Synovial Sarcoma in Children - AJR

Pe d i a t r i c I m a g i n g • P i c t o r i a l E s s ay Bixby et al. Synovial Sarcoma in Children Pediatric Imaging Pictorial Essay

Synovial Sarcoma in Children: Imaging Features and Common Benign Mimics Sarah D. Bixby 1 Simone Hettmer 2 George A. Taylor 1 Stephan D. Voss1 Bixby SD, Hettmer S, Taylor GA, Voss SD

OBJECTIVE. Synovial sarcoma is the most common malignant nonrhabdomyosarcoma soft-tissue sarcoma in children. This article shows examples of synovial sarcoma in children and corresponding examples of benign mimics. CONCLUSION. It is important for radiologists to recognize the often nonaggressive appearance of synovial sarcoma in the pediatric population to guide surgical resection and expedite diagnosis before the development of locoregional spread or metastatic disease.

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Keywords: MRI, pediatric imaging, synovial sarcoma DOI:10.2214/AJR.10.4348 Received January 25, 2010; accepted after revision February 23, 2010. 1 Department of Radiology, Children’s Hospital Boston and Harvard Medical School, 300 Longwood Ave., Boston, MA 02115. Address correspondence to S. D. Bixby ([email protected]). 2 Department of Oncology, Children’s Hospital Boston and Harvard Medical School, Boston, MA.

AJR 2010; 195:1026–1032 0361–803X/10/1954–1026 © American Roentgen Ray Society

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ynovial sarcoma is the most com mon malignant nonrhabdomyosarcoma soft-tissue sarcoma in children and adolescents [1, 2]. Although synovial sarcoma is more commonly seen in adults, with a mean age of 37 years [3], 30–50% of cases occur in patients younger than 20 years old [4–6]. Synovial sarcoma is thought to arise from primitive mesenchymal cells rather than from the synovial membrane as its name implies. Although these tumors can occur anywhere in the body, including locations distant from joint spaces such as the abdominal cavity, approximately 90% of synovial sarcomas in children occur in the extremities [2, 7]. The lower extremity is involved nearly 5 times more often than the upper extremity [7]. Clinically, synovial sarcoma most commonly presents as a painless mass, although it may also present as an area of tenderness and swelling without an obvious mass [7]. Constitutional symptoms are unusual, and the median duration of symptoms before presentation may be quite long, with a mean symptom duration of 98 weeks in one study [7]. Because of this vague, nonspecific clinical presentation, imaging plays an important role in evaluating patients with synovial sarcoma. Imaging Synovial sarcomas show a broad spectrum of imaging features in children, some of which have been illustrated previously by McCarville and associates [8]. Conventional radiography and ultrasound often play an important role in the early diagnostic workup.

However, MRI is the imaging technique of choice for evaluating both the primary lesion and the invasion into adjacent soft tissues. The common MRI features of synovial sarcoma in adults have been described [9–11]. In children, synovial sarcoma often shows a deceptively nonaggressive appearance on MRI and may mimic a benign process such as a vascular malformation, benign nerve sheath tumor, or inflammatory arthritis. Because synovial sarcomas commonly have a variable appearance on MRI and may present as small tumors with a smooth surface and without invasion of adjacent structures, they may be difficult to distinguish from benign lesions, thereby making it challenging to arrive at the correct preoperative diagnosis. Preoperative staging of biopsy-confirmed synovial sarcoma is helpful in assessing for local, regional, and metastatic spread of disease, which is essential in determining overall patient prognosis. The most common site for metastatic disease is the lung, followed by bone and lymph nodes [3]. Fluorine-18 FDG PET plays an increasingly important role in staging synovial sarcoma. These tumors are typically FDG-avid, and radiographically occult metastatic disease and locoregional spread may be readily detected on wholebody PET [12]. Important factors to consider before surgery include the location of the mass at proximal versus extremity sites, local invasion into bone or neurovascular structures, and tumor size greater than 5 cm; all of these factors have negative prognostic implications and may warrant adjuvant chemotherapy [4]. There is a significant difference in

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Synovial Sarcoma in Children metastasis-free survival that has been shown for patients with tumors smaller than 5 cm [3, 4]. In patients with metastatic disease, 5-year survival is estimated to be 10% of patients [3], emphasizing the importance of early detection and recognition of this tumor. Radiography Conventional radiography is often the first study performed. Radiographs may suggest the presence of a soft-tissue mass and also can identify subtle periosteal reaction and local bone invasion. Calcifications, which are unusual in other extremity soft-tissue sarcomas, are seen in approximately 30% of the cases of synovial sarcoma [13] and their presence should increase one’s level of suspicion that a lesion could be a synovial sarcoma (Fig. 1). Ultrasound Ultrasound is helpful in distinguishing solid from cystic masses. In particular, popliteal cysts (Fig. 2), ganglion cysts, and other peripheral or extremity cystic lesions can be readily distinguished from both benign and sarcomatous soft-tissue masses by ultrasound, obviating additional imaging. For noncystic soft-tissue masses, biopsy is usually required to make a diagnosis. Blood flow characteristics can also be evaluated through the use of Doppler ultrasound, although these findings are rarely discriminatory. Ultrasound plays a complementary role to MRI given that septations can occur within synovial sarcomas [5, 11], and ultrasound helps clarify whether the mass is solid or cystic when septations are present (Fig. 3). MRI MRI is the study of choice in further evaluating a child with a soft-tissue mass. MRI shows superior contrast resolution between the mass and adjacent soft tissues and is helpful in evaluating the relationship of the mass to adjacent structures such as the joint space, neurovascular bundle, and bone. Characteristic MR features of synovial sarcoma include a well-circumscribed lesion, often smaller than 5 cm, with bright, diffuse inhomogeneous patterns of enhancement [10] (Fig. 4). The lesions are most often localized to the deep, rather than the superficial, soft tissues [11] (Figs. 5 and 6). Although synovial sarcomas are typically juxtaarticular tumors, they occasionally arise in a joint [14] (Fig. 7). If present, calcifications within the lesion manifest as areas of low signal intensity on T1- and T2-weighted images [11] (Fig. 1).


