Lateral Stenosis of External Auditory Canal Secondary to Corrosive acid Injury: A Rare Case Report and Review of Literature

Abstract

Acquired external auditory canal (EAC) stenosis is an uncommon condition with an incidence of 0.6 in 100,000 population. Road traffic accidents and otology surgeries are the frequently reported causes for it to occur. The high rate of restenosis makes this condition difficult to manage. A 50 year old lady presented with history of accidental instillation of acid in her left ear at 6 months of age by the care giver. The patient developed stenosis of left EAC with hearing loss. Examination revealed pin point stenosis of left EAC. Puretone audiogram revealed a moderately severe conductive hearing loss. Computed tomogram showed soft tissue lesion obliterating the entire EAC and extending into the middle ear and antrum. Intra operatively only the cartilaginous EAC was stenosed. Surgical excision of the fibrotic scar with a tympanomastoidectomy and wide meatoplasty was done. Regular post operative aural toileting, packing with merocele strips and application of topical antibiotic -steroid preparations was done. 6 months post-surgery a patent EAC and healed tympanic membrane was achieved. In this report, we present a rare case of lateral EAC stenosis secondary to corrosive acid injury, highlighting the surgical steps, post operative care and surgical outcomes. A limited review of literature is also presented.

Introduction

Acquired stenosis of the external auditory canal(EAC) is uncommon with an incidence of 0.6 per 100,000 population [1]. It can be caused by infection, trauma, tumour, inflammation and radiation [2]. Trauma is one of the most frequent etiology implicated, among which previous ear surgery and road traffic accidents constitute a significant proportion [3]. Acid injury to the ear leading to EAC stenosis is not frequently reported. Surgical excision is the definitive treatment but the high rate of restenosis makes it a very challenging condition for the ENT surgeon to manage [4]. Stenosis can occur in isolation or involve both cartilaginous and bony EAC [5]. Here we present an interesting case of lateral EAC stenosis secondary to corrosive acid injury, highlighting the surgical treatment, post operative care and surgical outcome of this rare and challenging condition.

Case Report

A 50-year-old female presented to the outpatient department with alleged history of accidental instillation of acid in her left ear at 6 months of age by the care giver. The patient was not given any treatment at that time. Her only complaint since then was reduced hearing in the left ear. She developed left ear discharge from the past 6 months. Examination of the left ear revealed a pin hole stenosis of the external auditory canal(Fig. 1), through which purulent discharge was seen. The right ear was unremarkable. Pure tone audiogram showed moderately severe conductive hearing loss in the left ear, with air-bone gap of 45 dB and normal hearing in the right ear. High resolution computed tomogram (HRCT) of the temporal bones showed complete opacification of the bony and cartilaginous EAC with low attenuating soft tissue(Fig. 2). Soft tissue was seen filling the entire middle ear and extending into the aditus and antrum(Fig. 3.). The ossicles were unremarkable. The inner ear showed normal morphology. The right ear was essentially within normal limits.

Fig. 1.

Pin point stenosis of left EAC

Fig. 2.

HRCT temporal bone revealed complete opacification of bony and cartilaginous EAC.

Fig. 3.

HRCT temporal bone revealed complete soft tissue opacification of middle ear cleft

Under general anaesthesia, the pin point opening in the left stenotic EAC was identified and dilated with a ball probe. Radial incisions were made from the pinpoint opening and the cartilaginous EAC was widened. Thick pultaceous cheesy debris was seen filling the bony external canal (Fig. 4) which was removed. Through the post auricular approach, a meatotomy was done and the bony external auditory canal was found to be of normal size. The tympanic membrane was not identified and was replaced with granulations. A cortical mastoidectomy was done, the antrum was filled with granulation tissue which was removed. The dome of the lateral semi-circular canal was intact. The tympanomeatal flap was elevated. Middle ear was filled with granulations which were removed. The stapes supra-structure and incus was completely engulfed by granulations. The tip of the handle of malleus was eroded. The middle ear was inspected with a 4 mm 30 degree rigid Hopkins’s endoscope and no epithelium was identified in the anterior epitympanum, sinus tympani, facial recess and stapes foot plate region. A wide meatoplasty was done wherein a significant conchal cartilage and thick fibrotic skin from the posterior and inferior wall of the cartilaginous EAC were excised. Slices of conchal cartilage was placed below the remnant handle of malleus. Temporalis facia was placed in an underlay fashion over the cartilage graft. The tympanomeatal flap was repositioned, a small portion over the lateral end of the posterior bony EAC was exposed. The bony EAC was filled with antibiotic- steroid soaked gelfoam. The cortical mastoid cavity was obliterated with bone wax. The post aural wound was closed in two layers.

Fig. 4.

Stenotic lateral cartilaginous segment excised. Cheesy pultaceous debris seen in the bony EAC.

