Pleomorphic liposarcoma of the posterior mediastinum

Clinical History

The patient reported weight loss, fever and edema of the malleoli. The chest radiographs revealed a right oval mass of the posterior mediastinum.

Imaging Findings

The patient reported a weight loss of 10 kg over the last two months, fever (38-39ºC) of 15-day duration and edema of malleoli for a week and had no history of tobacco use. Chest radiographs revealed widening of the mediastinum due to a right oval mass located in the posterior mediastinum. The tumoral shadow featured a smooth right edge and showed obtuse angles at its margins. Neither the right heart border nor the right hilum were obscured. No lymphadenopathy was depicted. The patient was admitted to hospital for futher evaluation. Laboratory data diagnosed anemia (Hct: 27.3%, Hgb: 8,9 g/dl) and high ESR levels (130).
Chest CT revealed a solid and homogeneous, 8,5cm x 6,5 cm lesion with a broad base on the mediastinum which projected into the lung with regular edges. An enhanced capsule was demonstrated. The mass had no foci of calcification or necrosis.
MRI demonstrated the heterogeneous enhancement of the mass. The capsule was intensely enhanced as well. Intraspinal extension was excluded.
A malignant neural tumor was suspected due to clinical and radiological findings. The mass was surgically resected.

Discussion

Liposarcoma takes it origin from lipoblast and cytogenic analysis has revealed a translocation between chromosomes 12 and 16 [t(12;16), (q13;p11)] that is partially considered responsible for its etiology. It is the second most common soft tissue sarcoma encountered in adults but primary mediastinal involvement by liposarcoma is distinctly rare. Patients with mediastinal liposarcoma are usually older than 30 years of age and mainly males.
Liposarcomas are classified into four histological subtypes:
- well-differentiated (or atypical lipoma),
- myxoid (accounts for 50% of all cases),
- round cell and
- pleomorphic.
The demonstration of fat on CT and MRI occurs in all cases of well-differentiated liposarcomas (which consist of more than 75% of fat) but in less than 30% of round cell or pleomorphic ones that contain little or no fat at all.
Liposarcoma is indistinguishable from other sarcomas when fat is not revealed on imaging modalities (1). Mediastinal liposarcoma is mainly situated anteriorly.
The predominant finding of mediastinal liposarcoma on chest radiography is a widened mediastinum. Tracheal or vessel deviation may also be present (2). CT and MRI demonstrate liposarcomas as inhomogenous fat-containing masses that vary in appearance depending on the amount of soft tissue and fibrous bands in the tumor. Solid components may enhance and surrounding structures may be infiltrated or displaced (2). Thus, liposarcomas vary in appearance depending on if they predominantly contain fat or if they are solid (3).
Liposarcomas tend to be well circumscribed or encapsulated and usually show a macroscopic distinct multilobular pattern (4).
Well-differentiated liposarcomas demonstrate signal characteristics similar to subcutaneous fat except for a scattering of broader septa or more nodules than those seen in lipomas(5). These tumors show minimal or no enhancement. Because of the high signal intensity (SI) of fat on T1-weighted images, the enhancement pattern can best be seen on fat-suppressed images (4).
Myxoid liposarcoma reveals relatively homogeneous internal structure, isointense with muscle on T1-weighted images and of homogeneously high SI with linear septae dividing the lobules on T2-weighted images. The enhancement pattern is mildly heterogeneous with non-enhancing areas. Some cases of this liposarcoma type contain small amounts of fat due to increased lipid depositions in lipoblasts (4).
Pleomorphic and round cell liposarcomas often do not contain fat. Pleomorphic liposarcomas are the most aggressive high-grade sarcomas. MRI appearance of these liposarcomas is mostly low SI on T1-weighted images and high SI on T2-weighted images. Areas of hemorrhage may also be depicted. Markedly heterogenous enhancement may be also demonstrated and necrotic components of the lesion may then be diagnosed (4).
Round cell liposarcomas present moderate to markedly heterogeneous MRI features which are indistinguishable from other high-grade liposarcomas and not different from those of other malignant soft-tissue tumors (4).
Patients may have vague symptoms (dyspnea, cough, pain, weight loss, superior vena cava obstruction) or may be asymptomatic.
Pleomorphic liposarcomas often demonstrate polymorphonuclear infiltrations (inflammatory liposarcomas) and are accompanied by fever. Therapeutic approaches consist of surgical resection (or debulking) combined with radiotherapy and/or chemotherapy. Local recurrence is frequent although metastases (lungs, liver, bones) are rare.

Differential Diagnosis List

Final Diagnosis

Pleomorphic, spindle-cell liposarcoma of the posterior mediastinum

URL:	https://www.eurorad.org/case/2093
DOI:	10.1594/EURORAD/CASE.2093
ISSN:	1563-4086