was not different between patients with and without chronic otitis media at 3 and 6 months, and both groups showed significant improvement.

CONCLUSIONS

Prevalence of taste and salivation disturbance was similar between three groups until 6 months. However, taste disturbance did not improve in the manipulated group and salivation disturbance improved only in the intact group.

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.

Oral sensory nerve damage: Causes and consequences

Oral sensations (i.e., taste, oral somatosensation, retronasal olfaction) are integrated into a composite sense of flavor, which guides dietary choices with long-term health impact. The nerves carrying this input are vulnerable to peripheral damage from multiple sources (e.g., otitis media, tonsillectomy, head injury), and this regional damage can boost sensations elsewhere in the mouth because of central interactions among nerve targets. Mutual inhibition governs this compensatory process, but individual differences lead to variation in whole-mouth outcomes: some individuals are unaffected, others experience severe loss, and some encounter sensory increases that may (if experienced early in life) elevate sweet-fat palatability and body mass. Phantom taste, touch, or pain sensations (e.g., burning mouth syndrome) may also occur, particularly in those expressing the most taste buds. To identify and treat these conditions effectively, emerging clinical tests measure regional vs. whole-mouth sensation, stimulated vs. phantom cues, and oral anatomy. Scaling methods allowing valid group comparisons have strongly aided these efforts. Overall, advances in measuring oral sensory function in health and disease show promise for understanding the varied clinical consequences of nerve damage.

Hyposalivation after undergoing stapedectomy

BACKGROUND

Treatment for otosclerosis involves patients' undergoing stapedectomy. Inadvertent damage to the chorda tympani nerve's (CTN's) secretory fibers during stapedectomy can result in inadequate secretory stimulation of the submandibular salivary glands (SMSGs) and sublingual salivary glands (SLSGs). Because most saliva originates from these glands, hyposalivation and subjective xerostomia manifest during resting periods when parotid gland secretions are minimal. Stimulation with food increases parotid gland salivation enough to overcome the subjective sense of dryness.

CASE DESCRIPTION

The author examined a 52-year-old man who had undergone bilateral stapedectomy because of hearing loss; his rheumatologist referred him to the Salivary Gland Center (New York City) because of a complaint of dry mouth. After the author examined the patient, he concluded that the patient had decreased SMSG and SLSG secretion and recommended that the patient use sugarless chewing gum or sour candy frequently to stimulate his parotid glands and use oral lubricants and sip water as needed.

CLINICAL IMPLICATIONS

Stimulation of parotid gland secretion is independent of SMSG and SLSG activation. Therefore, the dental practitioner must become aware of the innervation of the salivary glands and each gland's secretory production during periods of oral stimulation and of rest.

Light and Electron Microscopic Observation of Regenerated Fungiform Taste Buds in Patients with Recovered Taste Function after Severing Chorda Tympani Nerve

Objectives:

The aim of this study was to evaluate the mean number of regenerated fungiform taste buds per papilla and perform light and electron microscopic observation of taste buds in patients with recovered taste function after severing the chorda tympani nerve during middle ear surgery.

Methods:

We performed a biopsy on the fungiform papillae (FP) in the midlateral region of the dorsal surface of the tongue from 5 control volunteers (33 total FP) and from 7 and 5 patients with and without taste recovery (34 and 29 FP, respectively) 3 years 6 months to 18 years after surgery. The specimens were observed by light and transmission electron microscopy. The taste function was evaluated by electrogustometry.

Results:

The mean number of taste buds in the FP of patients with completely recovered taste function was significantly smaller (1.9 ± 1.4 per papilla; p < 0.01) than that of the control subjects (3.8 ± 2.2 per papilla). By transmission electron microscopy, 4 distinct types of cell (type I, II, III, and basal cells) were identified in the regenerated taste buds. Nerve fibers and nerve terminals were also found in the taste buds.

Conclusions:

It was clarified that taste buds containing taste cells and nerve endings do regenerate in the FP of patients with recovered taste function.

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.

