False-positive finding on 18F-FDG PET after chemotherapy for primary diffuse large B-cell lymphoma of the thyroid: a case report.

Primary non-Hodgkin lymphoma of the thyroid is an uncommon disease. It is a potentially aggressive disease and diffuse large B-cell lymphoma of the thyroid may result in 5 year survival rates <50%. Hence adequate follow-up and multimodality treatment for recurrent or persistent disease are required. Since 18F-FDG PET is considered the imaging method of choice for the detection and staging of lymphoma, this was used for restaging of a case of diffuse large B-cell lymphoma of the thyroid after chemotherapy and its diagnostic value is questioned in the present case report. In fact, PET showed a false-positive finding which led to unnecessary surgery.