We review the clinical and radiological findings of the sarcomas located in the abdomen,
pelvis and abdominal wall,
showing the most representative cases of our hospital in the last 5 years.
1.
Radiologic Evaluation of Soft-Tissue Sarcomas
Ultrasonography may be used as an initial technique during the evaluation of patients with abdominal complaints or palpable abdominal wall masses.
Computed Tomography (CT) is the most widely used cross-sectional imaging modality for the abdomen and pelvis because of its availability,
ease of use,
and capability to get anatomic images for staging.
Can be used to define tissue components and establish a differential diagnosis.
Offers multiplanar reconstructions to study the anatomic site of origin of a mass and its relationship to adjacent organs and vasculature.
Magnetic Resonance (MR) imaging is a complement to CT for tissue characterization.
May help in assessing local invasion for staging,
but is less practical for overall staging because it is more difficult to image the entire body.
Combined imaging with Positron Emission Tomography and CT (PET-CT) is useful for identifying distant metastases.
2.
Most Common Sarcomas of the Abdomen and Pelvis
2.1. LIPOSARCOMA
The tumours that form this group are distinctly different and they vary in biologic behaviour.
Is the most common sarcoma in adults and the most commonly occurring sarcoma in the retroperitoneum.
Well-differentiated liposarcoma (40-45%),
it occurs in middle-aged and older adults.
Does not metastasize but it may progress into a dedifferentiated liposarcoma and then obtain the capability to metastasize.
Myxoid liposarcoma (30-40%),
it occurs almost exclusively in the extremities in a young adult population.
Does not usually occur as a primary tumour in the retroperitoneum.
Pleomorphic liposarcoma (5%),
it occurs with a male predominance in older adults.
Is extremely rare in the retroperitoneum.
Clinical symptoms are most often related to tumour size and because most liposarcomas occur in the retroperitoneum,
they are clinically silent until they grow.
Radiologic Findings.
Well-differentiated liposarcoma:
- Well-defined mass demonstrating fat attenuation at CT.
At MR imaging has high signal intensity on T1 and T2 weighted,
and loses signal intensity on fat-suppressed images.
- Is generally round/oval and exerts mass effect on adjacent normal anatomic structures.
- In the retroperitoneum frequently grows longitudinally and centripetally.
- The non-fat component demonstrates soft-tissue attenuation on CT and has a variable degree of high signal intensity on T2-weighted MR images.
- May contain thin or irregular septa,
minor nodular soft-tissue components,
and thin blood vessels.
The septa may enhance after administration of intravenous contrast material,
but in general,
is a tumour poorly vascularized with little or no enhancement.
- Myxoid components demonstrate water attenuation on CT images,
low signal intensity on T1-weighted MR images,
and high signal intensity on T2-weighted.
Fig. 1
Dedifferentiated liposarcomas:
- Heterogeneous solid soft-tissue masses on CT and MR images.
- Frequently contain regions of well-defined fat and myxoid areas.
- Calcification and ossification may be present.
- A sharp demarcation between fatty and nonfatty elements is characteristic on CT or MR images.
In some cases,
the fat component predominates,
which is suggestive of dedifferentiation within a well-differentiated liposarcoma.
Fig. 2
Myxoid liposarcoma:
- Contains an abundant myxoid matrix with a high water content that is hypoattenuating on CT images,
hypointense on T1-weighted MR images,
and hyperintense on T2-weighted.
- Enhancement of the myxoid matrix is important to distinguish it from a cystic mass.
- Thick enhancing septa characteristically course through the mass.
Pleomorphic liposarcoma:
- Poorly defined soft-tissue mass with no distinguishing features on CT and MR images.
- Areas of low-attenuation heterogeneity on CT represent degeneration,
necrosis,
or intratumoral haemorrhage.
- Fatty elements are not depicted on CT and MR images.
The imaging pattern of the recurrent tumour is usually similar to the pattern that was seen in the initial mass.
When distant metastases occur,
they most commonly arise in the lungs and liver.
