Thyroglossal duct cyst is the most common congenital cyst in the head and neck, which is defined usually occurring in children. However, intra-thyroid thyroglossal duct cyst in an adult is unusually found. Here we describe a case of a 45-year-old woman who was found neck mass along the midline for 5 years. During the surgery we found a separated nodule in the left inferior pole of the thyroid. Surprisingly the diagnosis of the nodule was confirmed by pathology and histological examination demonstrating that it was the thyroglossal duct cyst. Intra-thyroid thyroglossal duct cyst in an adult is a rare finding, with few cases reported. For it is generally thought that any thyroid tissue found in the lateral aspect of the neck may indicate metastatic deposits from well-differentiated thyroid carcinoma. Although pathogenesis of an alone thyroglossal duct cyst in the left inferior pole of the thyroid remains unknown, our case could suggest thyroglossal duct cyst should not be excluded in the differential diagnosis of lateral neck masses especially when it simulates nodules in the thyroid.
Keywords: Intra-thyroid thyroglossal duct cyst (ITTDC); nodule; thyroid gland; ultrasound (US).