Mature cystic teratoma in the posterior mediastinum.

From the Divisions of *Pathology and †Surgery, Japan Self-Defense Forces Hospital Yokosuka, Yokosuka; the Departments of ‡Pathology and Laboratory Medicine and §Thoracic Surgery, National Defense Medical College, Tokorozawa; and the ¶Department of Surgery, Japan Self-Defense Forces Central Hospital, Tokyo, Japan M ediastinal tumours tend to occur in particular subregions (superior, anterior, middle and posterior), according to their histology, and tumour location is considered to be an important differentiating criterion. Tumours in the anterior mediastinum include extragonadal teratomas. Teratomas are classified as germ-cell tumours that are composed of ectopic tissues from 2 or 3 germ layers, including mature, immature or malignant components. We present the case of a patient with a rare, mature cystic teratoma arising in the posterior mediastinum.