One of the most difficult problems of the roentgenologist is the distinction between the normal and the pathologic hilum. The clinician, in search of the roentgen-ray diagnosis, only too frequently receives the valueless information that the hilum is enlarged, suspicious looking, hazy, dense, swollen, or that there is a diffuse infiltration of the hilum.
In order to understand the pathology of the hilum, we must bear in mind, first, that it is composed of: (1) pulmonary arteries and veins; (2) bronchial tubes, and (3) lymph glands and lymph vessels.
The normal bronchial tubes and the normal lymph glands are practically invisible in a roentgen-ray film. The shadow, therefore, which is called "the normal hilum shadow," is caused by the pulmonary artery. Figure 1 shows the topography of the arteries and the bronchi. This picture was published, first, by my teacher Narath in Heidelberg. It demonstrates clearly the branches of the