Modified radical mastoidectomy obliterations in North Queensland

Introduction

Modified radical mastoidectomy (MRM), also known as Canal Wall Down Mastoidectomy, is a well-established surgical approach for managing a range of chronic middle ear conditions when disease cannot be adequately accessed, eradicated, or anatomy cannot be safely reconstructed (1). Indications include advanced cholesteatoma, chronic suppurative otitis media with irreversible mucosal disease, revision surgery after failed canal wall up procedures, or where patient factors may preclude close post-operative surveillance whereby MRM allows easier self-care (2). In Australia, the rate of cholesteatoma surgery is 8.1–8.6 per 100,000 person-years (3). MRM involves a post-auricular approach to externalise the mastoid and middle ear space by removing diseased tympanomastoid air cells and unifying the cavity with the external auditory canal, without reconstruction of the ossicular chain (2,4).

Although MRM is often definitive and associated with lower recurrence rates compared to canal wall up surgery, the open mastoid cavity can create persistent morbidity (1,5). Disrupted epithelial migration, susceptibility to water retention, chronic discharge, recurrent infection, hearing impairment, and the need for lifelong aural toilet are well-recognised challenges (1,6). These complications can significantly affect daily functioning, restrict water-based activities, and generate repeated healthcare presentations.

In North Queensland (NQ), these issues are amplified by multiple population-specific factors. First, NQ encompasses a vast tropical region north of the Tropic of Capricorn, with over 750,000 residents and a higher proportion of Indigenous Australians than the national average (7,8). Indigenous communities carry a disproportionately high burden of otitis media and chronic ear disease, with bacteriology characterised by higher rates of Staphylococcus aureus and Pseudomonas species—organisms associated with persistent otorrhoea and challenging cavity infections (9,10). Second, First Nations Australian groups in NQ, similar to Māori groups in New Zealand, place significant cultural value on swimming and connection with water, which profoundly affects their overall wellbeing (11,12). Restriction from water exposure after MRM therefore has broader psychosocial impacts than in non-Indigenous or non-coastal populations.

Third, the tropical climate, marked by heat and humidity, creates an environment where mastoid cavities are more prone to moisture retention and infection, a pattern also documented in other tropical countries (13). Finally, NQ’s vast geography means patients often travel hundreds of kilometres for follow-up and aural toilet, resulting in time away from work and family, high travel costs, and challenges maintaining regular care.

Taken together, the combination of disease burden, unique bacteriology, cultural factors around water use, tropical climatic effects on cavity health, and significant geographical barriers creates a distinctive set of challenges for patients undergoing MRM in NQ. This study is therefore uniquely positioned to examine outcomes within a population where multiple risk factors coexist simultaneously, rather than in isolation.

Options for MRM complications in NQ

MRM mastoid cavity elimination surgery is offered if disease burden cannot be controlled with proper clinic management, there is underlying disease, such as perforation, or if there are technical aspects of the MRM that cannot be improved. These are not limited to: a high facial ridge, bony overhangs, inadequate meatus, large cavity, exposed middle ear contents epithelium (cavity or via tympanic membrane perforation), avascular lining, irregular surface, and loss of self-cleaning (14). In such cases, three mastoid cavity elimination surgeries are available:

• Obliteration: the mastoid cavity is filled with local flaps or bone wax or bioactive glass then covered by vascularised soft tissue flaps.
• Reconstruction: the tympanic membrane is reconstructed and reinforced, typically with cartilage-perichondrial grafts, and the lateral mastoid cavity wall is then covered with a vascularised middle temporal artery flap.
• Ablation: the external auditory meatus is closed entirely (blind sac closure).

In this study, an obliterative reconstruction technique, combining elements of both option 1 and 2, is used. This rehabilitates the mastoid cavity, preventing further disease recurrence, and reconstructs the TM, enabling positive audiological outcomes. This technique is described in the methodology section and is referred to as obliteration throughout the text.

This study aims to collate outcomes for patients who received MRM obliteration surgery when indicated for complications sustained from MRM surgery indicated for acquired cholesteatoma. The obliteration surgeries were performed by a single surgeon at two sites in Townsville, NQ: Townsville University Hospital (TUH) and Mater Private Hospital Townsville (MPT). This case series aims to contribute to the foundation of evidence for mastoid rehabilitation recommendations in Australia and tropical regions globally.

