AJR 2002; 179:797-801
© American Roentgen Ray Society
Synovial Sarcoma in Pediatric Patients
M. Beth McCarville1,2,
Sheri L. Spunt3,4,
Stephen X. Skapek3,4 and
Alberto S. Pappo3,4,5
1 Department of Diagnostic Imaging, Mail Stop 210, St. Jude Children's Research
Hospital, 332 N. Lauderdale St., Memphis, TN 38105-2794.
2 Department of Radiology, College of Medicine, The University of Tennessee
Health Science Center, 800 Madison Ave., Memphis, TN 38163.
3 Department of Hematology—Oncology, St. Jude Children's Research
Hospital, Memphis, TN 38105-2794.
4 Department of Pediatrics, College of Medicine, The University of Tennessee
Health Science Center, Memphis, TN 38163.
5 Present address: Department of Hematology—Oncology, The Hospital for
Sick Children, 555 University Ave., Toronto, Ontario M5G 1x8,
Canada.
Received January 21, 2002;
accepted after revision February 28, 2002.
Supported in part by grant CA-21765 from the National Institutes of Health
and by the American Lebanese Syrian Associated Charities.
Address correspondence to M. B. McCarville.
Introduction
Although rare, synovial sarcoma is the most common malignant
non-rhabdomyosarcomatous soft-tissue sarcoma in children and adolescents.
Despite its name, synovial sarcoma does not appear to arise from the synovial
membrane but rather from primitive mesenchymal cells. Synovial sarcoma has
been classically described as occurring in the soft tissues of the
extremities, especially near large joints, but it can occur anywhere in the
body in locations distant from joint spaces. Although this tumor typically
affects adults in their fourth decade of life, nearly half the reported cases
have occurred in children and adolescents
[1]. Since 1964, 59 patients
from 2 to 22 years old (median, 12.7 years) have been treated at our
institution for synovial sarcoma that arose in the following sites: lower
extremity (n = 35), upper extremity (n = 11), head and neck
(n = 4), groin (n = 2), pelvis (n = 2), and other
sites (n = 5). The purpose of this article is to illustrate the
common and uncommon presentations of this rare childhood malignancy and to
review the clinical features and treatment of this tumor in the pediatric
population.
Imaging Features
Approximately 30% of synovial sarcomas contain calcifications that may be
apparent on radiographs or CT scans
[2] (Fig.
1A,1B).
MR imaging is the modality of choice in evaluating synovial sarcoma because it
provides greater contrast between tumor and normal tissue, can reveal
neurovascular and lymph node involvement, and has multiplanar capabilities. On
MR images, synovial sarcomas tend to be sharply marginated tumors that may
appear to be largely cystic (Fig.
2). Synovial sarcoma may be misdiagnosed as a hematoma, ganglion
cyst, Baker's cyst, or other benign cystic mass. In a review of the MR imaging
features of 34 synovial sarcomas, Jones et al.
[3] reported triple signal
intensity on T2-weighted images in 35% of patients. This pattern consisted of
mixtures of high signal intensity similar to that of fluid, intermediate
signal intensity that was iso- or slightly hyperintense to fat, and slightly
lower signal intensity that resembled fibrous tissue. They also found that
fluid—fluid levels were present in 18% of patients and that tumors
smaller than 5 cm in diameter had homogeneously low signal intensity on
T1-weighted images and marked heterogeneity on T2-weighted images. Further,
Morton et al. [4] described a
heterogenous, multiloculated appearance with various degrees of internal
septations, with or without fluid—fluid levels (Fig.
3A,3B).
Jones et al. reported that 71% of synovial sarcomas were intimately related to
bone, with 50% abutting bone and 21% showing cortical thinning or medullary
invasion (Fig.
4A,4B,4C).
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Fig. 1A. —12-year-old boy with synovial sarcoma who presented with
palpable pelvic mass. Anteroposterior radiograph shows extensively calcified
large pelvic mass. Calcifications are seen in approximately one third of all
synovial sarcomas.
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Fig. 1B. —12-year-old boy with synovial sarcoma who presented with
palpable pelvic mass. Contrast-enhanced axial CT scan of pelvis shows unusual
primary location of synovial sarcoma (arrows). Mixed cystic and solid
appearance of tumor is common in synovial sarcoma and may be due to
hemorrhage, necrosis, or both. B = bladder.
