Normal Thymus

Even though the mediastinum encompasses several different anatomic structures, including the esophagus, lymph nodes, and cardiovascular structures, the mediastinal organ covered in this section will be the thymic gland, which is of true mediastinal origin, unlike the other structures. Traditionally the mediastinum has been divided into the superior, anterior, middle, and posterior compartments, which has informed lists of tumors that more commonly originate from these different compartments. It also seems practical from the surgical and pathological point of view to separate the mediastinum along these lines. However, the radiological features of the various compartments may be more specific in terms of the boundaries between compartments. Therefore, before we embark on a discussion of the rich pathology of mediastinal tumors, it is crucial not only to define the normal radiological characteristics and demarcations of the mediastinum but also to become familiar with the normal aspects of the thymic gland in order to address both pathological features and immunohistochemical profiles of some tumors.