Ectopic thymoma presenting as a giant intrathoracic tumor: a case report

Abstract

Ectopic thymoma rarely presents as an intrathoracic tumor. We report a case of ectopic thymoma presenting as a giant right intrathoracic tumor that was treated with resection. The patient was a 50-year-old Japanese woman who presented with the chief complaint of chest pain. Detailed examination revealed a solid tumor measuring 15 × 10 × 8 cm in diameter, with a clear border. The Imaging findings suggested a solitary fibrous tumor, and surgery was performed. At surgery, the tumor was found to be adherent to the diaphragm, mediastinal pleura, and lower lobe of the lung, although it could be dissected with relative ease and was removed. Pathological diagnosis indicated a type B1 tumor with no capsular invasion according to the World Health Organization classification, and a diagnosis of Masaoka stage I thymoma was made. No continuity with the normal thymus tissue was seen, and the thymoma was considered to be derived from ectopic thymic tissue in the pleura.

Figure 1

Plain chest radiograph showing a mass lesion in the right lower lung.

Figure 2

Chest computed tomograph showing a solid tumor (15 × 10 × 8 cm) with a clear borders and internal calcification in the right thoracic cavity.

Figure 3

Chest magnetic resonance imaging. The tumor appeared isointense relative to the skeletal muscle on T1-weighted image, while T2-weighted images show partial inclusion of weak signal hypointensities of moderate signal strength.

Figure 4

Excised specimen of the tumor showing a smooth margin and calcification within.

Figure 5

Histopathological examination (hematoxylin and eosin, × 400) revealed abundant lymphocytes and large, bright tumor cells. Cells with chromatin-poor nuclei are evident.

Figure 6

Immunohistochemical staining (keratin staining × 400) showing epithelial cells distributed in a mesh-like form, mixed among lymphocytes at a ratio of nearly 1:1.