Fig. 3
2.2 LEIOMYOSARCOMA
Are soft-tissue sarcomas with tumour cells resembling differentiated smooth muscle cells.
The retroperitoneum is the most common locations,
and many of these tumours arise from the inferior vena cava (IVC) or other veins.
Has female predominance.
Middle-aged and older adults are the most commonly affected.
Is the second most common retroperitoneal sarcoma.
May also rarely arise in the peritoneal cavity and the abdominal wall.
They can grow to large sizes before causing clinical symptoms.
Radiologic Findings.
- On CT images,
are characteristically heterogeneous because of the enhancement of solid portions of the tumour admixed with nonenhancing areas of degeneration,
haemorrhage,
and necrosis.
- At MR imaging,
do not have specific findings.
Is most often iso-hypointense relative to skeletal muscle on T1-weighted,
heterogeneously hyperintense on T2-weighted,
and heterogeneously enhancing after intravenous contrast material administration.
- Does not contain fatty elements.
- Calcification is an uncommon finding.
- Leiomyosarcomas arising from major veins may manifest as an intraluminal mass,
an extraluminal mass,
or both.
- Tumour arising in the abdominal wall muscles tend to be smaller at the time of diagnosis.
Consequently,
usually demonstrate homogeneous attenuation and signal intesnsity at CT / MR imaging,
lacking necrosis and haemorrhage
Retroperitoneal and IVC leiomyosarcomas have a high recurrence rate.
Fig. 4
2.3 GASTROINTESTINAL STROMAL TUMOUR (GISTs)
Are the most common mesenchymal neoplasms of the gastrointestinal tract.
Most commonly found in older adults.
There is no race or gender predilection.
Approximately 60%–70% arise in the stomach,
followed by the duodenum and small bowel.
They can be from benign indolent lesions to highly aggressive malignancies.
Malignant GISTs are the most common intraperitoneal sarcomas,
and these tumours also occur in the retroperitoneum,
given the retroperitoneal location of parts of the gastrointestinal tract.
The clinical signs and symptoms depend on tumour location and size.
Radiologic Findings.
- Are well-circumscribed at cross-sectional imaging.
- Most GISTs arise from the muscularis propria of the stomach and intestine,
finding an attachment to them.
May be purely intramural or may have a variable intraluminal or extraluminal component.
- When an extraluminal component is present,
the tumour extends beyond the serosal surface into the peritoneal cavity and may directly invade adjacent organs and tissues.
- If no attachment can be identified,
GIST should still be considered because may be extraintestinal,
or it may lose its pedicle of attachment.
- A minority are primary to the omentum,
peritoneal cavity,
or retroperitoneum.
- On nonenhanced CT images,
GIST is usually isoattenuating to muscle.
After administration of intravenous contrast material,
shows variable enhancement.
Smaller tumours may have homogeneous enhancement.
Large GISTs commonly have intratumoral degeneration,
haemorrhage,
and necrosis that cause a more heterogeneous pattern.
- Calcification may be seen at CT,
and there is no distinctive pattern.
Metastatic disease occurs most commonly in the liver and peritoneal cavity.
Fig. 5
Fig. 6
Fig. 7
3.
Less Frecuent Sarcomas of the Abdomen and Pelvis
3.1 FIBROBLASTIC / MIOFIBROBLASTIC TUMOURS
3.1.1 Dermatofibrosarcoma Protuberans
It is a locally aggressive surface neoplasm that arises in the dermis or subcutaneous tissue.
Progression to fibrosarcoma occurs in 10%–15% of cases.
Most often occurs in young to middle-aged adults and is more common in blacks and in women.
The trunk wall (50%) and proximal extremities are the most common locations.
It grows slowly and indolently for several years before beginning a phase of rapid growth,
developing its characteristic protruding appearance.
Radiologic Findings.
- Dermatofibrosarcoma protuberans is in the skin and may extend into the subcutaneous fat,
wit occasional deep lesions.
- On CT images demonstrates soft-tissue attenuation with variable enhancement after intravenous contrast administration.
