Electric Lung Anatomy
Brad H. Thompson, M.D., William J. Lee, B.S., Jeffrey R.
Galvin, M.D. and Jeffrey S. Wilson, M.D
Peer Review Status: Internally Peer Reviewed
Each lobe is comprised of several smaller units referred to as pulmonary segments (TABLE). It is important to remember that segmental anatomy is predicated on bronchial anatomy. Similar to bronchial nomenclature, each segment can be named numerically, using a "S", and the same number of the corresponding bronchus that supplies it (TABLE).
Right Upper Lobe
The RUL is comprised of three segments: apical, posterior, and anterior (TABLE). Each segment is classified by the letter "S" followed by a number. In general, reference can be made to any particular segment with this nomenclature. The apical segment (or S1 segment ) is shaped like a truncated cone with its broadest base located superiorly filling the cupula of the lung. This segment thus extends over the pulmonary apex but does not extend inferiorly to the interlobar (minor fissure) surface. The posterior segment (S2) extends from the right hilum, posteriorly and inferiorly and forms the posterior half of the interlobar surface relating to the right major fissure. The anterior segment (S3) of the right upper lobe, which like S2 extends from the right hilar area, is oriented anteriorly and somewhat superiorly. The anterior surface of S3 extends to the chest wall ventrally, while the broadest inferior surface borders the minor fissure which separating S3 from the right middle lobe.
Right Middle Lobe
The right middle lobe has two pulmonary segments which are situated side by side; the more lateral segment (S4), approximates the size of its adjacent neighbor , S5 ( medial segment). S5 abuts the right heart border medially , while S4 extends to and comprises a portion of the lateral border of the right lung. Superiorly, both segments border the right minor fissure, and likewise, both abut the major fissure along their inferior margins. Both S4 and S5 touch the diaphragmatic surface at their anteroinferior edges. Anteriorly, both segments are adjacent to the anterior ribs ends of the 5th, 6th, and 7th ribs.
Right Lower Lobe
The right lower lobe is comprised of five pulmonary segments (TABLE): the superior segment (S6) is situated immediately inferior to the posterior segment of the right upper lobe (S2) from which it is separated by the right major fissure. S6 is bordered by the major fissure anteriorly and comprises a sizeable portion of the posterior margin of the right lower lobe superiorly. It is this segment that surprisingly occupies a sizeable area behind the anterior segment (S3) of the RUL. The posterior basal segment (S10) as its name implies occupies the posterior most and inferior most portion of the right lower lobe. As such, it can be best remembered as the pulmonary segment which occupies most of the posterior costophrenic gutter. S10 also comprises a large portion of the posteromedial border of the right lower lobe and is the segment which is located immediately inferior to S6. S10 characteristically tends to be the largest segment of the right lower lobe.
Immediately anterior to S10 is the medial basal segment (S7) which typically is the smallest pulmonary segment of the lower lobe. Along its superior margin, S7 forms a portion of the major fissure medially, and its location can be best thought of as being immediately inferior to the right hilum, abutting the major fissure ventrally. Inferior to S7 is the anterior basal segment S8, which tends to be rather large in size. This segment along with S6 comprise a large portion of the major fissure surface, laterally. S8 resides in a predominantly lateral location having a large peripheral surface. The lateral basal segment (S9), located between S8 and S10 is shaped like a triangle with its base directed laterally and as such forms a portion of the lateral surface of the right lower lobe.
The pulmonary segments which border or touch the right hemidiaphragm are S4, S5, S7, S8, S9, and S10. S8 and S10 have the largest surface areas abutting the diaphragm.
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