Methods

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Townsville Hospital and Health Service Human Research Ethics Committee (No. HREC/QTHS/65640) and individual consent for this retrospective analysis was waived.

This study used a multi-centre, retrospective, cohort study design. The study is reported in accordance with the STROBE reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-62/rc) (15).

Recruitment

Paediatric and adult patients who received MRM obliteration at TUH or MPT from January 2014 to February 2022 when indicated for MRM complications. Acquired cholesteatoma was the original pathology for all patients.

Inclusion criteria:

• Child and adult patients;
• Patients with pre- and/or post-procedure audiometry were eligible for analysis in this study.

Exclusion criteria:

• No audio data available for review;
• Patients without both pre- and post-operative audiometry were excluded from mean air conduction change analysis (but were included for other primary and secondary outcome analyses).

Objectives

It is hypothesised MRM obliteration in NQ successfully yields an improvement in air conduction on audiometry, otorrhoea rates, and quality of life.

Primary outcomes:

• Calculate mean audiometry air conduction changes from pre- to post- MRM obliteration;
  • Mean air conduction defined as mean thresholds for all patients combined at 500, 1,000, 2,000, and 4,000 Hz (Hertz) frequencies pre- and post-op.
• Evaluate the rate of ear discharge post-operation.

Secondary outcomes:

• Post-operative patient quality of life as measured by the Glasgow Benefit Inventory (GBI);
• Rate of re-presentation rate for ear care;
  • With ears being defined as “care free” if no intervention (surgical intervention to topical antimicrobial agent administration) was required after the first 6 post-operative months.
• Ability to swim (as a proxy for water aversion);
• Development of caloric effects.

Quality of life was measured by the GBI—a validated, post-intervention, questionnaire with 18 questions specifically designed to measure effects of ENT operations on lifestyle and wellbeing (16). Questionnaires were completed by participants via telehealth consultations with authors after gaining consent.

Data extraction

Public and private patient files were retrospectively screened for data concerning primary and secondary objectives. Data was extracted into a password-protected Microsoft Excel file, from where tables, graphs, and statistical calculations were derived.

Statistical analysis

The maximal eligible participant sample from the study investigation period was used. Descriptive statistics were used. Continuous variables are presented as mean ± standard deviation (SD) or median [interquartile range (IQR)], depending on distribution. Categorical outcomes are presented as counts and percentages

Quality of life data is presented as a table with final score, sum of responses, mean score, and answers to question 2 and 3. The GBI involves patients answering 18 questions on quality of life in relation to their surgery. A scoring system of 1–5 is used, 1 indicates a poor outcome, 5 indicates a good outcome, 3 indicates no change in outcome since surgery. The final GBI score is calculated using the formula [(sum of responses/18) − 3] × 50 to yield a score between −100 and +100 (16). A positive score (yielded from a mean score of greater than 3) indicates overall improvement in quality of life. Whereas, a negative score (yielded from a mean score of less than 3), indicates a deterioration in quality of life. A mean score of 3 yields a score of 0, indicating no change to quality of life since the procedure. Questions 2 and 3 (“Have the results of the operation made your overall life better or worse?” “Since the operation, have you felt more or less optimistic about the future?”) provide a sense of patient quality of life and optimism and therefore are provide a quick snapshot of quality-of-life post-surgery.

Obliteration technique

An obliteration technique was used in this study. Via a post-auricular incision, the lining of the mastoid cavity is lifted out and pealed forward over the facial ridge until the middle ear is encountered and the neotympanum is lifted. When selecting patients for this procedure, computed tomography (CT) scan demonstrating aeration of the middle ear is necessary. This suggests the eustachian tube is functional and therefore the selected patient has a reduced risk of failure and recurrence. The epithelium lining is lifted from the cavity as one unit to help prevent trapping of squamous material.

