Sage Journals: Discover world-class research

Abstract

Objective: To analyze the etiology, diagnosis, and treatment of unexplained conductive hearing loss (UCHL) with intact tympanic membrane. Methods: A systematic review was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 642 articles were retrieved from databases such as PubMed, Embase, Web of Science, and Cochrane. Fifty-four research articles and 21 case reports were screened out according to the inclusion and exclusion criteria for analysis of the etiology of UCHL. Seven research articles with UCHL who underwent exploratory tympanotomy were selected for data extraction and analysis of clinical characteristics. Results: UCHL is a common manifestation of various diseases, including congenital ossicular anomalies (COA), otosclerosis (OTS), congenital middle ear cholesteatoma (CMEC), oval window atresia, superior semicircular-canal dehiscence, congenital stapedial footplate fixation, middle ear osteoma or adenoma, congenital ossification of stapedial tendon, and so on. A total of 522 patients were included in the 7 articles; among whom OTS showed a tendency to increase with age. The main symptoms were hearing loss, followed by tinnitus, dizziness, ear fullness, ear pain, facial paralysis. A total of 87.5% to 93.0% patients with COA manifested as nonprogressive deafness that occurred since childhood, with tinnitus incidence of 15.6% to 30.2%, and 86.4% to 96.4% patients with OTS presented with progressive hearing loss, with tinnitus incidence of 60.1% to 90.9%. The diagnosis positive rate of high-resolution computed tomography (HRCT) was 33.8% to 87.1%, and CMEC was higher than that of COA (83.3%-100% vs 28.6%-64%). All the articles reported good hearing recovery. The most common surgical complications included taste abnormalities, tinnitus, and dizziness. Conclusion: UCHL presents with similar clinical manifestations and poses challenges in preoperative diagnosis. Exploratory tympanotomy is the primary method for diagnosis and treatment, with good prognosis after removing the lesion and reconstructing hearing during the operation. Children can also safely undergo the surgery.

Keywords

conductive hearing loss intact tympanic membrane exploratory tympanotomy ossicular anomalies otosclerosis

Introduction

Conductive hearing loss (CHL) results from abnormal sound transmission in the external, middle, and inner ears,¹ with various factors contributing to its occurrence, including genetic abnormalities, embryonic developmental issues, inflammation, trauma, and tumors.^1,2 Among these, inflammation stands out as the most commonly identified cause.^1-4 While most CHL patients can be diagnosed through comprehensive medical history and examination, instances of noninflammatory, nontraumatic CHL, with intact and normal tympanic membrane, present a diagnostic challenge. These cases lack significant abnormal signs, explicit audiological or imaging assessments results, and a history of otitis media or trauma, making it difficult to establish a clear diagnosis.^2,5,6 This particular condition is referred to as unexplained conductive hearing loss (UCHL), and exploratory tympanotomy is the primary method employed for its diagnosis and treatment.^2-8

UCHL arises from abnormalities in the middle ear’s sound transmission structure, manifesting primarily as CHL. Additional symptoms may include tinnitus, ear fullness, dizziness, and ear pain, and so on.^3-10 Congenital UCHL often manifests since childhood or is incidentally discovered, while acquired UCHL, such as otosclerosis (OTS), develops gradually over time.^8,11 Identifying the etiology of UCHL preoperatively proves challenging based solely on clinical manifestations, radiographic, and audiological examinations. Numerous previous articles have reported cases of preoperative diagnostic errors or difficulties. The objective of this article is to review and summarize the clinical characteristics of various types of UCHL reported in the literature, analyze factors affecting diagnosis, and evaluate the benefits of surgical treatment along with potential complications. This information aims to enhance the management and treatment of such diseases in clinical practice.

Materials and Methods

A comprehensive literature search was conducted across multiple databases, including PubMed, Embase, Web of Science, and Cochrane, focusing on the theme of “conductive hearing loss with an intact tympanic membrane.” The search terms utilized were “conductive hearing loss” and “intact tympanic membrane.” Two researchers carried out the literature review independently, culminating in a final search on September 30, 2023. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 642 articles were identified; after eliminating duplicates, 458 articles remained. A detailed flowchart of the study process can be found in Figure 1.

Figure 1.

Project flow chart. Literature evaluation and selection, according to PRISMA criteria (http://www.prisma-statement.org/). PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Exclusion criteria were: (1) various lesions or deformities of the external auditory canal; (2) tympanic membrane perforation; (3) inflammatory middle ear diseases such as secretory otitis media, suppurative otitis media, and so on; (4) sensorineural hearing loss; (5) congenital external ear malformation or genetic syndromes associated with hearing loss; (6) traumatic hearing loss; (7) jugular vein tumors; (8) animal experiments, cadaver studies; (9) conference abstracts, reviews, and meta-analyses; (10) missing references or articles published before 2003. In cases where the title and abstract did not clearly fit into any of the aforementioned criteria, the full text of the research report was reviewed to assess its relevance to this study. A total of 54 research articles were obtained, along with 21 case reports.

From the initial pool of 54 research articles, a refined selection process was undertaken to specifically extract literature related to UCHL. Full-text articles assessed for eligibility: (1) observational studies and experimental studies; (2) focus on CHL without deliberate exclusion or inclusion of specific major diseases; (3) confirmation of diagnosis through exploratory tympanotomy, with detailed reporting of general patient information, surgical procedures, and follow-up details. Seven retrospective studies met these criteria, and the extracted information included author details, publication year, sample size, general patient information, examinations, treatment measures, and outcomes.

On a thorough examination of the full texts, researchers observed that among the excluded inflammatory and traumatic cases, reported subtypes of CHL included congenital ossicular anomalies (COA), OTS, congenital middle ear cholesteatoma (CMEC), among others. The study then proceeded to succinctly summarize the primary diagnostic and therapeutic characteristics associated with each identified subtype.

Results

Characteristics of Various UCHL Diseases

In our systematic literature review, we purposefully excluded factors like inflammation and trauma, which are known to contribute to CHL. Our findings revealed that UCHL encompasses a spectrum of conditions, including (COA, OTS, CMEC, oval window atresia (OWA), superior semiregular-canal bony dehiscence, congenital stapedial footplate fixation (CSFF), middle ear osteoma, middle ear adenoma, congenital ossification of stapedial tendon (COST), among others.

