Concurrent intrathyroidal thymus and parathyroid in a patient with papillary thyroid carcinoma: a challenging diagnosis

During embryogenesis, the thymus and inferior parathyroid glands develop from the third pharyngeal pouch and migrate to their definite position. During this process, several anatomic variations may arise, with the thyroid being one of the most common sites of ectopic implantation for both organs. Here, we report the case of a young female patient, who underwent total thyroidectomy for papillary carcinoma of the thyroid. The patient’s history was remarkable for disorders of the genitourinary system. Histologic examination revealed the presence of well-differentiated intrathyroidal thymic tissue, containing an inferior parathyroid gland. While each individual entity has been well documented, this is one of the few reports in which concurrent presentation is reported. Given the fact that both the thymus and the inferior parathyroid are derivatives of the same embryonic structure (i.e. the third pharyngeal pouch), it is speculated that the present condition resulted from a failure in separation and migration during organogenesis. LEARNING POINTS: Intrathyroidal thymus and parathyroid are commonly found individually, but rarely concurrently. It is a benign and asymptomatic condition. Differential diagnosis during routine workup with imaging modalities can be challenging.