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.

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Introduction

Systematic studies of chronic ear disease and taste alteration prior to surgery are rare; in fact, there are no such studies for external auditory canal cholesteatoma (EACC). Therefore, we describe taste alteration, i.e., chorda tympani nerve (CTN) dysfunction and the related clinical consequences in EACC patients.

EACC is a rare disease, with an estimated incidence of approximately 1:1,000 adult [1] and 1.6:1,000 pediatric [2] otologic patients. Similar to the better known cholesteatoma of the middle ear, EACC has the potential to damage the facial nerve (FN) [1, 3, 4], which is one reason why preoperative computed tomography (CT) imaging is highly recommended to identify this complicating situation [5]. The FN and its branch, the CTN, may not only be affected by direct bone invasion by EACC [6] but also by pressure reactions or inflammatory complications of the neurovascular structures [7, 8].

In contrast to sporadic case reports on FN motor function impairment [9-13], we identified only a single report on CTN damage by EACC [14] in the MEDLINE. Moreover, we could not locate any systematic study about the relevance of CTN involvement and taste dysfunction caused by EACC. This lack of data contrasts with robust data about taste function being affected by middle ear cholestatoma and ear surgery [15]. Only little is known about taste function influenced by ear disease prior to surgery [16, 17]. Thus, this study provides the first case series of taste function and CTN involvement in EACC patients.

Methods and Patients

Between January 1992 and June 2021, we retrospectively studied the EACC patients in our outpatient clinic at the Inselspital, University Hospital of Bern, Switzerland (a tertiary referral center that serves 1.5 million inhabitants) and evaluated the history of all patients with either complaint of taste disturbance or abnormal objective taste test results. All identified EACC cases in our institution have been systematically assessed on etiologic grounds according to the modified classification by Holt [18, 19]. Preoperative CT analysis has been performed as proposed by Shin [20] and radiological EACC extension to the neural structure has been retrospectively analyzed using the software program 3DSlicerTM (http://www.slicer.org) [21]. For final decisions about disease staging [22] and CTN and FN involvement, descriptions of the intraoperative findings have been used as the proposed gold standard in the literature [23].

Assessment of Gustatory Function

All EACC patients had to answer specific questions about CTN dysfunction; i.e., regional qualitative changes in bitterness, sweetness, sourness, and saltiness; stimulated or unstimulated dysgeusia; and especially metallic-taste dysgeusia, as proposed by a large epidemiologic study in 1991 [24]. Patients’ records have been reviewed for medications with potential taste-disturbing side effects and for confounding comorbidities, e.g., uncontrolled hypothyroidism and diabetes mellitus.

In clinical routine, pre- and postoperative taste function was assessed using a qualitative suprathreshold test that includes four taste qualities: sweet, sour, salty, and bitter. Between 1992 and 2010, testing was performed solely with liquid solutions of 10% sucrose for sweet, 5% citric acid for sour, 7.5% sodium chloride for salt, and 0.1% quinine sulfate for bitter [24] at our institution. This screening test has been widely promoted [25, 26] and tested in otology patients [27]. The test solutions were applied using cotton tip swaps on a 1 × 2-cm area unilaterally at the anterior third of the protruded tongue. Care was taken in keeping a 1-cm distance from the midline of the tongue in order to exclusively test the unilateral region of CTN supply. The tested patient was confronted with a panel depicting the four tested taste qualities. With the tongue still protruded to prevent contamination from whole-mouth testing, the subject had to point to the corresponding taste quality in the list on the panel. The subjects had to use a forced-choice paradigm and to select the most accurate answer. The four taste qualities are presented randomly: first to the tongue side contralateral to the side of the affected ear, and then on the side of the tongue on the ipsilateral side of the EACC.

