A 73-year-old man presented with cough and shortness of breath. He was a non-smoker and had no history of previous respiratory problems. Twelve months previously a right occipital lobectomy was performed for a Grade IV astrocytoma. At that time his chest radiograph was normal (Fig. 1). He had received a post-operative course of cranial irradiation and dexamethasone 2 mg twice daily was commenced. On examination his chest was clear. In view of his symptoms a chest radiograph was requested (Figs 2, 3). What do the radiographs show and what is the differential diagnosis? How can the problem be resolved? In retrospect, the original radiograph of the chest still appears to be normal. The recent chest radiograph shows mediastinal widening with a large right paratracheal soft-tissue mass. There are prominent epicardial fat pads. The lateral radiograph shows a subcutaneous soft-tissue mass posterior to the upper thoracic spine and a crush fracture of a lower dorsal vertebra. The differential diagnosis of the smoth mediastinal widening should include: widespread lymphadenopathy, mediastinal haemorrhage, mediastinitis, and excess fat deposition. The history of high-dose glucocorticoid administration, the presence of epicardial fat, the “buffalo hump”, collapsed vertebrae and the absence of a discreet mediastinal mass on the lateral radiograph would lead one to suspect mediastinal lipomatosis secondary to steroid therapy.