Rare case of a large mediastinal cyst involved in Hodgkin's lymphoma

We report a case of a mediastinal cystic retrosternal process, discovered by magnetic resonance imaging (MRI) in a 19-year-old male patient, with unusual inhomogenous signals in both T1- and T2-weighted images and contrast-enhancing septation. Macroscopically, the tumor weighed 1330 g, and was constituted by one dominating cyst measuring 14 cm in diameter. Additional small cysts were seen microscopically. The cystic wall was continuously infiltrated by nodular sclerosing Hodgkin's lymphoma, also affecting adjacent lymph-nodes. Age and sex of the patient and the diagnosed subtype of Hodgkin's lymphoma are in line with previously reported rare cases of mediastinal cysts with Hodgkin's lymphoma. The cyst reported here, most likely a secondary thymic cyst, is larger than those reported before. The main reason for the development of these cysts might be the accompanying inflammation of the lymphoma. Little is known about the imaging features of mediastinal cysts caused by lymphoma. Plain thymic cysts are normally homogenous on T1- and T2-weighted images. Hodgkin's lymphoma might be homogenous on T1-weighted images and is mostly inhomogenous on T2-weighted images. In case of inhomogenous cysts with contrast-enhancing septation, one should consider the diagnosis of an associated neoplasm.