Cytological diagnosis of carcinoma showing thymus-like differentiation of the thyroid gland

Objective To investigate the cytological features and differential diagnosis of carcinoma showing thymus-like differentiation(CASTLE) of the thyroid gland.Methods The fresh specimen of a case of CASTLE of the thyroid gland underwent cytological and histological examination such as smears,frozen sections,paraffin hematoxylin-eosin staining and immunostaining sections,which were analyzed by light microscopy for contrast diagnosis.Results Examination of the smears showed that small sheets and clusters of poorly-differentiated malignant cells intermixed with benign-looking small lymphocytes.The tumor cells had an increased nuclear-cytoplasmic ratio,focally prominent atypia,a little amphophilic cytoplasm,indistinct cell borders,roundish-to-ovoid vesicular nuclei,small but prominent nucleoli,occasional macronuclei,and very sparse mitotic figures.Conclusions Cytological examination is of help in diagnosing CASTLE of the thyroid gland,while its cytological features closely resemble those in malignant lymphoma and metastatic lymphoepitheliod carcinoma in cervical lymph nodes and differentiations are required in the diagnosis of CASTLE.