Extremely rare case of B3/thymic carcinoma borderline tumor of the middle mediastinum in a myasthenic patient

Thymomas and thymic carcinomas are rare mediastinal tumors. Ectopic middle mediastinal thymomas/thymic carcinomas are even more rare. We report the first case of B3/thymic carcinoma borderline tumor of the middle mediastinum in a 61-year-old myasthenic woman. Preoperative chest tomography and magnetic resonance imaging documented a 4.0 × 3.5 × 2.7 cm mass in the retroinnominate space. A resection of the tumor of the middle mediastinum, associated with an extended thymectomy, was carried out through a median sternotomy. Pathological diagnosis was ectopic B3/thymic carcinoma borderline tumor, stage IIa in the Masaoka clinical staging system; the thymic tissue showed normal fatty involution. Postoperative course was uneventful and, at 1 year follow-up, the patient showed an improvement of Myasthenia Gravis and no sign of tumor recurrence.