The anterior junction anatomy

It is useful to consider the anterior junction anatomy in terms of three components: the superior recesses, the line, and the inferior recesses. Each component localizes to a specific area retrosternally: the superior recesses--behind the manubrium; the line--behind the upper two thirds of the sternal body; and the inferior recesses--behind the lower third of the sternal body and below where the cardiac mass abuts the anterior chest wall. Since the anterior chest wall curves backward from bottom to top (Figure 61), the coronal plane of the superior recesses is behind that of the anterior junction line, the coronal plane of the inferior recesses being in front of that of the anterior junction line. Accordingly, then, anteroposterior conventional tomograms will usually demonstrate the inferior recesses on the most anterior levels, the line a centimeter or so behind the inferior recesses, the superior recesses a centimeter or so behind the line. Understanding the anterior junction anatomy in terms of three components has widespread use, as shown above, by many examples obtained from everyday film reading. The presence, absence, and location of disease may be diagnosed. As well, mistaken diagnoses may be avoided. Since the anterior junction lung relates to the anterior pleural space, pleural space processes may alter the anterior junction anatomy. It must be realized that although visualization of the normal anterior junction anatomy components may help to exclude the presence of retrosternal abnormality, they are not infallible. It is possible for a small lesion to be entirely contained within the anterior mediastinum and, thus, not alter the normal anterior junction components. A deep retrosternal space, where normally the anterior junction line is formed, may allow an anterior mediastinal mass to be present and a normal anterior junction line to be seen if the mass does not occupy the entire depth of the space. Furthermore, in patients with markedly hyperexpanded lungs, it is conceivable that the cardiac mass may abut the chest wall at the level of the inferior recesses to a lesser degree than usual, or not at all. Marked lung hyperexpansion may also conceivably cause the superior recesses to extend above the manubrium.