Carcinoid tumors of the thymus are very rare, and their cytologic findings have not been reported previously in English. Retrospective study of fine needle aspiration (FNA) cytologic features in four histopathologically verified thymic carcinoid tumors ave described here in detail. The FNA cytology of thymic carcinoids is characterized by predominantly single and some loose clusters of small, round to oval cells with scanty cytoplasm, interspersed with same larger cells with moderate to abundant, granular cytoplasm. The differential diagnosis of the cytologic features between carcinoid tumor and other mediastinal tumors is also discussed.
