Liposarcomas are the most common of sarcoma tumours, they are usually located in the lower limbs, retroperitoneum,

or abdominal cavity; up to date, only a few cases of omental liposarcoma with different histotype have been described. We present a case of omental well-differentiated liposarcoma and discuss imaging findings on ultrasound, computed tomography, and magnetic resonance to  differentiate omental liposarcomas from other abdominal tumour entities

Cossu, Maria Laura

Feo, Claudio F.

Meloni, Francesco

Meloni, Giovanni Battista

Profili, Stefano

English

UnissResearch

September  2009    Vol. 5  No.3    Int  J  Biomed  Sci    www.ijbs.org 302
InternatIonal  journal of  BIomedIcal  scIence
Omental Well-Differentiated Liposarcoma: 
US, CT and MR Findings
Francesco Meloni1, Claudio F Feo2, Stefano Profili3, 
Maria Laura Cossu4, Giovanni B Meloni1   
1Department of Radiology, University of Sassari, Sassari, Italy; 2Department of Surgery, Istituto di Clinica Chirurgica,  
University of Sassari, Sassari, Italy; 3Service of Radiology, Paolo Dattori Hospital, Tempio Pausania, Italy; 
4Department of Surgery, Chirurgia dell’Obesità, University of Sassari, Sassari, Italy
AbstrAct
Liposarcomas are the most common of sarcoma tumours, they are usually located in the lower limbs, retro-
peritoneum, or abdominal cavity; up to date, only a few cases of omental liposarcoma with different histotyp
e have been described. We present a case of omental well-differentiated liposarcoma and discuss imaging findi-
ngs on ultrasound, computed tomography, and magnetic resonance to differentiate omental liposarcomas from ot
her abdominal tumour entities. (Int J Biomed Sci 2009; 5(3):302-304)
Keywords: computed tomography; liposarcoma; magnetic resonance; omentum; ultrasound
Corresponding author: Claudio F Feo, Istituto di Clinica Chirurgica, 
University of Sassari, Viale San Pietro 43, 07100 Sassari, Italy. Tel: +39-
079-228432; Fax: +39-079-228394; E-mail: cffeo@uniss.it.  
Received February 1, 2009; Accepted July 9, 2009
INtrODUctION
Primary tumours of the omentum are very rare, we 
don’t know their incidence and most of the information 
available is from case reports. Liposarcomas usually in-
volve the limbs, retroperitoneum, or abdominal cavity in 
adults (1). Up to date, in a review of the English medical 
literature we found only 14 cases of omental liposarcoma 
with different histological subtypes.
We present a case of omental well-differentiated lipo-
sarcoma and discuss imaging findings on ultrasound (US), 
computed tomography (CT), and magnetic resonance 
(MR) scans.
cAsE rEPOrt
A 34-year old man suffering from autism presented a 
2-year history of worsening abdominal distension. Phys-
ical examination revealed a large tender abdominal mass 
across the midline in the middle and lower quadrants. 
Laboratory tests were normal. Abdominal US (Philips 
ATL HDI-5000 system) revealed a hypomesogastric 
mass, measuring 18 × 13 cm in diameters, characterized 
by two components: a main hyper-echoic solid portion; 
and, superiorly, a second portion formed by multiple 
cystoid cavities (Fig. 1). The mass surrounded the ce-
liac trunk and mesenteric vessels but no flow alterations 
were detected at duplex and color doppler examination. 
CT scan (General Electric, High Speed,  Single Slice 
Spiral scanner) showed a 25 × 13 cm abdominal mass 
extended from the hepatic hilus to the pelvis (Fig. 2). 
The lesion was adjacent to the great vessels dorsally and 
to the renal fascia, duodenum, and pancreas laterally; 
small bowel loops and transverse colon were displaced 
downward and upward, respectively. It was composed 
of a fatty area (-85HU) near the mesentery and a hyper-
dense (32HU) portion located dorsally. MR examination 
(Shimadzu 1T scanner) performed before and after con-
trast medium injection with T1- (Fig. 3A, B - TR 243 ms, 
TE 4 ms) and T2-weighted images and suppression of 
fatty tissue (Fig. 3C - TR 415 ms, TE 80 ms) confirmed 
CASE REPORT
ImagIng fIndIngs In lIposarcoma
www.ijbs.org    Int  J  Biomed  Sci    Vol. 5  No. 3    September  2009 303
an abdominal mass with a dorsally located multicystoid 
area surrounded by fat.
The patient underwent surgical excision and pathologic 
examination revealed an omental well-differentiated lipo-
sarcoma. He was discharged after six days and no recur-
rence was observed during a 5-year clinical follow-up.
DIscUssION
Liposarcomas are the most common of sarcoma tu-
mours, they are usually located in the lower limbs, retro-
peritoneum, or abdominal cavity, and are the most frequent 
histological type of retroperitoneal tumours (1). Pathologi-
cally liposarcomas are malignant tumours formed by li-
poblasts and are divided in three subtypes with increasing 
malignity: well-differentiated liposarcoma, myxoid and 
round-cell liposarcoma, and pleomorphic (dedifferenti-
ated) liposarcoma (2). Liposarcomas can appear at any age 
but they occur more frequently in the sixth and seventh de-
cades of life with a male/female ratio of 2:1 (3). These tu-
mours are rarely located in the mesentery, Hasegawa T et 
al have studied 32 cases of dedifferentiated liposarcoma: 
27 were situated in the reroperitoneum and 5 in the mes-
entery (4). Symptoms are usually nonspecific: abdominal 
discomfort or distension, constipation, and rarely lower 
limb oedema may be present.
Liposarcomas often contains different histological 
subtypes with benign and malignant areas in the same le-