Among these conditions, COA, OTS, and CMEC emerged as the most prevalent types, as supported by references.^{2,4,5,8,9,12-15} Conceptual maps illustrating various UCHL diseases are presented in Figure 2. The subsequent section provides a concise summary of the key characteristics associated with each disease type.

Figure 2.

The conceptual maps of various UCHL diseases. UCHL, unexplained conductive hearing loss.

Congenital ossicular anomalies

COA represent the most prevalent form of UCHL,³ stemming from abnormal development in the first or second pharyngeal arches during embryonic stages.^16,17 In a study by Yang and Liu,¹⁸ it was observed that 50.9%, 48.0%, and 18.3% of patients exhibited deformities in the stapes superstructure, incus, and malleus bones, respectively. In addition, anomalies such as CSFF, OWA, and facial nerve abnormalities may coexist. The typical manifestation of COA includes moderate to moderate-severe unilateral hearing loss, often accompanied by symptoms like tinnitus and ear fullness.^5,16 Temporal bone s (HRCT) is a crucial diagnostic tool, although its success rate is deemed unsatisfactory. Nevertheless, sensitivity can be enhanced through post-processing imaging techniques.^19-21 Zhang et al²² highlighted that the long crus deformity of the incus, stapes superstructure deformity, and OWA are readily identified in preoperative HRCT, while ossicular fixation is prone to being overlooked. The primary method for treating COA is endoscopic ossicular reconstruction.^3,16,23

Otosclerosis

OTS is characterized by spongy degeneration in the bony labyrinth of unknown cause.²⁴ Potential contributing factors include genetics, environmental influences, viral infections, and autoimmune factors.²⁵ This condition predominantly affects middle-aged individuals, particularly women,⁵ presenting as bilateral progressive moderate to moderate-severe CHL.^5,24,26 In cases where the cochlea is involved, mixed deafness may ensue,²² often accompanied by symptoms such as tinnitus and ear fullness.^5,24 Typical findings on HRCT include abnormal low-density areas around the vestibular window and cochlea.^12,24 However, there exists considerable variability in sensitivity,²⁰ possibly attributable to differences in disease severity and equipment.²⁴ Studies indicate higher radiological sensitivity during the active phase of OTS (76.3%) compared to the inactive phase (61.9%).²⁶ Diagnosis primarily relies on typical symptoms and examinations, with confirmation requiring intraoperative evaluation of the mobility of the stapes footplate. The treatment involves implanting a piston following the fenestration of the stapes footplate,^5,27 leading to a significant improvement for approximately 90% of patients.^{11,24,25,28,29}

Congenital middle ear cholesteatoma

CMEC manifests as an invasive lesion, likely originating from residual ectodermal squamous epithelium.^17,20,30,31 This condition is clinically rare, primarily observed in children,⁵ accounting for roughly 2% to 5% of all middle ear cholesteatoma cases.^30,32 Initial symptoms tend to be mild,³³ typically manifesting as unilateral CHL in childhood. As the condition progresses, patients may experience sensations of ear fullness, otorrhea, dizziness, and even facial paralysis.^5,17,31 Endoscopic examinations often reveal pearly-white mass-like structures on the inner surface of the eardrum,^30,32 while HRCT displays intratympanic quasi-circular soft tissue density shadows.²⁰ Zhao et al¹⁷ suggests a comprehensive preoperative radiographic assessment and surgical exploration for any soft tissue density shadows within the tympanic cavity of UCHL patients to rule out the presence of minute cholesteatoma. Early suspected cases should undergo surgical intervention primarily focused on complete cholesteatoma removal rather than hearing improvement.^6,31,32 The typical surgical approach involves endoscopic endoaural incision, occasionally supplemented by microscopic mastoid incision when required, followed by long-term follow-up care.³¹

Oval and round window atresia

Oval and round window atresia (ORWA) is a congenital malformation within the labyrinthine wall, with OWA being the more prevalent subtype.^34,35 It may coincide with other external and middle ear deformities.³⁶ The key symptom involves moderate to severe CHL since childhood. HRCT often reveals irregularities or absence of the oval or round window, frequently accompanied by additional middle ear malformations.³⁵ Su et al³⁵ reported that 69.1% of ORWA patients lacked a long crus of the incus, 61.9% lacked the stapes, 45.1% had stapes superstructure deformities, and 69.1% exhibited facial nerve abnormalities. The primary treatment approach involves vestibule fenestration, although its efficacy remains suboptimal.^34-36 Henkemans et al³⁶ reported long-term success rates ranging from 12.5% to 75%, alongside several postoperative complications.

Superior semicircular canal dehiscence

Superior semicircular canal dehiscence (SSCD) is a condition resulting from a bony wall defect in the superior semicircular canal.^12,37 This condition is also referred to as the “third window lesion” and may be associated with genetic, infectious, or traumatic factors.¹² Typical patients, predominantly middle-aged and elderly individuals, manifest vestibular-cochlear symptoms indicative of SSCD syndrome, including episodic vertigo, CHL, and tinnitus.^12,15 Although HRCT is instrumental in identifying defects in the superior semicircular canal, such abnormalities can occasionally go unnoticed.³⁷ For mild SSCD symptoms, conservative treatment may be sufficient, but severe cases often necessitate surgical interventions like superior semicircular canal plugging and reinforcement.^12,37

Middle ear osteoma

Middle ear osteoma represents a rare, slow-growing osseous tumor that originates within the tympanum.^38-40 While its exact etiology remains unclear, the most frequent location of origin is the tympanic promontory (39.5%),³⁸ often observed in younger individuals. A hallmark presentation includes unilateral CHL, accompanied by tinnitus and sensations of ear tightness. However, smaller osteomas can remain asymptomatic.^38-41 Otoscopy might disclose a creamy-white mass situated on the inner surface of the eardrum.³⁸ Concurrently, HRCT imaging can indicate a localized, high-density bony lesion within the tympanum, potentially showing fusion with the ossicular chain or the tympanic wall.³⁹ During exploratory tympanotomy, one may encounter a bone-like neoplasm that has integrated with the adjacent bone tissue. Such lesions can be challenging to fully excise, often necessitating the use of a bone drill.³⁸ Fortunately, with ossicular reconstruction, hearing improvement is achievable in the majority of cases.^39-41

