[A case of thymic cyst with elevated CEA in the cystic fluid].

A 66 year-old male was admitted on October 31, 1987 because his chest X-ray film revealed a well-defined round shadow in the right inferior mediastinum. Chest CT showed a large homogenous mass in the right anterior mediastinum. The mass was identified as a cyst on echogram. Surgical removal of the cyst was done with right thoracotomy. The cyst was 15 cm in size and contained about 500 ml of grayish white fluid. Pathological examination showed a thymic cyst and no malignancy. Biochemical analysis of the cystic fluid revealed increased CEA value of 223.2 ng/dl in spite of normal CEA level in serum. CEA was demonstrated in the epithelium of the surface and Hassall's corpuscles by PAP stain. It is conceivable that this elevated CEA observed in the cystic fluid might be correlated with CEA-like antigens such as NCA, NFA and BGP.