A case of mucosa-associated lymphoid tissue (MALT) lymphoma of the thyroid

We report the cytologic findings of a mucosa-associated lymphoid tissue (MALT) lymphoma of the thyroid. The patient was an 80-year-old woman who had had medicaltreatment for Hashimoto disease. Many lymphocytes mixed with plasma cells and very few epithelial cells were seen in the aspiration smear. The lymphocytes varied in size and some cells had irregularly shaped nuclei and large nucleoli. The imprint smear was composed mainly of medium-sized lymphocytes. The lymphocytes had a coarse granular chromatin pattern, irregularly shaped nuclei and an increased nuclear-cytoplasmic ratio. Lymphoblasts and plasma cells were also seen in some degree. It was difficult to differentiate MALT lymphoma from Hashimoto disease. A shortage of epithelial cells was important for differentiation. It is difficult to diagnose a MALT lymphoma on the basis of cytology alone. However, it can be diagnosed from the clinical history.