Long-Term Surgical Outcome of Canal-Tympanoplasty in Patients With Schuknecht Type B Congenital Aural Stenosis
Article information
Abstract
Objectives.
Congenital aural atresia (CAA) is a complex condition that manifests in various forms, including Schuknecht type B stenosis, which is characterized by a congenitally narrow bony external auditory canal (EAC). This study aims to evaluate the long-term surgical outcomes of canal-tympanoplasty in patients with Schuknecht type B CAA.
Methods.
The study included 21 ears diagnosed with Schuknecht type B CAA, all of which underwent canal-tympanoplasty. Reconstruction of the large EAC and tympanic membrane involved conchal flap meatoplasty, bony EAC drilling, ossicular reconstruction, and overlay tympanoplasty. Standard pure-tone audiometry was analyzed at multiple post-surgery time points: 3, 6, 12, and 24–60 months. Additionally, the incidence of postoperative complications was assessed.
Results.
The hearing outcomes of canal-tympanoplasty in this case series were satisfactory. Serviceable hearing was achieved in all patients after 3 months and was maintained in 85% of patients for 1 year. The air-bone gap improved from a preoperative average of 39.3±15.1 dB to 13.7±7.4 dB at 3 months, 16.4±10.5 dB at 6 months, 19.1±11.7 dB at 12 months, and 21.5±16.1 dB at 2–5 years postoperatively. Three patients required revision canal-tympanoplasty due to hearing deterioration, representing 14.3% of the cases. There were no instances of postoperative infection, facial nerve weakness, vertigo, deterioration of bone conduction thresholds, or complete restenosis of the EAC.
Conclusion.
Canal-tympanoplasty proved to be a satisfactory surgical intervention for patients with Schuknecht type B CAA. This procedure led to significant improvements in hearing outcomes, providing serviceable hearing that lasted for several years. Moreover, the risk of postoperative hearing deterioration and/or the need for revision surgery within 1 year was considered acceptable.
INTRODUCTION
A congenitally narrow bony external auditory canal (EAC) is recognized as one type of congenital aural atresia (CAA) [1]. However, the primary objectives and indications for surgery in these patients differ from those with a completely obstructive type of atresia. According to Schuknecht’s criteria, a narrow bony EAC is categorized as type B, whereas a completely obstructive type of atresia falls under type C or D atresia [2]. For type C and D atresia, the risk of ear anomaly-related infection or inflammation is very low [3]. The main surgical goal is to enhance hearing. Consequently, various hearing solutions, including bone conduction devices (BCDs), are viable alternatives that yield favorable hearing results [4,5]. In contrast, type B CAA may result in EAC cholesteatoma and/or persistent infection in 43.0% of cases [3]. In such instances, surgery to remove the EAC cholesteatoma and reconstruct a safe EAC is mandatory. Therefore, the surgical objectives for patients with CAA type B are dual: to manage or prevent recurrent infections of EAC cholesteatoma and to improve hearing [6].
Canal-tympanoplasty is a surgical procedure designed to reconstruct the ear canal and middle ear in patients with CAA [7]. This term, recently proposed by our group, is a compound of “canaloplasty” and “tympanoplasty.” Canaloplasty involves the reconstruction of the EAC, including both the cartilaginous and bony sections. Tympanoplasty focuses on reconstructing the tympanic membrane and the middle ear ossicular chain. Older terms such as “atresiaplasty” [8] and “meatoplasty” [9] may not be the best nomenclature, as they do not convey these key concepts of the two surgical procedures. The surgical outcome of canal-tympanoplasty is satisfactory in only 60.3%–68.9% of patients when performed by highly experienced surgeons [4]. The International Microtia and Atresia Workgroup advises that canaltympanoplasty should be approached with the expectation that revision surgery might be necessary due to potential restenosis [10]. Given the suboptimal hearing outcomes and the significant risk of needing additional surgeries, some otologic surgeons are reluctant to undertake canal-tympanoplasty. Nevertheless, it is important to recognize that canal-tympanoplasty remains the standard treatment for CAA patients presenting with EAC cholesteatoma [1,11].