Congenital stapedial footplate fixation

CSFF is a nonprogressive CHL that manifests from childhood and is linked to the abnormal development of the annular ligament of the oval window in the embryo, potentially accompanied by other ossicular anomalies.^42-44 It is important to differentiate CSFF from juvenile otosclerosis (JO), a progressive condition that may have a familial history.^42,45 CSFF is characterized by poor hearing, often with an air-bone gap (ABG) exceeding 30 dB.^42,46 Some studies suggest that in HRCT, attention should be given to abnormalities in the dimensions of the pyramidal eminence and the aperture of the stapedial tendon, which may be more significant than stapes footplate fixation.^44,46 Surgical intervention for CSFF is similar to that for OTS, but the treatment outcomes are notably less favorable.^42,45

Neuroendocrine adenomas of the middle ear

Neuroendocrine adenomas of the middle ear (NAME) are rare, benign, and slow-growing primary tumors of the middle ear with an extremely low incidence.^47,48 The exact etiology of NAME is unclear,⁴⁹ but it may originate from neural crest stem cells.⁴⁸ Clinical manifestations include CHL, possibly accompanied by sensations of ear fullness, tinnitus, and ear pain. Otoscopic examination may reveal a nonpulsatile white or pink mass on the inside of the eardrum. HRCT and magnetic resonance imaging typically show a nonvascular lesion enveloping the ossicles without causing bone destruction, and it may potentially invade the posterior tympanum and the pharyngotympanic tube.⁵⁰ NAME exhibits invasive characteristics.^47,50 The treatment principle for NAME involves complete tumor resection, followed by pathological and immunohistochemical evaluation to assess the nature of the tumor.⁴⁹ Adjuvant radiation or chemotherapy may be considered in certain cases, and long-term monitoring is essential to detect recurrence, progression, or metastasis.^47,48

Salivary gland choristoma in the middle ear

Salivary gland choristoma in the middle ear is an infrequent congenital tumor.⁵¹ It is posited to arise from the abnormal development of the second branchial arch in the early embryo, leading to the heterotopic location of salivary gland tissue in the tympanum. This condition may potentially be accompanied by other malformations within the middle ear.^52,53 Clinical manifestations typically include unilateral CHL, possibly accompanied by symptoms such as tinnitus, ear fullness, and facial paralysis.⁵¹ HRCT unveils a well-defined soft tissue mass surrounding the ossicles in the middle ear without any evidence of bone destruction.⁵³ The recommended course of treatment involves the complete excision of the tumor and subsequent reconstruction of the ossicular chain. Pathological examination plays a crucial role in confirming the salivary gland origin of the mass,⁵¹ and the overall prognosis for patients is generally favorable.⁵³

Congenital ossification of stapedial tendon

COST is a rare hereditary middle ear disease.^54,55 This condition presents as unilateral or bilateral CHL,^54,56 posing a diagnostic challenge as it is difficult to differentiate from OTS and CSFF in the preoperative phase.⁵⁵ HRCT imaging may reveal linear, bony density shadows extending from the pyramidal eminence to the stapes superstructure.⁵⁵ A definitive diagnosis requires exploratory tympanotomy, during which intraoperative observation reveals ossification of the stapedial tendon along with poor mobility of the stapes. The restoration of stapes mobility can be achieved by releasing the stapedial tendon, leading to a favorable auditory prognosis.^55,56

Analysis of Articles About UCHL

Following careful screening by 2 researchers, we analyzed data from 7 articles to comprehensively examine symptoms, diagnosis, and treatment of UCHL.^3-5,7-10 The cohort comprised 522 patients, including 151 cases of COA, 93 cases of OTS, 205 cases of CMEC, 5 cases of COA and CMEC, and 9 cases of COWA. In addition, 59 cases were linked to traumatic or inflammatory factors. COA, OTS, and CMEC emerged as the primary contributors to CHL with intact tympanic membranes. Detailed information is meticulously documented in Tables 1 to 3. Consistent with prior literature, COA and OTS were identified as prevalent causes of UCHL across pediatric and adult populations. It is worth noting that the study by Xu et al⁵ significantly influenced the CMEC cases, potentially leading to an overestimation of the proportion of CMEC in our study.

Table 1.

Number of Ears and Types of Diseases Reported in the Literature.

Author	Ref	Number of ears	Affected side	Disease
Tomasoniet al	⁷	48	L 20, R 20	23 OTS, 17 COA, 8 TS*
Zhang and Tong	³	82		32 COA, 6 COWA, 280 TS, 6 CMEC, 10 TOI
Zhang et al	⁴	83		52 CMEC, 9 TOI, 7 COA, 2 OTS, 13 AOM*
Tan et al	⁸	16	L 5, R 11	6 COA, 5 CMEC, 2 COA and CMEC, 2 OTS, 1 TOI
Tang et al	⁹	82	L 42, R 40	40 COA, 3 COWA, 22 OTS, 8 CMEC, 6 TOI, 3 COA, and CMEC
Min and Woo	¹⁰	37		10 OTS, 27COA, 2 CMEC
Xu et al	⁵	189	L 95, R 94	132 CMEC, 31 COA, 6 OTS, 5TS*

Abbreviations: AOM, adhesive otitis media; CMEC, congenital middle ear cholesteatoma; COA, congenital ossicular anomalies; COWA, congenital oval window atresia; L, left; OTS, otosclerosis; R, right; TOI, traumatic ossicular injuries; TS, tympanosclerosis.

Inflammatory or traumatic factors.

Table 2.

Demographic Information.

Author	Years	Nation	Study design	Study time	Number of patients	Average age (y)	Sex
Tomasoni et al⁷	2022	Italy	Retrospective	2011-2019	48	51.08 ± 14.63	F 23, M 17
Zhang and Tong³	2021	China	Retrospective	February 2016-February 2019	77	26.40 ± 16.00	F 40, M 37
Zhang et al⁴	2020	China	Retrospective	January 2013-December 2019	83	MD = 7	F 30, M 53
Tan et al⁸	2020	China	Retrospective	January 2018-December 2019	16	20.3 ± 12.8	F 8, M 8
Tang et al⁹	2016	China	Retrospective	April 2011-September 2013	82	26.5 ± 13.7	F 41, M 41
Min and Woo¹⁰	2015	Korea	Retrospective	January 2009-June 2011	37	41
Xu et al⁵	2023	China	Retrospective	January 2019-November 2022	179	8.5 ± 3.1	F 54, M 125

Abbreviations: F, female; M, male.

Table 3.

