INTRODUCTION: Liposarcoma is derived from residual nests of primitive mesenchymal tissue. Primary mediastinum liposarcomas (ML) are rare neoplasms comprising only 0.13–0.75% of mediastinal tumors; there are less than ninety cases described in the literature worldwide.
CASE PRESENTATION: A 58 year old male teacher with a history of HTN & DM, presented with 3 months of productive cough, decreased exercise tolerance and non-exertional right sided chest pain. He denied weight loss, dysphagia or voice change. He had a 30 pack year history of smoking, and no history of tuberculosis or exposure. His physical exam was unrevealing. Labs were significant for a mild normocytic anemia. Chest x-ray was suggestive of a large mass in the lower mediastinum. CT scan (see image) demonstrated a large posterior mediastinal mass displacing the esophagus. This was different when compared to a prior abdominal CT scan performed 5 years ago (while being Rx for bladder ca), which showed only prominent fat around the same area. The patient underwent a postero-lateral thoracotomy, and a 17 cm posterior mediastinal mass was found, protruding into the right hemithorax and displacing the esophagus anteriorly. Histology was consistent with a low grade well-differentiated liposarcoma with secondary myxoid changes. The tumor was composed of lobulated mature adipose tissue separated by thick, broad fibrous septae, with identifiable spindle & pleomorphic cells. Cytogenetic analysis revealed abnormal clones with multiple numerical & structural alterations involving chromosomes 6, 11, 14, 15, 21 and 22 as well as a ring & giant chromosomes.
DISCUSSIONS: Liposarcoma usually occurs in the retroperitoneum and deep soft tissues of the trunk and extremities, representing approximately 20% of mesenchymal neoplasms. ML may arise from thymus fatty tissue in the anterior mediastinum but are also found occasionally in the posterior mediastinum. They grow insidiously and attain large size with invasion into surrounding structures like the pericardium and superior vena cava. They may be asymptomatic or cause dyspnea, chest pain and tachypnea. Four histological types of Liposarcoma have been described: well differentiated, myxoid, round cell and pleomorphic. Well-differentiated (the most common)and myxoid types have favorable prognoses, with 100% and 88% 5-year survival rates, respectively. However, these tumors are poorly circumscribed and recur locally after incomplete excision. Round-cell and pleomorphic types have a poor prognosis with a 5-year survival rate of about 50% each; both tend to metastasize quickly, mostly to the lungs. On CT, ML may appear as a fat containing mass or a solid lesion. MRI T1- weighted images show the fatty tissue with high signal intensity, making this imaging mode valuable to assess for vascular or thoracic duct invasion. Surgical resection is the treatment of choice of ML. Partial excision or debulking may be required to relieve symptoms of infiltrating lesions of the mediastinum. Liposarcomas have very low sensitivity to radiotherapy and chemotherapy. High doses of radiation may result in mediastinal fibrosis and is generally reserved for unresectable tumours or palliation. Chemotherapy has a very limited role. Long term survival is highest with well differentiated pseudo-encapsulated tumors where surgical excision is complete. Recurrence of ML is common, usually apparent within the first 6 months after resection, and carries a very poor outcome.
CONCLUSION: ML is derived from primitive mesenchymal tissue and is a rare neoplasm, with few cases described in the literature. They arise from either the anterior or posterior mediastinum and may cause symptoms. Aggressive surgical resection offers the best prognosis. Those unresectable respond poorly to radiotherapy or chemotherapy and have a high mortality.
DISCLOSURE: Amir Khan, None.