Correct!
1. The left lower thoracic lesion demonstrates an oblong configuration suggesting an origin from the left major fissure
The frontal and lateral chest radiograph shows a relatively circumscribed mass in the left lower lobe, without evidence of increased attenuation to suggest calcification, but without air lucency to suggest cavitation. The lesion has an oblong configuration, which can be seen with abnormalities arising from the fissural surfaces, in this case, the left major fissure. 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. 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 (see Figure 1A). 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 (Figure 2A). The “incomplete border” sign 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 (Figure 2B).
Figure 2. Panel 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. Panel 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.
The patient underwent unenhanced thoracic CT for further evaluation of the chest radiographic abnormality (Figure 3).
Figure 3: Axial thoracic CT displayed in soft tissue (A-C) and lung (D-I) windows. Lower left: video of thoracic CT scan in soft tissue windows. Lower right: video of thoracic CT scan in lung windows.
Which of the following represents an appropriate step for the evaluation of this patient? (Click on the correct answer to proceed to the fourth of six panels)