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Computed tomography of the thorax is normal
Medical expert of the article
Last reviewed: 04.07.2025
Normal anatomy
CT sections of the chest are also viewed from below. Therefore, the left lung is visualized on the right side of the image and vice versa. It is necessary to be familiar with the main vessels originating from the aortic arch. The left common carotid artery and the brachiocephalic trunk are adjacent to the subclavian artery in front. Further to the right and in front, the brachiocephalic veins are visible, which after merging on sections form the superior vena cava. In the axillary tissue, normal lymph nodes can often be recognized by their characteristic shape with a hilum of fatty density. Depending on the angle of section, the lymph nodes on the section, the hilum of low density are visualized in the center or along the edge. Normal lymph nodes of the axillary region are clearly delimited from the surrounding tissues and do not exceed 1 cm in diameter.
Behind the trachea, next to the esophagus, the azygos vein is visualized. Forming an arch above the right main bronchus, it passes forward and flows into the superior vena cava. When examining the paravertebral space, one should not confuse the azygos vein, hemiazygos vein, or accessory hemiazygos vein with the paraaortic lymph nodes.
Directly below the aortic arch is the pulmonary trunk, which divides into the right and left pulmonary arteries. It is also necessary to check the area under the bifurcation of the trachea between the two main bronchi near the pulmonary vessels - enlarged lymph nodes or malignant neoplasms can be found there. Lymphatic ducts from the internal parts of the mammary glands pass near the internal thoracic (mammary) vessels, while lymphatic ducts from the external parts of the mammary glands pass in the direction of the axillary lymph nodes.
The left atrium is the posteriormost chamber of the heart. In the center of the heart is the left ventricular outflow tract, which passes into the ascending aorta. On the right side is the right atrium, and the right ventricle is in front, just behind the sternum. Only the large branches of the pulmonary vessels are visible in the soft tissue window. Small, peripheral branches of the pulmonary vessels are best judged by the pulmonary window (not visible here).
The inferior vena cava is visualized on more caudal sections, and finally the dome of the diaphragm appears along with the upper pole of the liver. When bronchial cancer is suspected, many radiologists extend the area of interest caudally to include the entire liver, because lung cancer often metastasizes to the liver and adrenal glands. In the peripheral lungs near the diaphragm, the diameter of the pulmonary vessels is so small that they are not visible in the soft tissue window, as in the images shown. Therefore, the vascular pattern of the lungs must be assessed in the pulmonary window, which includes negative values of the Hounsfield density scale. Only then is the assessment of the thoracic organs complete.
Variations of normal anatomy
Among the many variations of normal anatomy of the chest, an atypical location of the azygos vein is relatively common on chest CT. Directed from the posterior mediastinum to the superior vena cava, it can pass through the upper lobe of the right lung. Located within the pleural fold, the lobe of the azygos vein is separated from the rest of the right upper lobe. This feature has no clinical significance and is usually discovered incidentally on conventional chest radiography.
Atypical arrangement and branching of the aortic arch vessels is uncommon. The right subclavian artery, known as the "artery of lusoria", should not be mistaken for a pathological formation of the superior mediastinum.
Note that normal breast tissue surrounded by fat may have very irregular contours. When viewing the lung window, it is important to look not only for focal lesions and inflammatory infiltration, but also for depletion or even absence of pulmonary vascular pattern.
A decrease in the number of vessels in the lung tissue during chest CT scanning is not always a sign of emphysema. After removal of part of the lung, asymmetry in the distribution of vessels and bronchi develops.
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