We present 10 cases of thymic
seminomas associated with prominent cystic changes. All patients were males, aged 16 to 79 years (median, 23.5). Clinically, two patients presented with
chest pain/four were asymptomatic and the
tumors were discovered on routine chest radiographs; one
tumor was discovered incidentally at autopsy; and in three patients no clinical information was obtained. Grossly, the
tumors were described as multilocular cystic lesions that ranged in size from 7 to 19 cm in greatest dimension, showing small focal areas of induration within the
cyst walls. Histologically, the lesions were characterized by cystic spaces lined by squamous or cuboidal epithelium showing severe chronic inflammatory changes with areas of
cholesterol cleft
granulomas, lymphoid follicular
hyperplasia, and scattered foci of residual thymic parenchyma within the walls of the
cysts, resulting in a picture indistinguishable from acquired multilocular
thymic cysts. Careful examination, however, revealed microscopic foci composed of a neoplastic proliferation of large polygonal cells with slightly eosinophilic to clear cytoplasm and large nuclei with prominent nucleoli. The atypical cells were admixed with an inflammatory background and were often accompanied by a florid granulomatous reaction.
Periodic acid-Schiff histochemical reaction with
diastase revealed moderate amounts of
glycogen within the cytoplasm of the
tumor cells. Immunohistochemical studies in five cases showed positive labeling of the
tumor cells with
placental alkaline phosphatase. Nine patients were treated by complete surgical excision of the mass, and additional postoperative
radiation therapy was given to two patients. Follow-up information available for five patients showed all to be alive and well from 2 to 19 years after diagnosis (mean follow-up, 9 years). Four of the patients were lost to follow-up. The pathogenesis of the cystic process in these cases remained unsettled but may represent a reactive change secondary to epithelial
hyperplasia of thymic epithelium. Thymic
seminoma should be considered in the differential diagnosis of cystic lesions of the anterior mediastinum; extensive sampling of such lesions is therefore recommended for proper evaluation.