Keywords
Abdominal wall tumor - soft-tissue sarcoma - synovial sarcoma
Introduction
Synovial sarcoma is a rare malignant mesenchymal tumor. It commonly occurs in adults
in the extremities in close association with joint capsule, tendon sheaths, bursae,
and fascial structures. It is the fourth most common type of soft-tissue sarcoma following
rhabdomyosarcoma, malignant fibrous histiosarcoma, and liposarcoma. Nearly 80%–90%
synovial sarcoma occurs in the extremities in the middle-aged patient, close to large
joint, particularly the knee joint in the popliteal fossa. Synovial sarcoma arising
in the anterior abdominal wall is rare with only 47 cases reported in the literature.
Synovial sarcoma in anterior abdominal wall occurs with greater frequency in females
while synovial sarcoma in extremities or the neck occurs with greater frequency in
males. Primary synovial sarcoma of anterior abdominal wall (SSAW) is a rare extra-articular
tumor site. It should be considered in the differential diagnosis of the anterior
abdominal wall masses.[1]
Case Report
A 40-year old male patient presented with swelling over the anterior abdominal wall
on the right side in lower abdomen for 1 month which was rapidly increasing in size.
There was a history of weight loss. The mass was painless. The ultrasonography showed
a large, well-defined solid mass with lobulated outlines in anterior abdominal wall
in the right paraumbilical and hypogastric region [Figure 1]. The mass was seen in the subcutaneous plane, causing extrinsic compression on adjoining
right rectus abdominis and external oblique muscle. It was predominantly hypoechoic
with small areas of the necrosis in its center and showed mild vascularity on color
Doppler. No calcification was seen. Plain and contrast enhanced computed tomography
(CT)-scan of the abdomen and pelvis was performed. A large, well defined solid mass
with lobulated outline measuring approximately 96 mm × 38 mm × 98 mm in transverse,
anteroposterior and craniocaudal dimension was noted in the anterior abdominal wall
on the right side in right iliac region extending to hypogastric region. It was slightly
hypodense with respect to muscle on the plain study with a CT value of 35–45 HU and
showed a mild heterogeneous enhancement in contrast study (CT value 55–65 HU). No
calcification was noted. The mass was in subcutaneous plane and was extending anteriorly
up the skin. Posteriorly, it was causing mass effect on the right rectus abdominus
and adjoining external oblique and internal oblique muscles which were compressed
and displaced posteriorly with obliteration of intervening fat planes [Figure 2]. An enhancing vessel was noted in the right rectus abdominus extending into the
mass suggestive of neovascularity. No intra-abdominal extension was noted. Rest of
the abdominal wall appeared normal. No hepatic or adrenal metastases, intra-abdominal
lymphadenopathy noted. On magnetic resonance imaging (MRI), the mass appeared slightly
hyperintense with respect to muscle on T1-weighted image, heterogeneously hyperintense
on T2-weighted image (T2WI), and hyperintense on short tau inversion recovery and
showed restricted diffusion on diffusion-weighted imaging with low apparent diffusion
coefficient (ADC) values (ADC = 800). It was causing mass effect on the right rectus
abdominus and adjoining external oblique and internal oblique muscles [Figure 3]
[4]
[5]
[6].
Figure 1: Ultrasound of the anterior abdominal wall with linear probe showing well-defned
solid hypoechoic mass with lobulated outlines in the right iliac fossa in subcutaneous
plane (a) causing extrinsic compression and posterior displacement of abdominal wall
muscles (b)
Figure 2: Computed axial tomography of abdomen - plain (a) and contrast (b) showing
well-definedsolid mass with lobulated outlines in the right iliac fossa and hypogastric
region in subcutaneous plane causing extrinsic compression and posterior displacement
of abdominal wall muscles appearing slightly hypodense on plain study (a) showing
heterogeneous enhancement in contrast (b)
Figure 3: Magnetic resonance imaging of the abdomen - axial T1 (a), axial T2 (b-d)
showing well-definedsolid mass with lobulated outlines in the right iliac fossa and
hypogastric region in subcutaneous plane causing extrinsic compression and posterior
displacement of abdominal wall muscles appearing slightly hyperintense on the T1-weighted
image and hyperintense on T2-weighted image
Figure 4: Magnetic resonance imaging of the abdomen - sagittal T2 (a), coronal T2
(b) showing well-definedsolid mass with lobulated outlines in the right iliac fossa
and hypogastric region in subcutaneous plane causing extrinsic compression and posterior
displacement of abdominal wall muscles appearing hyperintense on T2-weighted image
Figure 5: Magnetic resonance imaging of the abdomen - axial short tau inversion recovery
(a and b) showing well-definedhyperintense solid mass with lobulated outlines in the
right iliac fossa and hypogastric region in subcutaneous plane causing extrinsic compression
and posterior displacement of the abdominal wall muscles
Figure 6: Magnetic resonance imaging of the abdomen - axial diffusion-weighted imaging
(a), apparent diffusion coefficien (b) showing restricted diffusion on diffusion-weighted
imaging with low apparent diffusion coefficient value
Biopsy was suggestive of round cell sarcoma. On immunohistochemistry, tumor showed
predominantly monophasic growth pattern and was composed of spindloid cells arranged
in cellular and hypocellular fashioned. They showed diffuse and strong positivity
for Vimentin, BCL-2, and MIC-2. These cells showed focal priority for CK and EMA and
were negative for SMA, Desmin, and S-100 protein. The findings were suggestive of
monophasic synovial sarcoma.
Discussion
Synovial sarcoma accounts for 8% of all primary soft-tissue malignancy worldwide.
