Mediastinum
Updates to Article Attributes
The mediastinum is a space in the thorax that contains a group of organs, vessels, nerves, lymphatics and their surrounding connective tissue. It lies in the midline of the chest between the pleura of each lung and extends from the sternum to the vertebral column.
Gross anatomy
The mediastinum contains all the thoracic viscera except the lungs: heart and great vessels, internal mammary vessels, proximal aspect of azygos venous system, oesophagus, trachea, phrenic nerve, cardiac nerve, supra-aortic and para-aortic bodies, thoracic duct, thymus, and mediastinal lymph nodes.
Anatomical division
Division of the mediastinum is generally conceptualized as comprising 3 or 4 compartments, depending on the schema. For example, the mediastinum can be divided into parts based on their relationship to the fibrous pericardium:
- superior mediastinum: above the upper level of the pericardium and plane of Ludwig
-
inferior mediastinum: below the plane of Ludwig
- anterior mediastinum: anterior to the pericardium
- middle mediastinum: within the pericardium
- posterior mediastinum: posterior to the pericardium
Historically, there have been discrepant definitions of the mediastinal compartments between medical disciplines. For example, radiologists originally used arbitrary radiologic landmarks on lateral radiographs, while surgeons considered the mediastinum according to anatomic limits encountered intraoperatively (e.g. Shields classification). In response, there have been efforts to reconcile mediastinal classification systems for consistency.2 The
The more modern ITMIG classification system, developed in by a multidisciplinary group including radiologists and thoracic surgeons, relies on CT-based anatomic divisions.3It divides de mediastinum in three compartments:
Relations
-
superiorlyPré-vascular mediastinum:continuous with-
Superior limit: the
loose connective tissuethoracic inlet - Inferior limit: the diaphragm
- Lateral limits: parietal mediastinal pleura
-
Posterior limit: anterior aspecto of the
neckpericardium.
-
Superior limit: the
-
anteriorlyVisceral mediastinum:- Superior limit: thoracic inlet
- Inferior limit: the diaphragm
- Anterior limit: the posterior boundaries of the prevasccular compartment.
-
Paravertebral mediastinum:
- Superior limit: thoracic inlet
- Inferior limit: the diaphragm
- Anterior limit: posterior boundaries of the visceral compartment
- Posterior limit: a vertical line along the posterior margin of the chest wall at the lateral aspecto of the transverse processes.
laterally: lungs and pleuraposteriorly: thoracic spine-
inferiorly:diaphragm
Pathology
Broadly, pathology that affects the mediastinum can be divided into those that result in a focal mass, or those that result in diffuse disease involving the mediastinum.
The differential diagnosis of a mediastinal mass is highly dependent on its location within the mediastinum, as this may reveal the structure of origin. Thus, there is a specific differential diagnosis for each compartment:
- thoracic inlet masses
- anterior mediastinal masses
- middle mediastinal masses
- posterior mediastinal masses
In cases where localizationlocalisation is difficult due involvement of multiple compartments, the ITMIG recommends a "center"centre method" technique by which the central point on the axial slice where the lesion appears largest is used for localizationlocalisation.3 Alternatively, a "structure displacement" technique whereby displacement of organs from adjacent compartments may be used to localizelocalise the lesion.4
Diffuse mediastinal disease can be separated into groups depending on whether the mediastinal disease is smooth or lobulated:
- smooth
- lobulated
Finally, air tracking into the potential mediastinal spaces (pneumomediastinum) may occur when there is rupture of an air-containing structure, penetrating injury, or may be iatrogenic.
-</ul><p>Historically, there have been discrepant definitions of the mediastinal compartments between medical disciplines. For example, radiologists originally used arbitrary radiologic landmarks on lateral radiographs, while surgeons considered the mediastinum according to anatomic limits encountered intraoperatively (e.g. Shields classification). In response, there have been efforts to reconcile mediastinal classification systems for consistency.<sup>2</sup> The <a href="/articles/mediastinum-itmig-classification">ITMIG classification</a> system, developed by a multidisciplinary group including radiologists and thoracic surgeons, relies on CT-based anatomic divisions.<sup>3</sup></p><h5>Relations</h5><ul>-<li>superiorly: continuous with the loose connective tissue of the neck</li>-<li>anteriorly: chest wall</li>-<li>laterally: lungs and pleura</li>-<li>posteriorly: thoracic spine</li>-<li>inferiorly: <a href="/articles/diaphragm">diaphragm</a>- +</ul><p>Historically, there have been discrepant definitions of the mediastinal compartments between medical disciplines. For example, radiologists originally used arbitrary radiologic landmarks on lateral radiographs, while surgeons considered the mediastinum according to anatomic limits encountered intraoperatively (e.g. Shields classification). In response, there have been efforts to reconcile mediastinal classification systems for consistency.<sup>2</sup> </p><p>The more modern <a href="/articles/mediastinum-itmig-classification">ITMIG classification</a> system, developed in by a multidisciplinary group including radiologists and thoracic surgeons, relies on CT-based anatomic divisions.<sup>3 </sup>It divides de mediastinum in three compartments:</p><ul>
- +<li>Pré-vascular mediastinum: <ul>
- +<li>Superior limit: the thoracic inlet</li>
- +<li>Inferior limit: the diaphragm</li>
- +<li>Lateral limits: parietal mediastinal pleura</li>
- +<li>Posterior limit: anterior aspecto of the pericardium.</li>
- +</ul>
- +</li>
- +<li>Visceral mediastinum:<ul>
- +<li>Superior limit: thoracic inlet</li>
- +<li>Inferior limit: the diaphragm</li>
- +<li>Anterior limit: the posterior boundaries of the prevasccular compartment.</li>
- +</ul>
- +</li>
- +<li>Paravertebral mediastinum: <ul>
- +<li>Superior limit: thoracic inlet</li>
- +<li>Inferior limit: the diaphragm </li>
- +<li>Anterior limit: posterior boundaries of the visceral compartment</li>
- +<li>Posterior limit: a vertical line along the posterior margin of the chest wall at the lateral aspecto of the transverse processes. </li>
- +</ul>
-</ul><p>In cases where localization is difficult due involvement of multiple compartments, the ITMIG recommends a "center method" technique by which the central point on the axial slice where the lesion appears largest is used for localization.<sup>3</sup> Alternatively, a "structure displacement" technique whereby displacement of organs from adjacent compartments may be used to localize the lesion.<sup>4 </sup></p><p><a href="/articles/diffuse-mediastinal-disease">Diffuse mediastinal disease</a> can be separated into groups depending on whether the mediastinal disease is smooth or lobulated:</p><ul>- +</ul><p>In cases where localisation is difficult due involvement of multiple compartments, the ITMIG recommends a "centre method" technique by which the central point on the axial slice where the lesion appears largest is used for localisation.<sup>3</sup> Alternatively, a "structure displacement" technique whereby displacement of organs from adjacent compartments may be used to localise the lesion.<sup>4 </sup></p><p><a href="/articles/diffuse-mediastinal-disease">Diffuse mediastinal disease</a> can be separated into groups depending on whether the mediastinal disease is smooth or lobulated:</p><ul>