AbstractMediastinal masses incidentally discovered on chest imaging often suggest underlying malignancy such as lymphoma or metastatic cancer. However, the radiographic appearance of mediastinal edema can mimic a mediastinal mass in the context of acute fluid overload. We describe the case of a 75 year old woman known for end‐stage renal disease on hemodialysis who presented with acute pulmonary edema in the context of a Non ST‐Elevation Myocardial Infarction. Chest CT imaging showed pulmonary edema, pleural effusions, and a middle mediastinum soft‐tissue mass of 4.2 × 2.5cm. Malignancy was initially suspected, however given the clinical context of fluid overload and absence of other signs of malignancy, the possibility of the mass representing soft‐tissue edema was raised. Therefore, the patient's fluid overload was treated with a progressive reduction in the dry weight used for dialysis and a repeat chest CT was obtained 8 weeks later once the patient was euvolemic. The repeat CT showed complete resolution of the mediastinal mass. Fluid overload can manifest in many different ways on chest imaging. Mediastinal masses lead to concerns about a potentially malignant process and often prompt further evaluation with invasive procedures that carry significant risks. In the appropriate clinical context, it is important to consider the possibility of mediastinal edema presenting as a mass on chest imaging. Under such circumstances, it is more prudent to correct the fluid overload and repeat chest imaging before undertaking invasive diagnostic procedures with the potential to cause harm.