Since 2010, the more time-consuming quantitative testing with commercially available taste strips [28, 29] (Burghart Medizintechnik, Tinsdaler Weg 175, 22880 Wedel, Germany) has been applied in selected cases. The protocol for this study has been reviewed by the Local Ethical Committee and Institutional Review Board (protocol No. 17-09-13).

Assessment of Olfactory Function

In addition to taste perception, all patients were also asked about subjective abnormal sense of smell. We also screened patients for coexisting normal or abnormal smell function (hyposmia/anosmia) to identify potential altered olfactory function as a confounder of altered taste function [30, 31]. In clinical routine, we used smell diskettes as a suprathreshold olfactory screening test as outlined and validated by Briner et al. [32]. Because of time constraints in a busy outpatient clinic, we had to restrict olfactory screening to EACC patients with either a symptomatic smell or taste problem or with an abnormal taste test result.

Results

We reviewed all our EACC patients between January 1992 and June 2021. In 73 out of 127 cases, we could retrieve reliable records of symptoms of taste or smell dysfunction; patients who had incomplete files or had medications or comorbidities with potential taste dysfunction and side effects were excluded. Thirty-seven patients denied chemosensory dysfunction at the time of EACC diagnosis and had no objective test.

Thirty-six of the 73 patients also had documented objective assessments of taste and smell function, including all of the symptomatic patients who complained of gustatory dysfunction. Finally, we identified 12 cases with symptoms or abnormal (gustatory or olfactory) chemosensory test results (Table 1). Median age of the patients was 48 years (range 30–63), six right ears (no bilateral involvement).

Table 1.

EACC patients with anomalous subjective or objective gustatory function as well as additional symptoms

Remarkably, only 2 of 73 patients (2.7%, i.e., patient No. 1 and patient No. 4) remembered an acute onset of their taste deficit the last 4 weeks before the ENT consultation. The remaining patients were either completely unaware or only vaguely reported on the beginning of the chemosensory deficits. Four patients (No. 7, 9, 10, 11) complained of a reduced sense of smell (in 3 cases combined with gustatory symptoms), whereas 2 patients did not note a chemosensory deficit at all (No. 5, 6).

Pathological test results (n = 9) and the 3 cases with subjective gustatory problems but normal test results are described in Table 1. In 3 cases, the patients had mistaken a gustatory dysfunction for an objectively measured olfactory dysfunction. Five patients showed a smell test result compatible with hypo- or anosmia; in 3 cases, these results occurred in the context of mixed functional olfactory and gustatory impairment. Two of the 3 patients with additional complaints compatible with burning mouth syndrome had measurable taste dysfunction and additional subjective xerostomia.

Altered Taste Function according to the Different Etiological EACC Groups

Screening patients by their etiology of the EACC [18, 19], we obtained objective test results in addition to self-ratings for 19 of 38 idiopathic patients, 8 of 14 postoperative patients, 3 of 8 posttraumatic patients, 2 of 7 post-stenotic patients, and 4 of 6 radiogenic EACC patients. Unfortunately, the rare etiology of three children with post-tumorous EACC after remission of Langerhans’ cell histiocytosis [19] had to be excluded because chemosensory function has not been documented in the pediatric files.

The highest proportion of patients with severe objective chemosensory dysfunction was in the radiogenic EACC group, with 4 patients showing persistent severe chemosensory dysfunction. Three of them (No. 9, 10, 11) suffered from persistent xerostomia and subjective taste disturbance since their radiochemotherapy.

The second largest proportion with objective taste deficits was found among the group with postoperative EACC (n = 3). However, 2 of these three patients were unaware of their deficits, and 1 patient (patient No. 7) reported only transient reduced smell and taste function lasting for 4 months after her initial ear operation.

Rarely, patients with idiopathic (n = 3) and posttraumatic (n = 1) EACC complained about acute taste dysfunction. One patient with post-stenotic EACC (exostoses) mistook a taste deficit for objective measured smell dysfunction with preserved taste function.

