Bearing in mind this advice it is clear that the extended shoulder chest radiograph demonstrates an abnormal contour of the right side of the mediastinum. Loss of the ascending border of the aorta is present consistent with an anterior mediastinal mass abnormality. This is a further depicted on the subsequent chest radiograph which demonstrates the appearances of the "hilum overlay" sign with normal visualisation of the right hilar vessels. These are visualised distinct from the mediastinal mass which is anterior in the mediastinum. The subsequent CT examination demonstrates this mass lies along the right antero-lateral margin of the anterior ascending aorta and contains extensive areas of mature fat with peripheral linear minor calcification and some smaller nodular elements. The accompanying PET examination demonstrates that there is no FDG activity within this region.
In order to define the aetiology of this abnormality ibe has to also consider the patient age. This patient is an elderly and therefore aggressive fat containing anterior mediastinal tumours (principally immature teratoma is and rarely liposarcomas) are unlikely.Immature teratoma are far more likely in young male patients. Diagnostic considerations might include a thymolipoma or more likely based on heterogeneity and calcifications a mature dermoid. In this particular instance the lesion was resected and the diagnosis proved to be a mature cystic teratoma of the thorax.
Mature cystic teratoma of thyroid can be considered to be a variant of mature dermoid of the pelvis. There is a rare association of mature teratoma with Klinefelter's syndrome, however, the vast majority of cases are not associated with this syndrome. These lesions have absent/very low malignant potential and often contain exclusively ectodermal and mesodermal cells (squamous epithelium/skin) rather than the three embryological layers present in most immature teratoma tumours (endoderm, mesoderm, ectoderm). Immature teratomas have malignant transformation risk. All teratoma lesions usually arise in or near the body of the thymus and are usually well demarcated lesions that may displace rather than invade other mediastinal structures. As in this case they are frequently asymptomatic and incidentally detected. They may contain fat or calcifications - heterogeneity is common. Complete excision is required to definitively exclude malignant potential. In general cystic lesions tend to be benign whereas lesions with solid material are more likely to be immature teratomas or undergo malignant transformation. Even mature teratomas have a small risk of malignant transformation to a malignant germ cell tumours. Additionally even more rarely secondary somatic cell malignant transformation can occur in the non germ cell components of mediastinal mature teratomas resulting in carcinoma, sarcoma or leukaemia.