They usually present at 15–40 years of age and frequently seen in adolescent and young
adults. There is no gender, race or ethnic predilection. It presents as a palpable
slow growing mass. Delay in diagnosis often occurs due to gradual onset. Histologically,
they do not resemble synovial structures. They are named so due to the similarity
between synovial sarcoma tumor cells and primitive synoviocytes. Synovial sarcoma
is derived from multipotent stem cells. These can differentiate into mesenchyma and
epithelial structures. Histologically, three subtypes are described-biphasic, monophasic,
and poorly differentiated synovial sarcoma. Monophasic synovial sarcomas the most
common subtype (50%–60%) are entirely composed of spindle cells. Biphasic synovial
sarcoma (20%–30% of cases) has epithelial and spindle cell component in varying proportions.
The epithelial cells classically found are glands. The poorly differentiated synovial
sarcoma (15%–25% of cases) shows small blue round cell morphology with high mitotic
activity. Synovial sarcoma can be graded according to mitotic index, necrosis, and
tumor differentiation. Synovial sarcoma should be usually considered high-grade sarcomas.[2]
Synovial sarcoma is commonly seen in lower extremity in 70% of cases, other rare sites
are head and neck (5%), trunk (8%), and abdomen and retroperitoneum (7%).
Conventional radiography in synovial sarcoma can be normal or shows soft-tissue mass.
Nearly 20% cases show calcifications. Ultrasound appearance is nonspecific and seen
as a solid heterogeneous mass with heterogeneous echotexture with irregular margins.
It helps in USG-guided biopsy. On CT scan, the mass appears as a well-circumscribed
mass with heterogeneous density with attenuation value slightly lower than muscle.
Contrast study often shows heterogeneous enhancement. Small low attenuation areas
were noted within the mass represents the necrosis or cystic changes. Punctate calcification
can be seen in 30% cases, usually in the periphery of the mass. MR imaging is the
modality of choice for its diagnosis. On T1-weighted spin echo MR images, it appears
as a multilobulated soft-tissue intensity heterogeneous mass with signal intensity
equal to or higher that of muscle. On T2-weighted spin echo MR images, the mass appears
heterogeneous with high signal intensity. Areas of hemorrhage, cystic changes, and
fluid levels may be seen. A triple sign may be seen on T2WI showing triple signal
pattern, characterized by intermixed areas of high, intermediate and low-signal intensity.
Aggressiveness of the tumor can be judged by the detection of local invasion such
as muscle invasion, underlying bony involvement, and neurovascular encasement. Contrast-enhanced
MRI shows heterogeneous enhancement pattern.[2]
Only 47 cases of synovial sarcoma of the anterior abdominal wall (SSAW) have been
reported in the English journal.[3] Its incidence is 2.5 per lakhs. Metastases can be seen in 16%–25% cases on initial
presentation, which commonly occurs in lung and less commonly in lymph nodes and bones.
The majority of metastases occurs in the first 2–5 years of treatment. Doppler my
show increase internal vascularity. Although imaging findings of SSAW are not pathognomonic,
eccentric, or peripheral calcification can be seen in 30% of cases. Necrosis and hemorrhage
occur commonly. Ultrasonography can detect a complex honeycomb echotexture.[4] MRI is useful in detecting extension, multilobulation on T2WI, planning treatment,
and tumor response to chemotherapy.[3]
Synovial sarcoma does not arise from synovial membrane, but from unknown multipotent
stem cells. These can differentiate into mesenchymal and epithelial structures and
lack synovial differentiation.
On immunohistochemistry, EMA, cytokeratin AE1/AE2, and E-cadherin in combination CD-34
negativity are useful markers for the diagnosis of synovial sarcoma. BCL-2 and MIC-2
(LD-99) are usually positive in synovial sarcoma.
Triple sign occurs due mixture of solid cellular elements, necrosis or hemorrhage
and fibrotic or calcified lesions with fluid levels and septa creating the bowel of
grapes sign. The triple sign is seen in 35%–57% of synovial sarcoma. The triple sign
can also be seen in other soft tissue tumors, and hence, it is not a specific sign
of synovial sarcoma.
Synovial sarcoma show translocation fusion of two genes (SYT) on the chromosome 19q11
and SSX1, SSX2, or SXX4 located on chromosome Xp11 break point. Monophasic tumors
express either SYT-SSX1 or SYT-SSX2 genetic rearrangement. Biphasic tumors express
SYT-SSX1 fusion proteins and have a higher proliferation rate with poor outcome.[5]
The treatment of choice for synovial sarcoma is a wide local excision with negative
surgical margin to minimize the chance of recurrence. Radiotherapy is useful in local
control of disease in cases of residual tumor. Adjuvant chemotherapy is useful in
disease control and consists of regimes combining cyclophosphamide or ifosfamide (alkylating
agents) and anthracyclines.
There is a high rate of local recurrence (30%–50%) and metastatic disease in synovial
sarcoma. Metastasis occurs in 2–5 years of initial treatment. The 5-year survival
rate is 36% to 76% for intermediate to high-grade synovial sarcoma.
Positive surgical margins, invasiveness, metastasis, poor differentiation, and high
histological grades are indicative of advance prognosis in synovial sarcoma. Size
<5 cm, distal extremity location, age <15 years, monophasic synovial sarcoma, and
SYT-SSX2 gene fusion have better prognostic outcomes.[5]
The differential diagnosis includes desmoid tumor, neurofibroma, neurilemmoma and
fibroma among benign tumors and rhabdomyosarcoma, fibrosarcoma, mesenchymal chondrosarcoma
and metastasis for malignant tumors.[4]
Conclusion
Primary SSAW is a rare extra-articular tumor site. It should be considered in the
differential diagnosis of the anterior abdominal wall masses. MRI is useful in detecting
extension, multilobulation, planning treatment, and tumor response to chemotherapy.
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