Mediastinal lymph nodes are lymph nodes located in the mediastinum. The mediastinum is an area in the central part of the chest in between the two lungs.
Lymph nodes are small structures located all over the body around blood vessels and are a part of the lymph system of the body. Read more in Understanding the Lymph System.
Lymphomas are a group of cancers of the lymph system. It can affect any lymph nodes and mediastinal lymph nodes are affected in many lymphomas.