Fine-needle aspiration cytology of malignant lymphoma of the thyroid

Our experience with fine-needle aspiration cytology in five cases of malignant lymphoma of the thyroid is reported. Only one case was correctly diagnosed as malignant lymphoma from the original cytologic reports. Three cases were misdiagnosed as anaplastic carcinoma of small-cell type and two of these three cases were subsequently revised as malignant lymphoma after a second aspiration. The final case was misdiagnosed as chronic thyroiditis at both the first and second aspirations; following a third aspiration, 8 mo later, it was correctly diagnosed as malignant lymphoma. Cytological findings of malignant lymphoma are as follows: many malignant cells are distributed as isolated cells and show monotonous features. Malignant cells are slightly larger than normal lymphocytes. Sometimes cleaved cells or large nucleoli are visible. The differential diagnosis of cytologic findings of malignant lymphoma and the other thyroid diseases is discussed in detail.