The mediastinum can be divided into three parts: anterior,
middle and posterior compartment.
There are not true anatomic tissue plane between this three compartments,
in free communication with one another.
The anterior mediastinum contains the following structures: thymus,
lymph nodes,
ascending aorta,
pulmonary artery,
phrenic nerves and thyroid.
The middle mediastinum contains lymph nodes,
trachea,
esophagus, azygos vein,
vena cavae,
posterior heart and the aortic arch. The posterior mediastinum contains sympathetic ganglia,
nerve roots,
lymph nodes,
parasympathetic chain, thoracic duct,
descending thoracic aorta,
small vessels and the vertebrae.
The different compartments of the mediastinum can be separated on the lateral radiograph, by drawing an imaginary line anterior to the trachea and posteriorly to the inferior vena cava.
The middle and posterior compartments can be separated by an imaginary line passing one centimeter posteriorly to the anterior border of the vertebral bodies.
This division allows us to make a more narrow differential diagnosis.
It is important to know the fascial planes which communicate with cervical mediastinum and allow the progression of the deep cervical spaces infections.
The deep cervical fascia is composed of three layers (pretracheal, retrovisceral and prevertebral),
that partition the neck into three potential spaces,
which can serve as portals of entry into the mediastinum.
The pretracheal space lies in front of the trachea and behind the strap muscles.
Infections in this space may occur due to perforations of the trachea and lateral pharyngeal walls.
The pretracheal fascia fuses with the pericardium and the parietal pleura in the anterior mediastinum at the level of the carina.
The retrovisceral space lies posterior to the esophagus and anterior to the prevertebral fascia.
It extends inferiorly into the posterior mediastinum and is the most frequent way by which oropharyngeal infections extend to the mediastinum.
Infections can spread by the vascular structures into the mediastinum and pleural space,
through the carotid sheath that surround the perivascular compartment.