Mediastinal ultrasound is an ultrasound examination of anatomical and topographic features and macrostructure of organs located in the median part of the thoracic cavity. Transthoracic access is more often performed, however, transesophageal or endobronchial echo scanning is possible. It is used for recognition of volumetric formations, inflammatory processes of this anatomical region, assessment of the state of lymph nodes. The cost depends on the chosen access and the need for anesthesia: endoscopic sonography is more expensive.
Mediastinal ultrasound is a method of ultrasound imaging of the mediastinal space. The complex of mediastinal organs includes the thymus and the adipose tissue replacing it with age, the aortic arch, the heart and the surrounding pericardium, the bifurcation of the trachea and the main bronchi, the thoracic esophagus, the thoracic lymph duct, mediastinal lymph nodes, large nerve trunks. Pathology of the mediastinal organs is usually detected during a chest X-ray. If necessary, X-ray of the thoracic cavity organs with contrast of the esophagus is used. Methods of diagnostic choice for clarifying and differential diagnostics are ultrasound, CT, PET and MRI of the mediastinum. Less often they resort to invasive techniques – pneumomediastinography, mediastinoscopy.
The mediastinum has long been considered difficult to access for ultrasound imaging due to its spatial location in the chest and uninformative due to the reflection of ultrasound signals by the air lung tissue. However, the improvement of ultrasound diagnostic devices, as well as the accumulation of practical experience, made it possible to study the echosemiotics of mediastinal organs and develop convenient scanning algorithms.
Historically, the earliest method of echo scanning is transthoracic ultrasound of the mediastinum. In the future, with the development of intracavitary echography, the diagnostic capabilities of mediastinal ultrasound have expanded due to the introduction of transesophageal and endobronchial approaches into clinical practice. The basic principles and approaches for transthoracic ultrasound of the mediastinum were developed in 1990 by K. Wernecke; he also proposed a research methodology and described the echographic picture in normal and with various lesions of the mediastinum. K. Wernecke identified 8 areas available for transthoracic echo scanning:
- the supra-aortic region located above the aortic arch;
- aortopulmonary window located between the aorta and the trunk of the pulmonary artery, the left branch of the LA and the left main bronchus;
- the right paratracheal region located in front and on the sides of the trachea;
- the prevascular area located posteriorly from the sternum, between it and the ascending aorta, ERW and the trunk of the pulmonary artery;
- the pericardial area located in front and on the sides of the heart;
- the sub-bifurcation area located under the tracheal bifurcation and above the left atrium;
- the paravertebral region located on the sides of the vertebral column;
- the posterior mediastinum is the space located between the posterior surface of the heart and the thoracic spine.
When is assigned
Mediastinal ultrasound is most informative for the location of mediastinal tumors (thymoma, thoracic goiter, mediastinal cysts, abdominal-mediastinal lipomas, lymphomas, pericardial coelomic cysts, mediastinal lung cancer, etc.); detection of affected mediastinal lymph nodes in sarcoidosis, lymphogranulomatosis and ITLNTB; inflammatory changes in mediastinal fiber in mediastinitis; damage to the thoracic lymph duct.
Endobronchial and transesophageal (transesophageal) ultrasound examination of the mediastinum significantly improve the quality of visualization and diagnostic accuracy. Endobronchial access expands the diagnostic capabilities of endoscopy by examining the peribronchial and paraesophageal areas. In addition, endosonography allows for a transbronchial fine needle puncture-aspiration biopsy of volumetric formations of the mediastinum in real time.
In recent years, intraoperative ultrasound sonography has been increasingly used in thoracic surgery. Even with a small size of the surgical wound, with the help of an intraoperative sensor, it is possible to examine the deep parts of the mediastinum, make sure that the process is operable, determine the fit of the tumor to large vessels and other vital organs. Contraindications for performing transesophageal or endobronchial ultrasound are life-threatening arrhythmias, heart failure, acute or subacute myocardial ischemia, severe coagulopathy, critical hypoxemia.
Methodology of conducting
Preparation for transthoracic ultrasound of the mediastinum is not required. Before scanning, a conductive gel is applied to the chest. It is necessary that the skin of this area is intact, there are no purulent-inflammatory foci on them.
Suprasternalny (suprasternalny), parasternalny (okologrudinny), intercostal and subcostal (subcostal) approaches are used for echoscanning of intra-thoracic anatomical structures. Thoracic aorta, superior vena cava, and pulmonary artery are visualized from suprasternal access. The fatty tissue of the mediastinum, lymph nodes, heart, and thymus gland are viewed parasternally. Soft tissues, ribs, parietal pleura, lung surface, pleural sinuses are normally visible from the intercostals. From under the xiphoid process of the sternum, the right cardiodiaphragmal angle is clearly visible. The dome of the diaphragm, liver and spleen are located from the subcostal access, which serve as a reference point for ultrasound diagnostics.
Endoscopic ultrasound of the mediastinum is performed under local anesthesia after preliminary premedication or under intravenous sedation. 6 hours before the study, the intake of food and water is excluded. Additionally, a gastroscope or bronchoscope equipped with a special endoscopic sensor is used from the equipment. During the study, constant cardiac monitoring and pulse oximetry, blood pressure monitoring are performed. If the diagnostic procedure was accompanied by a biopsy, within a few days the patient may notice hemoptysis, feel chest pain.