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Fig. 2. —7-year-old boy with synovial sarcoma in left popliteal space.
Sagittal proton density—weighted MR image (TR/TE, 3000/17) shows 4-cm
well-defined cystic soft-tissue mass (M) adjacent to semimembranous tendon
(arrows) of left knee. Most synovial sarcomas, like one shown here,
arise near large joints in lower extremity and involve tendon sheaths, bursae,
or joint capsules. Because masses are often well defined and frequently have
cystic appearance, synovial sarcoma is malignant lesion most commonly
misdiagnosed as benign on MR imaging.
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Fig. 3A. —7-year-old girl with synovial sarcoma originating near right
hip. Contrast-enhanced T1-weighted axial MR image (TR/TE, 710/15) shows
inhomogeneously enhancing mass (arrows) adjacent to right hip. Many
synovial sarcomas, like this one, appear as heterogenous multiloculated masses
with internal septations and may contain fluid—fluid levels. Note
well-defined margins of mass, characteristic of synovial sarcoma seen on MR
images.
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Fig. 3B. —7-year-old girl with synovial sarcoma originating near right
hip. Contrast-enhanced axial CT scan of upper abdomen obtained 6 years after
original diagnosis shows recurrent synovial sarcoma (arrows) in
massively enlarged and necrotic retroperitoneal nodes. Regional nodal spread
is not unusual in synovial sarcoma; however, in this patient no other nodes
were involved between primary site (right hip) and upper retroperitoneum. Case
illustrates unpredictable nature of malignancy.
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Fig. 4A. —9-year-old girl with metastatic synovial sarcoma. Coronal
T1-weighted MR image (TR/TE, 500/9.9) of left knee shows soft-tissue mass
(arrows) interposed between cortex of distal left femur and
iliotibial tract. In one series, 50% of synovial sarcomas abutted bone, and
21% caused cortical thinning or showed medullary invasion
[3].
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Fig. 4B. —9-year-old girl with metastatic synovial sarcoma. Coronal
short tau inversion recovery MR image (3825/30; flip angle, 140°) obtained
after surgical resection and radiotherapy of primary tumor shows genu valgus
deformity caused by effects of therapeutic radiation. Although radiation
therapy provides excellent local control of microscopic residual disease, it
may result in substantial growth disturbance when applied near physeal plate
of growing bone. Note also bright signal in bones of knee, likely due to
radiation-induced ischemia, osteonecrosis, or both.
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Fig. 4C. —9-year-old girl with metastatic synovial sarcoma.
99mTc-labeled methyl diphosphonate nuclear bone scan of skull shows
metastatic focus involving left frontal bone (arrow). Synovial
sarcoma metastasizes to bone in 10-20% of cases.
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Clinical Behavior
Although 85% of synovial sarcomas arise in the extremities, sites in the
head, neck, and trunk can be involved
[1,
5] (Figs.
5,6,7A,7B,8A,8B).
Nonetheless, most lesions are extremity tumors that are paraarticular in
location and may arise from tendon sheaths, bursae, or joint capsules but
seldom involve the articular surface
[1]. The most common presenting
symptom is a painless mass that has been present for several weeks to years in
the soft tissues of the lower extremity
[1]. Four other patterns of
presentation also exist: a pretumor phase of pain and tenderness without a
mass, acute arthritis or bursitis, a chronic contracture, and a tumor noted
after an episode of trauma
[1].
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Fig. 5. —16-year-old boy with synovial sarcoma who presented with
vomiting and dull chest pain. Contrast-enhanced axial CT scan of chest shows
huge, predominantly cystic mass (M) arising from mediastinum that proved to be
synovial sarcoma at biopsy. Cystic and septate appearance of tumor is common
for synovial sarcoma.
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Fig. 6. —15-year-old boy with synovial sarcoma who presented with
right pneumothorax. Preoperative contrast-enhanced axial CT scan of chest
shows right pleural thickening or fluid (arrows). After unsuccessful
treatment of right pneumothorax with thoracostomy tube placement, patient
underwent parietal pleurectomy that revealed synovial sarcoma originating from
pleura. Case shows that tumor may arise nearly anywhere in body.
