[Benign mature teratomas of the mediastinum]

Mature teratomas of the mediastinum are rare. However, they represent the most common mediastinal germ cell tumours. The aim of this study is to describe their clinical and pathological characteristics.

Fourteen cases of mediastinal mature teratoma, diagnosed between January 1992 and December 2006, were reviewed retrospectively, noting the clinical, radiological, surgical, and pathological findings.

The patient population consisted of 10 females and 4 males with mean age of 29 years (5-56 years). Chest pain was the main symptom. Imaging features comprised a heterogeneous anterior mediastinal mass containing soft-tissue, fluid, fat, or calcium attenuation, or any combination of the four. Macroscopically all the tumours were cystic, or predominantly cystic, containing mostly grumous material. The mean size was 9 cm (5-12 cm). Histological examination constantly revealed skin with or without appendages. Other components identified were bronchial mucosa (12 cases), fat (12 cases), muscle (10 cases), cartilage (8 cases), bone (7 cases), gastrointestinal mucosa (7 cases), pancreas (5 cases), urothelial epithelium (3 cases), nervous and prostatic tissues (one case each). All the teratomas were mature, and 7 of them were intrathymic.

Every form of teratoma occurs in the mediastinum (mature, immature and with malignant transformation) but, in our study, they were exclusively mature. The histology is essentially similar to that of teratomas of gonads. However, pancreatic tissue occurs frequently in mediastinum (54% in literature, 25% in our study) but not in the gonads. On the other hand, thyroid follicles have not yet been seen in mediastinal teratomas.