Intrathyroidal branchial cleft-like cyst in chronic thyroiditis

An extremely rare case of intrathyroidal branchial cleft-like cyst is repor ted. A 71-year-old man complained of a growing mass in the right lateral ne ck. A cystic mass in the upper lobe of the right thyroid was demonstrated b y ultrasonography and computed tomography. The surgical specimen revealed a cystic mass with dense fibrous capsule, 22 x 20 x 10 mm in size. Microscop ically, the cyst walls and the surrounding thyroid tissue contained severe lymphoid cell infiltration with lymphoid follicle. Squamous epithelium line d the cyst wall. Immunohistochemically, squamous epithelium was positive fo r keratin, cytokeratin 19, carcinoembryonic antigen, and epithelial membran e antigen, but negative for calcitonin and chromogranin A. The patient is c urrently well with no evidence or recurrence for 43 months.