Chorda tympani nerve function after middle ear surgery

Complications of Surgery: Recognition and Management

The middle ear and mastoid spaces contain delicate and functionally important structures. Safe cholesteatoma surgery requires mastery of otologic anatomy as well as thorough preoperative investigation. Cholesteatoma can damage otologic structures on its own; however, there is also an opportunity for an iatrogenic complication given the distortion of anatomy by the disease process. This article explores complications that can occur during cholesteatoma surgery, guidance on how to avoid intraoperative complications, and treatment of such complications.

Taste Disorders After Middle Ear Surgery: Chorda Tympani Nerve Injury and Quality of Life

OBJECTIVE

To evaluate taste disorders after middle ear surgery, their modifying factors especially chorda tympani nerve injury or underlying otologic disease. We investigated consequences of taste disorders on quality of life.

STUDY DESIGN

Prospective cohort study.

SETTING

Monocentric study in tertiary care center.

METHODS

A total of 214 patients who underwent middle ear surgery were included. Data regarding taste disorders were collected by questionnaires over a 1-year follow-up period.

RESULTS

Taste disorders were reported in 42.7% at 10 days, in 23.3% at 4 months, and in 9.2% 1 year postoperatively. When the chorda tympani nerve was initially healthy, taste disorders were more frequent after its transection throughout the follow-up period. When it was involved in a cholesteatoma or inflammatory process, postoperative taste disorders were more frequent after nerve stretching. Postoperative discomfort in daily life was rated on the Likert scale at 3.5 out of 10. Dietary modifications were reported by 25.8% of patients, and mood alterations by 15% of patients.

CONCLUSION

Taste disorders are frequent after middle ear surgery although they mostly improve in the first months. When the CTN is healthy, cutting it leads to more taste disorders than stretching it, thus advocating its preservation to prevent these symptoms. However, in cases of pathological CTN, cutting this nerve, which is sometimes necessary to control the disease, is less likely to cause taste disorders than stretching it. These taste disorders are a source of discomfort and may present risks of dietary modifications and emotional impact.

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.

Taste Alteration in External Auditory Canal Cholesteatoma: Indicator of Impending N VII Affection

INTRODUCTION

External auditory canal cholesteatoma (EACC) is a rare disease, with an estimated incidence of approximately 1:1,000 adult and 1.6:1,000 pediatric otologic patients. Systematic studies of chronic ear disease and taste alteration prior to surgery are rare; in fact, there are no such studies for EACCs. Therefore, we describe chorda tympani nerve (CTN) dysfunction and the related clinical consequences in EACC patients.

METHODS/STUDY DESIGN

Between 1992 and 2021, we retrospectively analyzed the symptoms, signs, and radiological and intraoperative descriptions of CTN involvement in 73 patients. Liquid taste tests and, since 2009, Taste StripsTM as well as an olfactory screening test (Smell DiskettesTM) have been performed for all symptomatic patients and, when feasible, all other EACC patients.

LEVEL OF EVIDENCE: 4

RESULTS

Ten of 73 patients complained subjectively of dysfunction, and 8 showed abnormal taste test results. Four patients complained of olfactory dysfunction (3 cases with pathological taste tests). Gustatory dysfunction was most frequent in radiogenic EACC cases (n = 4), followed by postoperative EACC (n = 3). Two postoperative patients were asymptomatic despite abnormal test results. Rarely, patients with idiopathic (n = 2) and posttraumatic (n = 1) EACC showed acute taste dysfunction that was confirmed in each with abnormal test results.

DISCUSSION/CONCLUSION

CTN dysfunction often developed asymptomatically in chronic ears, except for idiopathic and posttraumatic EACCs under previous healthy middle ear conditions. Taste disturbance is not a cardinal symptom of EACC, but objective testing suggests that up to one out of 10 EACC patients with advanced disease may experience regional gustatory dysfunction prior to surgery. Especially in context of a new and acute presentation, regional taste dysfunction may alert the clinician of potential progressive EACC invasion and danger to the facial nerve.

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.

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.

