Multilocular Thymic Cyst with High F¹⁸ Fluorodeoxyglucose Uptake and Rheumatoid Arthritis: A Case Report

Background: multilocular thymic cysts are uncommon acquired cysts in the anterior mediastinum caused by incomplete thymic involution. They may be associated with autoimmune diseases, such as rheumatoid arthritis and systemic sclerosis. Methods: a 61-year-old man with a history of rheumatoid arthritis for 8 years was referred to our unit because of a multiloculated mass in the anterior mediastinum with a high F¹⁸ fluorodeoxyglucose uptake at PET-CT scan. Histology showed a multilocular thymic cyst with lymphoid tissue, organized in germinal centers and internodal areas. Results: rheumatoid arthritis-related symptoms progressively disappeared after the excision of the mass. Conclusions: to our knowledge, this is the first report in the English language of rheumatoid arthritis symptoms improvement after multilocular thymic cyst surgical removal.