Chest and Mediastinum

For interpretation of routine posteroanterior (PA) chest radiographs, the anatomy of the trachea, mediastinum, diaphragm, lungs, lung fissures, lung hila, other soft tissue structures and bony structures should be understood (Fig. 19.1). Important anatomic and imaging criteria for each of these structures will be discussed in this chapter. The normal trachea appears in the PA chest radiograph in the midline. The aortic arch causes slight deviation of the trachea to the right side. This shift is more marked in an expiratory film, due to shortening of the trachea. The transparency of the tracheal lumen normally decreases from cranial to caudal. The maximal width of the trachea is 25 mm (for men) and 21 mm (for women). The right tracheal border, where the trachea is in direct contact with lung tissue, can be traced from the clavicle to the right main bronchus. This border is referred to as the right paratracheal stripe or line and is visible in up to 60% of patients. Its width is normally less than 4 mm. A left paratracheal stripe is generally not visible, because the left tracheal border is in direct contact with the large vessels rather than lung tissue.