대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Liposarcoma

Radiologic Findings

PA and lateral chest radiographs show a large, well-defined mass in left hemithorax with mass effect. Note the homogenous low density of the mass. The pulmonary vascular structures are visible through the mass because of the low density of the mass, meaning probable fat component within the mass. CT scan shows a large mass in the left side of the anterior mediastinum with compressed left lower lobe. The mass composes largely of fatty tissue and some streaky soft tissue portion. The history of chest pain and weight loss (10kg / 6 months) suggests malignant nature of the lesion.

Brief Review

Primary mediastinal liposarcomas are rare tumors, composed largely of fat. Histologic differentiation between a lipoma and well differentiated liposarcoma depends on presence of mitotic activity, cellular atypia, fibrosis, neovascularization, and tumor infiltration. Patients more than 40 years old are at a higher risk of having this tumor. Liposarcomas can become large, and clinical symptoms result from compression and displacement of adjacent mediastinal structures. Common symptoms are dyspnea, chest pain, cough, and weight loss. Histologically, four main types of liposarcoma can be distinguished: the well-differentiated type, the myxoid type, the round cell type, and the pleomorphic type. In adults, the myxoid type is the most common form, accounting for 40-50% of the histologic subtypes.
On CT, liposarcomas usually show a homogenous appearacne, although areas of calcificagtion and ossification can be seen, especially in the myxoid cell type. Normal fat shows a low attenuation level (-70 to -130 H), whereas the attenuation of liposarcoma is higher because of the composition (fat and soft tissue) of these fatty tumors. Well-differentiated tumors have a CT attenuation greater than that of fat, whereas poorly differentiated liposarcomas, which are more cellular with less fat per cell, have CT attenuation similar to other solid tumors (+15 to +25H). CT findings suggesting liposarcoma include (a) inhomogeneous attenuation, with evidence of significant amounts of soft-tissue within the fatty mass, (b) poor definition of adjacent mediastinal structures, (c) evidence of infiltration or invasion of mediastinal structures. However, the diagnosis of a liposarcoma is often difficult using CT. The MR appearance of fatty tissue has been well described. Typically, fat has a high SI on both T1- and T2-weighted sequences, appearing identical to subcutaneous fat. However unfortunately, MRI has proven no more accurate than CT in differentiating liposarcoma from benign lipomas.

References

1. Dogan R, Ayrancioglu K. Aksu O. Primary mediastinal liposarcoma. Eur J Cardio-thorac Surg. 1989;3:367-370
2. Santamaria G, Serres X, Pruna X. Primary mediastinal liposarcoma with moderately high CT attenuation. AJR 1996;167:1064-5
3. Mendex G, Isikoff MB, Isikoff SK, et al. Fatty tumors of the thorax: demonstrated by CT. AJR 1979;133:207-212
4. KS Lee, SH Chung, JG Im. CT diagnosis of the fat containing mediastinal masses. J Korean Radiol Soc 1985;21:945-953

Keywords

Pleura, Malignant tumor,