Chorda tympani nerve course and feasibility of its preservation during atresiaplasty for congenital aural atresia

Objectives

The association between the chorda tympani nerve (CTN) and atresiaplasty has not been investigated. This study aimed to describe the course of the CTN observed during atresiaplasty for congenital aural atresia (CAA) and explore the feasibility of CTN preservation.

Methods

In this retrospective study, six consecutive patients who underwent atresiaplasty in a tertiary academic center were included. The course of the tympanic segment of the CTN and its preservation feasibility were evaluated. Atresiaplasty was performed using an anterior approach. The average Jahrsdoerfer score was 8.7 points (range, 8-9 points).

Results

The CTN was located in the atretic plate in all patients. It emerged from an average of 5.6 mm (range, 5.2-6.1) inferior to the incus buttress and crossed the middle ear in an anterior-superior direction. The distance between the neck of the malleus and the CTN varied in the absence of the malleus handle. However, when the malleus handle developed, the CTN passed between the incus and the malleus handle. The CTN was preserved in two of the six patients. They had a Jahrsdoerfer score of 9 and grade I microtia.

Conclusion

The CTN was located in the atretic plate, emerging from an average distance of 5.6 mm inferior to the incus buttress. The incus buttress might serve as a good anatomical landmark to identify and preserve the CTN. CTN preservation is feasible in atresiaplasty candidates with a Jahrsdoerfer score of 9 and auricular deformity of grade I.

Level of Evidence

4.

Change in chorda tympani nerve function after two-stage tympanoplasty for cholesteatoma

Objectives

Chorda tympani nerve (CTN) function may be damaged more by two-stage than by one-stage surgery for middle ear cholesteatoma. However, few studies have reported the relationship between two-stage cholesteatoma surgery and CTN function. This study aimed to investigate CTN function after two-stage surgery for cholesteatoma.

Methods

In this prospective study, 35 patients underwent two-stage canal wall up tympanoplasty (CWUT). Perioperative CTN function was assessed using questionnaires and electrogustometry (EGM). Participants were categorized into minor, major, and section groups, based on the degree of CTN manipulation during surgery.

Results

In the first-stage surgery, posterior tympanotomy with an intact canal wall reduced the degree of CTN manipulation. The incidence of taste disorder after the first-stage surgery was 71.4%. Postoperative taste disorder and the EGM threshold improved early in the minor manipulation group. In the second-stage surgery, no new CTN damage occurred, even if this surgery involved removal of residual cholesteatoma. The incidence of taste disorder after second-stage surgery was less than that after first-stage surgery, independent of CTN preservation. However, the recovery rate of the EGM threshold after second-stage surgery was significantly lower in the section group than in those with CTN preservation.

Conclusion

CTN function, including symptoms and EGM threshold, can be preserved during two-stage cholesteatoma surgery if care is taken to preserve the CTN in both the first- and second-stage surgeries. A two-stage CWUT, ensuring an intact bony annulus, may be effective to facilitate CTN preservation.

Level of Evidence

2b.

Taste impairment after endoscopic stapes surgery: Do anatomic variability of chorda tympani and surgical technique matter? : Post-operative dysgeusia after EStS

PURPOSE

To investigate how the anatomical configuration of the oval window region (OWR) influences the management of the chorda tympani (ChT) and the curetting of adjacent bony structures, in a setting of patients undergoing endoscopic stapes surgery (EStS); to assess the incidence of early and late post-operative dysgeusia and to identify anatomical and surgical factors influencing taste function after EStS.

METHODS

Surgical video recordings of 48 patients undergoing EStS for otosclerosis between January 2019 and July 2020 were retrospectively revised, to classify the anatomical variability of selected middle ear structures and the management strategies for the ChT. Clinical records of included patients were reviewed for subjective early and late post-operative taste impairment using a 5-point Likert-scale.

RESULTS

The most common configuration of the OWR was type III. The extension of the bony curettage resulted inversely proportional to the exposure of the OWR. The long-term rate of preserved post-operative taste function was 85%. Displacement of the ChT was necessary in 43/48 cases (90%), mostly medially (36/48, 75%).

CONCLUSION

Bone curetting during EStS does not correlate with post-operative taste impairment. Despite 100% ChT preservation rate, dysgeusia may occur in a minority of patients, with no apparent relationship to anatomical variability or intraoperative management of the ChT. The use of CO₂ laser could have a role in increasing the risk of post-operative dysgeusia after EStS.

