The compulsory part of the radiation examination of patients with lung cancer is to establish its prevalence. It is necessary to evaluate the following four points that determine the stage of the tumor lesion:
the prevalence of the tumor in the intrapulmonary structures, germination in the adjacent anatomical structures and organs of the thoracic cavity, metastasis to the intrathoracic lymph nodes, metastasis to the internal organs and the skeleton. Solving these problems is extremely difficult. Thus, according to the data, the clinical staging of lung cancer using the traditional radiological method coincides with the morphological staging of the “T” factor in 62%, ”in 46–55%,“ M ”in 76—%. A variety of special X-ray techniques, even such complex, invasive, as pneumomediastinography, angiopulmonography, phlebography of the mediastinum do not significantly increase the accuracy of determining the prevalence of lung cancer. In addition, each of them is designed to solve a particular problem. Therefore, all of them are currently not used for this purpose. New technologies of high technologies came to Nasmen: computed tomography, magnetic resonance imaging, echocardiography.
Inside the lung, a malignant tumor is spread by either direct growth or metastasis.
Direct growth, as is known, is directed mainly from the periphery to the root of the lung, with the involvement of ever larger bronchi and blood vessels.
Due to this tendency, a peripheral cancer node can reach a segmental, and sometimes, however, very rarely, even lobar bronchus. There is a so-called centralization of a peripheral tumor. Radiographically, this is displayed by a rather characteristic picture combining the presence of a roundish tumor shadow with signs of impaired bronchial patency. The extent of the lesion of the bronchial tree clarifies the tomographic study, in unclear cases, CT. These data, of course, have a certain value, as they reflect the intrapulmonary prevalence of peripheral cancer. However, such a process dynamics itself does not affect the operability and, as a rule, tumor resectability is not limited.
A completely different situation develops with central lung cancer. Its growth in the proximal direction can lead to the spread of the tumor to the main bronchus and even to the bifurcation of the trachea. This can be established by linear tomography. But still more accurate data provides CT.Although it must be borne in mind that the level of damage that is determined both tomographically and bronchoscopically and by CT scan does not correspond to the true one. In fact, tumor infiltration has a large extent.
A central tumor may also spread along the pulmonary artery. But according to X-ray and tomography data, this can be judged only very tentatively and, certainly, without determining the extent of the lesion. Even angiopulmonography does not provide reliable information, since such tumor invasion proceeds predominantly perivasally, without significantly altering the lumen of the artery. More informative angiography and MRI. These methods, which visualize not only the lumen of the vessel, but also its wall, are capable of giving an image of tumor infiltration, although, of course, not always.
Metastasis of lung cancer in the lung is observed in about 6%. It may be hematogenous or lymphogenous. Hematogenous metastases are nodular or miliary-disseminated. Nodal metastases are localized in the same, opposite, or both lungs. Radiological semiotics of them is identical to primary peripheral cancer. Therefore, one should keep in mind the probability of primary multiple cancer. But reliable differentiation of primary and metastatic lung lesions according to radiation studies is almost impossible. Miliary disseminated metastasis
radiologically indicated by the presence in both lungs of many small focal shadows, among which it is sometimes impossible to determine the primary tumor. Lymphogenous metastasis or so-called lymphogenous carcinomatosis occurs due to retrograde spread of tumor cells from metastatic lymph nodes of the mediastinum. Radiographically, it is manifested by a sharp increase and reticular deformation of the pulmonary pattern, due to interstinal changes, thickening of the walls of the bronchi, the appearance of many small and miliary foci.
The possibility of lung cancer germination in the mediastinum outside the main bronchus is evidenced by the following x-ray signs: the tumor site adjoins the medial shadow for a long distance, obtuse angles between the tumor and the mediastinum, the location of the center of the reconstructed pathological formation in the mediastinum, limited displacement or complete immobility of the tumor site during respiration, displacement of any anatomical structures of the mediastinum (trachea, main bronchi, esophagus) to the contralateral side. Involvement in the process of the pulmonary artery, accompanied by a decrease in blood flow, is manifested by the depletion of the pulmonary pattern. The spread of the tumor to the superior vena cava with the difficulty of outflow of blood leads to its expansion. On radiographs in a direct projection, this is indicated by the expansion of the upper part of the medial shadow to the right. Moreover, the intensity of this additional shadow is less than the density of the aorta, the contour is straight and tends to be rounded not medially, but laterally.