The changes in submandibular gland size and function following chorda tympani section

To investigate the effects of chorda tympani section on submandibular gland size and function in the early (postoperative day 7) and late (postoperative month 6) postoperative period by ultrasonography, scintigraphy, and biochemical analysis of the saliva patients with unilateral chronic otitis media. One-hundred and thirty patients (46 males and 84 females) who were ≥16 years of age and diagnosed with unilateral chronic otitis media and for whom type 1 tympanoplasty was indicated in 1st Outpatient Clinic of Kartal Dr. Lutfi Kirdar Training and Research Hospital between August 2004 and February 2007 were enrolled in the study. Of 130 patients, 102 patients who were eligible and gave written approval were included in the study. However, of these patients 99 underwent type 1 tympanoplasty and 3 had a canal down mastoidectomy. In 99 patients, chorda tympani nerves of 16 were cut, but 3 patients had to be excluded due to allergic reactions. Before the operation, bilateral submandibular gland ultrasonography was performed on all patients and the anterior-posterior length, the frontal lateral-medial width (transverse), and the paramandibular depth of both submandibular glands were measured. In scintigraphic examinations, perfusion index (PI), uptake ratio and excretion fraction were measured. Then, in biochemical analysis of the saliva the levels of sodium, potassium, chloride, calcium, magnesium, amylase, and the values of pH and density were assessed by the saliva collection through Wharton duct. In the statistical comparison of operated and healthy side of the patients with respect to these parameters Mann-Whitney U test, and in intragroup analysis Wilcoxon test was used. The volume of the submandibular gland of the operated side was significantly lower compared to the healthy side in postoperative month 6 (P < 0.05). According to the baseline volume of the submandibular gland of the healthy side, the increase in postoperative day 7 and month 6 were found to be statistically insignificant (P > 0.05). According to the baseline PI value, the decreases in the PI value in the postoperative day 7 and postoperative month 6 were statistically significant (P < 0.01). The uptake ratio of the patients was lower in the postoperative day 7 and month 6 than those at the baseline; however, the difference was statistically insignificant (P > 0.05). The excretion fraction values in the postoperative day 7 were significantly lower than the baseline values (P < 0.05), whereas the decrease in the EF values in the postoperative month 6 were statistically insignificant (P > 0.05). In conclusion, the present study was the first in the literature in which three parameters of assessment, such as ultrasonography, scintigraphy, and biochemical analysis, were used to determine the changes in submandibular gland size and function following the chorda tympani section. After chorda tympani section, the volume of submandibular gland decreased in the late postoperative period. Moreover, chorda tympani section led to decrease in the saliva secretion and the PI value of the patients in the early and late postoperative period.

Incidental Finding of Dysgeusia Relieved by Injections of Botulinum Toxin A

OBJECTIVE

We report the unique finding of hemifacial spasm and associated dysgeusia that resolved after treatment with botulinum toxin A (BTX-A).

STUDY DESIGN

Case report.

METHODS

Three years after undergoing resection of an acoustic neuroma and subsequent resolution of postoperative left-sided facial nerve palsy, a 38-year-old woman presented with new onset of facial spasm and dysgeusia.

RESULTS

After three courses of BTX-A injections during a 2-year period, symptoms of both facial spasm and dysgeusia resolved after treatments and returned between treatments.

CONCLUSIONS

These findings, which have not been reported previously in the literature, indicate a potential role for BTX-A in the treatment of surgically associated dysgeusia.

Clinical and biological features associated with taste loss in internal medicine patients. A cross-sectional study of 100 cases

Which are the main features associated with taste loss in patients exposed to a wide range of drugs and diseases? In 100 consecutive patients admitted to a ward of internal medicine, we assessed taste complaints, performance status, alcohol and tobacco consumptions, diseases, drugs and laboratory data, measuring the electrical taste threshold as primary outcome. After adjusting for age, taste thresholds were not associated with sex, body mass index, tobacco, thrush, drugs, aliageusia and phantogeusia. Features associated with threshold increase included alcohol intake>or=10 gd-1, impaired performance status, complaint of taste loss, atrophic glossitis, cerebral disease, and an erythrocyte mean corpuscular volume. A multivariate analysis identified age, alcohol intake, complaint of loss or altered taste, mean corpuscular volume, and performance status as independent factors associated with taste loss. Inpatients may be screened for taste loss by a few features, to identify those for whom a nutritional intervention should be focused.

The effects of the chorda tympani damage on submandibular glands: biometric changes

OBJECTIVE

It was aimed to analyze the biometric changes in ipsilateral submandibular glands of patients with unilateral chorda tympani (ChT) section during otological operations, compared with change in size of the contralateral glands and with those of healthy subjects.

METHODS

29 patients with unilateral complete ChT section and 29 healthy subjects with identical ages, genders, and weights to the patient group were examined ultrasonographically. The patients having a mean duration to follow-up examination of 32 months (2-84 months) were subdivided into two groups by their time to follow-up as short-term patient group (2-12 months, 14 patients) and long-term patient group (13-84 months, 15 patients). The ultrasonographic dimensions and volumes of submandibular glands were compared statistically between the groups.