Despite the necessity of surgical intervention, there is a lack of information regarding postoperative hearing outcomes specific to CAA type B. Surgical results are believed to be more favorable than those for type C atresia [6], as there are fewer anatomical anomalies in the middle ear [12]. We have recently reported on the hearing outcomes following canal-tympanoplasty and compared these results with those from implantable BCDs [13]. However, in our previous report, we combined all types of CAA. The aim of this study was to explore long-term hearing outcomes in patients with Schuknecht type B CAA who underwent canaltympanoplasty.
MATERIALS AND METHODS
Subjects
The present study was approved by the Institutional Review Board at Seoul National University Hospital (No. H-2408-083-1560) and was conducted according to the tenets of the Declaration of Helsinki. Informed consent was waived due to the retrospective nature of this study.This study included the medical records of 21 ears diagnosed with Schuknecht type B CAA that underwent canal-tympanoplasty. Because the surgical outcomes of canal-tympanoplasty are influenced by the surgeon’s technique and experience, only patients who underwent canal-tympanoplasty by a single surgeon (MWS) were evaluated. The hearing outcomes of these 21 ears were compared before and after the operation. Demographic data, including age at surgery and sex, were also collected along with other surgical information, such as the rates of postoperative infection and revision surgery.
Surgical procedure and materials
The surgical procedure of canal-tympanoplasty was performed similarly to the previous study conducted in our institution [13-16]. The endaural-conchal incision proposed by Chen and Zhang [17] was adopted in a modified form. An inverted question markshaped incision was made, starting at the incisura terminalis, running around the concave rim of the cavum concha, and ending at the inferior EAC (6 o’clock direction). A radial intrameatal incision was extended from this point (6 o’clock location of the EAC), meeting with a circumferential intrameatal incision on the posterior bony EAC (between 12 and 6 o’clock direction). The cavum conchal skin and posterior EAC skin were elevated in one piece from the cartilage and bone, resulting in a superiorly based concho-meatal flap. This concho-meatal flap was swung superiorly, covering the incisional gap in the incisura terminalis. The exposed cavum conchal cartilage was harvested for future use. Soft tissue under the concho-meatal flap was removed to expose the temporal bone posterior to the EAC. The periosteum was elevated posteriorly for future covering of the resected cartilage margins. Drilling was performed to widen the EAC and expose the hypoplastic tympanic membrane (if present). The cholesteatoma in the narrow EAC was removed during this process. The tympanomeatal flap (hypoplastic tympanic membrane and medial bony EAC skin) was elevated anteriorly if the epithelium was healthy. The tympanomeatal flap was removed in most cases because the size was too small or the skin was nonviable. A neobony anulus was drilled, resulting in a >8×8 mm sized opening of the tympanum. After drilling, the caliber of the medial and lateral bony EAC was >12×13 mm and >15×15 cm, respectively. The ossicles were evaluated for morphology and mobility. In all cases, the malleus-incus (MI) complex was anomalous and hypomobile: attached to adjacent bony structures such as the atretic plate. The incus-stapes joint was separated, and the MI complex was removed in such cases. The anatomy and integrity of the facial nerve and stapes were evaluated. Since the stapes was mobile in all cases, a titanium partial ossicular prosthesis (PORP; Medtronic Xomed Surgical Products) was placed between the stapes head and the reconstructed tympanic membrane. The length of the PORP was 1.5-3.5 mm. A >4×4-mm sized cartilage slice was interpositioned over the PORP to prevent extrusion. Exposed air cells were also covered with cartilage slices. Megaderm (100–300 µm thick homologous membrane derived from cadaveric dermis, L&C Bio) was used to reconstruct the new tympanic membrane with an overlay graft technique. A split-thickness skin graft (2×7 cm, 9/1,000 inch thickness) was harvested from the upper medial thigh. It was grafted to the new bony EAC to line the newly created EAC, ranging from the tympanic membrane to the bony meatus. The periosteum was sutured to the cavum conchal skin cut margin. The concho-meatal flap was inserted and sutured to the gap of the incisura terminalis. The new EAC was packed with nylon strips and antibiotics-soaked cotton wicks. Facial nerve monitoring was done continuously for every case.
