Thyroid Carcinoma Showing Thymus-Like Differentiation (CASTLE) with Tracheal Invasion: A Case Report

BACKGROUND Thyroid carcinoma showing thymus-like differentiation (CASTLE) is a rare disease entity. It arises from ectopic thymic tissue in the thyroid gland. Patients usually present with enlarging neck mass and hoarseness. CASE REPORT A 49-year-old man presented to our clinic with hoarseness and a right thyroid mass. Ultrasound showed a 6-cm right thyroid tumor and computer tomography confirmed invasion into the trachea. He received total thyroidectomy together with excision of one-third of the tracheal wall. No gross tumor was left behind. The tracheal defect was repaired using a pedicled right sternocleidomastoid muscle flap. He had a good recovery and was discharged 2 days after surgery. Histology revealed carcinoma showing thymus-like differentiation (CASTLE). The patient had regular follow-up and showed no clinical evidence of recurrence 18 months after surgery. CONCLUSIONS Thyroid carcinoma showing thymus-like differentiation (CASTLE) is a rare yet potentially extensive disease with favorable prognosis. Imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI), is helpful in aiding diagnosis and operative planning. Surgical resection is currently the treatment of choice, with generally favorable outcomes. The role of adjuvant therapies such as radiotherapy and chemotherapy require further studies.