The document discusses various pediatric mediastinal masses including lymphoma, thymic hyperplasia, thymoma, germ cell tumors, and cysts. Hodgkin's lymphoma typically presents as a primary mediastinal lesion while non-Hodgkin's lymphoma usually manifests as generalised disease. Thymic hyperplasia appears as diffuse enlargement of the thymus on imaging. Thymoma is the most common primary tumor and appears as a well-defined anterior mediastinal mass. Teratomas often contain fat, soft tissue, and calcium. Cystic lesions include bronchogenic cysts which are usually located near the trachea or bronchi, and pericardial cysts which abut