Mediastinal masses represent a diverse collection of tumors, vascular abnormalities, and cysts arising from and associated with each of the organs and structures found within the thorax.1–4 Cystic lesions account for up to 25% of reported mediastinal masses.1,3–5 These cysts may be congenital or acquired or may represent cystic degeneration of a previously solid tumor. In this chapter, we focus on congenital cystic lesions within the mediastinum, specifically addressing the spectrum of foregut cysts including bronchogenic cysts, esophageal duplication cysts, and neurenteric cysts. Together they constitute up to 9% of all primary mediastinal masses. In addition, we briefly consider simple cysts arising from the thymus, pericardium, and thoracic duct. Many other solid mediastinal neoplasms (dermoids, teratomas, thymomas, parathyroid adenomas, and thyroid goiters) may present with cystic components. These lesions are discussed in Chapter 82.
Cysts arise in each of the three distinct anatomic regions of the mediastinum:
The anterosuperior compartment extends from the manubrium of the sternum and the first rib to the diaphragm. The anterior border of this region is the posterior sternal table, while the posterior margin includes the pericardium and the innominate vessels. Thymic cysts and endocrine lesions, such as thyroid goiters and cystic adenomas of the parathyroid gland, are found in this compartment.6
The middle mediastinum is the site of origin of most bronchopulmonary foregut cysts. The boundaries of the middle mediastinum include the pericardial reflections superiorly and anteriorly and the diaphragm inferiorly. The posterior margin of the middle mediastinum is the anterior border of the spine. Pericardial cysts, as well as bronchogenic cysts, are found in this compartment.7
The posterior mediastinum extends from the superior aspect of the first thoracic vertebral body to the diaphragm. Its anterior border is the ventral aspect of the vertebral bodies and it extends posteriorly to the articulation of the vertebral transverse process with each rib. The posterior mediastinum includes both costovertebral sulci and segmental nerve roots as well as the sympathetic chain. Other structures found within the posterior compartment include the esophagus, vagus nerves, the thoracic duct, the azygos vein, as well as the descending aorta. Neurenteric cysts, thoracic duct cysts, as well as some esophageal duplication cysts, and occasional bronchogenic cysts are found in this compartment.7,8
Lesions that arise primarily within the mediastinum may extend above the chest into the neck or below the diaphragm into the retroperitoneum, where they present as extrathoracic mass lesions. In addition, cysts within one mediastinal compartment may also extend into the adjacent compartment since there are no strict anatomic barriers.
In reported series of mediastinal masses, the prevalence of primary cysts ranges from 10% to 25% and has remained steady for the past six decades (Table 81-1) with relatively similar incidences in males and females. Some ...