Retrosternal goiters are relatively rare, being present in 3–13% of patients undergoing thyroidectomy. It should also be stressed that metastases can present as a mediastinal mass in any of the mediastinal compartments. Most frequently, posterior mediastinal lesions are neurogenic in origin other possibilities include lymphadenopathy, extramedullary hematopoiesis, paraspinal abscess, and masses originating from the esophagus and aorta. The borders of the posterior mediastinum are delineated by the trachea and pericardium anteriorly, the diaphragm inferiorly, the vertebral column posteriorly, and the thoracic inlet superiorly. Apart from lymphadenopathy, middle mediastinal masses include aortic aneurysms and cystic lesions such as bronchogenic, enteric, neurenteric, and pericardial cysts. Lymphadenopathy is common in this location. The heart, pericardium, aorta, vena cava, trachea, and main stem bronchi reside in the middle mediastinum. The middle mediastinum confines consist of the pericardium anteriorly, the pericardium and posterior tracheal wall posteriorly, the thoracic inlet superiorly, and the diaphragm inferiorly. An anterior mediastinal mass may rarely be caused by ectopic thyroid tissue. The classic differential diagnosis for masses in the anterior mediastinum includes lymphadenopathy, thymoma, teratoma, and a thyroid goiter extending from the neck into the mediastinum. Thymus, nodal tissue, adipose tissue, and internal mammary vessels are normally present in the anterior mediastinum.Īnterior mediastinal masses account for 50% of all mediastinal lesions. Accordingly, pathology arising in each compartment has a variable likelihood among the range of differential diagnoses, on the basis of location. The mediastinum is further divided conventionally into anterior, middle, and posterior compartments, each with its own normal anatomic structures. Conversely, a mass defined clearly and sharply against adjacent aerated lung both above and below the clavicles on chest radiography is likely posterior given the surrounding posterior lung apex ( Figures 2, 5A, and 5B ).ĭifferential of Masses According to Mediastinal Compartment Below the clavicles, an anterior mediastinal mass will have sharply demarcated borders caused by the presence of adjacent aerated lung. Therefore, on a chest radiograph, an anterior cervicothoracic junction mediastinal mass will not be seen above the clavicles as a sharply bordered entity, but rather as an area of poorly marginated increased density ( Figures 1, 4A, and 4B ). Above the clavicles anteriorly, the soft tissues of the anterior mediastinum and lower neck are contiguous ( Figure 4A ). Given the more superior extent of aerated lung in the posterior apex, the sharpness of the interface of a cervicothoracic region mass with the lung can be used to differentiate masses that are predominantly anterior as opposed to posterior in location. Conversely, a lesion projecting above the clavicles with well-circumscribed borders, as in Figure 2, implies a posterior mediastinal location. A lesion projecting above the level of the clavicles with a poorly demarcated border, as in Figure 1, implies an anterior mediastinal location. The cervicothoracic sign, as demonstrated in this case, is a useful diagnostic finding that allows accurate localization of a mediastinal mass on a frontal radiograph. For example, when a neurogenic tumor (the most common differential for a posterior mediastinal lesion) is suspected, magnetic resonance imaging is the most appropriate cross-sectional imaging technique, whereas computed tomographic (CT) imaging is the most frequently used technique to evaluate other mediastinal masses. These findings are best explained by a large goiter in the left anterior neck extending into the anterior mediastinum.Īccurately localizing a mass within the anterior, middle, or posterior mediastinum on a chest radiograph provides valuable information for formulating differential diagnoses and may influence decisions regarding subsequent advanced-imaging procedures. Below the clavicles, the mass has sharply demarcated borders caused by the presence of immediately adjacent aerated lung ( black arrow, Figure 1 ). The margin is not demarcated clearly above the level of the left medial clavicle rather, it is seen as a hazy area of increased density ( white arrow, Figure 1 ). In the chest radiograph, the mediastinum on the left side is widened. Consequently, these lesions are often detected incidentally on chest radiography, a commonly used initial investigation in the evaluation of patients. Patients with mediastinal masses frequently present with either symptoms unrelated to the mass or nonspecific symptoms such as cough, chest pain, or dyspnea.
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