Tenosynovial giant cell tumor of the bony external auditory canal: a rare extra-articular case managed by transcanal endoscopic excision

INTRODUCTION

The term ‘tenosynovial giant cell tumor (TGCT) encompasses a group of lesions arising from synovium of joints, bursae, tendon sheaths and showing synovial differentiation.¹ It was first described by Chassaignac in 1852. It is classified into localized, diffuse and malignant sub-types. The localized type is called giant cell tumour of tendon sheath (GCTTS).¹

Head and neck involvement is unusual, and the External auditory canal (EAC) is an especially rare site.^2,3 Because the bony EAC has no true synovial lining, its origin in this location is not fully understood.¹ We report a rare localized TGCT of the bony EAC and describe its clinical, radiologic and histopathologic features, together with management by trans-canal endoscopic ear surgery (TEES).

CASE REPORT

A 20-year-old male with no significant medical history presented to the ENT outpatient department in September 2024 with one month of left aural fullness, a foreign body sensation and reduced hearing. He denied otorrhea, otalgia, trismus or prior ear trauma. There was no history of similar lesions elsewhere in the body.

On otoscopic examination, a smooth pinkish globular mass measuring approximately 9×9 mm was seen arising from the anterosuperior bony EAC and closely abutting the tympanic membrane. The lateral canal and pinna were normal. The lesion was firm, non-tender and did not bleed on touch. The tympanic membrane was partially visible and moved normally with Siegelization. Temporomandibular joint and facial nerve examinations were normal, and no other ENT abnormality was found. Pure tone audiometry showed mild conductive hearing loss on the left side. High-resolution computed tomography of the temporal bone with contrast demonstrated a well-defined soft tissue lesion measuring 6×12.5×10 mm in the left bony EAC, abutting the scutum and showing mild post-contrast enhancement. There was no bony erosion or middle ear extension.

The patient was advised excision of the aural mass under general anesthesia for both diagnosis and treatment. After informed consent, TEES was planned. Using a rigid oto-endoscope, the mass was completely excised with a 2-3 mm margin of healthy tissue. The underlying bony canal was normal and the tympanic membrane was intact. The specimen was sent for histopathological examination.

Microscopy showed stratified squamous epithelium with hyperkeratosis and acanthosis overlying sheets of spindle cells, evenly spaced osteoclast-like multinucleated giant cells, scattered mitotic figures, hemosiderin-laden macrophages and lymphocytes, along with focal osseous metaplasia. Immunohistochemistry showed diffuse vimentin positivity and focal desmin positivity. These findings were consistent with giant cell tumor of tendon sheath/localized TGCT.

Postoperative recovery was smooth. Canal patency was restored, and serial pure tone audiometry showed return of hearing to normal within six months. At 17 months of follow-up, there was no evidence of local recurrence.

DISCUSSION

TGCT is now regarded as a clonal neoplastic process of driven by CSF1 overexpression, with the recruitment of macrophages and osteoclast-like giant cells.¹ Localized TGCT is the commonest form and typically affects the hand and wrist. Extra-articular lesions are usually seen near peri-articular soft tissues, although intramuscular and subcutaneous presentations also occur.¹ In the head and neck, the temporomandibular joint region is the best-known site, while primary EAC involvement is distinctly uncommon.^2,3

The main challenge in this case was preoperative diagnosis. A small, smooth mass in the EAC can suggest osteoma, exostosis, canal cholesteatoma, fibrous dysplasia, vascular lesions or a cutaneous neoplasm.^4,6,8 Our patient had a benign clinical profile and imaging showed a confined lesion without erosion, but these findings were not specific enough to identify TGCT before excision.

Definitive diagnosis therefore depended on clinicopathologic correlation. The combination of spindle stromal cells, osteoclast-like giant cells, hemosiderin deposition and focal osseous metaplasia and immunohistochemistry findings were concurrent with the essential diagnostic criteria of localized TGCT.¹

The novelty of this case lies in its location in the bony EAC. Previous reports by Trani et al and Maghari et al have described lesions confined to the cartilaginous canal with normal medial canal.^2,3 In our patient, the absence of trauma, the lack of temporomandibular joint symptoms, the normal surrounding bone at surgery and the absence of radiologic destruction all support a truly isolated extra-articular lesion rather than extension from adjacent structures. Complete surgical excision is the mainstay treatment because incomplete removal increases the risk of recurrence.^1,4,9 Paniselvam et al previously emphasized complete excision of giant cell tumour of soft tissue with adequate margins and demonstrated successful removal through a trans canal endoscopic route.⁴ In this case, TEES allowed complete removal while preserving the tympanic membrane and surrounding canal skin. TEES is particularly useful in selected EAC lesions like cavernous hemangioma and osteoma because it offers a close-up, wide-angle view, improves access near the tympanic membrane and avoids a postauricular incision.^5-7 The postoperative course was favorable, with restored canal patency, hearing improvement and no recurrence to date. Continued surveillance remains important because TGCT can recur even after apparently complete excision.

Limitations

This report describes a single case with limited follow-up. Molecular testing for CSF1 rearrangement was not performed and could provide additional support in future similar cases.

CONCLUSION

Localized TGCT of the bony external auditory canal is exceptionally rare and can mimic other benign EAC masses hence should be considered as differential diagnosis. Histopathology with immunohistochemical support is essential for diagnosis. TEES provides a safe, minimally invasive and cosmetically favorable option for complete excision, with good functional outcome as seen in this case. Long-term follow-up is advisable because of the possibility of recurrence.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

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