Discussion
Liposarcomas are the second most common soft-tissue sarcoma, there are
four subtypes of liposarcoma confirmed by WHO [1]. MLS accounts for
about 5% of all soft tissue sarcomas and 15-20% of all liposarcomas.
It is usually located in deep soft tissue of the limbs and more than
half of the cases are seen in the thigh muscles [2]. MLS is a
translocation-related sarcoma and is characterized by translocation with
FUS-DDIT3 or EWSR1-DDIT3 fusion, as a result of the t (12;22) or t
(12;16) balanced translocation on the 12q13.3 locus [3]. The fusion
protein produced by these fusion genes acts as deregulated and activated
transcriptional factors, it stimulates the proliferation of tumor cells
[2-4]. Estourgie et al. [5] reported that 55% of MLS patients
with metastatic disease had extrapulmonary metastases. MLS usually
metastasizes to the retroperitoneum, abdominal wall, abdominal cavity,
and bone, but cardiac metastases are very rare [5-7]. To date, only
about 30 or so cases of cardiac metastases in MLS patients have been
reported, including pericardial [8]. It has been reported in the
literatures that the tendency to metastatic spread in extrapulmonary
sites was attributed to an affinity for adipose tissues. The number of
pericardial adipocytes is small compared to that within the soft tissues
of the extremities, retroperitoneum, etc, suggest that MLS transfer is
not predicated on the enrichment of the tissue with adipose tissue
cells. The time interval between primary lesion and cardiac metastasis
is relatively long, ranging from 1 to 25 years [8]. This patient had
a short delay between the first postoperative recurrence of the tumor
and cardiac metastasis. Only 10% of patients with cardiac metastasis
have been reported to show some symptoms [9]. Cardiac metastases
from liposarcoma often present as congestive heart failure or a heart
murmur, these signs and symptoms are associated with impaired myocardial
contraction or pericardial tamponade due to tumor invasion of the
myocardium [3]. The patient in this case presented clinically with
chest tightness and wheezing and lower extremity edema, and also had a
recurrence of MLS in the left groin and left popliteal fossa, which made
it difficult to identify the possibility of cardiac metastasis in the
patient. Early diagnosis of cardiac metastases is not adequate based on
the patient’s physical examination, US and CT alone.
On histopathological examination, the MLS can be seen under light
microscopy to consist of uniform, round or ovoid, small lipogenic cells
with an interstitium rich in fine venous structures [2]. The
cytoplasm and nucleus of some tumor cells are pushed to one side by the
contained lipid droplets and appear as imprinted adipoblasts. Some
tumors have round cell areas that represent histologic progression to
high-grade tumors. Histologically low-grade MLS has a better prognosis,
with a 5-year survival rate of 90%, and high-grade MLS with a round
cell component >5% has a relatively low 5-year survival
rate of 60% [10-11]. The fatty component of MLS is its special
sign, and histologically it is predominantly mucinous with minimal fat
content; therefore, this case shows a hypodense mass of indeterminate
nature with well-defined borders on US and CT, which was not easily
distinguishable from a common mucinous cyst. The high soft tissue
contrast and resolution of MRI scans, supplemented by fat suppression
techniques to detect a small fat component in the lesion, is key to the
diagnosis. The case shows isointensity on T1WI, slightly mixed
hyperintensity on T2WI, and significantly inhomogeneous high signal on
fat-saturated T2WI, with speckled low signal seen locally. It is
evidence of the presence of adipose tissue nodules within them,
pathologically areas of high adipoblast aggregation, provides an
important imaging basis for the diagnosis of MLS. Delayed enhancement
scan shows a strip of flocculent soft tissue density shadow with
heterogeneous mild enhancement within the lesion. In contrast, true
cystic masses are only mildly reinforced in the peripheral cyst wall and
are generally not reinforced internally, thus distinguishing them from
pericardial cysts. Myocardial thickening on CT images in this case, but
no infiltrative tumor growth was found on CMR, and the lesion was
clearly demarcated from the myocardium. The clinical symptoms of chest
tightness and wheezing in this patient were related to compression of
the myocardium or surrounding great vessels caused by the expansive
growth of the tumor, which corresponded to a decrease in left
ventricular end-diastolic volume and end-systolic volume on CMR. The
whole-body MRI and PET-CT are the most reliable modalities for
surveillance of all likely sites of extrapulmonary metastases. In this
case, the pericardial metastasis of MLS has low uptake on PET.
Surgery is the mainstay of treatment for limited MLS, wide local
excision of the tumor with a minimum margin of 3 cm in consideration of
their tendency to occur locally [12]. When a cardiac metastasis is
found incidentally, it is usually incurable, this may be because the
poor control of the primary lesion and systemic dissemination that make
excision ineffective [7-8]. For patients with locally advanced or
metastatic MLS, systemic therapy is usually used. MLS is radiosensitive,
whether preoperative, intraoperative or postoperative radiotherapy
[13].