Mediastinal CT is a layered X-ray scanning of the mediastinal space, which has a high resolution and the ability to construct three-dimensional reconstructions of CT images. The study area covers the trachea, esophagus, thymus, heart, brachiocephalic veins, part of the superior vena cava, arch and descending thoracic aorta, pulmonary arteries and veins, lymphatic duct and lymph nodes, nerve trunks and plexuses. Mediastinal CT is prescribed in case of suspicion of primary tumor formation or metastases to the mediastinal organs, sarcoidosis, lymphogranulomatosis, mediastinitis, damage to the thoracic duct, etc. If a more thorough examination of lymph nodes or volumetric formations of the mediastinum is necessary, the study is performed with intravenous bolus contrast.
Modern specialists use several methods for diagnosing pathological changes in the mediastinal organs. The main alternative to CT is radiography. When comparing these research methods, the advantage of mediastinal CT becomes obvious, taking into account more accurate results and less radiation load on the patient. At the same time, radiography is more accessible and has a low cost, therefore it is used at the initial stage of examination, and CT is prescribed, if necessary, to clarify the data obtained during radiography, to conduct differential diagnostics or to determine treatment tactics. In rare cases, mediastinoscopy is performed to assess the condition of the mediastinal organs – a rather complex invasive procedure that is inferior to CT according to this criterion. Thus, mediastinal CT is a procedure of choice, the indisputable advantages of which include non-invasiveness, obtaining a three-dimensional image, layering of the study and low radiation load. Mediastinal CT is used according to indications, if necessary, it can be repeated, with control of the total dose of radiation load. The importance of the survey in extreme cases allows exceeding the maximum permissible values.
The procedure can be part of a chest CT scan or carried out as an independent study exclusively of mediastinal structures. Mediastinal CT is prescribed by oncologists, thoracic surgeons, pulmonologists, cardiologists, endocrinologists. Often, the indication for mediastinal CT is the presence of its expanded shadow on the X-ray. In this case, the procedure makes it possible to exclude primary volumetric processes and metastasis of tumors of other localizations, makes it possible to find the cause of lung root expansion, including visualizing lymph nodes for mapping and labeling them, as well as searching for the most suitable lymph nodes for biopsy. In the upper mediastinum, a chest goiter is detected using CT, thymomas and teratomas are detected in the upper anterior mediastinum, lipomas and coelomic cysts are detected in the lower anterior mediastinum, and neurinomas are detected in the posterior mediastinum.
According to the results of the study, lymphomas and lymphadenopathies can be diagnosed (mediastinal lymph nodes must be distinguished from vessels, for which contrast is used, staining the vessels white), sarcoidosis. With the help of mediastinal CT, the causes of pain in the thoracic region of unclear etiology are determined, anomalies of development, cysts are detected. Manipulation allows you to detect the foci of pathological changes, to establish their structure, prevalence, degree of development. As part of a chest CT, the procedure can precede surgery, is performed in order to assess the state of the mediastinal space and choose the tactics of the upcoming operation. In addition, the procedure is carried out during routine preventive examinations of operated cancer patients in order to detect metastases early.
Absolute contraindications to mediastinal CT are pregnancy and childhood (up to 14 years) due to the negative effect of X-rays on the fetus and cells of the growing organism. There are restrictions when the patient is overweight (if the body weight does not meet the technical characteristics of the tomograph), claustrophobia (if the patient refuses to take sedatives on the eve of the study), severe mental disorders with uncontrolled motor activity. As contraindications to mediastinal CT with contrast, the lactation period is considered (if necessary, the procedure should be stopped by patients on the day of the study and resumed two days later), allergy to iodine, as well as severe diabetes mellitus, renal and hepatic insufficiency due to possible intoxication with contrast agents. In addition, contrast mediastinal CT is carried out with caution in severe cardiac pathology and the presence of an artificial pacemaker, since an adjustment of the contrast dose is required to exclude a negative effect on the work of the myocardium in heart failure and a special adjustment of the intensity of the tomograph to exclude an overload of the pacemaker.
Manipulation without contrast does not require special training. Contrast enhancement involves mediastinal CT on an empty stomach (food intake is stopped 8 hours before the procedure, drinking 2 hours before). All previously taken pictures are brought to the procedure with them. Before mediastinal CT, patients remove all metal objects, warn the doctor in advance about the presence of implants and a pacemaker. Manipulation is carried out in comfortable loose clothes, sometimes patients are given disposable sets of underwear. Sufferers of claustrophobia are offered sedatives. Before using the radiopaque preparation, a skin test is performed for its tolerability by the patient. A negative result allows for bolus intravenous contrast. To do this, an iodine-containing agent is injected through a catheter with a valve in the ulnar vein, a bolus is activated with 100 ml of saline solution. During the introduction, the patient may feel warmth, a metallic taste in the mouth, slight itching, which pass on their own.
Methodology of conducting
Mediastinal CT is carried out in a specially shielded room from X-rays. The radiologist is in the next room and communicates with the patient through a microphone built into the tomograph. The subject is placed on the mobile table of the device, which is then automatically guided through the tunnel. The quality of the images directly depends on the patient’s immobility, so the chest is sometimes fixed with special rollers. During mediastinal CT, the ring of the tomograph with sensors rotates around the table, numerous scanners receive X-rays and transmit the received information about the state of healthy and altered tissues to the computer. Then the information is processed by special programs, resulting in a large number of scans and a 3D image. Scans can be stored in the patient’s medical record in paper form or transferred to external electronic media. The procedure does not cause discomfort, during operation the tomograph may make a small noise and crackle.
The interpretation of the results of mediastinal CT is carried out on the same day. The conclusion is given by the radiologist. The document draws attention to the anatomical features of the mediastinum, the size and structure of the organs of the mediastinal space, and describes pathological changes. The absence of pathology is regarded as the norm. The patient receives the pictures and the conclusion in his hands and subsequently gives them to the specialist who prescribed the mediastinal CT. The attending physician, based on the conducted research, makes a clinical diagnosis and carries out further management of the patient. The specialist can refer the patient for additional examination, observe on an outpatient basis, hospitalize according to indications in an emergency or planned manner. Preparation of the conclusion and recording of images on digital media takes from one hour to a day. At the request of the patient, the pictures can be sent to his e-mail.