The peripheral pattern in the normal bronchogram and its relation to peripheral pulmonary anatomy.

The appearances in a bronchogram of the more proximal branches of the bronchial tree are well known and have been fully described (Huizinga and Smelt, 1949; Twining and Kerley, 1951; Fischer, 1953; Brock, 1954; Ritvo, 1956). This is not so in regard to the more distal and final branches, and there is, moreover, some confusion as to which structures are outlined by the contrast medium at the periphery of a well-filled clinical bronchogram. The earlier belief that the rather woolly shadows sometimes seen in a wellfilled bronchial tree, and illustrated in Fig. 4, represented alveolar filling is to-day thought unsatisfactory (Twining and Kerley, 1951; Fischer, 1953), but the term "peripheral filling," which is tending to replace the earlier description, does not give an exact indication of the structures outlined. Twining suggests, as the result of stereoscopic examination of a lung specimen injected with "lipiodol," that an appearance " like a tree in bud" was the result of filling of respiratory bronchioles, and Ritvo describes a similar granular appearance as being characteristic of filling of respiratory bronchioles. A more detailed description of the normal appearances of the distal part of the bronchial tree would be of value both in the detection and localization of abnormalities of the peripheral bronchi and bronchioles, such as are seen in chronic bronchitis (Simon and Galbraith, 1953), and in the localization in relation to the peripheral bronchi of small abnormal shadows such as are seen in tuberculosis and sarcoidosis. Several hundreds of apparently normal clinical bronchograms were therefore examined, and these form the basis for the description of the normal pattern of the peripheral part of the bronchial tree given in Part I of this paper. Part II describes how, by histological examination of injected specimens, the