Following this, residual air cells were removed and cavity surfaces smoothed using a diamond burr. The mastoid is obliterated with bioactive glass and covered in cartilage. Bonalive^® S53P4 bioactive glass was used in our cases. Bioactive glass has advantages of being radio-opaque and identifiable on surveillance scans, holding in-vitro antibacterial properties, and maintain volume over time (17). Cartilage chips were used to build up the epitympanum to the level of the scutum and a vascularised Middle temporal artery flap is then placed over the obliterated mastoid cavity covered in bioactive glass and cartilage. The middle ear is reconstructed with either a Dornhoffer Total Ossicular Replacement Prosthesis (TORP) or Partial Ossicular Replacement Prosthesis (PORP) depending on the ossicular chain status and this determines the position of the neotympanum. The addition of ossicular chain reconstruction and removal of residual mastoid air cells to the procedure builds on the obliteration techniques previously studied in Queensland (18). All patients are screened for disease recurrence with a surveillance CT at 1 and 5 years looking for signs of bony erosion as a marker of disease activity. A CT is also more easily accessible in many regions of NQ compared with magnetic resonance imaging (MRI), which patients may have to travel vast distances to access.

Figure 1A,1B show an endoscopic image of a left MRM obliteration 6 years post-operatively. A middle temporal artery flap was placed on Bonalive^® glass used in this patient to obliterate the mastoid cavity.

Figure 1 Endoscopic image of modified radical mastoidectomy obliteration. Endoscopic image of right ear MRM obliteration labelled (A) and unlabelled (B). C, cartilage graft; M, malleus; MRM, modified radical mastoidectomy; MTA flap, middle temporal artery flap; Nat TM, native tympanic membrane.

Results

A total of 29 patients were included in the study, with 32 MRM obliteration procedures performed (2 patients underwent bilateral procedures and 1 patient underwent revision obliteration). Table 1 presents the baseline demographics. The cohort comprised 15 females and 14 males, with a median age of 41.8 years (IQR, 27–56 years; range, 11–70 years). Two patients were under 18 years at the time of surgery. In terms of smoking status, 12 patients (41.4%) were active smokers, and 5 (17.2%) were ex-smokers. Eight patients (27.6%) identified as Aboriginal and/or Torres Strait Islander. Regarding follow-up, one patient did not attend any post-operative review, and four were lost to follow-up after six months. Additionally, eight procedures lacked either pre- or post-operative audiometry data, limiting their inclusion in hearing outcome analysis.

Audiometry

Out of 32 eligible 23 procedures (72%) had both pre- and post-MRM obliteration audiometry data available. Figure 2 summarises air conduction results for these 23 procedures. Air conduction improved by close to 10 decibels (dB) across all frequencies in both groups. However, 1SD ranges overlapped for all frequencies, showcasing substantial variability in audiometry outcomes. Table 2 shows numerical values for audiological outcomes. Mean air bone gap (ABG) at 0.5, 1, 2, and 4 Kilohertz (kHz) pre-operatively was 41±11.3 dB, which decreased to 28±10.9 dB post-operatively, a 32% reduction.

Figure 2 Audiometric results following modified radical mastoidectomy obliterative reconstruction. Mean value with ± standard deviation shown. MRM, modified radical mastoidectomy.

Ear discharge

As shown in Table 3, 27 patients had data available concerning ear discharge. Only 7 patients (26%) reported ear discharge, all of whom presented with their discharge between 12–18 months post obliteration.

Secondary outcomes

Of patients with available data, 17 remained ear-care free, whereas 9 patients (35%) re-presented for varying degrees of ear care, ranging from surgical intervention to topical antimicrobial agent therapy. Data on swimming ability were available for 21 patients, of which 18 patients (86%) were able to swim, and 3 (14%) were not. No patients reported caloric effects. To date, no recurrence of squamous debris in the mastoid cavity or middle ear has been encountered.

Seventeen patients were recruited for the GBI Questionnaire. Scores range from −100 to +100. As shown on Table 4, 11 patients (65%) had a final score ≥50, indicating a moderate-to-strong improvement in quality of life. Four participants had mean scores between 3–3.5, indicating mild improvement. Two participants scored small negative final scores, suggesting mild deterioration in quality of life following the procedure.

