A Case of a Thymic Epidermoid Cyst Enlarged during 3-year Follow-up Period

Abstract

A 66-year-old woman referred to our hospital for treatment of a mediastinal tumor was found having a 56 × 35 mm poorly enhanced and clearly demarcated tumor at the anterior mediastinum with contrast-enhanced CT scan. The tumor had enlarged by 8 mm in diameter during the past 3 years. Upon MRI, the anterior mediastinal tumor exhibited homogeneous high signal intensity on T1-weighted images and a combination of high and low signal intensities on T2-weighted images. A mature cystic teratoma was suspected and the patient was operated on. As the left diaphragmatic nerve had firmly adhered to the tumor, the nerve and the tumor were combinedly resected, resulting in total thymectomy. Histopathology did not demonstrate malignant cells and we diagnosed the tumor as epidermoid cyst. The postoperative course was uneventful and the patient was discharged on 8^th postoperative day.

Epidermoid cyst of the thymus is so rare that only seven cases including our case have been reported so far. In considering a surgical indication to a gradually enlarging mediastinal tumor, we must remember that clinical observation can be a choice of therapy if the lesion would be an epidermoid cyst.