Normal pulmonary x-ray anatomy

On a general radiograph in a direct projection, the upper 5-6 pairs of ribs are visible almost along their entire length. Each of them can be distinguished by a body, anterior and posterior ends. The lower ribs are partially or completely hidden behind the shadow of the mediastinum and organs located in the subdiaphragmatic space. The image of the anterior ends of the ribs breaks off at a distance of 2-5 cm from the sternum, since the costal cartilages do not give a distinguishable shadow on the images. In people over 17-20 years of age, lime deposits appear in these cartilages in the form of narrow stripes along the edge of the rib and islets in the center of the cartilage. They, of course, should not be mistaken for compaction of the lung tissue. On radiographs of the lungs, there is also an image of the bones of the shoulder girdle (clavicles and scapulae), soft tissues of the chest wall, mammary glands and organs located in the chest cavity (lungs, mediastinal organs).

Both lungs are seen separately on a plain X-ray; they form the so-called pulmonary fields, which are crossed by the shadows of the ribs. Between the pulmonary fields there is an intense shadow of the mediastinum. The lungs of a healthy person are filled with air, so they appear very light on the X-ray. The pulmonary fields have a certain structure, which is called the pulmonary pattern. It is formed by the shadows of the arteries and veins of the lungs and, to a lesser extent, the connective tissue surrounding them. In the medial parts of the pulmonary fields, between the anterior ends of the 2nd and 4th ribs, the shadow of the roots of the lungs is outlined. The main sign of a normal root is the heterogeneity of its image: it is possible to 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 (tail) part is hidden behind the shadow of the heart.

The lung fields and their structure are visible only because the alveoli and bronchi contain air. In a fetus or stillborn child, neither the lung fields nor their pattern are reflected in the image. Only with the first breath after birth does air enter the lungs, after which an image of the lung fields and the pattern in them appears.

The lung fields are divided into the apexes - the areas located above the clavicles, the upper sections - from the apex to the level of the anterior end of the 2nd rib, the middle - between the 2nd and 4th ribs, the lower - from the 4th rib to the diaphragm. From below, the lung fields are limited by the shadow of the diaphragm. Each half of it, when examined in a direct projection, forms a flat arc running from the lateral part of the chest wall to the mediastinum. The outer section of this arc forms an acute costophrenic angle with the image of the ribs, corresponding to the outer section of the costophrenic sinus of the pleura. The highest point of the right half of the diaphragm is projected at the level of the anterior ends of the 5th - 6th ribs (on the left - 1 - 2 cm lower).

In the lateral image, 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 expressed more sharply than the opposite one. The image of the apex of the lung, the shadow of the sternum, the contours of both shoulder blades and the shadows of ThIII-ThIX with their arches and processes are clearly distinguished. From the spine to the sternum, the ribs go obliquely downwards and forwards.

In the pulmonary field on the lateral image, two light areas stand out: the retrosternal space - the area between the sternum and the shadow of the heart and the ascending aorta, and the retrocardiac space - between the heart and the spine. Against the background of the pulmonary field, one can discern a pattern formed by the arteries and veins that go to the corresponding lobes of the lungs. Both halves of the diaphragm on the lateral image look like arcuate lines running from the anterior to the posterior chest wall. The highest point of each arc is located approximately at the border of its anterior and middle thirds. Ventral to this point is the short anterior slope of the diaphragm, and dorsal to this point is the long posterior slope. Both slopes form acute angles with the walls of the chest cavity, corresponding to the costophrenic sinus.

The lungs are divided into lobes by interlobar fissures: the left into two - upper and lower, the right into three - upper, middle and lower. The upper lobe is separated from the other part of the lung by an oblique interlobar fissure. Knowledge of the projection of the interlobar fissures is very important for the radiologist, as it allows establishing the topography of intrapulmonary foci, but the boundaries of the lobes are not directly visible on the images. Oblique fissures 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 fissure goes from the intersection of the right oblique fissure and the middle axillary line to the place of attachment of the IV rib to the sternum.

A smaller structural unit of the lung is the bronchopulmonary segment. This is a section of the lung ventilated by a separate (segmental) bronchus and supplied by a separate branch of the pulmonary artery. According to the accepted nomenclature, the lung is divided into 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 branches of one terminal bronchiole with alveolar passages and alveoli. Several acini make up a pulmonary lobule. The boundaries of normal lobules are not differentiated on images, but their image appears on radiographs and especially on computer tomograms with venous congestion of the lungs and compaction of the interstitial tissue of the lung.

General radiographs produce a summative image of the entire thickness of the tissues and organs of the chest - the shadow of some parts is partially or completely superimposed on the shadow of others. X-ray tomography is used for a more in-depth study of the structure of the lungs.

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

Linear tomograms produce a sharp image of those formations that are in the layer being examined. The shadows of structures located at a different depth are not sharp ("smeared") in the image. The main indications for linear tomography are the following: studying the condition of large bronchi, identifying areas of decay or lime deposits in pulmonary infiltrates and tumor formations, analyzing the structure of the lung root, in particular determining the condition of the lymph nodes of the root and mediastinum.

More valuable information about the morphology of the chest organs can be obtained by computed tomography. Depending on the purpose of the study, the doctor selects the "window width" when analyzing the image. Thus, he focuses on studying the structure of either the lungs or the mediastinal organs.

