Normal X-ray anatomy of the lungs

On the survey radiograph in a direct projection, almost all along the top 5-6 pairs of ribs appear. Each of them can be distinguished body, front and back ends. The lower ribs are partially or completely hidden behind the mediastinal shadow and organs located in the sub-diaphragmatic space. The image of the anterior ends of the ribs terminates at a distance of 2-5 cm from the sternum, as the costal cartilages do not give a discernible shadow on the pictures. In people older than 17-20 years in these cartilages appear deposits of lime in the form of narrow strips along the edge of the rib and islets in the center of the cartilage. They, of course, should not be taken for compaction of lung tissue. On the radiographs of the lungs, there is also a picture of the bones of the shoulder girdle (clavicles and scapula), soft tissues of the chest wall, mammary glands and organs located in the thoracic cavity (lungs, mediastinum organs).

Both lungs are seen separately on the direct X-ray diffraction chart; they form the so-called pulmonary fields, which are intersected by the shadows of the ribs. Between the pulmonary fields is an intense shadow of the mediastinum. The lungs of a healthy person are filled with air, therefore on the roentgenogram they are very light. Pulmonary fields have a certain structure, which is called a pulmonary pattern. It is formed by the shadows of the arteries and veins of the lungs and to a lesser extent by the connective tissue surrounding them. In the medial sections of the pulmonary fields, between the anterior ends of the II and IV ribs, a shadow of the roots of the lungs appears. The main feature of the normal root is the heterogeneity of its image: it can distinguish the shadows of individual large arteries and bronchi. The root of the left lung is located slightly above the root of the right, its lower (caudal) part is hidden behind the shadow of the heart.

Pulmonary fields and their structure are visible only because air is contained in the alveoli and bronchi. At the fetus and the stillborn child, neither the meadow fields, nor their pattern in the picture, are reflected. Only with the first inspiration after birth, air penetrates into the lungs, after which appears an image of the pulmonary fields and the pattern in them.

Pulmonary fields are divided into tops - areas located above the clavicles, the upper sections - from the tip to the level of the anterior end of the second rib, the middle - between the II and IV ribs, the lower - from the IV ribs to the diaphragm. From below, the pulmonary fields are limited by the shadow of the diaphragm. Each half of it, when examined in a direct projection, forms a plane arc, extending from the lateral part of the thoracic wall to the mediastinum. The outer part of this arc forms an acute rib-diaphragmatic angle corresponding to the outer part of the rib-diaphragmatic sinus of the pleura with an image of the ribs. The highest point of the right half of the diaphragm is projected at the anterior ends of the V-VI ribs (on the left - 1 to 2 cm below).

On the side picture, the images of both halves of the chest and both lungs are superimposed on each other, but the structure of the lung closest to the film is sharper than the opposite. The image of the apex of the lung, the shadow of the sternum, the contours of both scapulas and the shadow of ThIII-ThIX with their arches and processes are clearly distinguished. From the spine to the sternum in an oblique direction down and forward come the ribs.

In the pulmonary field, two light areas are distinguished in the lateral picture: the posterior-chest (retro -steral) space - the area between the sternum and the heart shadow and the ascending aorta, as well as the posterior cardiac (retrocardial) space - between the heart and the spine. Against the background of the pulmonary field, one can distinguish the pattern formed by the arteries and veins that are sent to the appropriate lobe of the lungs. Both halves of the diaphragm on the side picture are arched lines extending from the anterior chest wall to the posterior. The highest point of each arc is located approximately at the border of its front and middle thirds. Ventral to this point is a short front ramp of the diaphragm, and dorsal to the long posterior stingray. Both rays with the walls of the thoracic cavity form acute angles corresponding to the rib-diaphragmatic sinus.

Between the lobes of the lungs, the lungs are divided into lobes: the left into two - the upper and lower, the right to three - the upper, middle and lower. The upper lobe is separated from the other part of the lung by an oblique interlobar slit. Knowledge of the projection of the interlobar gaps is very important for the radiologist, since it allows setting the topography of intrapulmonary foci, but the borders of the lobes are not directly visible on the photographs. Slanting slits are directed from the level of the spinous process of Thin to the junction of the bone and cartilaginous parts of the IV rib. The projection of the horizontal slit goes from the point of intersection of the right oblique slit and the middle axillary line to the place of attachment to the sternum of the IV rib.

The smaller structural unit of the lung is the bronchopulmonary segment. This is a segment of the lung, ventilated by a separate (segmental) bronchus and fed from a separate branch of the pulmonary artery. According to the accepted nomenclature, in the lung secrete 10 segments (in the left lung the medial basal segment is often absent).

The elementary morphological unit of the lung is the acinus - a set of ramifications of one terminal bronchioles with alveolar courses and alveoli. Several acini make up the pulmonary lobe. The boundaries of normal lobules do not differentiate on the images, but their image appears on radiographs and especially on computer tomograms with venous pulmonary embolism and compaction of the interstitial lung tissue.

On the survey radiographs, a summary image of the entire thickness of the tissues and organs of the thorax is obtained - the shadow of some of the details is partially or completely superimposed on the shadow of the others. For more in-depth study of lung structure, X-ray tomography is used.

As already mentioned, there are two types of X-ray tomography: linear and computer (CT). Linear tomography can be performed in many X-ray rooms. Due to its availability and cheapness, it is still widespread.

Linear tomograms produce a sharp image of those formations that are in the layer under study. Shadows of structures lying at a different depth are not sharp ("smeared") on the picture. The main indications for linear tomography are the following: the study of the state of large bronchi, the detection of decay or lime deposits in pulmonary infiltrates and tumor formations, the analysis of the structure of the lung root, in particular, the determination of the status of the lymph nodes of the root and mediastinum.