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.

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.

[The modern state and prospects of development of endoscopic otosurgery]

In this review presents data on efficiency endoscopic operations at some ear diseases. Now endoscopic operations are widely applied at primary and residual (or recuring) middle ear cholesteatomas, tympanic membrane perforation, otosclerosis and cochlear implantation. Proceeding from resolving power of endoscopic technology, endoscopic operation can be applied as an independent method, or as an endoscopic assisted, to be combined with otomicrosurgery operation. Efficiency of endoscopic operation in many respects is defined by a possibility of panoramic visualization of anatomical structures of middle and inner ear, and also carrying out high-quality elimination of focus lesion from areas, being remote when performing otomicrosurgery operation.

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.

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.

Taste and olfaction in middle ear surgery

OBJECTIVE

The aim of this study was to assess pre- and postoperative taste ability in patients undergoing middle ear surgery for otosclerosis or chronic otitis media. Olfactory function was also evaluated to rule out taste deficits due to concomitant nasal pathology.

METHODS

All patients underwent ear, nose, and throat examination, otomicroscopy, nasal endoscopy, anterior rhinomanometry, taste testing, and olfactory testing. Patients were evaluated at 1 to 5 days preoperatively (T0), and at 1 (T1), 6 (T6), and 12 (T12) months postoperatively.

RESULTS

Both groups of patients experienced worsening of the mean taste threshold postoperatively. This phenomenon was more serious in poststapedotomy patients. Follow-up showed progressive improvement in both groups. All values of olfactory testing were within the normal range for otosclerosis patients. Patients with chronic otitis media showed variable postoperative findings.

CONCLUSION

Chorda tympani function can be negatively affected by middle ear surgery. Deficits may be more marked in stapedotomy patients than in those undergoing tympanoplasty. Postoperative recovery of taste is satisfactory, although with different timelines for the 2 types of pathology.

Contemporary surgical management of vestibular schwannomas: analysis of complications and lessons learned over the past decade

BACKGROUND

Despite advanced microsurgical techniques, more refined instrumentation, and expert team management, there is still a significant incidence of complications in vestibular schwannoma surgery.

OBJECTIVE

To analyze complications from the microsurgical treatment of vestibular schwannoma by an expert surgical team and to propose strategies for minimizing such complications.

METHODS

Surgical outcomes and complications were evaluated in a consecutive series of 410 unilateral vestibular schwannomas treated from 2000 to 2009. Clinical status and complications were assessed postoperatively (within 7 days) and at the time of follow-up (range, 1-116 months; mean, 32.7 months).

RESULTS

Follow-up data were available for 357 of the 410 patients (87.1%). Microsurgical tumor resection was performed through a retrosigmoid approach in 70.7% of cases. Thirty-three patients (8%) had intrameatal tumors and 204 (49.8%) had tumors that were <20 mm. Gross total resection was performed in 306 patients (74.6%). Hearing preservation surgery was attempted in 170 patients with tumors <20 mm, and good hearing was preserved in 74.1%. The main neurological complication was facial palsy (House-Brackmann grade III-VI), observed in 14% of patients (56 cases) postoperatively; however, 59% of them improved during the follow-up period. Other neurological complications were disequilibrium in 6.3%, facial numbness in 2.2%, and lower cranial nerve deficit in 0.5%. Nonneurological complications included cerebrospinal fluid leaks in 7.6%, wound infection in 2.2%, and meningitis in 1.7%.

CONCLUSION

Many of these complications are avoidable through further refinement of operative technique, and strategies for avoiding complications are proposed.

