Thymic carcinoma is a malignant and invasive tumour that easily metastasizes [1]. It usually arises in the anterior mediastinum while few occurs in ectopic locations, including thyroid gland, pericardium, and middle or posterior mediastinum [2]. Very rarely, thymic carcinoma arises intrapericardially. Because the pericardial cavity has limited space, intrapericardial thymic carcinoma may induce mechanical compression or pericardial effusion, as it did in this case. To our knowledge, this was the largest pericardial thymic carcinoma ever to be reported.
Multimodality imaging is necessary for preoperative estimation of mediastinal mass. FDG-PET/CT and FDG-PET/MRI are recommended for management of thymic tumours. A high SUV of 5.0 may differentiate thymic carcinoma from thymoma, thymic hyperplasia, and normal thymus [3]. The mass in this case showed high intensity on T2 weighted imaging, limited diffusion on diffusion weighted imaging, high FDG avidity on PET, and increased size on follow-up, indicating that it was malignant. For thymic tumours, en bloc resection of mass is one of the most important prognostic factors. In this case, CTA provided anatomic information for surgical planning of en bloc resection. Pathological diagnosis of thymic carcinoma was eventually reached. Positivity for CD5 and CD117, in combination with cell morphology, provided strong evidence for the diagnosis of thymic cancer. Also, positive expression of cytokeratin and p63 support the diagnosis of thymic carcinoma [4].
This case demonstrates the utility of multimodality imaging in evaluating the pericardial mass and the validity of surgery for the giant pericardial thymic carcinoma.