Imaging description

Mature teratomas are made up of well-differentiated tissue from two or more embryonic germ cell layers. Thus, any combination of fat, fluid, soft tissue, or calcium may be present. In one large series soft tissue attenuation was observed in 100%, fluid in 88%, fat in 76%, and calcification in 53% of cases [1]. Although MRI is excellent at identifying various combinations of these tissues, CT is usually sufficient to make the diagnosis [1]. Lack of fat or calcification does not rule out the diagnosis, but the presence of these findings makes the imaging diagnosis more straightforward.

On CT, a mature teratoma presents as a well-marginated, lobulated, heterogeneous cystic mass with soft tissue in the form of septa or nodules along with components of fat and/or calcification (Figures 31.1 and 31.2). They are almost always in the anterior mediastinum. A fat/fluid level within the lesion is virtually diagnostic (Figure 31.2), but is reported to be present in only about 11% of cases [1–3]. Pure foci of fat or calcification may also be identified (Figure 31.1). The densities of the cysts on CT vary due to the amount of proteinaceous or lipid-rich material present. Thus the cystic components of the mass may also have a more variable appearance on MRI. Cystic components will vary from low to high signal intensity on T1, while soft tissue components are generally isointense to muscle and fat is high signal intensity on T1-weighted images (Figures 31.3A and 31.3B) [1, 4].