mediastinal cysts

Types

 bronchogenic cyst
 pleuro-pericardial cyst
 mediastinal primitive foregut cyst (mediastinal digestive duplication cyst)

• oesophageal duplication cyst
• gastric duplication cyst

Various cysts can originate in the mediastinum. While not actually neoplasms, they represent space-occupying lesions that usually result from abnormal embryologic development. These include:
 foregut cysts
 gastroenteric cysts
 neurenteric cysts
 mesothelial cysts
 thoracic duct cysts.

Cysts can also be associated with teratomas within the mediastinum. Thymic cysts cab be considered as Thymic Tumors.

Foregut cysts are believed to develop from abnormal primitive foregut development.

Bronchogenic cysts likely arise from an abnormality of the normal budding of the ventral foregut, the precursor of the trachea and major bronchial structures.

The walls of these cysts are lined by ciliated pseudostratified columnar epithelium and may contain bronchial glands, smooth muscle bundles, and other tissues found in the tracheobronchial tree.

Enterogenous cysts arise from abnormal development of that portion of the dorsal foregut that becomes the gastrointestinal tract. Most commonly, these cysts are lined with some form of gastrointestinal epithelium. Esophageal duplication cysts are believed to arise in early development, when vacuolization of the solid early esophagus occurs to form the esophageal lumen. If an isolated vacuole fails to merge with the central esophageal lumen, a duplication cyst may occur.

Neurenteric cysts develop at a location in which the dorsal foregut and the primitive notochord are in close relationship. Many theories have been offered about the development of these cystic abnormalities; however, the common feature noted in many of them is that an adhesive process of some type appears to cause a vacuole of the foregut to become incorporated into the notochord tissue. The classic cyst is lined with enteric and neural tissue. They are often associated with other defects and anomalies of the vertebral column, and many cases described in the literature are those in which the cyst communicates with, or extends into, the spinal canal.

Mesothelial cysts are generally made up of a capsule of fibrous tissue with an inner single-cell layer of mesothelial cells. The most common type of mesothelial cyst found in the mediastinum is the pleuropericardial cyst, which is generally located at the anterior cardiophrenic angle. Other mesothelial cysts occurring in the mediastinum are simple mesothelial cysts and lymphogenous cysts.

Other primary cysts of the mediastinum include thymic cysts and thoracic duct cysts, the latter being very rare. Thymic cysts usually have an inner lining that is a single layer of cuboidal cells and islands of normal thymic tissue in the wall. Thoracic duct cysts may or may not communicate with the duct itself. They are composed of the same tissue as the normal lymphatic channels.

Although these abnormalities are considered benign lesions, a few cases have been reported in which malignant tissue has been found within the wall of a resected bronchogenic cyst. Malignant cell types found include squamous cell carcinoma and adenocarcinoma.

See also

 Cysts

• malformative cysts

 mediastinal anomalies

• mediastinal macroscopical anomalies