Background: Thymoma is a relatively rare type of thoracic solid tumor, and all thymomas subtypes are considered to have malignant potential. Timely diagnosis and appropriate interventions can effectively prevent this catastrophic event. Case presentation: In this case, we report a 56-year-old man with progressive dyspnea and chest tightness. An integrated imaging assessment combining echocardiography, computed tomography and magnetic resonance were performed. The multimodal imaging results revealed a large anterior mediastinal mass, companying with the pericardial effusion and right pleural effusion, and the tumor had already invaded the lungs, pleura, heart, blood vessels, and liver. Subsequently, an ultrasound-guided percutaneous biopsy of chest wall metastatic nodules was performed. The histological diagnosis showed the type B3 thymoma with multiple metastases (Masaoka stage IV b). Obviously, the patient had lost opportunity for surgery, thus, the chemotherapy and adjuvant therapy can only be selected. After a period of follow-up, the condition of this patient was stable and without recurrence. Conclusions: Multimodality imaging plays an essential role in confirming the primary diagnosis of invasive thymoma and guiding treatment decisions.