Number of Ears for Different Diseases Reported in Each Article.

Author	Number of ears	COA	OTS	CMEC	COA and CMEC	COWA	TOI	AOM	TS
Tomasoni et al⁷	48	17	23						8
Zhang and Tong³	82	32	28	6		6	10
Zhang et al⁴	83	7	2	52			9	13
Tan et al⁸	16	6	2	5	2		1
Tang et al⁹	82	40	22	8	3	3	6
Min and Woo¹⁰	37	18	10	2			7
Xu et al⁵.	174	31	6	132					5
Total	522	151	93	205	5	9	33	13	13

Abbreviations: AOM, adhesive otitis media; CMEC, congenital middle ear cholesteatoma; COA, congenital ossicular anomalies; COWA, congenital oval window atresia; OTS, otosclerosis; TOI, traumatic ossicular injuries; TS, tympanosclerosis.

Of the 7 articles, 5 are from China and 2 are from South Korea and Italy, respectively. The publication dates extend from 2015 to 2023, encompassing retrospective studies, as comprehensively summarized in Table 2. On closer examination, 2 articles specifically reported pediatric cases,^4,5 with the youngest patient recorded at 2 years old. Furthermore, a solitary article exclusively focused on adult patients over 18 years old.⁷ The average age of patients in the remaining literature ranged from 20 to 41 years old.^3,8-10 Notably, excluding factors such as inflammation and trauma, the incidence of OTS in the 2 articles pertaining to pediatric patients was markedly lower than that reported in other literature. Moreover, there is a discernible trend of increasing incidence with the average age of patients (P = .009, Figure 3).

Figure 3.

Proportion of OTS patients with average age. OTS, otosclerosis.

The predominant symptoms observed in patients with UCHL encompass hearing impairment, tinnitus, along with sensations of dizziness, ear stuffiness, ear pain, and facial paralysis.^3,5,8-10 Among patients diagnosed with COA, 87.5% to 93.0% exhibit CHL that manifests from childhood, with an associated tinnitus incidence of 15.6% to 30.2%.^3,5,9 In contrast, OTS patients, ranging from 86.4% to 96.4%, present with progressive CHL, and a tinnitus incidence ranging between 60.1% and 90.9%.^3,5,9 TOI results in immediate hearing loss, accompanied by tinnitus in 50.0% to 80.0% of cases.^3,9 The duration of the disease was reported in 5 articles,^4,5,7-9 spanning from 7 days to 50 years. In addition, 3 articles delved into the positive rate of temporal bone CT in preoperative diagnoses of noninflammatory CHL with an intact tympanic membrane, with rates ranging from 33.8% to 87.1%.^4,5,8 Specifically, COA demonstrated rates of 28.6% to 64%, while CMEC exhibited rates of 83.3% to 100%. The observed differences were significant, potentially attributable to the superior capability of temporal bone CT in identifying abnormal low-density shadows within the tympanic cavity.

All studies employed exploratory tympanotomy to confirm the etiology of CHL. Among them, 2 articles explicitly detailed the use of an endoscope for surgical procedures,^3,8 1 utilized a microscope,⁹ and another employed both.¹⁰ Comprehensive final diagnostic results from all studies are consolidated in Table 3.

Each article conducted preoperative and postoperative assessments of average hearing thresholds (Pure-tone averag, PTA) and ABG at frequencies of 0.5, 1, 2, and 3/4 kHz. The collective PTA and ABG values from 7 articles are summarized in Table 4. The studies universally analyzed hearing outcomes by comparing preoperative and postoperative PTA and/or ABG. Specifically, 4 articles reported the primary hearing indicators (PTA and/or ABG) before and after surgery for each disease,^3,5,7,9 and detailed information is presented in Table 5. The follow-up duration in all cases exceeded 3 months. Overall, most patients achieved good hearing recovery goals.

Table 4.

Postoperative Hearing Improvement and Complications.

Author	Surgery	PTA (dB)			ABG (dB)			Follow-up time	Postoperative complication
Author	Surgery	Pre	Post	△	Pre	Post	△	Follow-up time	Postoperative complication
Tomasoni et al⁷	Tympanotomy	61.6	42.6		38.39 ± 12.25	14.77 ± 12.38	24.03 ± 16.17		Chorda tympani nerve injury in 7 cases; dizziness in 3 cases
Zhang and Tong³	Endoscopic tympanotomy	60.09 ± 8.83	29.77 ± 8.70	30.32 ± 10.01	40.82 ± 8.83	11.83 ± 6.83	28.99 ± 10.33	>3 mo	Taste abnormalities in 5 cases; transient vertigo in 2 cases; short-term tinnitus in 6 cases
Zhang et al⁴	Tympanotomy	42.6 ± 14.9	35.6 ± 12.6					>6 mo	Failure to report
Tan et al⁸	Endoscopic tympanotomy	61.7 ± 6.5	29.8 ± 10.7		36.8 ± 3.2	10.7 ± 6.9		3-12 mo	Taste abnormalities in 1 case; transient vertigo in 1 case
Tang et al⁹	Microscopic tympanotomy	60.0 ± 11.4	32.2 ± 12.1		43.2 ± 12.0	16.3 ± 9.4		>2 y	None
Min and Woo¹⁰	Endoscopic tympanotomy in 28 cases and microscopic tympanotomy in 9 cases	64.3 ± 16.3	42.0 ± 20.8		39.0 ± 10.8	20.7 ± 12.7			Failure to report
Xu et al⁵	Tympanotomy	50.8 ± 12.9	36.1 ± 14.5		30.8 ± 9.4	20.0 ± 8.6			Failure to report

Abbreviation: ABG, air-bone gap

Table 5.

Preoperative and Postoperative Audiological Data of Different Diseases (Excluding Traumatic Inflammation).

