3. Trachea and carina — tomogram, coronal plane
The use of tomography has largely been supplanted by CT and MRI, the cross-sectional
imaging modalities. However, it's useful here to display the position of major
bronchi relative to the rest of the mediastinal shadow. Because tomography brings
one plane of interest into focus, the airways are better seen here than in the
PA radiograph (see Image #1). The carina
is the apex of the bifurcation point of the trachea; it's located at the lower
border of the T5 vertebra. Each main bronchus traverses the middle mediastinum
to reach the lung via the hilum. The left main bronchus is more horizontally
oriented than the right. The left pulmonary artery loops backward over the left
main bronchus (See Image #5, MRI through the left
hilum). The right main bronchus is more of a direct vertical continuation
of the trachea. The azygos vein arches forward over it before entering
the superior vena cava.