Taste Dysfunction in Relation to Cardinal EACC Symptoms

On first visit, cardinal symptoms of EACC patients with altered taste function included otorrhea (n = 9), aural dysesthesia (n = 5), hearing problems (n = 1), tinnitus (n = 1), and dizziness (n = 1). Only 1 patient reported predominantly acute taste disturbance; another mentioned acute taste alterations only as a minor problem in addition to his putrid otorrhea. Only 3 patients with objective taste dysfunction suffered from otalgia as a potential sign of deep periosteal and bone invasion [4], one of these cases consequently showed intraoperative FN canal erosion (Table 2).

Table 2.

Localization, staging, and treatment of EACC with CTN or FN involvement

CT and Intraoperative CTN Involvement

Localization, CT, and intraoperative EACC extension are summarized in Table 2. Acute symptoms and signs of CTN dysfunction were found in 2 cases which intraoperatively presented a complex surgical situation with bone erosion to the CTN. The first patient had idiopathic EACC (Fig. 1) and transcanal removal of the inflamed bone was possible, with preservation of the CTN. The debrided bony canal wall and nerve were sealed with temporalis fascia and covered by a meatal skin flap.

Fig. 1.

Preoperative coronal CT image of idiopathic EACC (patient No. 1) showing bone sequestration in the region of CTN (thin arrow) and fallopian canal (thick arrow). C indicates cholesteatoma. Frame bottom right: CT scout depicting imaging plane in the coronal view of the skull.

The second patient suffered from posttraumatic EACC and reported putrid otorrhea and acute taste alteration with ipsilateral numbness of the tongue. Because of the destroyed posterior external ear canal (EAC) and superficial spread into the lateral mastoid system (Fig. 2), a canal wall down mastoidectomy with resection of the CTN had to be performed to clean the infected EAC and remove the cholesteatoma.

Fig. 2.

Preoperative coronal CT image of posttraumatic EACC (patient No. 4) with CTN surrounded by bone sequestration (thin arrow) and with fallopian canal (thick arrow). C indicates cholesteatoma. Frame bottom right: CT scout depicting imaging plane in the coronal view of the skull.

FN Affection in CT and Intraoperative Findings

FN affection corresponding to a Naim stage IIIF or higher EACC [22] was encountered in 2 patients. Denuded and swollen FN was present in one case of postoperative EACC (Fig. 3). The patient with postoperative EACC recalled only a transient alteration in taste perception for a period of 4 months after his first ear surgery (antrotomy and tympano-ossiculoplasty) with preservation of CTN. Six years after the operation, she presented with chronic otorrhea but no longer noted regional taste deficits. Preoperative CT depicts the focal erosion of the dorsal EAC and a mastoid system filled by cholestatoma. Intraoperatively, partly denuded and swollen FN has been described by the surgeon performing curative canal wall down revision mastoidectomy (Table 2).

Fig. 3.

Coronal CT image prior to revision surgery of a postoperative EACC (patient No. 7) showing CTN (thin arrow) and fallopian canal (thick arrow). C indicates cholesteatoma with breach in the posterior EAC. Frame bottom right: CT scout depicting imaging plane in the sagittal view of the skull.

One patient with radiogenic EACC (Fig. 4) complained of combined gustatory and olfactory problems. Intraoperatively, extensive osteoradionecrosis was present and a canal wall down mastoidectomy with pedicled muscle flap was necessary to allow proper healing and eradicate the chronic infection.

Fig. 4.

Preoperative coronal CT image of radiogenic EACC (patient No. 10) indicating the course of CTN (thin arrow) and fallopian canal (thick arrow). C indicates cholesteatoma, O indicates osteolytic bone. Frame bottom right: CT scout depicting imaging plane in the coronal view of the skull.

In both of these cases of FN affection, extensive disease with a significant risk to the FN was anticipated in the preoperative CT scan. Both cases were successfully treated with canal wall down mastoidectomy.

