Development of Primary Thyroid Lymphoma during an Ultrasonographic Follow-up of Hashimoto's Thyroiditis: A Report of 9 Cases.

We herein experienced 9 patients with primary thyroid lymphoma that developed during 3-18 years of ultrasonographic follow-up of Hashimoto's thyroiditis. All nine patients had localized mucosa-associated lymphoid tissue (MALT) lymphoma. Two patients had diffuse type, one had mixed type, and six had nodular type according to the ultrasonographic classification. A clearly enlarging goiter was observed before the diagnosis of lymphoma in 3 patients. An enlarging goiter was not apparent in the remaining 6 patients with nodular type lymphoma, however, the emergence or enlargement of a hypoechoic nodular lesion was observed. Thyroid MALT lymphoma may be diagnosed early by an ultrasonographic follow-up of Hashimoto's thyroiditis.