More specific data on the prevalence of the tumor on the large vessels of the mediastinum are obtained by linear tomography, although its sensitivity and especially its specificity are low. To address this issue, it was previously proposed to use various options for contrast study of blood vessels (asigography, cavagraphy, angiopulmonography, aortography). But these techniques were not informative enough.
The defeat of the phrenic nerve is manifested by the rise and restriction of the respiratory mobility of the corresponding half of the diaphragm. The condition of the esophagus is assessed by the usual radiopaque study with the patient taking a water suspension of barium sulphate. With involvement in the tumor process, there may be a displacement of the esophagus, a local depression on its wall on the side of the tumor, a narrowing of the lumen. However, the absence of these signs does not completely exclude such a probability.
The very fact of transpleural mediastinal invasion of lung cancer and its degree is most accurately established at CT. The direct sign of such a spread is the visualization of a single array of tumor tissue, passing from the lung to the mediastinum, where it, having high densitometric density (+18 … +28 HU), is clearly defined against the background of low-density fatty tissue (-115 … + 3 HU). In this case, special attention should be paid to the depth of the tumor in the mediastinum. If it extends beyond the median line, then, according to our data, as a rule, it turns out to be unresectable.
Invasion of lung cancer on the mediastinum can be assumed in contact with the tumor site with the mediastinal pleura for more than 3 cm, thickening of the pleura in this place, the absence of a strip of adipose tissue separating the tumor and mediastinal structures. But such an assumption on operations is confirmed in no more than 1/4 of cases. Of great importance, in our opinion, have negative data. The absence of these signs reliably indicates that, in the overwhelming majority of cases, there is no invasion of lung cancer on the mediastinum at all, and if so, only limited, not reducing resectability. Overall, the accuracy of CT in
determining the spread of lung cancer on the mediastinum reaches 75% (Gamsu G., 1992). Magnetic resonance imaging is not inferior to this radiation method.
CT and MRI are significantly more informative in detecting tumor invasion of large vessels. In this respect, according to the data of EVLovyagin et al. (1996), the sensitivity of CT scan is 2 times higher than linear tomography (33 and 66%, respectively). This, of course, is about angio-CT. Our own recent research indicates that spiral CT has even greater potential, of course, also performed in angiogram. Magnetic resonance imaging in terms of sensitivity and accuracy of determining the prevalence of lung cancer on the vessels is somewhat superior to CT.
Semiotics of tumor invasion of the vessels in the display of these radiation methods is almost identical. The first, however, low-specific sign is the close adherence of the tumor to the vessel wall, exceeding 90 ° around the circumference . Direct symptoms are compression, narrowing and, of course, a complete block of vessels. On their involvement in the tumor process is also evidenced by the establishment of an impaired blood flow during MRI. This possibility is based on the fact that with a decrease in blood flow velocity, especially acquiring a turbulent character, the intensity of the radio signal increases. This allows us to judge the presence and extent of tumor vascular obstruction.
Secondary tumor lesions of the heart in lung cancer are either of continuous growth or metastasis. The first option is met much more often.
In direct spreading, the tumor passes directly from the lung to the heart, germinating sequentially the pericardium, the epicardium, and in some cases even the myocardium.
Beam investigation is primarily and should be aimed at establishing the direct transition of lung cancer to the heart. A purely indicative view can be obtained by multiprojection fluoroscopy and X-ray. Additional data can give a linear tomography. However, its sensitivity is low (no more than 20%), and its specificity is even lower, since all this diagnostics is based only on an indirect sign – the merging of the shadow of a lung tumor with the contours of the heart, which reliably establish the spatial- topographical relationship of lung cancer with the heart. True, the judgment about the degree of tumor infiltration deep into the heart wall often remains conjectural.