The patient was using steroid antibiotic drops in the left ear post operatively. At one month post operative follow up visit, the meatoplasty was wide and patent and minimal granulations were seen over the exposed posterior bony EAC. The cartilage graft was insitu and the neotympanum had healed well. The patient was advised to stop using ear drops and keep the ear dry. Examination after two months showed granulations in the lateral part of the external auditory canal in the region of the obliterated cortical mastoid cavity (Fig. 5). Minimal narrowing of the meatal opening was also noticed. Merocele was placed in the external auditory canal to stent the cartilaginous external auditory canal and combined steroid antibiotic drops were instilled on it. The merocele was removed one week later and there was a significant reduction in the size of the granulation tissue. The remaining granulation tissue was cauterised with silver nitrate solution and merocele was placed to stent the canal. The patient was reviewed every week, residual granulation tissue was cauterised with silver nitrate and EAC stented with merocele.

Fig. 5.

Post operative - Granulations at the lateral end of the EAC

8 weeks later, minimal granulation tissue was seen and the meatal opening was adequate revealing a healed EAC. The patient was advised to apply antibiotic steroid ointment in the left ear. The patient was reviewed weekly thereafter. The patient had completed 6 months post operatively at the time of writing the manuscript, the lateral external auditory canal had completely epithelialized with a patent lumen(Fig. 6) and the tympanic membrane had also healed well (Fig. 7). The patient reported a significant improvement in hearing in the left ear. Pure tone audiogram showed mild conductive hearing loss with air-bone gap of 28.33 dB.

Fig. 6.

Patent and healed EAC at 6 months of follow-up

Fig. 7.

healed tympanic membrane at 6 months of follow-up

Discussion

Acquired stenosis of the EAC is not commonly seen. It’s incidence is more in males, with a male to female ratio of 2–3:1 [3]. The most common symptom is decreased hearing followed by otorrhoea and cosmetic complaints [6]. Solid stenosis occurs initially due to granular myringitis, thus beginning from the tympanic membrane and ending at the EAC with a stenotic skin segment [7]. The less common membranous type occurs due to focal circumferential injury to the EAC skin, resulting in granulation formation which merges together and final epithelisation of the granulation tissue leads to a stenotic segment [7]. Epithelial debris can get accumulated in the space between the stenotic segment and the tympanic membrane which can lead to development of secondary canal cholesteatoma over time [3].

Medical treatment comprises of reducing the inflammation and granulation tissue formation with regular aural toileting and topical antibiotic steroid ear drops. Once fibrosis has progressed and matured medical treatment offers no benefit and surgical excision will be required if there is significant ear complaints [6]. A computed tomogram of the temporal bones is useful in determining the length and type of stenosis, ruling out secondary cholesteatoma and its extent into the middle ear and mastoid air cells if present. A cortical mastoidectomy would be required in addition to a meatoplasty and canaloplasty if cholesteatoma involves the middle ear cleft [1]. In our patient the external auditory canal was filled with thick cheesy pultaceous material which could be infected desquamated epithelial debris and the tympanic membrane was replaced with granulation tissue. The computed tomogram showed soft tissue in the middle ear and mastoid air cells. Taking the long duration of symptoms, intra operative tympanic membrane and HRCT findings into consideration, cortical mastoidectomy was done to rule out cholesteatoma. However, no epithelium was seen in the antrum or in the middle ear in this patient.

Complete excision of the fibrous plug, enlarging the EAC and re-covering the exposed bone with skin graft constitutes the basic principles of the surgical management [1, 6]. In this patient canalplasty was not required since the cartilaginous external auditory canal was only involved and a meatoplasty alone was sufficient to permit complete visualisation of annulus and the anterior tympan-meatal angle. Split thickness skin graft is the most common techniques used for re-epithelising the EAC, other techniques described are full thickness skin graft, regional flaps [1].

Restenosis is the most common complication, incidence ranging from 6-27% [6]. Use of a stent, antibiotic steroid topical ear drops and regular aural toilet can reduce the incidence of restenosis [1, 4]. In this patient the patient was reviewed weekly, during the visits granulation tissue was removed and cauterised with silver nitrate solution to promote epithelialisation [8]. Merocele strips was used to stent the external auditory canal and antibiotic steroid drops were applied on it regularly. Rubber tubes, silastic tubing, silicon drain, acrylic prosthesis, ear molds and finger cot pack are various materials used as stents in maintaining the patency of the EAC [9]. Injection of triamcinolone around the meatal opening has also been done as an adjunct to stents to prevent restenosis [10]. Meticulous post operative care is essential in preventing restenosis in patients operated for EAC stenosis and optimising surgical outcomes [4]. Bone wax is generally safe and is commonly used in mastoid surgery [11]. In this patient bone wax was used to obliterate the cortical mastoid cavity, as a wide meatoplasty was done and the cavity would communicate with the EAC. Foreign body granuloma formation have been reported with use of bone wax, this is more commonly seen with patients with drug allergies and immunohypersensitivity [12].

