Bronchopulmonary
Segments
A bronchopulmonary segment is that portion of the
lung supplied by the primary branch of a lobar bronchus. Each segment is
surrounded by connective tissue that is continuous with visceral pleura and
forms a separate, functionally independent respiratory unit. The artery
supplying a segment follows the segmental bronchus but the segmental veins are
at the periphery of the segment and thus can be helpful in delineating it.
Right Lung
The right main bronchus gives rise to
three lobar bronchi: upper, middle, and lower. An two of these may occasionally
have a common stem.
Right Upper Lobe
The apical segment (S1) of the
right upper lobe forms the apex of the right lung. It extends into the root of
the neck as high as the vertebral end of the first rib. Toward the lateral
aspect of the lung, the apical segment dips downward slightly between the
posterior and anterior segments. This boundary line is roughly at the level of
the first rib anteriorly and almost down to the second rib posteriorly.
The posterior segment (S2)
extends from the apical segment down to the lateral portion of the horizontal
fissure and the upper part of the oblique fissure.
The anterior segment (S3)
extends from the apical segment above down to the horizontal fissure at about
the level of the fourth rib.
Right Middle Lobe
The middle lobe bronchus branches into
two segmental bronchi, the complete branchings of which become the lateral
segment (S4) and medial segment (S5) of the lobe. These segments are
separated by a vertical plane extending from the hilum out to the costal
surface of the lung and reaching its inferior border just anterior to the lower
end of the oblique fissure. The segments are related to the anterior parts of
the fourth and fifth ribs and their costal cartilages.
Right Lower Lobe
The lower lobe bronchus gives off a
posteriorly directed superior segmental bronchus just below the level of the
orifice of the middle lobe bronchus. The superior segment
(S6) of the lower lobe occupies the entire superior part of the lower lobe
and extends from the upper part of the oblique fissure at about the level of the
vertebral end of the third rib to the level of the vertebral end of the fifth or
sixth rib.
Inferior to the level at which the
superior segmental bronchus arises, the lower lobe divides into four basal
segmental bronchi: medial (S7), anterior (S8), lateral (S9),
and posterior (S10). The basal segments of the lower lobe form the base
of the lung and rest on the diaphragm. The medial basal segment is sometimes
partially separated from other basal segments by an extra fissure; in this
event, it has sometimes been called the cardiac lobe of the lung.
Left Lung
The left main bronchus is longer than
the right and not in such direct a line with the trachea. Foreign bodies,
therefore, are somewhat more likely to enter the right than the left bronchus.
Left Upper Lobe
The upper lobe bronchus subdivides
into a superior division bronchus and an inferior or lingular division
bronchus. The superior division can be thought of as corresponding to the right
upper lobe, with the lingular division corresponding to the right middle lobe;
there is usually no fissure separating the two, and their segmental subdivisions
are not the same.
Unlike the situation on the right, the
superior division of the left upper lobe has only two segments: the apicoposterior
segment (S1 and S2), which corresponds to a combination of the right apical
and posterior segments, and the anterior segment (S3). The inferior or
lingular division also has two segments, the superior (S4) and inferior
(S5) segments.
Left Lower Lobe
The segments here are similar to those
of the right lower lobe except that the portion corresponding to the right
anterior basal and medial basal segments is supplied on the left by two bronchi
that have a common stem and thus forms a single anteromedial basal (S8)
segment. Other left lower lobe segments are rior (S6), lateral basal (S9),
and posterior basal (S10).