Surgery of the ear and the lateral skull base: pitfalls and complications

Surgery of the ear and the lateral skull base is a fascinating, yet challenging field in otorhinolaryngology. A thorough knowledge of the associated complications and pitfalls is indispensable for the surgeon, not only to provide the best possible care to his patients, but also to further improve his surgical skills. Following a summary about general aspects in pre-, intra-and postoperative care of patients with disorders of the ear/lateral skull base, this article covers the most common pitfalls and complications in stapes surgery, cochlear implantation and surgery of vestibular schwannomas and jugulotympanal paragangliomas. Based on these exemplary procedures, basic "dos and don'ts" of skull base surgery are explained, which the reader can easily transfer to other disorders. Special emphasis is laid on functional aspects, such as hearing, balance and facial nerve function. Furthermore, the topics of infection, bleeding, skull base defects, quality of life and indication for revision surgery are discussed. An open communication about complications and pitfalls in ear/lateral skull base surgery among surgeons is a prerequisite for the further advancement of this fascinating field in ENT surgery. This article is meant to be a contribution to this process.

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.

Endoscopic transcanal stapedotomy: how I do it

Current paper presents a surgical technique and preliminary results of the first eight consecutive fully endoscopic transcanal stapedotomies. All eight procedures were performed under local anesthesia by the same surgeon using rigid endoscopes of 3-mm diameter, 14-cm length, 0° and 30°. A posterior tympanomeatal flap was elevated transmeatally with the 0° endoscope and then transposed anteriorly. Stapes fixation was confirmed, the stapes tendon was cut with curved micro-scissors, and the stapes was separated from the incus in the incudo-stapedial joint. The anterior and posterior stapedial crus were carefully fractured, and the superstructure was removed. The hole in the foot-plate was created with a Skeeter microdrill using a 0.5-mm-diameter diamond burr. A platinum/fluoroplastic piston prosthesis (0.4-mm diameter) was placed into this hole and fitted along the long process of the incus. The tympano-meatal flap was repositioned, and the external auditory canal was filled with Gelfoam(®). The chorda tympani nerve was preserved in all cases. A 4.5-mm prosthesis was used in six cases and a 4.75-mm prosthesis in two. Pure tone audiograms demonstrated improved air- and bone-conduction threshold averages across the three speech frequencies (0.5-1.2 kHz) 6 months after surgery (64 vs. 29.8 dB and 30.6 vs. 25.1 dB, respectively). The average postoperative air-bone gap was within 10 dB in six ears and between 10 and 15 dB in the other two ears. Our preliminary results indicate that transcanal fully endoscopic stapedotomy is a feasible and safe technique for surgical management of hearing loss associated with otosclerosis.

Reactive microglia after taste nerve injury: comparison to nerve injury models of chronic pain

The chorda tympani (CT), which innervates taste buds on the anterior portion of the tongue, is susceptible to damage during inner ear surgeries. Injury to the CT causes a disappearance of taste buds, which is concurrent with significant microglial responses at central nerve terminals in the nucleus of the solitary tract (nTS). The resulting taste disturbances that can occur may persist for months or years, long after the nerve and taste buds have regenerated. These persistent changes in taste sensation suggest alterations in central functioning and may be related to the microglial responses. This is reminiscent of nerve injuries that result in chronic pain, where microglial reactivity is essential in maintaining the altered sensation (i.e., pain). In these models, methods that diminish microglial responses also diminish the corresponding pain behavior. Although the CT nerve does not contain nociceptive pain fibers, the microglial reactivity after CT damage is similar to that described in pain models. Therefore, methods that decrease microglial responses in pain models were used here to test if they could also affect microglial reactivity after CT injury. Treatment with minocycline, an antibiotic that dampens pain responsive microglia, was largely ineffective in diminishing microglial responses after CT injury. In addition, signaling through the toll-like 4 receptor (TLR4) does not seem to be required after CT injury as blocking or deleting TLR4 had no effect on microglial reactivity. These results suggest that microglial responses following CT injury rely on different signaling mechanisms than those described in nerve injuries resulting in chronic pain.

Gustatory changes in patients with chronic otitis media, before and after middle-ear surgery

Objective:

We investigated gustatory changes in patients with chronic otitis media, before and after middle-ear surgery.

Methods:

This prospective study included 38 patients with unilateral chronic otitis media. We used taste testing solutions to evaluate each patient's taste function. Intra-operative assessments of the chorda tympani nerve were also compared and analysed.

Results:

Patients with chronic otitis media had significantly worse ipsilateral perception of sour, bitter and salty tastes. In patients with good intra-operative preservation of the chorda tympani nerve, there was significant improvement in gustatory function one month post-operatively, compared with the pre-operative baseline. In patients who sustained intra-operative chorda tympani nerve injury, one month post-operative gustatory function was the same as the pre-operative baseline.