A limited review of literature of all the case reports published in the English language from the PubMed database from the year 2013 to 2023, using keywords such as acquired; stenosis; external auditory canal; external auditory meatus and surgery in various combinations, is presented in Table 1. Only those cases which complies with the definition of acquired stenosis and provided information on the etiology, surgical management as well as outcome with respect to incidence of restenosis were included in the review. EAC stenosis caused by tumours were also not included in the review, as the surgical management is different and treatment of tumours in this site can itself lead to stenosis.

Table 1.

Characteristics of the reported cases of acquired external auditory canal stenosis in English from the year 2010 to 2022

Serial no.	Authors	No of cases	Aetiology	Definitive management	Method of canal re-epithialisation	Type of post op stents Used	Re- stenosis
1	Pace A et al. [13]	17	Chronic otitis externa(8) Chronic otitis media(5) Iatrogenic trauma (3) Epidermolysis bullosa(1)	Surgical excision	Thiersch graft	Silastic sheet with gelfoam	0/17
2	Gu A et al. [14]	1	Lymph- edema(1)	Coablation	Not done	Merocele sponge	0/1
3	Bansal C et al. [6]	20	Iatrogenic trauma(7) Non iatrogenic trauma (8) Inflammation(4) Idiopathic(1)	Surgical excision	Pre-auricular flap + SSTG	Silastic sheet + BIPP$ wick/merocele sponge	4/20
4	Pan, J. C et al. [9]	1	Chronic otitis media(1)	Surgical excision	Not done	Non -latex glove + gelfoam	0/1
5	Sasikumar S et al. [10]	1	Otitis externa	Microdebrider assisted excision	Not done	NG tube	0/1
6	Ng, C. S et al. [5]	1	Non iatrogenic trauma	Canalplasty	Not done	Modified tracheostomy tube	0/1
7	Hosoya M, et al. [15]	1	Subcutaneous thrombosis post COVID-19	Surgical excision	Perichondrium	Not used	0/1
8	Wong Chung JE et al. [16]	1	Non iatrogenic trauma(1)	Surgical excision	Not done	Antibiotic ear pack	0/1
9	Mikals SJ et al [17]	1	Chemical injury-silver nitrate (1)	Tympanomastoidectomy + canalplasty + meatoplasty	SSTG#	Not used	0/1
10	Giacomarra V et al. [18]	14	Iatrogenic trauma(13) Non iatrogenic trauma(1)	Conchomeatoplasty	Not done	Not used	1/14
11	Nagaoka M et al. [19]	1	Post radiation(1)	Canalplasty	Post auricular flap	Thin silk cloth and antibiotic soaked gauze	0/1

#- Split skin thickness graft $- Bismuth iodoform paraffin paste.

In our limited review of literature, the most common causes for EAC stenosis is trauma followed by chronic otitis externa. Unusual isolated causes include lymphedema [14], post COVID-19 subcutaneous thrombosis [15] and chemical injury [17]. Surgical excision of the fibrotic scar tissue was done in most of the cases. In one case series only conchomeatoplasty was done, this was because all the cases in the series had only stenosis of the cartilaginous EAC [18]. Coablator [14] and microdebrider [10] to remove the fibrotic scar tissue and widen the canal were used in isolated cases. SSTG, Thiersch graft, perichondrium,pre auricular flap and post auricular flaps were the techniques used to resurface the canal. Bulky nature, introduction of apocrine and sebaceous glands deep in the EAC, insufficient length and defects at donor site are the disadvantages with flaps [1]. In one case series [6] SSTGs were used in addition to pre auricular flaps where the length of the flap was not sufficient to cover all the exposed bone.Stents were used in most of the cases. In one series where only chonchomeatoplasty was done, stents were not used in any patient. Silastic sheet with gelfoam [13], BIPP pack [6], merocele sponge [14], antibiotic ear pack [16], modified tracheostomy tubes [5], NG tubes [10] and non latex gloves with gelfoam(finger cot dressing) [9] were the materials used to stent the canal in various studies. Rate of restenosis ranged from zero [13]in one series to 20% [6] in another series.

Conclusion

Acquired external auditory canal stenosis is a rare entity. Road traffic accidents and iatrogenic trauma are the most common reported causes, whereas corrosive acid injury leading to EAC stenosis is not frequently reported. This condition is difficult to treat because of the high rate of restenosis. In our patient meticulous post operative care with repeated removal and cauterisation of granulations, timely packing of the canal and use of steroid antibiotic topical preparations made us establish a patent EAC. A well healed tympanic membrane was also achieved in this patient. Bone wax must be used with caution as granulations and infection at the site of application can occur in some patients.

Funding

No funds, grants, or other support was received.

Declarations

Conflict of Interest

The authors have no relevant financial or non-financial interests to disclose.