Primary intra-abdominal synovial sarcoma
Surgical exploration revealed a lobulated fleshy mass with solid
and cystic areas and few regions of osseous consistency. The mass
appeared to be arising from the psoas muscle tendon sheath.
Debulking of the tumor was attempted and chemotherapy was
initiated. Following gross and histopathologic examination, a
diagnosis of synovial sarcoma arising from the tendon of the psoas
muscle was made.
A CT scan performed at the 6-month follow-up revealed recurrent
soft tissue masses in the postoperative tumor bed and in other
sites within the abdomen (the left subphrenic region, the lesser
sac, the left renal fossa, and the perisplenic region) (Figure 3).
Contiguous invasion of adjacent organs (the left kidney, the
pancreatic tail, and the spleen) was noted. Compared with previous
scans, the tumor masses showed more heterogenous enhancement and
confluent necrotic nonenhancing areas. No calcific foci were
identified within the recurrent tumor deposits. Multiple subpleural
cavitating metastatic nodules were also seen in posterobasal
segments of the lungs bilaterally (Figure 4). The patient died
within 3 months of the follow-up scans.
Radiographs of the abdomen showed a soft tissue mass with clumps of
calcification in the left iliac fossa and lumbar region that were
displacing the colonic gas shadow and small bowel medially (Figure
1). A chest X-ray was performed that showed no abnormality (not
shown). On ultrasound, a large mass was seen in the left lumbar and
iliac fossa region (not shown). The mass showed both solid and
cystic components and hyperechoic areas that were suggestive of
calcification. The left kidney and pancreas were seen separate from
the mass, although posteriorly it appeared to be fixed to the
abdominal wall. The mass was also seen to displace the iliac
vessels anteriorly. Color Doppler flow imaging revealed peripheral
and central vascularity with multiple feeding vessels arising from
the ipsilateral iliac vessels and the aorta (not shown).
Computed tomography (CT) showed a large, heterogeneously
enhancing, lobulated soft tissue mass. Lumps and specks of
calcification and few central, poorly enhancing regions suggestive
of necrosis were seen within the mass (Figure 2A). The tumor was
inseparable from the iliopsoas muscle complex and was seen
predominantly in the left iliac fossa and lumbar region (Figure
2B). Inferiorly and medially the rectosigmoid and descending colon
were displaced medially by the tumor and superiorly the mass
extended up to the lower pole of the left kidney. With these
findings, the possibility of an extraperitoneal tumor likely
originating from the iliopsoas muscle was proposed. No focal
lesions were noted in the liver. There was no evidence of
associated lymphadenopathy or extension in to the intervertebral
The differential diagnosis included primary calcifying
extraperitoneal neoplasms like malignant fibrous histiocytoma,
malignant mesenchymoma leiomyosarcoma, liposarcoma, osteosarcoma,
and, rarely, hemangiopericytoma.
Primary retroperitoneal neoplasms include a diverse pathologic
spectrum of tumors: liposarcoma, leiomyosarcoma, malignant fibrous
histiocytoma, malignant peripheral nerve sheath tumor,
fibrosarcoma, hemangiopericytoma, etc. CT and magnetic resonance
(MR) imaging can depict important characteristics of these tumors.
Sarcomas that arise from the retroperitoneum are rare tumors,
accounting for only 10% to 15% of all soft tissue
Historically, synovial sarcomas are thought to originate from
primitive pluripotent mesenchyme that is capable of synovial
differentiation. This theory is consistent with the origin of the
malignancy from sites devoid of normal synovium, such as the
retroperitoneum, pelvis, head and neck, mediastinum, and pleural
cavity. However, these sites are infrequently reported. The tumor
occurs most often near tendons or tendon sheaths and next to joint
capsules, most commonly affecting the extremities in the vicinity
of large joints. These malignancies typically occur in adolescents
and young adults between 15 and 40 years of age. The reported
5-year survival rates of synovial sarcoma range from 25% to
Synovial sarcomas in the abdominal wall tend to occur with a
much greater frequency in females, which such tumors in the
extremities or the neck tend to occur with a much greater frequency
in males.3 Primary intra-abdominal synovial sarcoma is
rare; there are only approximately 33 previously reported cases.
Most of these cases are retroperitoneal and few have pelvic origin.
Retroperitoneal synovial sarcomas represent approximately 1% of
retroperitoneal tumors and remain confined to the abdomen. Synovial
sarcomas elsewhere do not metastasize remotely. Conversely, tumors
arising from the pelvis often develop remote metastasis to the
lungs. This is supported by the findings in our patient, in whom
the tumor originated in the pelvic sidewall and soon developed
pulmonary secondary sites. This likely reflects the close
relationship of pelvic tumors to skeletal
The most important factor in the recognition of synovial sarcoma
on histopathologic examination is its biphasic pattern-ie, the
presence of both epithelial and spindle cell types; hence, it is
considered a carcinosarcoma. The monophasic synovial sarcomas
consist of spindle cells only.
CT is valuable in detecting aggressive tumors, predicting
resectability, detecting distant metastases, and evaluating
response to treatment. Tumor masses appear large, irregular, and
necrotic with heterogeneous contrast enhancement. MR imaging of
synovial sarcomas reveals a mosaic of mixed low, intermediate, and
high signal intensity on T2-weighted images as a result of the
admixture of solid components, cystic degeneration, hemorrhage,
myxoid stroma, and fibrous tissue (known as the "bowl-of-fruit"
sign). This feature is also seen in other retroperitoneal masses,
such as Ewing's sarcoma, and malignant fibrous histiocytoma, and
is, therefore, nonspecific.5
Primary intra-abdominal synovial sarcoma is a rare aggressive
tumor with high fatality rates. Synovial sarcoma most commonly
affects the extremities, especially the lower thigh and knee
region; other primary sites have been reported infrequently. We
report a rare case of malignant intra-abdominal synovial sarcoma
arising from the pelvic side-wall and review reported cases of
intra-abdominal synovial sarcoma. These tumors should be included
in the differential diagnosis of extraperitoneal masses in young
adults and middle-aged patients.
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- Al-Dewachi HS, Sangal BC, Zakaria MA. Synovial sarcoma of the
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- Fisher C, Folpe AL, Hashimoto H, Weiss SW. Intra-abdominal
synovial sarcoma: A clinicopathological study. Histopathology.
- Nishimura H, Zhang Y, Ohkuma K, et al. MR imaging of
soft-tissue masses of the extraperitoneal spaces. RadioGraphics.