AB175. SOH23ABS_026. An unusual case of thyroglossal duct cyst carcinoma presenting in the sublingual space, and its multidisciplinary management

Background: Thyroglossal duct cysts (TGDCs) are the most common congenital anomaly of thyroid gland development, with a <1% risk of malignancy occurring within them. It's rare for a TGDC to be located in floor of the mouth region or the sublingual space since both these areas are not part of the typical embryological migration route of the thyroid gland.

Methods: Herein we report a 42-year-old female patient presenting with a neck mass.

Results: A 42-year-old female patient presented with a neck mass, shown on imaging to be located in the sublingual area, with magnetic resonance imaging (MRI) reported findings of a ranula, which on subsequent ultrasound guided fine needle aspiration cytology (FNAC) showed malignant cytology of thyroid origin. Surgical excision and histopathological analysis revealed a TGDC papillary carcinoma within the cyst, a rare diagnosis. Multidisciplinary discussion included review of the imaging, intraoperative and histopathological findings and the case was stratified as low-risk disease with no adjuvant treatment indicated at the time. The patient will be observed closely with active clinical surveillance.

Conclusions: There were several important points worth gathering from this case including the need to include TGDC carcinoma in a list of differential diagnoses for a midline and/or submental neck mass despite its rarity, and the importance of a full workup for an unusual neck mass such as this one in order to avoid misdiagnosis. It also serves as another example that to provide the best management plan and optimise patient outcomes for head and neck cancers, referral to a regional subspecialty multidisciplinary team (MDT) is required.

Keywords: Multidisciplinary team (MDT); neck mass; papillary carcinoma; sublingual space; thyroglossal duct cyst carcinoma (TGDC carcinoma)