Key Points

• The location of mediastinal masses—based on the division of the mediastinum into anterior, middle, and posterior compartments—has important implications for diagnostic stragtegies and treatment.
• Cytologic or histologic diagnosis is often required to confirm a presumed diagnosis based on clinical evaluation and on the radiologic characteristics on CT scan, especially for masses located in the anterior mediastinum.
• Techniques used for diagnosis and therapy of mediastinal masses are strongly related to their availability and to the expertise of the investigators.
• In general, cystic lesions and well-encapsulated mediastinal masses smaller than 7 cm can be completely removed, resection being diagnostic and therapeutic simultaneously.

The mediastinum is anatomically defined as the space between the two lungs; it is demarcated by the thoracic inlet superiorly, the diaphragm inferiorly, the sternum anteriorly, and by the spine and paravertebral thoracic sulci posteriorly[1],[2]. For practical reasons, it is further divided into anterior, middle, and posterior compartments based on anatomic landmarks seen on lateral radiographs (Figure 1). Because the localization, extent, and radiologic characteristics of a mediastinal mass are best evaluated on computed tomographic (CT) scans, these landmarks are applied there accordingly. This has important implications for diagnosis and treatment of mediastinal masses because specific lesions have a predilection for a certain compartment[3]. In adults, 54% of mediastinal tumors develop in the anterior mediastinum, 20% in the middle mediastinum, and 26% in the posterior mediastinum. In children, the percentages are comparable: 43%, 18%, and 39%, respectively. Although more than two thirds of mediastinal masses are benign, predilection for malignancy is greater in the anterior mediastinum (60%), compared with 30% in the middle mediastinum and 15% in the posterior compartment[1],[4].

Figure 1 

Shields’ three-compartment model of the mediastinum (FROM SHIELDS TW: MEDIASTINAL SURGERY. PHILADELPHIA, LEA & FEBIGER, 1991, [unknown entity=Rho] 4.)

In most patients with primary mediastinal tumors, identification of the lesion results from the onset of local symptoms or from a routine chest radiographic examination in an asymptomatic patient. It has been shown that symptomatic patients are more likely to have a malignant process because about 85% of patients with a malignancy are symptomatic at diagnosis, compared with 45% of patients with benign lesions[3],[4]. Most commonly, symptoms are related to local compression or direct invasion of neighboring structures, or they are paraneoplastic systemic symptoms. Nonspecific symptoms such as cough, chest pain or discomfort, and dyspnea may result from local compression. Superior vena cava syndrome, Horner’s syndrome, hoarseness, and neurologic signs are more frequently associated with infiltration of adjacent structures. Systemic symptoms are rare and typically are caused by the release of excess hormones, antibodies, or cytokines[1]. In addition to clinical signs, laboratory and/or radiologic findings can help in the elaboration of a presumed diagnosis in some patients.

The initial workup of a mediastinal mass includes posterior and lateral chest radiographs. In all patients with normal renal function, complete evaluation proceeds to CT of the chest with intravenous contrast, which is important in planning further diagnostic and treatment strategies. Other examinations, such as CT angiography, PET-CT scans, magnetic resonance imaging (MRI), and nuclear scans, can also be used to further characterize a mediastinal mass.

In the following section, the clinical, laboratory, and radiographic features of the most commonly encountered mediastinal masses are reviewed. In the next section, a detailed overview of the various diagnostic methods is presented. The differential diagnosis of mediastinal masses based on their location in the mediastinum is summarized in Table 1.