Under normal conditions, the density of lung tissue, according to densitometry data, fluctuates between -650 and -850 N. Such a low density is explained by the fact that 92% of the lung parenchyma is air and only 8% is soft tissue and blood in the capillaries. On computer tomograms, the shadows of the pulmonary artery and veins are determined, the main lobar and segmental bronchi are clearly differentiated, as well as intersegmental and interlobar septa.

The mediastinal organs are surrounded by mediastinal fat. Its density ranges from -70 to -120 HU. Lymph nodes may be visible in it. Normally, they are round, oval, or triangular. If the size of the lymph node exceeds 1 cm, it is considered pathologically altered. Using sections at different depths, we can image the pre- and paratracheal lymph nodes, nodes in the aortopulmonary "window", in the roots of the lungs, and under the bifurcation of the trachea. CT plays an important role in assessing the condition of the mediastinal organs: it allows us to study the fine details of the morphology of the lung tissue (assessing the condition of the lobules and perilobular tissue, identifying bronchiectasis, areas of bronchiolar emphysema, small foci of inflammation, and tumor nodules). CT is often necessary to establish the relationship of the formation detected in the lung to the parietal pleura, pericardium, ribs, and large blood vessels.

Magnetic resonance imaging is used less frequently in lung examination due to the low signal that lung tissue produces. The advantage of MRI is the ability to isolate layers in different planes (axial, sagittal, frontal, etc.).

Ultrasound examination has become very important in the examination of the heart and large vessels of the chest cavity, but it also provides important information about the condition of the pleura and the superficial layer of the lung. With its help, a small amount of pleural exudate is detected earlier than with X-ray.

With the development of CT and bronchoscopy, indications for a special X-ray examination of the bronchi - bronchography - have narrowed significantly. Bronchography involves artificial contrasting of the bronchial tree with radiopaque substances. In clinical practice, the indication for its implementation is a suspected anomaly in the development of the bronchi, as well as an internal bronchial or bronchopleural fistula. Propyliodone in the form of an oil suspension or a water-soluble iodine preparation is used as a contrast agent. The study is carried out mainly under local anesthesia of the respiratory tract using a 1% solution of dicaine or lidocaine, but in some cases, mainly when performing bronchography in young children, intravenous or inhalation anesthesia is used. The contrast agent is administered through radiopaque catheters, which are clearly visible under fluoroscopy. Some types of catheters have a control system for the end part, which allows the catheter to be inserted into any part of the bronchial tree.

When analyzing bronchograms, each contrasted bronchus is identified, the position, shape, caliber and outlines of all bronchi are determined. A normal bronchus has a conical shape, departs from a larger trunk at an acute angle and gives off a number of subsequent branches at the same angles. In the initial part of the bronchi of the second and third orders, shallow circular constrictions are often noted, corresponding to the locations of physiological sphincters. The contours of the bronchial shadow are smooth or slightly wavy.

The blood supply to the lungs is provided by the pulmonary and bronchial arteries. The former constitute the pulmonary circulation; they perform the function of gas exchange between air and blood. The system of bronchial arteries belongs to the systemic circulation and provides nutrition to the lungs. The bronchial arteries do not provide an image on radiographs and tomograms, but the branches of the pulmonary artery and pulmonary veins are quite well outlined. In the root of the lung, the shadow of the branch of the pulmonary artery (respectively, the right or left) stands out, and from it their lobar and further segmental branches radiate into the pulmonary fields. The pulmonary veins do not originate from the root, but cross its image, heading towards the left atrium.

Radiation methods allow us to study the morphology and function of the blood vessels of the lungs. Spiral X-ray tomography and magnetic resonance imaging can be used to obtain an image of the initial and proximal parts of the pulmonary trunk, its right and left branches, and to establish their relationships with the ascending aorta, superior vena cava, and main bronchi, to trace the branching of the pulmonary artery in the lung tissue down to the smallest subdivisions, and to detect defects in vessel filling in thromboembolism of the pulmonary artery branches.

According to special indications, X-ray examinations are carried out that involve the introduction of a contrast agent into the vascular bed - angiopulmonography, bronchial arteriography, venocavography.

Angiopulmonography is the study of the pulmonary artery system. After catheterization of the elbow vein or femoral vein, the end of the catheter is passed through the right atrium and right ventricle into the pulmonary trunk. The further course of the procedure depends on the specific tasks: if it is necessary to contrast large branches of the pulmonary artery, then the contrast agent is poured directly into the pulmonary trunk or its main branches, but if small vessels are to be studied, then the catheter is advanced in the distal direction to the desired level.

Bronchial arteriography is the contrasting of the bronchial arteries. For this, a thin radiopaque catheter is inserted through the femoral artery into the aorta, and from there into one of the bronchial arteries (there are several on each side, as is known).

Indications for angiopulmonography and bronchial arteriography in clinical practice are not very wide. Angiopulmonography is performed when there is a suspicion of an arterial developmental anomaly (aneurysm, stenosis, arteriovenous fistula) or pulmonary embolism. Bronchial arteriography is necessary in case of pulmonary hemorrhage (hemoptysis), the nature of which could not be established by other studies, including fibrobronchoscopy.

The term "cavography" refers to artificial contrasting of the superior vena cava. Studying the subclavian, innominate and superior vena cava facilitates the choice of venous approach to rational placement of catheters, installation of a filter in the vena cava, determination of the level and cause of venous blood flow obstruction.

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