Imaging description

Thymolipomas consist of mature adipose tissue and normal thymic tissue. On CT, they present as a well-circumscribed, large fat density mass in the anterior mediastinum (Figure 30.1). They may extend down to the costophrenic angles as they become large [1, 2] (Figure 30.2). The soft tissue present is usually seen as linear bands between areas of fat, but can present as small round opacities [1, 2]. On MRI, the fat is seen as high signal intensity on T1-weighted images and the soft tissue as low to intermediate signal intensity [3]. In thymolipomas with large amounts of fat, the lesions tend to conform to the contours of adjacent structures without causing mass effect (Figure 30.2) [2]. Change of shape of thymolipomas can be seen with change in position because of the relatively “soft” nature of the lesion secondary to the prominent fat content [2].

Importance

Thymolipomas are benign tumors of the thymus that represent 2–10% of all thymic neoplasms [4]. They can be very large at the time of detection as they are slow growing and generally do not cause symptoms. However, in one study over 50% presented with symptoms including infection, chest pain, and dyspnea [2].