The document discusses various types of anterior and posterior mediastinal masses. In the anterior mediastinum, it describes thymic masses such as thymic cysts and thymomas. It also discusses intrathoracic thyroid masses and teratomas. In the posterior mediastinum, it summarizes peripheral nerve sheath tumors, neurogenic tumors, bronchogenic cysts, esophageal duplication cysts, and neurenteric cysts. The document provides imaging characteristics to help differentiate these various mediastinal masses.