RESULTS

In the patient group, the glands on the contralateral, non-operated side were found to be greater than the ipsilateral, denervated glands in terms of both paramandibular depth dimension (P<0.05) and volume (P<0.01). The differences could be determined only in long-term patient group. When comparing the submandibular glands of the patient group with those of the control group, it was found that paramandibular depth dimension and volume of the submandibular glands on the contralateral, non-operated side were statistically greater (P<0.01). There was no difference between submandibular glands on the operated side of the patient group and those of the control group (P>0.05).

CONCLUSION

The late (13-84 months) biometric results of ChT damage on submandibular gland were significant for increase in the size of the contralateral, non-denervated submandibular gland. An atrophying effect was not ascertained in the submandibular glands denervated parasympathetically due to the section of the ChT.

Taste disturbance in two patients after dental anesthesia by inferior alveolar nerve block

We report two cases of temporary taste disturbance after inferior alveolar nerve block. The first patient to present with this rare complication of anesthesia for dental surgery was a 41-year-old woman. She lost the sense of taste on the left side of her tongue after local anesthesia for treatment of a left mandibular molar and first visited our outpatient clinic complaining of taste disorder 3 months later. Electrogustometry (EGM) and filter paper disk (FPD) testing revealed a taste disturbance in the innervation area of the left chorda tympani nerve and atrophy of the fungiform papillae on the left side of the tongue was observed. Eleven months after the dental treatment, the fungiform papillae and the results of EGM were normal. The second patient, a 22-year-old woman, received local anesthetic for extraction of a right mandibular molar and subsequently developed loss of taste on the right side of the tongue. When she visited our outpatient clinic 3 months later, atrophy of the fungiform papillae on the right side was observed. Her gustatory sense began to improve 4 months after the dental surgery and was normal at 13 months. From these findings we conclude that taste disturbance on the same side as the inferior alveolar nerve block in each case was due to direct injury to the chorda tympani and lingual nerves during administration of the local anesthetic. The results of EGM and FPD testing were diagnostic: atrophy of the fungiform papillae on the same side and disappearance of taste on the same side in the intravenous taste test provided complementary diagnostic information. The outcome was satisfactory in both cases.

Response of the gustatory system to peripheral nerve injury

Peripheral taste nerve damage occurs as a result of disease and surgery. The response depends on the taste field affected and the species. Nerve regeneration is robust after the nerve is crushed or after it is cut if the severed ends are anastomosed. Taste buds, which appear after nerve regeneration, may be derived from dormant stem cells outside of taste buds or from remnants of taste buds that persist following denervation. Sprouting by intact taste nerves into denervated fields apparently does not occur. Regenerated primary afferents have taste response specificity, but it is unknown if neural response types are retained peripherally or centrally. Recent behavioral studies show specific deficits following loss of restricted taste fields in rodents, but little is known about recovery after nerve regeneration. Specific deficits have not been demonstrated in humans, although taste sensitivity has been correlated with numbers of taste buds. Enigmas such as these may be solved once the response of the central nervous system to gustatory nerve injury is defined.

The effect of chorda tympani section on ipsilateral and contralateral salivary secretion and taste in man

Bilateral chorda tympani section is an accepted treatment for troublesome sialorrhoea. Nevertheless the effects of this operation have been poorly studied. Twenty patients were studied with unilateral chorda tympani section and a healthy contralateral ear. The effects on ipsilateral and contralateral stimulated submandibular and parotid flow and taste recognition and detection thresholds were measured. Stimulated submandibular flow accounted for only 27% of the total salivary flow. Chorda tympani section had no effect on submandibular flow in seven patients and only reduced submandibular flow by approximately 54% in the remaining 13 patients. No significant effect was observed on ipsilateral parotid flow rate. Electrogustometric taste detection thresholds were more than twice the accepted upper limit of normal on the lesioned side and taste recognition thresholds were also markedly abnormal. Chorda tympani section alone is a poor method of reducing stimulated salivary flow.

The effects of tympanic neurectomy and chorda tympanectomy on experimentally induced parotid duct fistulae in rabbits

To study the effects of parasympathetic denervation on the secretory activity of parotid fistulae, polyethylene catheters were introduced bilaterally into the parotid main excretory ducts of 10 rabbits, followed by unilateral parasympathectomy performed by segmental resection of the tympanic plexus and the chorda tympani nerve. Although salivary flow from the fistulae of the denervated parotid glands stopped up to 8 days earlier than that from the healthy (control) glands, the effect of parasympathectomy was not strong enough to recommend this operation as the method of choice for the clinical inactivation of persistent parotid fistulae.