[A case of myasthenia gravis with an invasive thymoma infiltrating the superior vena cava and right atrium and causing lung metastasis].

A 72-year-old woman was admitted to a local hospital with general fatigue, ptosis and dysarthria. Her anti-AchR antibody titer was high, so myasthenia gravis was diagnosed. She was given a cholinesterase inhibitor, but her symptoms did not improve. CT and MRI scans revealed a mass in the anterior mediastinum infiltrating the superior vena cava (SVC) and the right atrium (RA) . The diagnosis was an invasive thymoma extending into the SVC and the RA. Moreover, there was a mass in the right middle lobe of her lung, which was suspected to be the result of metastasis of the thymoma. She was transferred to our hospital for medication and surgery for the invasive thymoma. Urgent surgery was performed without preoperative therapy, because the tumor was nearly obstructing her tricuspid valve. An expanded thymomectomy and a right middle lobectomy were performed. As the tumor had infiltrated into the SVC, the SVC was replaced with an artificial graft. The clinicopathological diagnosis of thymoma (Masaoka Stage IVb) was given. The patient had a myasthenic crisis for several weeks after surgery, so her breathing was controlled by an artificial respirator. Her symptoms improved after treatment with steroids, tacrolimus and a cholinesterase inhibitor. Although major surgery was required to prevent tumor embolism, the patient survived. Careful observation is necessary to detect signs of relapse of invasive thymoma.