Correct!
2. The “cervico-thoracic” sign
The “cervico-thoracic” sign describes the appearance of a mediastinal lesion near the thoracic inlet. At the thoracic inlet, the anterior first ribs and clavicle demarcate the anterior aspect of the lung, whereas the posterior lung extends more cranially (Figure 3).
Figure 3. Thoracic inlet anatomy. Sagittal volume-rendered neck CT shows the relationship of the clavicle (arrow), anterior first rib (single arrowhead) and posterior first rib (double arrowhead), and lung apex (curved arrow). The trachea and lungs appear blue in this image. The first rib defines the junction of the neck and mediastinum at the thoracic inlet. Note that the posterior portion of the first rib (double arrowhead) is more cranially located than the anterior portion of the first rib (single arrowhead), with the clavicle (arrow) also positioned anteriorly and relatively caudal to the posterior portion of the first rib. Similarly, the posterior portion of the lung at the apex also extends more cranially than the anterior portion of the lung. This anatomical arrangement explains the “cervico-thoracic” sign, in which anteriorly located mediastinal lesions will lose their sharp interface with lung at about the level of the clavicle, whereas posteriorly located mediastinal lesions will maintain this sharp interface more cranially, to the level of the posterior first rib.
Therefore, a lesion in the anterior mediastinum will show a sharply demarcated contour to the level of the first ribs and clavicle, above which such a lesion will enter the neck, thereby losing contact with the lung, resulting in “disappearance” of the abnormal contour. In contrast, a lesion in the posterior mediastinum will maintain contact with the lung to the level of the posterior first rib, and therefore the abnormal contour on the chest radiograph will extend more cranially in the presence of a posterior mediastinal lesion (Figure 4C) compared with an anterior mediastinal lesion.
The “hilum overlay” sign is present when a mass overlies the hilum, but the hilum can still be seen “though” the mass - this implies that there is still aerated lung parenchyma around the vessels of the hilum, so the mass cannot reside in this area and must reside anterior or posterior to the hilum (Figure 4A).
Figure 4. Imaging signs. A: “Hilum overlay” sign. Note that the vessels of the left hilum (arrowhead) can be “seen through” the mass (arrows) projected over the left hilum. The pulmonary artery lies medial to the anterior mediastinal mass, which represented thymic neuroendocrine malignancy. B: “Incomplete border” sign. Note the circumscribed inferior margin (arrowhead) of the opacity overlying the right upper lobe, with the cranial margin of this opacity “fading” indistinctly. The cause of the finding was multiloculated pleural effusion. C: “Cervico-thoracic sign. Note how the lateral margin of the lesion (arrowhead) can be readily seen to the level of the posterior 1st costovertebral junction, consistent with a posterior mediastinal lesion; the abnormality was due to a schwannoma. D: “Ground-glass halo” sign. Note several lung nodules with central, solid foci of opacity surrounded by ground-glass opacity, due to hemorrhagic metastases. E: “Atoll” sign. Note focal opacity with central ground-glass opacity surrounded by consolidation, due to organizing pneumonia.
The hilum overlay sign was originally conceived to distinguish an enlarged heart and pulmonary artery from a mediastinal mass. It was noted that the proximal portions of the pulmonary arteries in the hilar regions typically lie just lateral to the heart border or may overlap the lateral heart border, even when cardiomegaly is present. Occasionally an anterior mediastinal mass can simulate cardiomegaly, but such masses cannot lie medial to the pulmonary artery since this position is occupied by the heart and pericardium; therefore, anterior mediastinal masses will overlap the pulmonary artery as it exists the hilum, and the pulmonary artery will be seen “through” the mass. The “incomplete border” sign (Figure 4B) is present when a lesion shows a circumscribed margin on one side, and an obscured, or “fading” margin on the other side- this configuration is typical of extraparenchymal lesions, such as those arising from the pleura or chest wall. The “ground-glass halo” sign (Figure 4D) is a CT sign that represents a solid, nodular area of consolidation surrounded by ground-glass opacity, and is typical of a hemorrhagic lesion, often encountered in the setting of invasive fungal infection in severely immunocompromised patients. The “atoll” sign, or “reverse ground-glass halo” sign (Figure 4E), is also an imaging finding seen at CT in which a nodular focus of ground-glass opacity is surrounded by a partial or complete ring of consolidation, is often encountered in patients with organizing pneumonia.
Which of the following pathological conditions is least likely to account for the lesion seen at chest radiography? (Click on the correct answer to proceed to the fifth of nine pages)