Bronchopulmonary Segment

Bronchopulmonary Segment     

        Beonchopulmonary segment of individual lobes are basal on the subdivisions of the lung, Which is supplied by an integral and relatively constant segmental bronchus and blood vessels. The boundaries between various segments are complex and with the rare exception of accessory fissure, the segments are not divided by septae. Although many pathological process may predominate in one segment or another, these usually never confirms precisely to whole of just one segment since collateral air drift occur across segmental boundaries. However, information of segmental involvement in disease process is particulary important to surgeons since these segments can be removed separately. These bronchopulmonary segments are designated as per the divisions of segmental bronchi. There is lot of overlap of bronchopulmpnary segments on a PA view of chest but they project separately on a lateral view. Their approximate location as seen on frontal and lateral radiographs is illustrated

                                   Upper and middle lobe/lingula on PA projection

                                                       Lower lobe on PA projection

Right lung on lateral projection

                                               Left lung on lateral projection

Radiographic density of the two lungs is symmetrical on a well-taken PA film. If the patient is rotated, the hemithorax closer to the film appear more radiodense. Both PA and lateral views are necessary to localise in one or more of the pulmonary segment. Since the normal bronchi are not visualised in the peripheral lung fields, it is difficult to make out the boundary of different pulmonary segment on plain radiograph of the chest.

Hilum and Pulmonary Vasculature   

The structures contributing to the formation of the hilum are the pulmonary arteries and their main branches, upper lobe pulmonary veins, the major bronchi and lymph glands. Of all the structures in the hilum, only the pulmonary arteries and upper lobe veins significantly contribute to the hilar shadows on a plain radiograph. Normal lymph nodes are not seen. The left hilum is usually 0.5 to 2 cm higher than the right . Both hila are of equal density and size with a concave lateral border on PA film.

    The diameter of the normal descending branch of right pulmonary artery is between 10-16 mm in males and 9-15 mm in female. The course of the pulmonary vessels can be described by dividing them into three zones depending upon their positions in the lunges, i.e. hilar, mid lung and peripheral. Mid lung vessels extend from hilum apto 2 cm from the chest wall. Peripheral vessels are present in other 2 cm of the lung fields and these are rarely seen on a normal chest radiograph. The pulmonary veins have fever branches and are straighter. The distinction between intrapulmonary arteries and veins is difficult and seldom useful so that they are collectively referred to us pulmonary vasculature. The pulmonary vessels taper radiographs; the upper zone vessels are comparatively narrower than lower zone vessels because of the effect of gravity. The bronchial vessels are normally not seen on chest radiograph.