Conclusion:

Middle-ear surgery for chronic otitis media not only treats the ear but also improves gustatory function in the majority of patients. In patients with intra-operative injury to the chorda tympani nerve, post-operative taste decline is only temporary.

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.

Patients with Phantogeusia Show Increased Expression of T2R Taste Receptor Genes in Their Tongues

Objectives:

The taste receptor gene family T2R has been implicated in the sensation of bitter taste. Phantogeusia is a spontaneous abnormal taste with no external stimulus. We analyzed the expression of T2R taste receptor genes in the tongues of patients with phantogeusia to assess their role in the pathogenesis of phantogeusia.

Methods:

We obtained specimens from 43 patients with phantogeusia and 24 normal volunteers by scraping the foliate papillae and examined these specimens for the expression of 10 T2R taste receptor genes using reverse transcription–polymerase chain reaction and electrophoresis.

Results:

The expression rate (subjects with detectable expression) of the 10 taste receptor genes in the healthy subjects ranged from 16.7% to 100%; 3 receptor genes were found in 50% or fewer of these subjects. In the patients with phantogeusia, the expression rate was increased significantly compared to that in the healthy control subjects for 3 of the 10 receptor genes examined.

Conclusions:

Our results show that the expression rate of some of the T2R taste receptor genes was increased significantly in patients with phantogeusia. These results suggest that increased expression of taste receptor genes is involved in the pathogenesis of phantogeusia; this finding may contribute to elucidation of the mechanism of this disorder.

Taste disturbance after mastoid surgery: immediate and long-term effects of chorda tympani nerve sacrifice

Objective:

To determine the immediate and long-term taste effects of chorda tympani nerve sacrifice in patients undergoing open cavity mastoidectomy.

Design, setting and participants:

A retrospective, questionnaire survey of patients receiving follow up and aural toilet following open cavity mastoidectomy, over a four-month period. The questionnaire assessed taste disturbance, both immediately post-operative and current. Available surgical records were reviewed for chorda tympani references.

Results:

Of 57 patients, six had undergone surgery to both ears. Of those who could recall (37/57), 24.3 per cent were aware of taste disturbance immediately after surgery, while 8.7 per cent reported current disturbance (median post-operative interval, 28.5 years; range, one month to 67 years). No bilateral surgery patients were aware of taste disturbance.

Conclusion:

Mastoidectomy consent procedure emphasises the risk of hearing loss and facial nerve injury, yet in open cavity surgery chorda tympani division is almost inevitable. Reassuringly, most post-operative taste disturbance resolves, and most patients are not aware of long-term disturbance. However, a small percentage suffer ongoing taste disturbance; this could be significant for professional chefs and wine-tasters. The risk of taste disturbance should be addressed in the consent procedure.

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.

Chorda tympani nerve analysis with electron microscopy in chronic suppurative otitis media

CONCLUSION

Chronic suppurative otitis media causes some disturbance to the chorda tympani nerve (CTN), which may affect the facial nerve. It is not possible to perform a biopsy of the main truncus of the facial nerve, therefore studies of the CTN might show possible pathologic or physiologic changes of the facial nerve in the future.

OBJECTIVES

The specific aim of this study was to investigate the effects of chronic suppurative otitis media on the CTN.

METHODS

The tympanic segments of CTNs were collected for ultrastructural investigations in patients with chronic suppurative otitis media who underwent canal wall-down tympanoplasty. The study population comprised 10 patients, 7 males, 3 females; the age range was 16-66 years, and the mean age was 38. Qualitative and semiquantitative evaluations were performed on the specimens of CTN by electron microscopy.

RESULTS

Our histopathologic examinations showed that there were changes of varying severity in all the CTNs such as scarcity of unmyelinated nerve fibers, Schwann cell nucleus condensation, scarcity of Schwann cell cytoplasm, adaxonal vacuolation and edema, myelin sheath disintegration, shrunken electron-dense axoplasm, increased collagen fibers, adaxonal circular lamellar complex, interstitial edema, and vacuolation of Schwann cell cytoplasm.

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.