Author	Disease	Number of cases	PTA (dB)			ABG (dB)
Author	Disease	Number of cases	Pre	Post	△	Post	Pre	△
Tomasoni et al⁷	COA	17				39.56 ± 11.14	18.01 ± 14.21	21.58 ± 13.43
Tomasoni et al⁷	OTS	23				35.33 ± 12.99	9.73 ± 9.99	25.82 ± 18.00
Zhang et al⁴	COA	7	58.2 ± 9.9	49.3 ± 12.1
	OTS	2	30.2 ± 9.9	28.5 ± 7.7
	CMEC	52	40.8 ± 13.1	36.8 ± 12.6
Tang et al⁹	COA	22				47.6 ± 8.9	20.6 ± 10.8	27.0 ± 12.4
	OTS	15				34.1 ± 9.1	13.3 ± 4.4	20.8 ± 9.0
	CMEC	6				54.2 ± 7.7	15.3 ± 3.4	38.9 ± 9.3
	COA and CMEC	3				45.6 ± 21.1	8.3 ± 11.1	37.2 ± 14.4
Xu et al⁵	COA	31	57.1 ± 11.7			35.4 ± 9.8
	OTS	6	63.5 ± 7.81)			35.3 ± 7.5
	CMEC	132	47.8 ± 14.5			28.8 ± 10.5

Abbreviations: ABG, air-bone gap; CMEC, congenital middle ear cholesteatoma; COA, congenital ossicular anomalies; COWA, congenital oval window atresia; OTS, otosclerosis.

Four articles have documented postoperative complications.^3,7-9 The detailed information is presented in Table 4. Common postoperative complications include taste disorders, tinnitus, and dizziness. Taste disorders are primarily attributed to damage to the chorda tympani nerve during surgery, with the potential for gradual recovery over time if the chorda tympani nerve is not completely severed. Tinnitus and dizziness are predominantly short-term or transient postoperative complications with a favorable prognosis. None of the reviewed articles reported severe complications such as sensorineural hearing loss, facial paralysis, or intracranial infection.

Discussion

UCHL encompasses a spectrum of diseases characterized by common clinical presentations, specifically CHL with an intact tympanic membrane and the absence of inflammation or trauma history. Diagnosis solely based on preoperative examination poses challenges. Consequently, exploratory tympanotomy becomes imperative for a meticulous inspection of the middle ear’s structure, aiming to eliminate middle ear pathology and enhance hearing.^{3,5,7,21,22,27,57} Common UCHL diseases include COA, OTS, CMEC, OWA, SSCD, CSFF, middle ear osteoma, middle ear adenoma, COST, and so on.^{2-9,12,15,35,38,41,42,47,51,55}

UCHL can significantly affect patients’ quality of life, especially children in crucial speech development stages. The literature suggests that children affected by CHL might delay seeking medical attention due to limited cognitive ability, a lack of medical awareness, and a tendency to adapt or endure symptoms.¹⁸ In a study conducted by Xu et al,⁵ involving 179 children with noninflammatory CHL, the average time from parents recognizing symptoms to a confirmed diagnosis was 2.2 ± 2.9 years. The shortest diagnostic duration was observed in cases of CMEC (average 1.3 years), while cases related to ossicle defects or OTS took approximately 5 years. This discrepancy might be attributed to CMEC exhibiting more invasive symptoms, whereas the latter 2 primarily cause hearing loss with a singular symptom. Shin et al⁵⁸ suggests that delaying the identification of cholesteatoma in children could lead to more extensive erosion, poorer hearing outcomes, and an increased risk of recurrence. Hence, it is crucial to pay close attention to any abnormal speech or behavioral signs in children, and suspected UCHL cases should be promptly referred to a hospital. In addition, regular hearing screenings for school-age children prove to be an effective method to detect concealed instances of UCHL.

Given the potential risks associated with hearing loss in children, it is recommended to consider an approach involving exploratory tympanotomy at an opportune time.⁵⁹ Subsequent decisions regarding artificial ossicular reconstruction or artificial auditory implants should be informed by the findings of the exploratory procedure, representing an optimal approach to diagnose and treat children with UCHL, particularly in cases involving cholesteatoma. Some perspectives suggest that suspected cases of COA and OTS should initially incorporate hearing aids to improve auditory function.⁶⁰ For bilateral cases, surgery may be considered at 5 to 6 years old, while unilateral cases might be deferred until 10 years old or later. However, an opposing viewpoint argues for early intervention in unilateral hearing loss, emphasizing that the temporal bone completes ossification around age 6, allowing for middle ear surgery.⁶¹ Debates arise regarding inner ear window procedures in children, with some proposing waiting until the age of 15 to prevent window closure over time.⁶² Nevertheless, Tolisano et al⁶³ asserts that children can safely undergo stapes surgery, noting a notably higher success rate in children compared to adults due to the shorter duration and less severe pathological changes in the footplate. Ching et al⁶⁴ indicates that children with CMEC undergoing surgery after the age of 3 do not exhibit a worse prognosis. For those under 1 year of age with no significant intratympanic growth, surgery can be delayed until 1 to 2 years of age. However, suspicion of CMEC in those over 3 years old should prompt early surgical intervention to minimize further damage to the middle ear caused by cholesteatoma.³⁰ Jenks et al⁶⁵ found that children in Potsic stage III were significantly older than those in stage I to II. Given that Potsic stage is a major risk factor for cholesteatoma recurrence and hearing loss, the early identification and intervention in children with CMEC are considered advantageous. Therefore, early diagnosis and intervention play a pivotal role in the management of UCHL in children. Our clinical experience suggests that surgical interventions in UCHL children aged 3 to 6 years do not result in significantly worse outcomes or increased complications.

The use of temporal bone HRCT is essential for the preoperative diagnosis of UCHL.¹ However, routine HRCT encounters challenges in accurately depicting the intricate structures of the middle ear, potentially leading to misdiagnosis and overlooking cases.^{4,6,17,22,24,26} Studies have highlighted variations in the effectiveness of HRCT in detecting middle ear diseases. Tang et al⁹ reported an accuracy of only 40.0% in identifying congenital middle ear malformation (CMEM). Similarly, Zhang et al²² found that only 62.1% of CMEM cases could be detected via HRCT, while Zhao et al¹⁷ reported abnormal findings in the auditory bones in 9 out of 10 UCHL cases, including 5 cases with localized cholesteatoma. However, intraoperatively, all 10 patients were diagnosed with COA and CMEC, emphasizing that HRCT alone cannot conclusively determine the etiology of UCHL.

