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. © 1985 Raven Press, Ltd.
