Necrotic Thymoma Discovered Due to Subjective Symptoms: A Report of Three Cases

Abstract

Introduction: Thymomas are solid tumors that usually grow slowly and rarely cause symptoms or spontaneously regression. We have observed three cases of thymoma in which the patient presented with fever and chest pain, and pathological examination showed relatively extensive necrosis. The tumors spontaneously shrank during the course of the diseases.

Case presentation: The patients, of a 30-year-old man, 46-year-old man, and 76-year-old man presented with fever and/or chest pain, and blood tests showed high levels of inflammation. Contrast-enhanced chest computed tomography (CT) showed masses with low-density area and contrast-enhanced margins. Two patients had repeat chest CT just prior to surgery, and the tumors had shrunk. In all cases, the masses were removed by a median sternotomy. The mediastinum tissue was hard due to inflammation, and in all cases the tumors were adherent to the lungs and in one case wedge resection of the left lung was required. Histopathological examination revealed extensive necrosis of the tumors, and based on residual viable tumor cells, the three tumors were diagnosed as follows respectively; type B2, type B2 with some type B3 components, and type AB thymoma. All tumors were classified as pT1aN0M0, Stage I, and Masaoka stage II.

Conclusions: Necrotic thymoma is associated with inflammation and spontaneous regression may be observed during the course of the disease. Since necrosis can be extensive, pathological examination should be performed throughout.

Keywords: mediastinal tumor; necrotic thymoma; spontaneous regression.

Fig. 1. Case 1. Finding of chest computed tomography (CT). (A) Chest CT showed an 87 × 52 × 38 mm multilocular cystic tumor in the anterior mediastinum with contrast enhancement in the walls (arrow). (B) A small amount of pleural effusion was observed on the left side (arrow). (C, D) Chest CT 2 months after the first presentation revealed tumor regression (arrow) and disappearance of the pleural effusion.

Fig. 2. Case 1. Histological findings of the resected specimen. (A) Hematoxylin and eosin staining showed that the tumor was composed of an extended necrotic area. (B) Hematoxylin and eosin staining showed that the thymic epithelium was proliferating with lymphoid cells and tumor cells. (C, D) Immunohistochemical analyses with TdT and CK AE1/AE3 were positive in the tumor area.

Fig. 3. Case 2. Finding of chest CT. (A) Chest CT showed an 88 × 60 × 29 mm cystic tumor in the anterior mediastinum with contrast enhancement in the walls (arrow). Pleural effusion was not observed. (B) ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) computed tomography shows FDG uptake with a maximum standardized uptake value of 3.2.

Fig. 4. Case 2. (A) More than 75% of the tumor was necrotic. (B) Hematoxylin and eosin staining showed that the thymic epithelium was proliferating with lymphoid cells and tumor cells. (C) Hematoxylin and eosin staining showed that germinal center formation was observed in the thymus and it was hyperplastic.

Fig. 5. Case 3. Finding of chest CT. (A) Chest CT showed a 74 × 66 × 58 mm tumor with internal low-density area and contrast enhancement at the margins in the anterior mediastinum (arrows). A small amount of pleural effusion was observed on the left side. (B) Chest CT about 2 months after the first presentation revealed tumor regression (arrow) and disappearance of the pleural effusion.

Fig. 6. Case 3. (A) More than 75% of the tumor was necrotic. (B) Hematoxylin and eosin staining showed areas of lymphocyte-based formation and areas of spindle-shaped epithelial cells.