Audiological evaluation
Standard pure tone audiometry was performed before and after surgery. Audiometric data of air and bone conduction thresholds at 500 Hz, 1 kHz, 2 kHz, and 4 kHz were compiled [1], and a weighted four-tone average was calculated as follows: (0.5 kHz+ 1 kHz×2+2 kHz×2+4 kHz)/6. Hearing outcomes were analyzed at the time before surgery and on postoperative day 3, 6, and 12 months. Additionally, postoperative results from 2–5 years after surgery or from those who were followed up long enough were also collected. Hearing gain was defined as the difference between the preoperative and postoperative thresholds. To compare our results with those reported in previous literature, this study defined successful hearing outcomes using the following three criteria: an air conduction threshold ≤40 dB HL, based on the definition of serviceable hearing; an air conduction threshold ≤30 dB HL, based on the classification of Nadaraja et al. [4]; and an air-bone gap (ABG) ≤30 dB. The success rate was based on the ABG criteria.
Continuous variables are expressed as means±standard deviations. Statistical analyses were performed with IBM SPSS version 25.0 (IBM Corp.). A paired t-test was used to compare proportions of successful outcomes. A P-value of <0.05 was considered to indicate statistical significance.
RESULTS
Demographics
The study group comprised 21 ears from 20 patients, including 10 males and 10 females. Only patients with a Jahrsdoerfer score between 7 and 10 were selected for surgery aimed at improving hearing. The average age at the time of the initial surgery was 13.3 years (standard deviation, 9.7 years; range, 5–50 years); the group included two adults and 18 children. Thirteen patients exhibited unilateral CAA, with 10 cases affecting the right ear and 3 affecting the left ear. Seven patients had bilateral CAA, but only one of these underwent bilateral canal-tympanoplasty. All 21 ears that underwent surgery were diagnosed with type B CAA, comprising 12 right ears and 9 left ears. Three patients underwent revision canal-tympanoplasty due to deterioration of the ABG.
Preoperative hearing threshold
The preoperative air conduction threshold (weighted four-tone average) was 49.4±14.4 dB HL, the bone conduction threshold was 10.1±5.5 dB HL, and the ABG was 39.3±15.1 dB (Fig. 1). The air conduction thresholds were 54.0±17.1 dB HL at 500 Hz, 53.3±14.1 dB HL at 1 kHz, 44.5±15.8 dB HL at 2 kHz, and 46.7±16.9 dB HL at 4 kHz. The bone conduction thresholds were 7.6±6.4 dB HL at 500 Hz, 6.9±5.4 dB HL at 1 kHz, 17.4±10.3 dB HL at 2 kHz, and 7.9±7.7 dB HL at 4 kHz.
Preoperative hearing threshold. Before surgery, the weighted four-tone average of the air conduction (AC) threshold was 49.4±14.4 dB HL, and that of the bone conduction (BC) threshold was 10.7±6.4 dB HL. The air-bone gap was 39.3±15.1 dB.
Postoperative hearing threshold
The four-tone average of the air conduction threshold was 21.5±7.0 dB HL at 3 months, 24.4±10.6 dB HL at 6 months, 27.0±12.6 dB HL at 12 months, and 28.9±14.6 dB HL at 2–5 years (Fig. 2A). Compared to the preoperative hearing threshold of 49.4±14.1 dB HL, postoperative hearing showed significant improvement at all time points: 3 months (P<0.001), 6 months (P<0.001), 12 months (P<0.001), and 2–5 years (P<0.001). When individual air conduction hearing thresholds were assessed, serviceable hearing (as indicated by the red broken line in Fig. 2A and C) was achieved in all patients (100%) at 3 months. However, by 6 months, hearing had deteriorated in two ears, resulting in a serviceable hearing rate of 90.5%. After 12 months, hearing further deteriorated in two additional ears. Among these four ears with unserviceable hearing outcomes, three patients underwent revision canal-tympanoplasty. The air conduction threshold improved in two of these subjects (as indicated by the orange lines in Fig. 2C).