Discussion

In contrast to growing data of the effect of middle ear surgery on postoperative taste function [15], there is little information about taste alteration for specific otologic diseases prior to surgery [16, 17, 33-35]. For EACC, none of the 19 more extensive case series published in the English literature [1, 2, 4, 5, 18-21, 36-47] systematically described the symptoms and signs of taste dysfunction. All of these studies focus on the cardinal symptoms, i.e., frequent unilateral otorrhea or otalgia, or they discuss symptoms of potential distinctive features of EACC caused by keratosis obturans (KO) [36].

Sporadic case reports document acute taste alteration as a sign of CTN damage from EACC [14], middle ear cholestatoma [48], EAC lesion [49], or atypical KO [50]. Regarding EACC, however, reports of FN invasion predominate [9-13]. Although our data were limited by the retrospective nature of our study and the rarity of the disease, they illustrate that 12 of 73 EACC patients showed either subjective or objective taste dysfunction. This number of patients might even be higher, especially in cases of chronic unilateral taste disturbance because we did not routinely test every patient and thus cannot exclude cases of missed CTN damage in asymptomatic patients.

Remarkably, we identified two symptomatic patients with acute unilateral taste alteration. In these 2 patients, this ominous sign heralded an intraoperative CTN involvement in the vicinity of FN from invasive EACC. Hence, acute taste dysfunction might be taken as an indicator of more complicated disease.

The highest proportion of patients with taste dysfunction was found in the radiogenic EACC group. In this group, the majority of patients complained of chronic mixed gustatory and olfactory dysfunction. Taste dysfunction is a well-characterized side effect of radiotherapy (RT) or radiochemotherapy [51]. EAC involvement and EACC formation are reported to affect up to 15–33% of patients after RT [52] and were more frequent in the follow-up of radiochemotherapy (n = 3) than unimodal RT (n = 1). Our radiogenic EACC group showed frequently bilateral abnormal taste test results that cannot be explained solely by regional CTN damage ipsilateral to the EACC. As a result of multimodal therapy, the patients had simultaneous epithelial, salivary, and potentially neuropathic alterations that represent competing factors for chemosensory dysfunction.

However, intraoperative erosion of the FN and CTN as complicating factor was reported in one of these cases. This patient (No. 12) described isolated chronic hypogeusia which developed 1 year after local RT of a squamous cell carcinoma of the concha. In contrast to the majority of radiogenic EACC patients with combined mucosal, sensorial, and neural damage to taste function, this case may be the only patient of his group in which isolated EACC formation in osteoradionecrosis was causative for disturbed taste function.

Three out of eight tested postoperative EACC patients (n = 14) had abnormal functional taste test results. However, none of them noticed acute changes in taste function in relation to the EACC formation and patient No. 7 complained of transient taste disturbance in the first 4 months following his first surgery (Table 2). Considering the limited initial surgery performed (i.e., antrotomy and tympano-ossiculoplasty with preservation of the dorsal canal wall) and the subjective recovery of the taste function in the postoperative phase, patient No. 7 might be taken as very plausible example of a postoperative EACC causing his CTN dysfunction.

The habituation to unilateral ageusia is a well described and frequent compensation of the gustatory system for unilateral CTN damage caused by ear surgery [34, 35]. This fact may explain why CTN dysfunction has been gone unnoticed in the discussion of the cardinal symptoms (otorrhea, dull pain, hearing loss) in previous EACC case series, especially in postoperative EACCs.

In the idiopathic and posttraumatic EACC groups, altered taste function had a low incidence. Isolated symptoms of taste dysfunction and in 50% of cases unilateral numbness or metal dysgeusia and the absence of a history for mucosal or neural damage as a competing factor let EACC appear to be the sole causative factor for taste dysfunction in these patients.