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Fig. 7B. —17-year-old boy with synovial sarcoma of right cheek.
T2-weighted axial MR image (TR/TE, 3500/120) shows well-circumscribed cystic
mass (arrows) with internal septations, abutting right maxilla. Cheek
is unusual primary location. Synovial sarcoma has also been reported to occur
in infratemporal fossa, external temporal fossa, posterior neck, parotid
region, tongue, and other parts of neck.
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Fig. 8A. —4-year-old girl with synovial sarcoma who presented with neck
pain. Contrast-enhanced T1-weighted axial MR image (TR/TE, 975/20) shows
soft-tissue mass (arrows) in right prevertebral space obtained at
level of first cervical vertebra. In neck, synovial sarcoma has predilection
for prevertebral soft tissues, as in this patient.
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Fig. 8B. —4-year-old girl with synovial sarcoma who presented with neck
pain. Unenhanced axial CT scan of upper neck shows destruction
(arrow) of right anterior arch of first cervical vertebra, which was
not evident on MR image. Although most synovial sarcomas have well-defined
margins on MR imaging, they may invade bone, as shown here.
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Synovial sarcoma most commonly metastasizes to the lung (74-81%), lymph
nodes (12-23%), and bone (10-20%)
[2]. Chest CT is used to detect
pulmonary metastases, and 99mTc-labeled methyl diphosphonate
nuclear bone scanning is used to detect bony metastatic disease. MR imaging is
useful in assessing regional lymphadenopathy.
Pathology and Molecular Biology
Synovial sarcoma occurs in two histologic subtypes: the biphasic type
containing epithelial and spindle cell elements and the monophasic type
containing only spindle cells
[1]. Much insight into the
molecular biology of synovial sarcoma has come from cytogenetic studies
[6]. Synovial sarcoma cells are
characterized by the presence of a translocation involving chromosomes X and
18 [t(X,18) (p11,q11)]. Molecular genetic studies have shown that this
translocation fuses two normal genes, SYT and SSX1 (or the
related SSX2) to create an abnormal fusion protein. The mechanism by
which the SYT—SSX fusion protein confers malignant potential to
the cells is unknown. Recently, retrospective studies have shown that the
presence of the SYT—SSX1 fusion transcript is correlated with
biphasic histology, a higher proliferative rate, and a shortened
metastasis-free survival
[6].
Prognostic Features
Patients with localized synovial sarcoma have a good prognosis and most
become long-term survivors. In contrast, those who have metastatic disease
have a dismal outlook and only a minority survive. The prognostic features
most frequently associated with an unfavorable outcome include tumor size
greater than 5 cm, invasion into bone or neurovascular structures, and high
histologic grade [7,
8]. Older age, nonextremity
primary site, and the biphasic histologic pattern have also been associated
with a less favorable outcome.
Treatment
The optimal approach to the treatment of synovial sarcoma remains undefined
because no prospective clinical trials have compared differing therapeutic
approaches [7,
8]. Complete surgical resection
of the primary tumor is the mainstay of treatment. Adjuvant radiotherapy to
treat microscopic residual disease after surgery provides excellent local
control and obviates amputation for most patients with extremity tumors. The
role of adjuvant chemotherapy remains controversial, and the small number of
randomized prospective trials complicates interpretation of results. Most
regimens that have shown activity in patients with measurable disease include
doxorubicin used with or without an alkylating agent (cyclophosphamide or
ifosfamide). Despite the chemosensitivity of synovial sarcoma, some series
have failed to show a significant improvement in survival with the addition of
chemotherapy. Chemotherapy is probably beneficial only for those with
high-risk features of distant disease recurrence, such as large tumor size,
invasiveness, and high histologic grade. Prospective clinical trials to
evaluate the benefit of adjuvant chemotherapy in the treatment of synovial
sarcoma are needed.
Conclusion
After rhabdomyosarcoma, synovial sarcoma is the most common soft-tissue
sarcoma in children. The tumor does not appear to arise from the synovium and
has the potential to develop almost anywhere in the body. It is characterized
by a consistent molecular genetic abnormality that offers insight into its
biology. Prognosis is good when the tumor is smaller than 5 cm, noninvasive,
and of low or intermediate histologic grade.
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Introduction
Imaging Features