(A) Postoperative changes in the hearing threshold and air-bone gap over time. The air conduction (AC) threshold improved significantly after canal-tympanoplasty at all time points, from 3 months to 2–5 years. (B) Similar findings were identified for the air-bone gap (ABG) at all time points. When individual ears were evaluated, a successful outcome (AC ≤40 dB HL, ABG ≤30 dB, indicated by the red broken line) was achieved in all patients (100%) at 3 months. (C) Three patients underwent revision canal-tympanoplasty, and the surgical outcome was good in two ears (indicated by the orange lines). (D) The bone conduction (BC) threshold was preserved or improved in all patients. *P<0.05 by the paired t-test.
The ABG was 13.7±7.4 dB at 3 months, 16.4±10.5 dB at 6 months, 19.1±11.7 dB at 12 months, and 21.5±16.1 dB at 2–5 years (Fig. 2B). Compared to the preoperative ABG of 39.3± 15.1 dB, the postoperative ABG was significantly better at all time points: 3 months (P<0.001), 6 months (P<0.001), 12 months (P<0.001), and 2–5 years (P<0.001). When defining a successful hearing outcome as an ABG ≤30 dB, the success rates were 100% at 3 months, 85.7% at 6 months, and 85.0% at 12 months (Table 1). The four-tone average of the bone conduction threshold was 7.9±4.6 dB HL at 3 months, 8.0±4.5 dB HL at 6 months, 7.9±3.4 dB HL at 12 months, and 7.4±4.5 dB HL at 2-5 years (Fig. 2D). Compared to the preoperative bone conduction hearing threshold of 10.1±5.5 dB HL, the postoperative bone conduction hearing was significantly better at all time points: 3 months (P=0.008), 6 months (P=0.017), 12 months (P=0.031), and 2–5 years (P=0.021). Notably, no patient experienced a deterioration in bone conduction hearing following canal-tympanoplasty.
Proportions of patients with successful hearing outcomes
When the air conduction threshold was analyzed at each frequency, hearing improvement was observed across all four frequencies in a linear pattern (Fig. 3). At 500 Hz, the hearing gain was 22.4±6.8 dB HL at 3 months, 26.5±12.6 dB HL at 6 months, and 27.6±11.8 dB HL at 12 months. At 1 kHz, the hearing gain was 22.9±7.8 dB HL at 3 months, 24.5±12.1 dB HL at 6 months, and 25.0±11.9 dB HL at 12 months. At 2 kHz, the hearing gain was 19.3±8.8 dB HL at 3 months, 22.8±10.6 dB HL at 6 months, and 23.7±13.8 dB HL at 12 months. At 4 kHz, the hearing gain was 22.6±11.7 dB HL at 3 months, 28.0±15.9 dB HL at 6 months, and 30.5±19.3 dB HL at 12 months.
Postoperative air conduction hearing threshold at four different frequencies. Hearing improved across all four frequencies. Regardless of the time point (3 months, 6 months, 12 months, and 2–5 years postoperatively), the mean hearing threshold was less than 32 dB HL for every tested frequency.
Problematic cases
Over the course of 12 months, the hearing of four patients deteriorated. Among these, three underwent revision surgery, resulting in improved hearing thresholds for two of them, as shown by the orange line in Fig. 2C; improvements were from 53.3 to 20.8 dB HL and from 44.2 to 21.7 dB HL. The presumed cause of hearing loss was a combination of restenosis and fixation of the POR. One patient declined revision surgery; however, his hearing improved from 45.0 dB HL to 21.7 dB HL after repeatedly performing the Valsalva maneuver. Some degree of meatal narrowing was observed due to circular soft tissue growth, yet the EAC remained patent and dry in all cases. We endeavored to identify the chorda tympani nerve in all cases, but its preservation could not be confirmed in most instances. As most patients were children, we could not perform detailed taste tests. However, none of the patients reported any change in taste following surgery. There were no instances of postoperative infection, facial nerve weakness, vertigo, deterioration of bone conduction threshold, or complete restenosis of the EAC.