Remarkably in this group, objectively measured dysfunction was noticed as an acute change in taste perception in both of the affected patients. These findings for the EACC pathology support the hypothesis that patients without pre-existing middle ear disease were more sensitive to newly compromised CTN function than patients already adapted to chronic compromised CTN function caused by middle ear disease or prior interventions [16, 17, 53-56].

Impact on Treatment Plan

EACC treatment is still a matter of debate. Although the treatment plan is primarily based on the stage of the EACC [20], it should also be tailored to the risks and to the patient’s needs [19, 21, 40, 45]. In this context, taste alterations can have a significant impact on clinical decision-making. Not only can acute taste dysfunction herald extended disease with an impending risk to the main branch of the FN, it should also be taken as a warning sign before too aggressive local EACC cleaning in the outpatient clinic setting is performed. Moreover, information about taste alterations can also help to inform the patient preoperatively and to direct attention regarding the risk of additional FN involvement in its least-demarcated mastoid course, which is notoriously prone to accidental injury during mastoid surgery.

CTN Involvement in EACC Compared with Middle Ear Cholestatoma

Histological data about CTN involvement in chronic ear disease is rare and mostly limited to the tympanic part of the CTN. Previous studies show that the mastoid portion, which contains the iter chordae posterius of the CTN, is better preserved in disease than the tympanic portion [7]. Available data suggest that myelinated fibers transmitting taste function [57] seem to be affected most by inflammatory degeneration [58]. In Naim stages I and II [22], EACC, and especially idiopathic EACC, the middle ear is mostly healthy; thus, the tympanic segment and CTN function are hardly affected by prior disease. Compared with middle ear cholestatoma or KO, idiopathic EACC is said to have the propensity to erode through the dorsal wall into the mastoid [4]. Thus, it could be assumed that EACC spreads toward the mastoid segment of the FN and the CTN [56], whereas middle ear cholestatoma is believed to invade the middle ear cavity through the annulus and tympanic membrane, affecting the CTN first along its tympanic course. One might assume that an acute change in previously normal taste function has a high chance of becoming noticed especially in the idiopathic or posttraumatic with otherwise normal middle ear conditions. However, more research and confirmatory studies are needed.

Conclusion

Taste dysfunction is not a cardinal symptom of EACC, regardless of its etiology. With a conservative estimate, only 1 of 10 EACC patients might be affected corresponding to eight out of 73 EACC patients with pathological taste test results. Regarding the limitations and retrospective nature of our study, more confirmatory research is needed.

Nevertheless, the symptom of taste disturbance especially with acute presentation and with confirmed unilateral abnormal taste function may be an indicator of CTN damage and might potentially herald complicating progression of the disease to the FN. Regional taste dysfunction as sign of CTN involvement developed unnoticed by the majority of the patients, except for those with idiopathic and posttraumatic EACC who had previously healthy middle ear and CTN conditions.

In sum, subjective complaints of taste disturbance are rare in EACC. However, if present and if identified, they might help the otologist to anticipate more complicated disease and to intervene before disease progression to motor dysfunction of FN.

Statement of Ethics

The study has been conducted in accordance with the Declaration of Helsinki. The protocol for this study had been reviewed and approved by the Local Ethical Committee “Kantonale Ethikkomission Bern KEK” with project number 17-09-13 and by the Director of Lehre and Forschung. The need to collect informed consent for every patient was waived by the IRB due to the almost 30 years of retrospective study and the advanced age of the study population of which a substantial proportion already died.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

All the authors declare that they received no funding for this study.

Author Contributions

Lilia Matosevic: data collection and writing; Hergen Friedrich: testing, data collection, and graphics; Simona Negoias: testing and data collection; Cilgia Dür: imaging analysis and graphics; Marco Caversaccio: study design and review; Patrick Dubach: study design, writing, and review.

Data Availability Statement

According to the IRB Guidelines, patients’ raw data had to be stored in the local institution and had to be password saved. Excerpts of the anonymized data can be ordered by appointment with the first author (Patrick Dubach).

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