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Clearing of the lung field or part of it
Last reviewed: 04.07.2025
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Increased transparency of the lung field or part of it may be due to either the presence of air in the pleural cavity (pneumothorax) or a decrease in the amount of soft tissue and, accordingly, an increase in the amount of air in the lung or part of it. This condition may be a consequence of swelling of the lung tissue (emphysema) or reduced blood flow to the lung (pulmonary anemia), which is observed mainly in some congenital heart defects.
It is not difficult to distinguish between the above conditions. In the case of pneumothorax, there is no pulmonary pattern against the background of enlightenment and the edge of the collapsed lung is visible. In case of anemia, the pulmonary pattern is depleted, only thin vascular branches are visible. Emphysema is characterized by an increase in the pulmonary pattern due to the expansion of the branches of the pulmonary artery.
Bilateral diffuse increase in the transparency of the lung fields is observed in pulmonary emphysema. In case of severe emphysema, a characteristic picture is observed. The lung fields are enlarged, the diaphragm is flattened and located low. The mobility of the diaphragm is reduced. The transparency of the lung fields during inhalation and exhalation changes little. Large branches of the pulmonary artery (lobar, segmental arteries) are dilated, but then suddenly their caliber decreases ("caliber jump"), which is why the roots of the lungs seem to be cut off. The sternum protrudes forward, and the retrosternal space is enlarged. The heart is small in size, which is associated with a decrease in blood flow to it. Due to pulmonary hypertension, contractions of the right ventricle are increased.
CT scans show impoverishment and fragmentation of the pulmonary pattern in emphysema. The X-ray density of the lung tissue on inspiration is unusually low (below -850 HU). The difference in density between expiration and inspiration is less than 100 HU.
A characteristic picture of increased transparency of part of the lung field is observed with pneumothorax.
Special consideration should be given to perforation (spontaneous) pneumothorax. It occurs as a result of a violation of the integrity of the visceral pleural layer, when air from the lung suddenly begins to enter the pleural cavity. The cause of pleural perforation may be a rupture of the wall of a cavern, abscess, cyst, emphysematous bladder, etc. The condition of the lung must be assessed using radiographs and the localization of the pathological focus must be established. If this cannot be done when analyzing conventional images, then tomography or computed tomography is performed.
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