DISCUSSION
The hearing outcomes of canal-tympanoplasty in this case series involving patients with Schuknecht type B CAA were satisfactory. Serviceable hearing was achieved in all patients (100%) after 3 months, and this outcome was sustained for 1 year in 85% of the cases. Initially, the ABG was approximately 40 dB HL prior to surgery. It improved to 13.7 dB at 3 months post-surgery and to 19.1 dB after 1 year, with a success rate of 85.0%. These results are superior to those reported in our previous study [13], which primarily included patients with Schuknecht type C atresia. In that study, the ABG was 20.5 dB after 3 months and 23.8 dB after 6 months, with a success rate of 50.0%.
It may be inappropriate to compare the outcomes of this study with those of other studies, which primarily included patients with Schuknecht type C atresia. Only a handful of reports have specifically focused on Schuknecht type B CAA. However, these reports either did not specify the time point (ranging from 1 month to 13.1 years) of hearing evaluation [18,19] or had very short postoperative follow-up period (1 month) [1], making comparisons with this study difficult. Overall, the reported ABG (19.9– 20.0 dB) appears similar to that of this study (13.7–19.1 dB), but systematic comparisons with detailed information are required to draw a firm conclusion [19].
There could be several reasons why the hearing outcomes were favorable. First, the anatomical abnormalities of the temporal bone in these patients may be less severe. The success of canal-tympanoplasty is heavily influenced by the inherent anatomy of the middle ear, the temporomandibular joint (TMJ), and the dura. In cases where the TMJ or dura overhangs, it may obstruct the optimal placement of the new tympanic membrane. For example, it has been reported that inferior displacement of the tegmen is a significant prognostic factor for hearing outcomes [20]. Additionally, the morphology, location, angulation, and mobility of the ossicles might be less favorable in some patients. Generally, the middle ear anatomy tends to be more abnormal when the EAC is completely obstructed rather than partially open [6,12,21,22]. Second, the processes of wound healing and bony regrowth following surgery may vary between Schuknecht type B and type C atresia. It appears that lateralization of the tympanic membrane and restenosis of the bony EAC post-surgery occur more frequently in type C atresia. We hypothesize that the osteocytes in the mucosa-lined trabeculated bone differ from those in the skin-lined cortical bone. Consequently, the regenerative capacity for bony regrowth to repair the reconstructed EAC might be weaker in CAA type B, particularly in cases with EAC cholesteatoma, due to the biological homeostasis of osteocytes that are in contact with the skin [1,6]. Third, Eustachian tube function may be superior in patients with Schuknecht type B CAA. Effective aeration of the middle ear or successful performance of the Valsalva maneuver can lead to a smaller ABG, as observed in our patient who experienced improved hearing without the need for revision surgery. The height of the middle ear has also been identified as a prognostic factor for hearing outcomes and is associated with middle ear aeration [20].
The concept of the surgical approach may vary between Schuknecht types B and C atresia. In type C atresia, the goal of canal-tympanoplasty is to remove all soft tissue and bone obstructing the pathway between the skin and the tympanum. As there is no EAC, the procedure primarily focuses on the thorough removal of tissue in the precise location. For Schuknecht type B CAA, it is crucial to make optimal use of the remaining anterior EAC skin and tragal cartilage [1]. The surgery aims to preserve the intact EAC skin and maintain the aesthetic integrity of the EAC cartilage framework, while also eliminating the elastic force of the soft tissue that tends to constrict the EAC back to its original narrow state. This surgical approach is akin to cutting one side of an O-shaped ring and stretching it into a larger C-shaped structure. According to our experience, the conchal flap meatoplasty, as proposed by Chen and Zhang [17], is an effective technique for achieving these objectives. However, this method may not be suitable for patients with Schuknecht type C atresia.
