A Rare Case of Multilocular Thymic Cyst with Follicular Lymphoid Hyperplasia: Radiologic and Histopathologic Features.

Multilocular thymic cysts are rare and acquired lesions induced by an inflammatory arising within the thymus. We report a rare case of multilocular thymic cyst with follicular lymphoid hyperplasia in a 59-year-old female. Chest CT and MRI revealed a large multilocular cystic mass, which contains thick septa and nodules in the thymus. F-18 FDG PET/CT showed almost no FDG uptake of the multilocular cystic mass but moderate FDG uptake of the solid nodules. Extended total thymectomy was performed. Histopathological findings revealed follicular lymphoid hyperplasia of thymic tissue but no neoplastic lesion. Based on these findings, diagnosis of multilocular thymic cyst with follicular lymphoid hyperplasia was made. This is a rare case that preoperatively was difficult to diagnose.