Discussion

This study represents the largest series of MRM revisions with obliteration in tropical Australia. Obliteration with a vascularised flap and Bonalive^® glass achieved durable cavity stability, a 26% postoperative ear-discharge rate, and a reduction in mean air-bone gap from over 40 to 28 dB, with no patient experiencing worsened hearing. Most patients reported improved quality of life, including enhanced social engagement and the ability to swim. Despite the modest audiometric gains, most patients reported perceived functional improvement, consistent with literature suggesting that even partial ABG closure can restore communicative ability in social settings when coupled with a dry ear (19,20).

Postoperative ear discharge occurred in 7 patients, all presenting 12–18 months after surgery. This rate aligns with findings from Johns Hopkins, which reported 15% persistent discharge following obliteration (21). The delayed onset mirrors patterns described in a revision cholesteatoma cohort from India, supporting the likelihood that discharge prevalence in this study will remain stable with longer follow-up (6).

Studies from other tropical regions report similar challenges in maintaining cavity dryness without obliteration. Ekanyake et al.’s Sri Lankan cohort undergoing MRM without obliteration experienced wet ear episodes in over 50% of cases (22). Conversely, early results from Louie et al.’s series of 88 obliterations in Manila showed no wet ear episodes at 3 months (23). These findings reinforce the relevance of obliteration in tropical climates with large rural populations.

Historically in Queensland, Black et al.’s series of 124 reconstructions using porous hydroxyapatite with a musculoperiosteal flap demonstrated improved canal soft-tissue viability but a 27% complication or recurrence rate (18). Differences in material properties and environmental exposure limit direct comparison, particularly given contemporary use of Bonalive^® glass. Skoulakis et al.’s recent review of synthetic materials used for mastoid obliterations demonstrated low otorrhoea rates (<10%) and no reported material rejection across 7 of 15 studies using S53P4 (17). Similarly, a systematic review of mastoid obliteration materials used in tympanoplasty found no reported cases of recurrence or infection in studies based in humid climates (Egypt and Delhi) (24).

The study is limited by its small audiometry sample (23 procedures), variable follow-up duration, and retrospective design. Patients who underwent surgery earlier in the study period naturally received longer surveillance. Follow-up inconsistency was exacerbated by COVID-19-related service disruptions in 2020–2021. These factors restrict inference regarding long-term complication rates and may underestimate late presentations.

The findings highlight meaningful patient-centred benefits, including improved hearing, reduced ear-care burden, and the return to water activities that hold significant sociocultural importance in NQ. This population faces multiple compounding challenges: tropical climate conditions predisposing mastoid cavities to chronic discharge, vast travel distances required for surveillance, a strong sociocultural connection to swimming, and a higher proportion of Indigenous patients with reduced access to healthcare and an ear microbiology profile more prone to chronic infection. Performing revision MRM with obliteration locally avoids substantial personal and financial travel costs for rural and Indigenous patients, supporting broader goals of health equity. Prospective data collection with standardised follow-up intervals would strengthen future analyses. Emerging artificial-intelligence-supported otoscopy for rural clinics may further enhance timely triage and reduce geographic barriers to postoperative surveillance (25).

Conclusions

This study is the largest study of MRM obliterations in NQ and contributes to the emerging foundation of evidence for mastoid rehabilitation. Improvement in Air Conduction was shown as well as reduced rates of ear discharge for patients who previously had no treatment options locally in NQ for MRM side effects. Moreover, reductions in water aversion and rates of presentation for ear-care were demonstrated, along with improvements in quality of life. To date, no recurrence of disease has been encountered, however, data continues to be monitored and collected.

Acknowledgments

The authors express sincere gratitude to Professor Bruce Black, MD, FRACS, FRCSEd, FRCS, for his review of this manuscript and for providing additional clinical context to the use of modified radical mastoidectomy with obliteration.

Findings from this study were presented at the 2022 Annual Scientific Meeting of the Australian Society of Otolaryngology Head and Neck Surgery.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-62/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-25-62/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-62/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-62/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Townsville Hospital and Health Service Human Research Ethics Committee (No. HREC/QTHS/65640) and informed consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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