Adenoid Cystic Carcinoma of the External Auditory Canal and Temporomandibular Joint - A Case Report

Abstract

Rationale:

Adenoid cystic carcinoma (AdCC) of external auditory canal (EAC) is a rare malignancy. It presents significant diagnostic and surgical challenges due to complex anatomy and functional implications.

Patient Concerns:

A 39-year-old female presented with progressive left ear pain, hearing loss and discharge, initially treated as otitis media.

Diagnosis:

Subsequent investigations confirmed AdCC of the EAC extending to the temporomandibular joint (TMJ).

Treatment:

The patient underwent wide local excision of the EAC AdCC lesion, including a superficial parotidectomy and partial TMJ tissue removal, guided by frozen section analysis. Final histopathology confirmed clear surgical margins across all 26 evaluated samples.

Outcome:

Post-operative recovery was uneventful with no residual disease or metastasis by 6 months. The patient reported mild trismus with preserved jaw function.

Take-away Lessons:

Early diagnosis and multidisciplinary management are critical for EAC AdCC with TMJ involvement. Meticulous surgical planning, clear resection margins and vigilant follow-up are crucial for optimal outcomes.

INTRODUCTION

Adenoid cystic carcinoma (AdCC) is a rare malignant tumour of glandular origin affecting the external auditory canal (EAC), with an incidence of 5–20% of primary EAC malignancies. It is characterised by an indolent course, local invasion and perineural spread. Malignancies of the EAC account for <0.2% of all head and neck cancers, with AdCC being one of the most uncommon histologic subtypes. Due to its rarity, AdCC of the EAC is often underdiagnosed or misdiagnosed as benign conditions such as chronic otitis media, leading to delays in appropriate management. Its tendency for perineural invasion contributes to a high rate of local recurrence and distant metastasis, particularly to the lungs. Given the critical structures in proximity, including the facial nerve, temporomandibular joint (TMJ) and middle ear, the involvement of AdCC in these areas can significantly impact function and prognosis.[1,2,3,4,5,6]

Involvement of the TMJ poses unique challenges due to the complex anatomy and potential impact on jaw function. The rarity of this malignancy, combined with its aggressive nature, necessitates a multidisciplinary approach for accurate diagnosis and optimal treatment planning.

CASE REPORT

A 39-year-old female presented with a 6-month history of progressive left ear pain, hearing loss and a sensation of fullness with a discharge for the past 4 months. She sought treatment elsewhere 5 months back that was initially diagnosed and treated as chronic suppurative otitis media with multiple, empirical antibiotic courses with no obvious improvement. When a culture analysis was performed, an absence of microbial infection led to further investigation. Subsequent superficial biopsy under local anaesthesia diagnosed the lesion as a malignant, glandular lesion with features suggestive of epithelial–myoepithelioma. A deep biopsy was done under general anaesthesia, which revealed the lesion to be AdCC.

Subsequently, imaging was carried out. High-resolution computed tomography and magnetic resonance imaging demonstrated a mass lesion in the left EAC extending to the TMJ without bony destruction [Figure 1a-d]. Physical examination was non-significant except for the absence of facial nerve involvement. Otoscopic examination showed a reddish, polypoid mass partially obstructing the canal.

Figure 1.

(a) Coronal view represents a soft tissue mass within the external auditory canal (EAC) and extending into adjacent soft tissue planes. (b) The lesion involving the EAC and extending medially towards the temporal bone and possibly encroaching on the middle ear. (c) Pre-operative three-dimensional view of the skull. (d) No gross involvement of the maxilla and mandibular bone is noted

Wide local excision of the ECS AdCC lesion measuring 1.6 cm × 1.5 cm × 0.3 cm was planned. Under nasoendotracheal intubation, using a modified Blair’s incision with an endaural extension was marked, and dissection was initiated in the neck region. The sternocleidomastoid (SCM) muscle was exposed and traced to its origin at the mastoid process. The external jugular vein was identified, and a Level II lymph node was excised. The posterior belly of the digastric muscle was exposed and retracted.

The main trunk of the facial nerve was identified, and an anterograde dissection was performed to delineate and preserve its branches. The primary tumour involved the EAC and extended to the overlying skin, tympanic membrane, incus, malleus, mastoid process and the superficial lobe of the parotid gland. These involved structures were resected en bloc. Intraoperative frozen sections (FSs) were sent from the TMJ capsule, anterior and superior skin margins, zygomatico-temporal branch of the facial nerve and parotid tissue [Figure 2a-g].

Figure 2.

(a) Modified Blair’s with endaural incision marking. (b) Circumferential dissection around primary tumour with skin intact. (c) Branches of facial nerve-temporofacial and cervicofacial and their divisions. (d) Cable nerve grafting of the temporal branch of the facial nerve using great auricular nerve. (e) Primary closure. (f) Resected primary tumour external surface (skin, external auditory canal and superficial parotid gland). (g) Anterior temporalis margin (ink away from the tumour)

FS analysis confirmed tumour involvement in the TMJ capsule, necessitating the removal of the TMJ condyle along with the capsule and articular disc. In addition, tumour infiltration was noted in the zygomatico-temporal branch of the facial nerve and the temporal nerve, prompting their resection following informed consent. Nerve reconstruction was performed using cable grafting with the great auricular nerve. The defect was reconstructed using an SCM muscle flap. Haemostasis was achieved, a suction drain was placed and layered closure was performed. The patient was extubated and had an uneventful post-operative recovery. All resected tissues were sent for histopathological evaluation. Post-operative radiotherapy was advised as part of the comprehensive treatment plan.

