Abstract
BACKGROUND: An atypical type A thymoma variant was newly added to the WHO classification of type A thymoma family in 2015. CASE PRESENTATION: A 72-year-old female was present a large round mass in the anterior mediastinum. The radiological examination led to a preoperative diagnosis of non-invasive thymoma. Tumor resection was undertaken via median sternotomy. Complete removal of the mediastinal tumor was achieved. Pathological examination revealed that the tumor cells were spindle- and oval-shaped with atypia. Immunohistochemical work-up revealed that the tumor was type A thymoma. On the basis of these findings, the tumor was finally diagnosed to be an atypical type A thymoma variant. CONCLUSIONS: Preoperative diagnosis as atypical type A thymoma variant based on radiological examination is difficult. In case of atypical type A thymoma variant, a careful postoperative systemic follow-up should be done.