While canal-tympanoplasty may not match the hearing improvement offered by an implantable BCD, it could be a better option for patients with Schuknecht type B CAA and EAC cholesteatoma. A systematic review on BCD reported a 100% success rate in achieving ABG resolution, with 92%–100% of subjects attaining a hearing threshold of less than 30 dB HL [4]. This finding was also replicated in our previous report on BCD (success rate, 100%) [13]. However, the primary surgical objective for patients with Schuknecht type B CAA may extend beyond restoring hearing. A recent systematic review found a 43.0% risk of EAC cholesteatoma in this group [3]. The review also noted the potential for EAC cholesteatoma infection in patients ranging from 5 to 72 years old. Although the large curvature of the osseous EAC may contribute to this risk, the size of the EAC does not [3]. Considering the risk of EAC cholesteatoma infection and the favorable hearing outcomes, canal-tympanoplasty may be the preferable solution for these patients.
There were several postoperative complications that warrant attention. Within 12 months, hearing had deteriorated in four patients, and three of these patients underwent revision canaltympanoplasty. The ABG was resolved in one patient by performing the Valsalva maneuver. Among the three patients who underwent revision surgery, which represents 14.3% of the sample, the ABG was resolved in two. However, in some cases, particularly after 2–5 years of follow-up, we were unable to correct the large ABG. Given the slow progression of the ABG, it is likely that more patients will require intervention over a longer follow-up period. EAC restenosis was also observed in some patients. The most common form was circular soft tissue stenosis affecting the outer part of the EAC. Despite being narrow, the EAC opening remained patent, and hearing levels were satisfactory unless the patient developed severe keloid formation. This type of restenosis differed from that seen in patients with Schuknecht type C atresia, where stenosis of the bony EAC poses greater challenges.
The limitations of this study include the small number of patients and a follow-up period of less than 2 to 5 years, with four subjects who were recently operated on not reaching the 2-year follow-up mark. Further research should involve a larger patient cohort and extend over a longer duration. Conducting a direct comparison of Schuknecht type B and C patients within the same timeframe and at the same institution could enhance our understanding of this issue. Additionally, it remains uncertain whether the surgical outcomes are consistent among different surgeons performing the procedure. There may be a need to develop a standardized surgical protocol that can be disseminated to all otologists to ensure consistent and reliable outcomes.
Canal-tympanoplasty has proven to be an effective surgical intervention for patients with Schuknecht type B CAA. This procedure has led to significant improvements in hearing outcomes, achieving serviceable hearing in all patients after 3 months, with 85% maintaining these results for 1 year. The risk of postoperative hearing deterioration necessitating revision surgery within 1 year was considered acceptable (14.3%).
HIGHLIGHTS
▪ This study presents the first longitudinal analysis of long-term (2–5 years) hearing outcomes in patients with congenital aural atresia Schuknecht type B stenosis who have undergone canal-tympanoplasty.
▪ A prevalent misconception among otologists is that the hearing outcomes of canal-tympanoplasty are generally poor, which our study disproves for patients with Schuknecht type B stenosis.
▪ In this article, we detail the hearing outcomes at each follow-up interval and discuss why these results are particularly favorable in this patient group.
Notes
No potential conflict of interest relevant to this article was reported.
ACKNOWLEDGMENTS
This study was supported by the Child Cancer & Rare Disease Project (FP-2022-00004-009, 90%) and Intensive Nurturing Research Project (0320210160, 2021-1512, 10%) of Seoul National University Hospital.
The authors would like to honor the two mentors, Professor Sun O Chang and the late Professor Seung Ha Oh, who developed and passed down the detailed surgical methods to the younger generation at Seoul National University Hospital.
AUTHOR CONTRIBUTIONS
Conceptualization: MKP, JHL, SYL, MWS. Data curation: YL, MWS. Formal analysis: YL, MKP, JHL. Funding acquisition: MWS. Investigation: all authors. Methodology: YL, SYL. Project administration: YL, MWS. Resources: YL, MWS. Software: YL, MWS. Supervision: MKP, JHL, SYL, MWS. Validation: MKP, JHL, SYL, MWS. Visualization: YL, MWS. Writing–original draft: YL, MWS. Writing–review & editing: all authors. All authors read and agreed to the published version of the manuscript.