Various advanced imaging technologies, such as multislice computed tomography, cone beam computed tomography (CBCT), Multiplanar reconstruction (MPR), and Volume Rendering (VR), have been shown to enhance scanning precision and improve the quality of ossicular chain reconstruction, thereby increasing the success rate of preoperative diagnoses.^19-21 Liu et al¹⁹ demonstrated that MPR and Computed tomography volume rendering (CTVR) effectively display the ossicular chain, particularly excelling in showcasing the stapes superstructure and incus deformity. Li et al²⁰ proposed that HRCT post-processing techniques, such as MPR and CTVR, have the potential to reveal early, hidden minute cholesteatoma. Debeaupte et al²¹ found that CBCT offers advantages over multidetector computed tomography with lower radiation exposure and higher resolution, significantly aiding in OTS diagnosis and staging. Therefore, the continued development of more refined scanning techniques and higher-quality imaging methods holds the potential to further enhance the success rates of preoperative diagnosis for UCHL.

Most congenital UCHL cases stem from genetic and embryonic developmental abnormalities.³⁰ Developmental impediments in the first or second branchial arch of the ectoderm may result in multiple coexisting pathologies.^15,30 Furthermore, due to the nonspecific symptoms of UCHL, manifestations of one disease may mask another—a scenario not uncommon in clinical practice.^5,6,12,37 For instance, CMEC could originate from residual epithelium associated with auditory bone development, potentially co-occurring with COA.^6,17,32 Zhao et al¹⁷ recommended a thorough examination for any soft tissue density shadows found in the tympanic cavity via HRCT to rule out minute cholesteatomas. In cases of stapes footplate fixation, SSCD may coexist and mask its symptoms. SSCD may also be present and mask its symptoms. Neglecting SSCD while addressing SFF alone can lead to poor postoperative hearing recovery.¹² Hence, for UCHL patients, thorough preoperative imaging examinations to identify more suspicious lesions and comprehensive intraoperative exploration of the middle ear structure are essential approaches to elucidate the etiology and enhance surgical benefits.^{8,20,24,31,32,46}

To advance the diagnosis and treatment of patients with UCHL, otologists should prioritize several key aspects. First, it is imperative to expand the overall understanding of UCHL. This involves not only mastering common diseases such as COA, OST, and CMEC but also delving into rare diseases. Attention to detail during medical history collection, preoperative examinations, and surgical exploration is crucial.^{4,15,37,41,42,44,46,47,51,55} Second, there is a necessity to improve the ability to interpret imaging studies with precision. Thoroughly examining various parts, including the middle ear cavity, ossicular chain, stapes footplate, oval and round windows, and semicircular canals, is essential. Checking for the integrity of middle ear structures, the presence of abnormal tissue shadows, and density differences in structures like the stapes footplate, promontory, and semicircular canals is crucial.^{6,20,21,24,44,46,55} This aids in the preoperative identification of potential causes, facilitates surgery preparation, and improves communication with patients. In addition, it supports the study of surgical plans in advance and enables thorough exploration and reconstruction during surgery. Third, meticulous intraoperative exploration of the middle ear is vital, involving the complete removal of any abnormal lesions within the middle ear. For eligible cases, artificial ossicular implantation should be performed based on the type of lesion.^{3,10,16,23,45,47,56} For those not suitable for artificial ossicular implantation, the consideration of delayed implantation of bone conduction hearing aids is recommended to enhance the patient’s hearing level.⁵⁷ Fourth, post-surgery, a tissue pathology examination of suspicious neoplasms obtained should be conducted. Different postoperative intervention and recovery plans should be developed for different patients.^31,48,51,53 Finally, there is a pressing need to bolster patient follow-up procedures by implementing regular reviews and closely monitoring tumor residue and recurrence. Especially for tumors with recurrent tendencies such as cholesteatoma and adenoma, the follow-up time should not be less than 5 years.^31,47-49,51

The inherent limitations in this study are readily apparent. First, the heterogeneity of the research and the insufficient sample size impede a more comprehensive analysis of differences among various components and hinder the formulation of definitive conclusions. The diverse themes and methodologies employed in each study pose challenges in extracting and summarizing data. Consequently, the primary aim of our study is to further elucidate the definition of UCHL. We seek to engage in discussions with clinical professionals to refine diagnostic and treatment methods, ultimately enhancing the clinical benefits for patients. We assert that the etiology of UCHL is complex, and the existing preoperative examination methods are inadequate in definitively determining the patient’s condition. Exploratory tympanotomy surgery and comprehensive diagnosis remain central to the treatment paradigm.

Conclusions

In summary, UCHL represents a spectrum of diseases with analogous clinical manifestations. Preoperative diagnosis poses a formidable challenge, with exploratory tympanotomy emerging as the primary method for both diagnosis and treatment. Meticulous intraoperative exploration of middle ear tissues, lesion clearance, and ossicular chain reconstruction contribute significantly to favorable prognoses. Surgical intervention, even in children aged 3 to 6, is a viable option. Otologists should augment their overall comprehension of UCHL diseases, emphasizing the significance of preoperative imaging examinations and surgical exploration to optimize patient outcomes.

Footnotes

Acknowledgements

Not applicable.

Author Contributions

Conceptualization, H.X.; software, Y.H. and H.S.; resources, H.X.; data extraction, Y.H. and X.Y.; data curation, Y.H., X.Y., Y.W., D.H., and S.Z.; writing—original draft preparation, Y.H., D.H., and X.Y.; writing—review and editing, Y.H., H.S., D.H., and S.Z.; project administration, H.X., X.Y., S.Z., and H.S. All authors have read and agreed to the published.

Data Availability Statement

Not applicable.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by the National Natural Science Foundation of China (Grant numbers 82071057 and 82101229).

Institutional Review Board Statement

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology (approval number: UHCT21836; approval date: February 28, 2022).

Informed Consent Statement

Patient consent was waived because this study is a retrospective analysis of the treatment effects on patients and poses no foreseeable harm to them.

ORCID iDs

Haiying Sun

Hongjun Xiao

References

Robson

. Conductive hearing loss in children. Neuroimaging Clin N Am. 2023;33(4):543-562.

Zhang

Huang

Liu

Yang

. Comparative study of unilateral conductive hearing loss in patients with an intact tympanic membrane. Acta Otolaryngol. 2021;141(3):226-230.

Zhang

Tong

. Endoscopic ossiculoplasty for conductive hearing loss with intact tympanic membrane: a report of 77 cases. Chin J Otol. 2021;19(2):213-217.

Zhang

Chen

Liu

, et al. Management strategies in 83 cases of pediatric conductive deafness with intact tympanic membrane. Chin J Otol. 2020;18(6):1002-1006.

Zhou

. Etiology analysis and diagnosis of noninflammatory conductive hearing loss in children. J Clin Otorhinolaryngol Head Neck Surg. 2023;37(3):206-212.

