Mediastinal cystic hygromas: CT characteristics and pathogenetic consideration.

Two cases of asymptomatic primary mediastinal cystic hygroma in adults are reported. The CT findings, including: paratracheal and paravertebral location; round, smooth, and sharp outline; homogeneous density with low attenuation number; compression of surrounding tissue without gross invasion; and lack of calcification, together with the superior mediastinal location are sufficiently characteristic to suggest the diagnosis.