Topography Of The
Lungs (Posterior View)
The apex of the lung extends as far superiorly as
the vertebral end of the first rib and therefore as high as the first thoracic
vertebra. From there, the lung extends inferiorly as far as the diaphragm, with
the base of the lung resting on the diaphragm and fitted to its superior
surface. Because of the diaphragm’s domed shape, the level of the highest point
on the base of the right lung is about at the eighth to ninth thoracic
vertebrae. The highest point on the base of the left lung is a fraction of an
inch lower. From these high points, the bases of the two lungs follow the
curves of the diaphragm to reach the levels described earlier for the inferior
borders of the lungs.
The highest point on the oblique
fissure of the two lungs is on their posterior aspects, at about the level of
the third to fourth thoracic vertebrae, a little over 1 inch from the midline.
If the arm is raised over the head,
the vertebral border of the scapula approximates the position of the oblique
fissure of the lung. If the shoulder is brought forward as far as possible, the
scapula is carried laterally, so that the area in which auscultation can be
satisfactorily carried out on the posterior aspect of the chest is significantly
widened.
The parietal pleura is separated from
the visceral pleura by a potential space (the pleural cavity), which under
normal circumstances contains only a minimal amount of serous fluid. Caudal to
the inferior margin of the lung, the costal parietal pleura is in contact with
the diaphragmatic parietal pleura, forming the costo- diaphragmatic recess
(costophrenic sulcus). This allows for the caudal movement of the inferior
margin of the lung on inspiration.
Under abnormal circumstances, the
pleural cavity may contain air, increased amounts of serous fluid, blood, or
pus. The accumulation of a significant amount of any of these in the pleural
cavity compresses the lung and causes respiratory difficulties.
The diaphragm separates the base of
the left lung from the fundus of the stomach and the spleen. Because of this
relationship, if the stomach is distended by food or gas, it may push the
diaphragm upward and embarrass respiratory activity.
The diaphragm similarly separates the
base of the right lung from the liver, which, if enlarged, elevates the
diaphragm and pushes against the lung, possibly
limiting its expansion. A hepatic
abscess may rupture through the diaphragm to involve the related pleural cavity
and lung.
In this illustration, the lungs are
shown in relation to the bony thorax, scapula, and diaphragm, but overlying the
structures shown are the deep and superficial muscles of the back in addition to
the superficial fascia and skin.