The histopathology revealed an AdCC with predominantly tubular with some cribriform and solid nests pattern with perineural invasion [Figure 3a-f]. Intrasurgery FS and final histopathology were performed on multiple tissue margins and lymph nodes. The lesion involved EAC and superficial parotid gland. FS showed tumour involvement was present at the inner EAC margin, TMJ capsule, superior soft tissue margin and zygomatico-temporal branch of the facial nerve, which was accordingly managed. All other margins, including mastoid, ossicles, mandible and lymph nodes (Level II), were free of malignancy. No lymphovascular invasion or nodal metastasis was detected. The final histopathology was confirmatory, and all surgical margins (26 in all) were devoid of lesion. The histopathology also noted that the lesion was very close to the aural and TMJ cartilages as well as within the lesional capsule.

Figure 3.

(a) Medium power, haematoxylin and eosin stain, section showing the closest spread of lesion to the overlying epithelium – surface epithelium not involved. (b) Medium power, haematoxylin and eosin stain, section showing the association of the adenoid cystic carcinoma lesion involving temporomandibular joint (TMJ) and closely associated with parotid salivary glandular capsule. (c) High power, haematoxylin and eosin stain, section showing the association of the adenoid cystic carcinoma lesion involving TMJ and closely associated with parotid salivary glandular capsule. (d) Low power, haematoxylin and eosin stain, section showing the association of the adenoid cystic carcinoma lesion – note the arrangement of the duct like pattern. (e) Medium power, haematoxylin and eosin stain, section showing the association of the adenoid cystic carcinoma lesion – note the arrangement of the duct like pattern. In few areas, a classic “Swiss-Cheese pattern” is noted which is characteristic of adenoid cystic carcinoma. (f) Low power, haematoxylin and eosin stain, section showing the association of the adenoid cystic carcinoma lesion involving TMJ and closely associated with parotid salivary glandular capsule

Post-operative recovery was uneventful, with no immediate complications [Figures 4a and b, 5a and b]. The patient was advised for radiotherapy. At 1-year follow-up, imaging showed no evidence of residual disease or distant metastasis. The patient reported mild trismus, but maintained adequate jaw function [Figure 6a-c]. Long-term follow-up is ongoing to monitor for recurrence.

Figure 4.

(a) Three-dimensional computed tomography of the skull images represents post-operative changes around the external auditory canal region. (b) Post-surgical changes in the left temporomandibular joint region, including absence of the left condylar head and presence of soft tissue haemostatic clips

Figure 5.

(a) Immediate post-operative view. (b) Post-resection of tumour showing satisfactory healing after follow-up of 1 year

Figure 6.

(a) Pre-operative view. (b) Immediate post-operative view with preservation of facial nerve. (c) Long-term follow-up (1 year) adjuvant radiation therapy with no changes in facial nerve function

DISCUSSION

The uniqueness of this case lies in the rare occurrence of AdCC in the EAC, with significant involvement of the TMJ, a site that is not commonly affected in such malignancies.[2,3,5] The surgical approach was particularly complex due to the lesion’s proximity to critical structures such as the parotid gland, TMJ and aural cartilage. The need for extensive tissue excision, including a superficial parotidectomy and part of the TMJ, highlights the importance of ensuring clear surgical margins.[3,6] The final histopathology confirming the absence of tumour in all 26 evaluated margins underscores the meticulous surgical planning required to achieve complete resection when preserving function.

Furthermore, the role of evidence-based antibiotic prophylaxis in such cases cannot be understated. Given the high risk of post-operative infections due to the involvement of the EAC and TMJ, targeted antimicrobial therapy is essential in reducing complications and promoting optimal healing. Broad-spectrum antibiotics covering common pathogens of the head and neck region should be considered, particularly in the setting of extensive soft tissue resection and parotidectomy.[3,4]

Ensuring lesion-free margins in AdCC is of paramount importance, as incomplete excision significantly increases the risk of recurrence.[3,4] The aggressive nature of AdCC, coupled with its propensity for perineural invasion, necessitates comprehensive surgical excision with intraoperative FS evaluation to guide further resection if necessary.[4,5] Given the proximity of the lesion to aural and TMJ cartilages, achieving negative margins without excessive functional compromise was a delicate balance that required precise surgical expertise.[7] Post-operative surveillance with imaging and clinical assessments remains crucial in detecting any signs of recurrence early.[7]

CONCLUSION

This case underscores the importance of early recognition and comprehensive treatment planning for AdCC of the EAC involving the TMJ. Multidisciplinary collaboration is crucial in optimising functional and oncological outcomes. Meticulous surgical planning, evidence-based antibiotic use and ensuring clear resection margins remain the cornerstone of successful management in such rare and challenging malignancies.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.