Annals of the American Thoracic Society

A 77-year-old woman presented with acute shortness of breath. A posteroanterior chest radiograph showed a mediastinal mass (Figure 1).

  • 1. What are the salient abnormalities in Figure 1?

  • 2. What is the differential diagnosis?

Patients with mediastinal masses frequently present with either symptoms unrelated to the mass or nonspecific symptoms such as cough, chest pain, or dyspnea. Consequently, these lesions are often detected incidentally on chest radiography, a commonly used initial investigation in the evaluation of patients.

In the chest radiograph, the mediastinum on the left side is widened. 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). Below the clavicles, the mass has sharply demarcated borders caused by the presence of immediately adjacent aerated lung (black arrow, Figure 1). These findings are best explained by a large goiter in the left anterior neck extending into the anterior mediastinum.

Accurately 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. 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.

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. A lesion projecting above the level of the clavicles with a poorly demarcated border, as in Figure 1, implies an anterior mediastinal location. Conversely, a lesion projecting above the clavicles with well-circumscribed borders, as in Figure 2, implies a posterior mediastinal location.

Thoracic Inlet Anatomy

The mediastinum interfaces with the lower neck at the thoracic inlet, which is demarcated by the course of the first rib (Figure 3). The clavicles, which overlie the first ribs anteriorly, also indicate the junction of the thoracic inlet and anterior mediastinum. Below this point, the anterior mediastinum extends from the sternum to the anterior aspect of the pericardium posteriorly and to the diaphragm inferiorly. In the anterior thorax, lung is present only below the level of the thoracic inlet, first anterior rib, and clavicles (Figure 3). In contrast, in the posterior thorax, the posterior costovertebral junction of the first rib is at a higher level, and aerated lung extends more superiorly than in the anterior thorax (Figure 3). Therefore, the lung apices visualized above the level of the clavicles on a frontal projection radiograph are positioned posteriorly.

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. Above the clavicles anteriorly, the soft tissues of the anterior mediastinum and lower neck are contiguous (Figure 4A). 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). Below the clavicles, an anterior mediastinal mass will have sharply demarcated borders caused by the presence of adjacent aerated lung. 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).

Differential of Masses According to Mediastinal Compartment

The mediastinum is further divided conventionally into anterior, middle, and posterior compartments, each with its own normal anatomic structures. Accordingly, pathology arising in each compartment has a variable likelihood among the range of differential diagnoses, on the basis of location. Thymus, nodal tissue, adipose tissue, and internal mammary vessels are normally present in the anterior mediastinum.

Anterior mediastinal masses account for 50% of all mediastinal lesions. 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. An anterior mediastinal mass may rarely be caused by ectopic thyroid tissue.

The middle mediastinum confines consist of the pericardium anteriorly, the pericardium and posterior tracheal wall posteriorly, the thoracic inlet superiorly, and the diaphragm inferiorly. The heart, pericardium, aorta, vena cava, trachea, and main stem bronchi reside in the middle mediastinum. Lymphadenopathy is common in this location. Apart from lymphadenopathy, middle mediastinal masses include aortic aneurysms and cystic lesions such as bronchogenic, enteric, neurenteric, and pericardial cysts.

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. 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. It should also be stressed that metastases can present as a mediastinal mass in any of the mediastinal compartments.

Retrosternal goiters are relatively rare, being present in 3–13% of patients undergoing thyroidectomy. Goiters are often detected incidentally or can present with symptoms including dyspnea, dysphagia, hoarseness, hyperthyroidism, and superior vena cava syndrome. Ultrasound is used routinely to image goiters; however, these lesions are frequently detected incidentally on chest radiograph and CT scanning. Chest CT imaging, in particular, can clearly delineate the degree of retrosternal extension and the relationship of the thyroid to the trachea and mediastinal vascular structures and may be valuable in planning the surgical approach if thyroidectomy is being considered. Patients with a retrosternal goiter who undergo thyroidectomy are at a higher risk of postoperative complications including recurrent laryngeal nerve injury, bleeding, and hypoparathyroidism when compared with patients undergoing thyroidectomy who do not have retrosternal extension. Incidental identification of thyroid enlargement such as on preoperative radiography may affect the method of intubation undertaken and can be associated with tracheomalacia.

In conclusion, when an upper mediastinal lesion lacks sharp margins above the clavicles on radiography, the cervicothoracic sign accurately localizes the lesion to an anterior or posterior mediastinal location, with important etiologic and clinical implications. In general, the most appropriate next step in evaluating mediastinal lesions is CT (or possibly ultrasound in the case of suspected goiter); however, if a lesion is localized posteriorly on radiography and a neurogenic tumor is suspected, magnetic resonance imaging is warranted because of it its ability to accurately depict the tumor’s relationship to the spinal canal.

1. What are the salient abnormalities in Figure 1?

The chest radiograph in Figure 1 shows a mediastinal mass. The mass has a smooth, sharply demarcated lateral border below the level of the left proximal clavicle caused by an interface with adjacent lung. The margin is indistinct above the level of the clavicle, because the mass is located anterior to, and separate from, aerated lung in the posterior thorax. The trachea is deviated to the left with a focal impression of the mass.

2. What is the differential diagnosis?

The most likely diagnosis is a thyroid goiter. Other considerations include lymphadenopathy, thymoma, and teratoma. This differential diagnosis can be remembered as “the 4 Ts.”

A CT pulmonary angiography performed to assess for causes of the patient’s shortness of breath revealed acute pulmonary embolism. The goiter was felt to be an incidental finding and unrelated to the patient’s presentation with acute dyspnea.

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Correspondence and requests for reprints should be addressed to Darragh Halpenny, M.D., Memorial Sloan Kettering Cancer Center, Department of Radiology, 1275 York Avenue, New York, NY 10065. E-mail:

Author Contributions: D.H.: case selection, literature review, and manuscript preparation and editing; B.N.: case selection, image processing, and manuscript preparation; G.M.: manuscript preparation and editing; J.B.: manuscript preparation and editing; P.B.: image processing and manuscript preparation; J.L.: manuscript preparating and editing; and J.K.: case selection, literature review, and manuscript preparation and editing.

Author disclosures are available with the text of this article at www.atsjournals.org.

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