In this sense, bronchogenic cysts and esophageal cysts (duplications) share a similar developmental background, namely foregut budding errors, rather than being separate disease entities., A distinction is made between bronchogenic and esophageal cysts when cartilage is present, which suggests the cyst is bronchogenic in origin. However, Nobuhara et al advocated naming both types as “foregut cysts” because of their common embryological origin, anatomic proximity and histologic similarities.
Mesothelial cysts, including pericardial and pleural cysts, are estimated to occur in approximately 1 in 100,000 persons. Ochsner and Ochsner reported 33% mesothelial cysts among 42 cysts in the mediastinum. These cysts accounted for 18.1% in our series. These anomalies are formed by the parietal recess persisting during development, namely aberrant recess fusion; therefore, the pericardial diverticulum, having a communication with the pericardial cavity, is regarded as an incomplete form of pericardial cyst in terms of its embryogenesis.
Thymic cysts used to be regarded as a rare anom-aly; however, reports described a higher incidence of thymic cysts. In the current series, thymic cysts represented the second most common type: 28.6% of the mediastinal cysts and 3.7% of the mediastinal tumors. Thymic cysts may occur at any anatomic level, from the base of the neck to the diaphragm. There has been some controversy as to the causes of thymic cysts. Bieger and McAdams reported that thymic cysts derived from the thyropharengeal duct, that is, they are congenital in origin. Graeber et al divided cystic lesions of the thymus into three major categories: congenital, neoplastic, and degenerative. The latter two mechanisms in pathogenesis were cystic degeneration of thymomas and cystic masses after chemotherapy for Hodgkin disease.