Micronodular Thymoma with Lymphoid Stroma in a Multilocular Thymic Cyst: A Case Study
A previously healthy 73-year-old male presented with an acute onset of chest pain for one month in duration. Chest computed tomography showed a heterogeneously enhancing mass in the right anterior mediastinum approximately 5.1 cm in size, most likely representing an intermediate-grade thymic epithelial tumor (). Trans-sternal extended thymectomy was performed. Upon gross examination, the external surface of the thymus was smooth and micronodular in appearance (). Upon opening, the thymus was completely replaced by a yellowish brown ovoid mass that was solid and cystic in appearance, and yellowish turbid fluid was expelled from the cystic portions. The largest cyst measured 2.5×2.0×2.0 cm (). Prominent macro- and microcystic changes were observed, and the cystic spaces were lined by flattened cuboidal cells (, inset) with occasional mucinous epithelium (, inset). Microscopically, the mass consisted of two components: a nodular epithelial component and mature lymphoid cells with prominent germinal centers (). Of the nodular structures, the epithelial cells had a spindle to round appearance, with bland euchromatic nuclei and plump cytoplasm. Occasional bluish mucin was observed in the tumor. At the subepithelial area, accumulation of foamy macrophages was also observed as well as infiltrating spindle- to round-shaped epithelial cells. Some areas of the cyst wall showed extensive fibrosis. The patient was diagnosed as having a micronodular thymoma with lymphoid stroma accompanied by a pre-existing multilocular thymic cyst.\nPreoperatively, the patient showed an uneventful course for twelve months. Symptoms such as myasthenia gravis were not observed before or after removal of the mass.