sion, therefore CT and MR scans may vary according to 
the dishomogenity in tissue composition. Particularly, the 
signal density on CT and signal intensity on MR images 
from a well-differentiate liposarcoma are similar to those 
found in normal fat, and differential diagnosis with other 
abdominal tumour entities can be difficult.  
A well-differentiated liposarcoma is characterized by 
thinner and more irregular septa than a lipoma; these sep-
Figure 3. MR examination performed before (A) and after (B) contrast administration with  T1- and T2-weighted images and suppres-
sion of fatty tissue (C) confirmed an abdominal mass with a dorsally located multicystoid area surrounded by fat.
Figure 2. CT scan showed an abdominal mass extended from 
the hepatic hilus to the pelvis; it was composed of  fatty areas 
(-85HU) near the mesentery and a hyperdense (32HU) portion 
located dorsally.
Figure 1. Abdominal US scan revealed a hypomesogastric 
mass, characterized by two components: a solid portion and  a 
second portion formed by multiple cystoid cavities.
ImagIng fIndIngs In lIposarcoma
September  2009    Vol. 5  No.3    Int  J  Biomed  Sci    www.ijbs.org 304
ta present signal density (CT) and intensity (MR) similar 
to those found in muscles and may show enhancement by 
gadolinium-contrast MR imaging. Some authors found fo-
cal areas with a signal different from fat tissue both in 
well-differentiated liposarcomas and benign lipomas (5). 
These features should be evaluated for the differential di-
agnosis with more invasive liposarcomas, such as the de-
differentiated subtype characterized by a worsen progno-
sis and higher recurrence rate (6), and the myxoid subtype 
that accounts for 50% of all liposarcomas (7). Areas that 
disappear in the fat suppression sequences and show dif-
ferent enhancement levels on MR scan are consistent with 
a well-differentiate liposarcoma. 
Myxoid liposarcomas show a dishomogeneous aspect 
with CT attenuation values lower than muscular tissue. 
Fat and soft tissues distribution pattern may sometimes 
produce fluid attenuation values, therefore the lesion ap-
pears cystic on scans without contrast medium misleading 
diagnosis. MR images reveals a signal intensity similar 
to water; however it is sometimes possible to observe in-
dented, linear, or amorphous areas with increased signal 
intensity on T1- and mean signal intensity on T2-weighted 
images. These features indicates the presence of intratu-
moral fat and allow the correct diagnosis. Furthermore, 
these lesions are better defined after intravenous contrast 
medium injection showing a slow progressive and reticu-
lar enhancement, which indicates the solid nature of the 
tumour.
The diagnosis of a dedifferentiated liposarcoma should 
be considered when an abdominal mass shows on CT and 
MR imaging intense enhancement, adjacent organs inva-
sion, vascular infiltration, calcification or ossification, and 
areas of necrosis or haemorrhage (8, 9).
In our case, we observed a liposarcoma with two com-
ponents: a solid area with fat signal intensity and a second 
multicystoid portion. Fat suppression sequences confirmed 
the presence of adipose tissue in the former area and the 
cystic appearance of the latter. No foci with signal inten-
sity different from fat were detected; CT and MR scans 
didn’t show any significant variation after intravenous 
contrast medium injection. There was no evidence of other 
organs or vascular invasion.  These features were consist-
ent with a well-differentiated lipasarcoma which was then 
confirmed by pathological examination.
In conclusion, omental well-differentiated liposarco-
mas are extremely rare and differential diagnosis with 
other abdominal tumour entities can be challenging. We 
stress the importance of fat suppression sequences and 
gadolinium administration on MR scan to identify ab-
dominal masses of difficult diagnosis.
rEFErENcEs
1. Weiss SW. Lipomatous tumors. Monogr Pathol. 1996; 38:207-239.
2. Dei Tos AP. Liposarcoma: new entities and evolving concepts. Ann 
Diagn Pathol. 2000; 4:252-266.
3. Milic DJ, Rajkovic MM, Zivic SS. Primary liposarcomas of the omen-
tum: a report of two cases. Eur J Gastroenterol Hepatol. 2004; 16:505.
4. Hasegawa T, Seki K, Hasegawa F, Matsuno Y, et al. Dedifferentiated 
liposarcoma of retroperitoneum and mesentery: varied growth pat-
terns and histological grades--a clinicopathologic study of 32 cases. 
Hum Pathol. 2000; 31:717-727.
5. Matsumoto K, Takada M, Okabe H, Ishizawa M. Foci of signal intensi-
ties different from fat in well-differentiated liposarcoma and lipoma: 
correlation between MR and histological findings. Clin Imag. 2000; 
24:38-43.
6. Singer S, Antonescu CR, Riedel E, Brennan MF. Histologic subtype 
and margin of resection predict pattern of recurrence and survival for 
retroperitoneal liposarcoma. Ann Surg. 2003; 238:358-370.
7. Pereira JM, Sirlin CB, Pinto PS, Casola G. CT and MR imaging of 
extrahepatic fatty masses of the abdomen and pelvis: techniques, diag-
nosis, differential diagnosis, and pitfalls. Radiographics. 2005; 25:69-
85.
8. Tateishi U, Hasegawa T, Beppu Y, Satake M, Moriyama N. Primary 
dedifferentiated liposarcoma of the retroperitoneum. Prognostic sig-
nificance of computed tomography and magnetic resonance imaging 
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Omental well-differentiated liposarcoma: US, CT and MR findings

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