Chinese Medical Journal 2010;123(13):1818-1820
A giant primary myxoid liposarcoma of the posterior mediastinum

LIU Li-gang,  WEI Xiang,  PAN Tie-cheng

LIU Li-gang (Department of Cardiothoracic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China)

WEI Xiang (Department of Cardiothoracic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China)

PAN Tie-cheng (Department of Cardiothoracic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China)

Correspondence to:WEI Xiang,Department of Cardiothoracic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China (Tel: 86-27-83663408. Fax:86-27-83663671. E-mail:xwei_tjh@hotmail.com)
Keywords
mediastinal neoplasm; liposarcoma; radiology; surgery
Abstract

Primary mediastinal liposarcoma is an uncommon neoplasm of intrathoracic origin. A case of a giant primary posterior mediastinal liposarcoma, mimicking a benign lipomatous lesion in shape and biological behavior and being successfully managed by complete surgical excision is presented here.

CASE REPORT

A 44-year-old male, without obvious medical history or family disease history, visited our hospital, complaining of chest distress and abdominal distention for 2 months. A subsequent chest X-ray indicated the abnormal shape of the heart and enlarged main bronchus angle (Figure 1). Precordial echocardiaography failed to detect any structural heart abnormalities, except for the compressed left atrium and inferior vena cava. Contrast-enhanced computed tomography (CT) scan revealed a large posterior mediastinal mass which occupied the posterior mediastinum and compressed heart tightly to the posterior side of the sternum and further extended into the left thoracic cavity and upper abdominal cavity, adjacent to the left lobe of the liver, with a clear margin (Figure 2). From the low attenuation values and without enhancement of the mass on CT it might be diagnosed as lipoma or liposarcoma of the posterior mediastinum.

The patient was explored through the left 6th intercostal space and prepared for a combined thoracoabdominal incision if necessary during the operation. Upon exposure of the left pleural cavity, a large mass was visualized extending and occupying almost the half portion of the left thoracic cavity. The lower lobe of the left lung was displaced and elevated. After a period of blunt dissection and manipulation, the entire mass was successfully removed en-bloc. In gross appearance, it was a thinly encapsulated, dull mass in a pale yellow color which had a smooth surface covered with many nourish vessels and was soft to the touch. The tumor weighed a total of 3560 grams and measured 22 cm× 21 cm× 20 cm. On cut section of the mass it consisted of adipose tissue with a fibrous core (Figure 3).


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Figure 1. Chest X-ray film revealed the shadow of the heart was widened and the angle between the left and right main bronchus was enlarged, as well as the existence of less effusion in the left pleural cavity.
Figure 2. Contrast-enhanced CT scan revealed a large posterior mediastinal mass, without obvious enhancement, extending into the left thoracic cavity and the upper abdominal cavity and compressing the heart tightly to the posterior side of the sternum.
Figure 3. In gross appearance, the entire mass after surgical extirpation was a thinly encapsulated, red dull ball-like mass which had a smooth surface covered with many nourish vessels, 22 cm× 21 cm× 20 cm in size. From the transection of the mass, it consisted of adipose tissue with a fibrous core.

Histologic examination of the tumor revealed the diffused distribution of lipoblastic mesenchymal cells with increased cellularity and atypical nuclei, and a plexiform capillary network, all set in a myxoid matrix, scattered strands of fibroconnective tissue, with positive results of protein S-100, Vimentin (Vim) and CD34 and negative results of protein smooth muscle actin (SMA) and desmin, examined by immunohistochemical methods. The histological features were consistent with the diagnosis of a myxoid liposarma. Considering there were no suspected lipomatous lesions in other sites of his body, the final diagnosis was made as a primary myxoid liposarma of posterior mediastinum. The patient’s postoperative course was uneventful and was followed up closely after he was discharged in the 13th day postoperatively.

DISCUSSION

Primary liposarcoma of the mediastinum, with less than 200 cases reported in the literature by now, is an extremely rare neoplasm, comprising less than 1% of all mediastinal tumors. Liposarcomas occur most commonly in the lower extremities (75%) and less frequently in the retroperitoneum, with most cases occur in patients more than 40 years old.1-3 For this case, such a giant malignant liposarcoma develops in the posterior mediastinum, mimicking a benign tumor in shape and biological behavior is even rare.

Mediastinal liposarcomas may, on account of excessive size or direct invasion of contiguous vital structures, such as heart, trachea, bronchi, and esophagus etc., cause functional limitations, such as pain, cough, shortness of breath with exertion or dyspnea, dysphagia etc.4,5 They are usually identified by routine chest radiograph or are discovered after the patient presents with symptoms secondary to the intrathoracic structure compression.6 In this case the patient had got a presentation of chest distress and dyspnea, caused by the compressed heart and bronchi.

The radiologic features of mediastinal liposarcomas are nonspecific but are suggestive of the diagnosis. The predominant finding on its conventional chest radiography usually reveals a widened mediastinum. On CT, the appearance of mediastinal liposarcomas, the same as those located in other sites of body, varies from a predominantly fat-containing mass to a solid mass. Low attenuation values between –50 and –150 Hounsfield Unit are consistent with a tissue composed of fat. Greater values are related to the necrosis, heterogenity and soft tissue component in liposarcomas. A differential diagnosis should be made between lipoma, thymolipoma, teratoma, lymphoma, germ cell tumor etc.7

Liposarcomas are characterized by their large size and their variable histologic subtypes, which correlate with the clinical behavior and the prognosis. The most recent World Health Organization classification of soft tissue tumors recognizes 5 categories of liposarcomas: (1) well differentiated, which includes the adipocytic, sclerosing, and inflammatory subtypes; (2) dedifferentiated; (3) myxoid; (4) round cell; and (5) pleomorphic. Patients with dedifferentiated or pleomorphic liposarcomas have a significant poor survival and prognosis than those with myxoid or well differentiated liposarcomas.8 Well differentiated low-grade liposarcomas, also known as atypical lipomatous tumors, have histologic features in many areas resembling mature adipose tissue. Evans reported that atypical lipomatous tumors may transform to dedifferentiated liposarcomas and usually do not metastasize.7 In this case, there were no evidences of tumor metastasis preoperatively and the giant mass was fully encapsulated, without surrounding tissues invaded and could be excised en-bloc successfully. Maybe lipomatous malignant degeneration was its cause.

Surgical removal is the optimal treatment for a mediastinal liposarcoma. If the entire tumor can not be resected, surgical debulking often results in symptomatic relief. Chemotherapy and radiotherapy are ineffective modalities, may be added as adjuncts to surgical excision used in unresectable or incompletely resected tumors, but liposarcomas seem to have low sensitivity.9,10

Recurrence is common in deep-seated liposarcomas and it becomes apparent within the first 6 months in most cases, but it may be delayed for 5 or 10 years following the initial excision.11 In this case, though the patient underwent a complete tumor removal, he was still recommended to receive a routine dose radiotherapy (200 cGy×25) to enhance therapeutic effects and diminish the possibility of tumor recurrence after his discharging from our hospital. By now nearly 4 months have passed and the patient has no evidence of tumor recurrence or metastasis. A long-term, careful follow-up should be still strongly recommended.

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