Liang

Wang

Gong

Wang

. Clinical analysis of missed diagnostic congenital cholesteatoma. J Clin Otorhinolaryngol Head Neck Surg. 2020;34(1):45-48.

Tomasoni

Borsetto

Deretti

, et al. Exploratory tympanotomy in conductive hearing loss with normal pre-operative investigations. Acta Otorhinolaryngol Ital. 2022;42(6):569-581.

Tan

Peng

Liu

, et al. Clinical application of transcanal endoscopic ear surgery in the diagnosis and treatment of conductive hearing loss with intact tympanic membrane. J Clin Otorhinolaryngol Head Neck Surg. 2020;34(12):1070-1074.

Tang

Zhang

Han

, et al. Analyses of the clinical characteristics of unilateral conductive hearing loss with intact tympanic membrane. Chin J Otorhinolaryngol Head Neck Surg. 2016;51(5):348-354.

10.

Min

Woo

LIL

. Clinical characteristics of exploratory tympanotomy and role of otoendoscope. J Clin Otolaryngol. 2015;26(2):208-212.

11.

Bartel

Sanz

Clemente

, et al. Endoscopic stapes surgery outcomes and complication rates: a systematic review. Eur Arch Otorhinolaryngol. 2021;278(8):2673-2679.

12.

Sioshansi

Drury

Babu

Schutt

. Outcomes of stapedotomy in patients with concomitant otosclerosis and superior semicircular canal dehiscence: should a radiographic third-window be a contraindication to stapes surgery? Otol Neurotol 2022;43(2):165-169.

13.

Choi

Kwak

Kang

Chung

. Endoscopic ear surgery for congenital cholesteatoma in children. J Int Adv Otol 2022;18(3):236-242.

14.

Carter

Hoff

. Endoscopic middle ear exploration in pediatric patients with conductive hearing loss. Int J Pediatr Otorhinolaryngol. 2017;96:21-24.

15.

Sarioglu

Pekcevik

Guleryuz

Cetin

Guneri

. The relationship between the third window abnormalities and inner ear malformations in children with hearing loss. J Int Adv Otol. 2021;17(5):387-392.

16.

Chung

Kang

Kim

Choi

. Microscopic vs endoscopic ear surgery for congenital ossicular anomaly. Otolaryngol Head Neck Surg. 2020;162(4):548-553.

17.

Zhao

Chen

Zhao

, et al. Concurrent occurrence of congenital ossicular anomaly and localized cholesteatoma: series of 10 cases. ORL J Otorhinolaryngol Relat Spec. 2020;82(3):139-149.

18.

Yang

Liu

. Reporting and description for congenital middle ear malformations to facilitate surgical management. Ann Otol Rhinol Laryngol. 2018;127(10):717-725.

19.

Liu

Yang

Zhao

. Value of section plane, MPR, and 3D-CTVR techniques in the fine differential diagnosis of ossicular chain in the case of conductive hearing loss with intact tympanic membrane. J Otol. 2017;12(2):80-85.

20.

Liu

Zhao

Liu

Sun

. The aetiology of ossicular chain defects in congenital cholesteatoma. J Laryngol Otol. 2022;136(5):391-395.

21.

Debeaupte

Hermann

Pialat

Martinon

Truy

Boudrigua

. Cone beam versus multi-detector computed tomography for detecting hearing loss. Eur Arch Otorhinolaryngol. 2019;276(2):315-321.

22.

Zhang

, et al. Isolated congenital middle ear malformations: comparison of preoperative high-resolution CT and surgical findings. Ann Otol Rhinol Laryngol. 2020;129(3):216-223.

23.

Guneri

Cetin

. Ossicular chain reconstruction: endoscopic or microscopic? J Laryngol Otol. 2020;134(12):1108-1114.

24.

Kösling

Plontke

Bartel

. Imaging of otosclerosis. Rofo. 2020;192(8):745-753.

25.

Babcock

Liu

. Otosclerosis: from genetics to molecular biology. Otolaryngol Clin North Am. 2018;51(2):305-318.

26.

Karosi

Csomor

Sziklai

. The value of HRCT in stapes fixations corresponding to hearing thresholds and histologic findings. Otol Neurotol. 2012;33(8):1300-1307.

27.

Cheon

Kim

Choi

Bae

. Diagnostic value of the air-bone threshold gap in stapes fixation. Audiol Neurootol. 2023;28(4):255-261.

28.

Saerens

Van Damme

Bihin

Garin

. Hearing results in 151 primary stapedotomies for otosclerosis: the effects of using different audiologic parameters and criteria on success rates. Otol Neurotol. 2021;42(10):e1436-e1443.

29.

Nitta

Sano

Furuki

Yamashita

. Long-term outcomes of stapes surgery. Auris Nasus Larynx. 2023;50(3):337-342.

30.

Gilberto

Custódio

Colaço

Santos

Sousa

Escada

. Middle ear congenital cholesteatoma: systematic review, meta-analysis and insights on its pathogenesis. Eur Arch Otorhinolaryngol. 2020;277(4):987-998.

31.

Denoyelle

Simon

Chang

, et al. International Pediatric Otolaryngology Group (IPOG) Consensus Recommendations: congenital cholesteatoma. Otol Neurotol. 2020;41(3):345-351.

32.

McCabe

Lee

Fina

. The endoscopic management of congenital cholesteatoma. Otolaryngol Clin North Am. 2021;54(1):111-123.

33.

Wei

Zhou

Zheng

Zhao

Zheng

. Congenital cholesteatoma clinical and surgical management. Int J Pediatr Otorhinolaryngol. 2023;164:111401.

34.

Zhao

Gong

Han

, et al. Round window application of an active middle ear implant (AMEI) system in congenital oval window atresia. Acta Otolaryngol. 2016;136(1):23-33.

35.

Yuan

Song

, et al. Congenital middle ear abnormalities with absence of the oval window: diagnosis, surgery, and audiometric outcomes. Otol Neurotol. 2014;35(7):1191-1195.

36.

Henkemans

Rovers

Thomeer

HGXM

. Surgical outcome in class 4 congenital anomalies of the ossicular chain: a systematic review of the literature. Eur Arch Otorhinolaryngol. 2023;280:4327-4337.

37.

Kontorinis

Lenarz

. Superior semicircular canal dehiscence: a narrative review. J Laryngol Otol. 2022;136(4):284-292.

