[A case of multilocular thymic cyst with myasthenia gravis].

We reported a case of 53-year-old male who was admitted to our hospital for ptosis and difficulty in chewing. Because of positive for Tensilon test and high dose anti-acetylcoline receptor antibody, we established diagnosis for myasthenia gravis. Additionally he was pointed out a cystic lesion at anterior superior mediastinum on CT and MRI. As a result we diagnosed him as thymic cyst with myastenia gravis. The extended thymectomy was performed. Histological examination revealed that the mass was a multilocular thymic cyst which is reported by Suster, who suggested that the multilocular thymic cyst arises from processes of reactions to an acquired inflammatory change. There was no report for cases of multilocular thymic cyst with myastenia gravis. MTC-like changes are sometimes presented in association with thymic Hodgkin's disease or thymic seminoma. Malignant transformation of thymic cyst were also reported. So careful examination and evaluation for cystic lesion within thymus are required.