- At MR imaging,
the tumour is isointense or hyperintense relative to skeletal muscle on T1 weighted and is isointense or hyperintense relative to the adjacent fat on T2 weighted.
Fat-suppressed T2 weighted sequences are helpful to see the extent of the lesion because of its high signal intensity on MR images.
- Linear extensions into the skin and satellite nodules may also be seen.
Has a high local recurrence rate if the lesion is not excised with a wide margin.
3.1.2 Solitary Fibrous Tumour (hemangiopericytomas).
It is most common in adults aged 20–70 years.
Typically arises in deep soft tissues (thigh,
retroperitoneum,
pelvis,
and pleura).
Clinically is a slow-growing painless mass.
Radiologic Findings.
- Is seen as a sharply marginated mass.
- May be single or may form multiple masses.
- May show intense enhancement in the arterial phase and persistence of enhancement in the portal venous and delayed phases.
This has been correlated to highly vascular cellular areas within the tumour.
- Cystic areas may be present,
such that the lesion resembles a GIST or leiomyosarcoma.
In the retroperitoneum and pelvis tend to behave aggressively.
Local recurrence and distant metastases to the lung,
bone,
and liver may be seen.
Fig. 8
3.2 MALIGNANT PERIPHERAL NERVE SHEATH TUMOUR (MPNST)
Is typically a high-grade sarcoma that usually arises in a neurofibroma or a nerve trunk.
Previously known as neurofibrosarcoma,
malignant schwannoma,
and neurogenic sarcoma.
Approximately 50% occur in patients with neurofibromatosis type 1,
10% are radiation induced,
and the remainder of them occur sporadically.
The mean age at diagnosis is 35 years.
MPNST is seen in a variety of locations.
The paraspinal regions of the retroperitoneum are the most common location in the abdomen and pelvis.
Radiologic Findings.
- On CT and MR images,
is characteristically a large aggressive tumour with well-defined or ill-defined margins.
- Is typically heterogeneous before and after administration of intravenous contrast.
- May invade and infiltrate into adjacent organs and tissues and erode bone.
Are highly aggressive sarcomas with poor survival rates.
3.3 RHABDOMYOSARCOMA
Are malignant tumours with exclusively skeletal muscle differentiation.
They are the most common sarcomas of childhood and are rare in adults.
Radiologic Findings.
- The imaging data in adults are limited,
reflecting the rarity of these tumours.
- In the perineal regions (vulva / paratesticular) are infiltrating masses with poorly defined borders.
- In the retroperitoneum are large masses at the time of clinical presentation.
- On CT images are predominantly isoattenuating to skeletal muscle.
They may have areas of degeneration and haemorrhage.
- At MR imaging the lesions are isointense to skeletal muscle on T1 weighted and demonstrate high signal intensity on T2 weighted.
- Calcification is not frequent.
Lymphadenopathy is an important feature of metastatic disease.
The lung is the most common site for distant metastatic disease.
3.4 VASCULAR SARCOMAS
Are exceedingly rare in the soft tissues of the abdomen and pelvis.
3.4.1 Epithelioid hemangioendothelioma
3.4.2 Angiosarcomas
3.5 CHONDRO-OSSEOUS SARCOMAS
Composed of malignant cells that produce osteoid matrix.
Occurs predominantly in older patients.
May be seen in the retroperitoneum but is more common in the thigh and buttocks.
The imaging diagnosis is based on observing a chondroid or osseous matrix within a retroperitoneal soft-tissue mass at CT.
3.6 SARCOMAS OF UNCERTAIN DIFFERENTIATION
Represent less than 1% of all soft-tissue sarcomas.
Includes:
- Synovial sarcoma,
epithelioid sarcoma,
alveolar soft part sarcoma,
clear cell sarcoma of soft tissue,
extraskeletal myxoid chondrosarcoma,
extraskeletal Ewing sarcoma,
desmoplastic small round cell tumour,
extrarenal rhabdoid tumour,
and malignant perivascular epithelioid cell tumour (also called “PEComa”).
The imaging features are nonspecific,
and they may occur in the retroperitoneum and abdominal wall and,
very rarely,
in the peritoneal cavity.
