Mucoepidermoid carcinoma in a thyroglossal duct remnant

Abstract

Introduction: Thyroglossal duct cysts (TDC) are common midline neck swellings resulting from embryological remnants of the thyroglossal duct. They often contain ectopic thyroid tissue and malignant transformation has been reported, most commonly to papillary thyroid carcinoma. Mucoepidermoid carcinoma (MEC) usually occurs in the salivary glands and only rarely in the thyroid. This is the first case of a MEC occurring within a thyroglossal duct remnant.

Presentation of a case: A 73 year old lady presented with a thyroglossal duct cyst. She declined surgical excision, as she was adamant she wanted to avoid surgery. The neck mass rapidly enlarged at two years following initial diagnosis. Fine needle aspiration cytology was suspicious for carcinoma. She underwent total thyroidectomy and selective central compartment neck dissection with adjuvant radiotherapy. She remains alive and well two years post treatment.

Discussion: Mucoepidermoid carcinoma is the most common malignant neoplasm of salivary glands, although it has rarely been reported in diverse locations including the thyroid, lung and pancreas. To the best of our knowledge, this is the first reported case of mucoepidermoid carcinoma arising from a thyroglossal duct remnant.

Conclusion: This case adds weight to the literature favouring surgical excision of thyroglossal duct remnants due to the risk of malignant transformation.

Keywords: Head and neck neoplasm; Mucoepidermoid carcinoma; Salivary gland; Thyroglossal duct.

Fig. 1

Ultrasound images from initial clinic presentation. A: Midline view showing central cystic lesion. B: Doppler showing no evidence of increased vascularity. C: Right lobe of the thyroid showing evidence of colloid cyst, otherwise normal appearances. D: Left lobe of thyroid showing normal appearances of the gland.

Fig. 2

CT scan of the neck (sagittal view). A: Sagittal (non-contrast) view of the neck showing anterior midline neck mass extending from the suprasternal notch to the hyoid bone.

Fig. 3

T2 weighted MRI axial (A) and coronal STIR (B) images demonstrating a 68 mm × 47 mm × 93 mm mixed T2 isointense/hyperintense infrahyoid lesion. It indents the superior thyroid gland and displaces the larynx and trachea posteriorly.

Fig. 4

Macroscopic histopathology. A: Macroscopic specimen from total thyroidectomy: a single spherical mass 89mm × 80mm × 55 mm without identifiable left or right lobes, or obvious thyroid capsule. B: Cut surface demonstrates well circumscribed, partly necrotic tumour mass

Fig. 5

Microscopic histopathology demonstrating mucoepidermoid tumour. A: High power image showing epidermoid, clear and mucinous cells. B: Cytokeratin 5/6 immunohistochemistry confirms epidermoid differentiation (brown stain). C: B/PAS stain reveals mucin secretion (blue).