[Intrapulmonary rupture of a dermoid cyst: MRI findings]

We report a case of dermoid cyst of the mediastinum ruptured into the lung. Only a few reports of ruptured mediastinal dermoid cyst have appeared in the literature. A 18-year-old female patient developed a tumor in the anterior mediastinum, which was coincidentally detected by a conventional chest X-ray. CT and MRI demonstrated two components: a cystic mediastinal mass and adjacent parenchymatous condensation. The cystic mass (no enhancement during or after injection) had a fatty structure: high-intensity T1 signal and low-intensity T2 signal. The thin wall (low-intensity signal on T1 and T2) was strongly enhanced during the systemic time and was ruptured. The parenchymatous condensation included a fatty effusion and an inflammatory reaction with the same T1 signal as the cyst, remaining slightly hyperintense on T2 with enhancement after injection. Cine-MRI demonstrated that the mass and the compressed right atrium were independent.