3.7 UNDIFFERENTIATED / UNCLASSIFIED SARCOMAS
20% of soft-tissue sarcomas show no lines of differentiation and are classified as undifferentiated sarcomas.
These lesions are most often undifferentiated pleomorphic sarcoma (previously known as pleomorphic malignant fibrous histiocytoma).
Usually occurs in older adults.
Men account for two-thirds of cases,
and is more common in white subjects.
Approximately 15% arise in the abdomen and pelvis.
Is the most common sarcoma to develop at sites of prior irradiation.
Radiologic Findings.
- On CT images are well-circumscribed,
multinodular,
or infiltrating masses of soft-tissue attenuation.
- Are often large at the time of diagnosis and invade adjacent structures.
- After administration of intravenous contrast material,
the enhancement is variable and large intratumoral vessels may be seen.
Centrally areas of low-attenuation necrosis,
haemorrhage,
or myxoid change can be seen.
- Calcification from osseous or chondroid metaplasia occurs in approximately 16% of cases.
- Hemoperitoneum from tumoral haemorrhage has been reported.
Fig. 9
4. Differential Diagnosis
The anatomic location and the CT attenuation and/or MR imaging signal intensity are the most important factors to consider when establishing a radiologic differential diagnosis.
Of these factors,
the finding of FAT WITHIN THE LESION is very important because liposarcoma is the most common retroperitoneal sarcoma.
- Other fat-containing masses that may mimic well-differentiated liposarcoma include angiomyolipoma,
myelolipoma,
lipomatosis,
and,
rarely,
mature lipoma.
- Also,
in the differential diagnosis of fatcontaining lesions,
omental infarction and fat necrosis may be masslike and mimic liposarcoma.
Soft-tissue sarcomas with a substantial CYSTIC COMPONENT,
such as GISTs,
can be misdiagnosed as an abscess or evolving hematoma.
MYXOID COMPONENTS in soft-tissue sarcomas show low attenuation on CT images and show high signal intensity on T2 weighted MR images.
These imaging findings may mimic fluid in an abscess,
a resolving hematoma,
a seroma,
or a cystic mass such as a lymphangioma.
- In the mesentery and abdominal wall,
desmoid tumours can have a myxoid or soft-tissue stroma and appear similar to a soft-tissue sarcoma.
CALCIFICATION can be seen in dedifferentiated liposarcoma,
GIST,
and pleomorphic undifferentiated sarcoma.
- Calcifications are also seen in common abdominal malignancies such as mucinous adenocarcinoma of ovarian,
colorectal,
pancreatic,
or gastric origin.
The classic mucinous calcification is a dot-dash pattern in a hypoattenuating mass.
- Treated lymphoma,
metastatic carcinoid,
teratomas,
and sclerosing mesenteritis may also contain calcification.
In these diseases,
the soft-tissue component and associated findings typical of the disease are distinguishing features.
In general,
a SOFT-TISSUE MASS IN THE RETROPERITONEUM that is not associated with a retroperitoneal organ should be considered a sarcoma until proven otherwise.
- The lymphoma may manifest as a primary retroperitoneal mass,
but it shows homogenous CT attenuation and homogeneous MR signal intensity,
since they lack degeneration and / or necrosis.
Splenomegaly and regional or distant adenopathy may also be present to support the diagnosis.
- Abscesses or phlegmons can simulate tumours.
- Retroperitoneal haemorrhage can also be masslike.
On the INTRAPERITONEAL SOFT-TISSUE MASSES it may be more difficult to determine if the mass is arising from the soft tissues or the gastrointestinal tract.
Special differential diagnostic considerations are given for those LESIONS ARISING IN THE ABDOMINAL WALL.
- The differential diagnosis for skin lesions such as dermatofibrosarcoma protuberans includes cutaneous and subcutaneous metastasis,
nerve sheath tumours,
sebaceous cysts and hemangiomas.
- The differential diagnosis for deep lesions of the abdominal wall includes desmoid tumour,
endometriosis,
and metastatic disease.