More valuable information about the morphology of the thoracic cavity allows one to obtain a computed tomography. Depending on the purpose of the study, the doctor chooses the "width of the window" when analyzing the image. Thus, he emphasizes the study of the structure of either the lungs or the organs of the mediastinum.

In normal conditions, the density of lung tissue, according to densitometry, ranges from -650 to -850 N. This low density is explained by the fact that 92% of the pulmonary parenchyma is air and only 8% are soft tissues and blood in the capillaries. On computer tomograms, the shadows of the pulmonary arteries and veins are determined, the main lobar and segmental bronchi are clearly differentiated, as well as intersegmental and interstitial septa.

The background for the mediastinal organs is the adipose tissue of the mediastinum. Its density ranges from -70 to -120 HU. In it, lymph nodes can be seen. Normally they are round, oval or triangular in shape. If the value of the mind exceeds 1 cm, then it is considered pathologically changed. With the help of sections at different depths, pre- and paratracheal lymph nodes, nodes in the aortopulmonary "window", in the roots of the lungs and under the bifurcation of the trachea are displayed. CT plays an important role in the evaluation of the state of the mediastinal organs: it allows you to study the fine details of the morphology of the lung tissue (assessment of the state of lobules and peridolkovaya tissue, the detection of bronchiectasias, areas of bronchiolar emphysema, small foci of inflammation and tumor nodules). CT is often necessary to establish the relationship found in the lung formation to the parietal pleura, pericardium, ribs, large blood vessels.

Magnetic resonance imaging is so far less commonly used in the study of the lungs due to the low signal that pulmonary tissue gives. The advantage of MRI is the ability to separate layers in different planes (axial, sagittal, frontal, etc.).

Ultrasound research has become very important in the study of the heart and large vessels of the chest cavity, but it also provides important information about the condition of the pleura and the surface layer of the lung. With its help, a small amount of exudate of the pleural cavity is revealed earlier than with radiography.

In connection with the development of CT and bronchoscopy, the indications to a special radiographic examination of the bronchi - bronchography were significantly narrowed. Bronchography consists in artificial contrasting of the bronchial tree with radiopaque substances. In clinical practice, the indication for its implementation is the suspicion of an anomaly in the development of the bronchi, as well as the internal bronchial or bronchopleural fistula. As a contrast agent, propyl iodone is used in the form of an oil suspension or a water-soluble iodide preparation. The study is carried out mainly under local anesthesia of the respiratory tract with 1% solution of dicain or lidocaine, but in some cases, mainly when performing bronchography in young children, resort to intravenous or inhalation anesthesia. Contrast substance is injected through radiopaque catheters, which are clearly visible in fluoroscopy. Some types of catheters have an end-part control system that allows the insertion of a catheter into any areas of the bronchial tree.

In the analysis of bronchograms, each contrasted bronchus is identified, the position, shape, caliber and shape of all bronchial tubes are determined. Normal bronchus has a conical shape, it moves away from a larger trunk at an acute angle and at the same angles gives off a series of subsequent branches. In the initial part of the bronchi of the 2nd and 3rd orders, shallow circular loops, corresponding to the locations of physiological sphincters, are often noted. The contours of the bronchus shade are even or slightly wavy.

Blood supply to the lungs is carried out by pulmonary and bronchial arteries. The first form a small circle of blood circulation; they serve as a gas exchange between air and blood. The system of bronchial arteries refers to a large range of blood circulation and provides nutrition to the lungs. Bronchial arteries on radiographs and tomograms do not give an image, but the branches of the pulmonary artery and pulmonary veins are emerging pretty well. In the root of the lung, the shadow of the branch of the pulmonary artery (respectively, right or left) is prominent, and from their share and later segmental branches branch radially into the pulmonary fields. Pulmonary veins do not originate from the root, but cross its image, heading towards the left atrium.

Radiation methods allow one to investigate the morphology and function of the blood vessels of the lungs. With the help of spiral X-ray tomography and magnetic resonance imaging, one can obtain an image of the initial and proximal parts of the pulmonary trunk, its right and left branches, and establish their relationship with the ascending aorta, upper vena cava and the main bronchi, and follow the branching of the pulmonary artery in the lung tissue small units, as well as to detect defects in the filling of blood vessels in thromboembolism of the branches of the pulmonary artery.

According to special indications, X-ray studies are carried out related to the introduction of a contrast agent into the vascular bed, angiopulmonography, bronchial arteriography, venocavagraphy.

Under angiopulmonography is the study of the pulmonary artery system. After catheterization of the vein of the ulnar fold or femoral vein, the end of the catheter is guided through the right atrium and right ventricle into the pulmonary trunk. The further course of the procedure depends on specific tasks: if it is necessary to contrast large branches of the pulmonary artery, then the contrast substance is poured directly into the pulmonary trunk or its main branches; if small vessels are to be studied, the catheter is advanced distally to the desired level.

Bronchial arteriography is the contrast of bronchial arteries. To do this, a thin radiopaque catheter through the femoral artery is inserted into the aorta, and from it into one of the bronchial arteries (they are known to be several on each side).

Indications for angiopulmonography and bronchial arteriography in clinical practice are not very wide. Angiopulmonography is performed if there is a suspected anomaly of the development of the artery (aneurysm, stenosis, arteriovenous fistula) or pulmonary embolism. Bronchial arteriography is necessary for pulmonary hemorrhage (hemoptysis), the nature of which has not been established through other studies, including fibrobronchoscopy.

The term "kavografiya" means artificial contrasting of the superior vena cava. The study of the subclavian, nameless and upper hollow veins facilitates the choice of a venous approach to the rational placement of catheters, the installation of a filter in the vena cava, the determination of the level and cause of obstruction of venous blood flow.

[1], [2], [3]