38.

Zhang

Ning

Liu

Han

. Analysis of clinical characteristics of middle ear osteoma at different locations. Chin J Otorhinolaryngol Head Neck Surg. 2021;56(3):273-279.

39.

Crohan

Kuthubutheen

. Middle ear osteoma with assimilation of ossicles: an unusual case of conductive hearing loss. Cureus. 2023;15(5):e38478.

40.

Sievert

Mantsopoulos

Hornung

, et al. Ossicular osteoma of the malleus—a rare diagnosis of middle ear mass. Radiol Case Rep. 2022;17(11):4365-4367.

41.

Piazza

Frisina

. Ossicular chain reconstruction using costal cartilage in malleoincudal osteoma. J Laryngol Otol. 2022;136(3):268-270.

42.

Daniel

Budiono

Rao

Low

GKK

Ellis

Lee

. Juvenile otosclerosis and congenital stapes footplate fixation. A systematic review and meta-analysis of surgical outcomes and management. Int J Pediatr Otorhinolaryngol 2023;166:111418.

43.

Totten

Marinelli

Carlson

. Incidence of congenital stapes footplate fixation since 1970: a population-based study. Otol Neurotol. 2020;41(4):489-493.

44.

Burkett

Oien

Benson

Nassiri

Carlson

Lane

. Absent stapedial tendon: imaging features of an underrecognized entity: clinical neuroradiology. Clin Neuroradiol. 2023;33(3):645-651.

45.

Sobolewska

Clarós

. Surgical treatment in children with otosclerosis and congenital stapes fixation: our experience and outcome. Otolaryngol Pol. 2018;73(2):23-28.

46.

Nassiri

Benson

Doerfer

, et al. Absent pyramidal eminence and stapedial tendon associated with congenital stapes footplate fixation: intraoperative and radiographic findings. Am J Otolaryngol. 2021;42(6):103144.

47.

Katabi

. Neuroendocrine neoplasms of the ear. Head Neck Pathol. 2018;12(3):362-366.

48.

Bell

El-Naggar

Gidley

. Middle ear adenomatous neuroendocrine tumors: a 25-year experience at MD Anderson Cancer Center. Virchows Arch. 2017;471(5):667-672.

49.

Yang

Asiry

Khader

. Adenomatous neuroendocrine tumors of the middle ear (MEANTs) with local invasion and lymph nodes metastasis: a brief report of a rare neoplasm. Diagn Cytopathol. 2021;49(4):E141-E145.

50.

Alciato

Lahlou

Tankéré

, et al. Middle ear adenomatous neuroendocrine tumours: single institution experience with five cases. Clin Otolaryngol. 2021;46(5):1136-1141.

51.

Hao

Wang

. A rare case of salivary gland choristoma in the middle ear with pharyngeal hamartoma. Chin Med J (Engl). 2019;132(8):1000-1002.

52.

Ookouchi

Honda

Gyo

. Salivary gland choristoma of the middle ear in a child: a case report. Otolaryngol Head Neck Surg. 2003;128(1):160-162.

53.

Young

Evans

. Middle ear salivary choristoma: a rare case report and update on congenital associations, facial nerve involvement, and treatment strategies. Case Rep Otolaryngol. 2020;2020:8435140.

54.

Thies

Sperling

Reis

Handrock

. [Small abnormality of the middle ear—a genetically-induced defect?] HNO. 1998;46(8):757-761.

55.

Yoo

Lee

Yang

Lee

. Complete restoration of congenital conductive hearing loss by staged surgery: a case report. World J Clin Cases. 2021;9(33):10286-10292.

56.

Zawawi

Varshney

Schloss

. Shortened stapedius tendon: a rare cause of conductive hearing loss. J Laryngol Otol. 2014;128(1):98-100.

57.

Choi

Lee

Park

Lee

Jang

. Conductive hearing loss with an intact tympanic membrane due to non-inflammatory causes. Auris Nasus Larynx. 2016;43(2):144-148.

58.

Shin

Kang

Park

Chung

Ahn

. Is there a clinical difference in paediatric congenital cholesteatoma according to age? J Laryngol Otol. 2023;137(6):643-650.

59.

Ito

Furukawa

Ohshima

, et al. Multicenter study of congenital middle ear anomalies. Report on 246 ears. Laryngoscope. 2021;131(7):E2323-E2328.

60.

Ren

Chi

. Reconstruction of congenital non-syndromic middle ear malformations. J Clin Otorhinolaryngol Head Neck Surg. 2016;30(13):1009-1012.

61.

Abdel-Aziz

. Congenital aural atresia. J Craniofac Surg 2013;24(4):e418-e422.

62.

Esteves

Silva

Coutinho

Abrunhosa

e Sousa

. Congenital defects of the middle ear—uncommon cause of pediatric hearing loss. Braz J Otorhinolaryngol. 2014;80(3):251-256.

63.

Tolisano

Fontenot

Nassiri

, et al. Pediatric stapes surgery: hearing and surgical outcomes in endoscopic vs microscopic approaches. Otolaryngol Head Neck Surg. 2019;161(1):150-156.

64.

Ching

Spinner

. Pediatric tympanic membrane cholesteatoma: systematic review and meta-analysis. Int J Pediatr Otorhinolaryngol. 2017;102:21-27.

65.

Jenks

Purcell

Federici

, et al. Transcanal endoscopic ear surgery for congenital cholesteatoma: a multi-institutional series. Otolaryngol Head Neck Surg. 2022;167(3):537-544.

Diagnosis and Management of Unexplained Conductive Hearing Loss With Intact Tympanic Membrane: A Systematic Review

Abstract

Keywords

Introduction

Materials and Methods

Results

Characteristics of Various UCHL Diseases

Congenital ossicular anomalies

Otosclerosis

Congenital middle ear cholesteatoma

Oval and round window atresia

Superior semicircular canal dehiscence

Middle ear osteoma

Congenital stapedial footplate fixation

Neuroendocrine adenomas of the middle ear

Salivary gland choristoma in the middle ear

Congenital ossification of stapedial tendon

Analysis of Articles About UCHL

Discussion

Conclusions

Footnotes

Acknowledgements

Author Contributions

Data Availability Statement

Declaration of Conflicting Interests

Funding

Institutional Review Board Statement

Informed Consent Statement

ORCID iDs

References