Table 4 Teaching points and imaging pitfalls for the diagnostic approach to mediastinal masses before and after treatment

• CT is accurate in distinguishing mediastinal masses which usually differ in their appearance and the pattern of metastatic spread, both of which are readily detected by chest CT

• Pericardial fat pads and lipomatosis are correctly interpreted as normal findings rather than possible pathological lesions

• When lipoma and liposarcoma are situated in the cardiophrenic space, the imaging findings are very similar to those of Morgagni hernia

• MRI more accurately distinguishes between cystic and solid lesions than CT

• Soft-tissue components associated with cystic lesions can be related to a malignant process (e.g. soft-tissue nodules in a cystic anterior mediastinal lesion suggest that the lesion is a cystic thymoma rather than a congenital cyst)

• Non-neoplastic thymic enlargement must not be confused with thymoma. The normal thymus in young children and the hyperplastic thymus may mimic a mass

• When differentiation between non-neoplastic thymic enlargement and thymoma cannot be achieved at CT or conventional MRI, chemical-shift MRI with in-phase and out-of-phase gradient-echo sequences can be helpful

• Thymoma rarely manifests with lymphadenopathy, pleural effusions, or extrathoracic metastases

• The role of imaging is to initially diagnose and properly stage thymoma, with emphasis on the detection of local invasion and distant spread of disease, to identify candidates for preoperative neoadjuvant therapy

• Late recurrence in thymoma is not uncommon. Imaging of treated patients is directed at identifying resectable recurrent disease, since patients with completely resected recurrent disease have similar outcomes as those without recurrence [23]

• Findings associated with significantly more frequent recurrence and metastases of thymic tumours include lobulated or irregular contour, oval shape, mediastinal fat invasion or great vessel invasion and pleural seeding

• Mediastinal lymphadenopathy, pleural effusions, and pulmonary metastases are characteristic of thymic carcinoma or non-teratomatous germ cell tumour

• Lymphoproliferative disorders typically present pleural effusions, pericardial fluid, and mediastinal lymphadenopathy in many cases

• Heterogeneous appearance (due to necrosis, cystic change, or haemorrhage) is typical of thymic carcinoma, lymphoma, sympathetic ganglion tumour, peripheral nerve tumour and non-teratomatous germ cell tumour. It can be seen in about one-third of thymomas

• A cystic anterior mediastinal mass with intrinsic fat attenuation typically represents a mature teratoma