NOMENCLATURE FOR PERIPHERAL BRONCHI
Two nomenclature systems are commonly used to identify the segmental anatomy of the lungs. The one proposed by Boyden uses numerical ordering, and the one proposed by Jackson and Huber names the bronchi. It is recommend that one become familiar with both systems.
There are 10 segments in the right lung and nine in the left (see Plates 1-14 and 1-15). Subdivisions of the bronchial tree correspond to the anatomic segments and are named accordingly. These tertiary bronchi were regarded by Jackson and Huber as the ﬁnal branches, but the advent of the ﬂexible bronchoscope led Ikeda to introduce additional nomenclature for the fourth, ﬁfth, and sixth divisions because these can now be visualized. A convenient numerical system is used in which segmental bronchi are numbered from 1 to 10 on each side and identiﬁed by the capital letter B for bronchus. This may be preﬁxed by a capital letter R for right and L for left, so that RB3 identiﬁes the bronchus to the anterior segment of the right upper lobe. The apicoposterior segment of the left upper lobe is LB1+2, and the anteromedial basal segment of the same side becomes LB8 because each of these paired segments is supplied by a single tertiary bronchus. With rare exceptions, there is no LB7 designation.
Subsegmental or fourth-order bronchi are indicated by the lower case letter a for posterior and b for anterior. The letter c may also be used when necessary for additional bronchi.
Fifth-order bronchi are designated by the Roman numerals i (posterior) and ii (anterior). Finally, those at the level of the sixth order of division are characterized by α and β.
Endobronchial variations from the normal anatomy are frequent and are more common in peripheral airways.