Intrathyroidal branchial cleft-like cyst in chronic thyroiditis.

An extremely rare case of intrathyroidal branchial cleft-like cyst is reported. A 71-year-old man complained of a growing mass in the right lateral neck. A cystic mass in the upper lobe of the right thyroid was demonstrated by ultrasonography and computed tomography. The surgical specimen revealed a cystic mass with dense fibrous capsule, 22 x 20 x 10 mm in size. Microscopically, the cyst walls and the surrounding thyroid tissue contained severe lymphoid cell infiltration with lymphoid follicle. Squamous epithelium lined the cyst wall. Immunohistochemically, squamous epithelium was positive for keratin, cytokeratin 19, carcinoembryonic antigen, and epithelial membrane antigen, but negative for calcitonin and chromogranin A. The patient is currently well with no evidence or recurrence for 43 months.