Imaging of cystic masses of the mediastinum.

Cystic masses of the mediastinum are well-marginated round lesions that contain fluid and are lined with epithelium. Major cystic masses include congenital benign cysts (ie, bronchogenic, esophageal duplication, neurenteric, pericardial, and thymic cysts), meningocele, mature cystic teratoma, and lymphangioma. Many tumors (eg, thymomas, Hodgkin disease, germ cell tumors, mediastinal carcinomas, metastases to lymph nodes, nerve root tumors) can undergo cystic degeneration-especially after radiation therapy or chemotherapy-and demonstrate mixed solid and cystic elements at computed tomography (CT) or magnetic resonance (MR) imaging. If degeneration is extensive, such tumors may be virtually indistinguishable from congenital cysts. A mediastinal abscess or pancreatic pseudocyst also appears as a fluid-containing mediastinal cystic mass. However, clinical history and manifestations, anatomic position, and certain details seen at CT or MR imaging allow correct diagnosis in many cases. Familiarity with the radiologic features of mediastinal cystic masses facilitates accurate diagnosis, differentiation from other cystlike lesions, and, thus, optimal patient treatment.