Most synovial sarcomas are predominantly T2-bright, although approximately one third of lesions show a triple-signal pattern on T2weighted images [15]. The latter pattern consists of mixtures of fluid-signal-intensity, intermediate-signal-intensity, and low-signal-intensity components (Fig. 6). Septations within the lesion may also be noted [5, 11] (Fig. 8). Susceptibility-weighted sequences may be useful in showing blood products, aiding in the distinction of synovial sarcoma from vascular malformations, such as a venous malformation, that often have an imaging appearance similar to synovial sarcoma. Discrimination between benign lesions and malignant lesions in children, however, is often difficult with MRI alone. Synovial sarcomas can present with MR features such as small size, smooth contours, lack of invasion into adjacent structures, and homogeneous signal characteristics; these findings often suggest a nonaggressive lesion and contribute to diagnostic uncertainty. Because most synovial sarcomas enhance inhomogeneously after contrast administration, any MR examination showing a soft-tissue lesion should include IV contrast administration with contrast-enhanced imaging to optimize diagnostic accuracy unless the lesion is clearly shown to be a simple cyst, either by ultrasound or based on location and unequivocal MR signal characteristics—that is, uniformly bright signal intensity on fluidsensitive sequences and loss of signal on corresponding fluid-attenuated sequences. Summary Although the diagnosis of synovial sarcoma must be established by biopsy, it is important for radiologists to recognize the nonaggressive appearance that is often associated with synovial sarcoma in children. It is critical to pay careful attention to imaging details that may suggest synovial sarcoma at MRI. MR evaluation of a soft-tissue mass in a child should include fluid-sensitive sequences and contrast-enhanced imaging. It is important to recognize that synovial sarcomas often show bright signal intensity on fluid-sensitive sequences, although these lesions are rarely as bright as simple cyst fluid. In contrast to purely cystic lesions, synovial sarcomas enhance after contrast administration. Susceptibility-weighted sequences (i.e., gradient refocused-echo sequences) may be helpful in distinguishing a mass from a venous malformation. Low signal on T1- and T2-weighted imaging sequences may indi-

cate the presence of calcifications, which can be confirmed on radiography. Ultrasound can be invaluable in discriminating between potentially malignant solid masses, such as synovial sarcoma, and benign cystic lesions. This article illustrates multiple examples of synovial sarcomas in children that have deceptively nonaggressive imaging features on MRI. They are shown together with their common benign mimics, including nodular synovitis, venous malformation, desmoid tumor, inflammatory arthritis, schwannoma, and nodular synovitis. With this knowledge, practicing radiologists are less likely to mistake these lesions for other benign soft-tissue lesions. References 1. McGrory JE, Pritchard DJ, Arndt CA, et al. Nonrhabdomyosarcoma soft tissue sarcomas in children: the Mayo Clinic experience. Clin Orthop Relat Res 2000; 374:247–258 2. Dillon P, Maurer H, Jenkins J, et al. A prospective study of nonrhabdomyosarcoma soft tissue sarcomas in the pediatric age group. J Pediatr Surg 1992; 27:241–245 3. Palmerini E, Staals EL, Alberghini M, et al. Synovial sarcoma. Cancer 2009; 115:2988–2998 4. Sultan I, Rodriguez-Galindo C, Saab R, Yasir S, Casanova M, Ferrari A. Comparing children and adults with synovial sarcoma in the Surveillance, Epidemiology, and End Results program, 1983 to 2005: an analysis of 1268 patients. Cancer 2009; 115:3537–3547 5. Tateishi U, Hasegawa T, Beppu Y, et al. Synovial sarcoma of the soft tissues: prognostic significance and imaging features. J Comput Assist Tomogr 2004; 28:140–148 6. Lee SM, Hadju SI, Exelby PR. Synovial sarcoma in children. Surg Gynecol Obstet 1974; 138:701–704 7. Chotel F, Unnithan A, Chandrasekar CR, et al. Variability in the presentation of synovial sarcoma in children: a plea for greater awareness. J Bone Joint Surg Br 2008; 90:1090–1096 8. McCarville MB, Spunt SL, Skapek SX, et al. Synovial sarcoma in pediatric patients. AJR 2002; 179:797–801 9. Morton MJ, Berquist TH, McLeod RA, Unni KK, Sim FH. MR imaging of synovial sarcoma. AJR 1991; 156:337–340 10. Blacksin MF, Siegel JR, Benevenia J, et al. Synovial sarcoma: frequency of nonaggressive MR characteristics. J Comput Assist Tomogr 1997; 21: 785–789 11. Mahajan H, Lorigan JG, Shirkhoda A, et al. Synovial sarcoma, MR imaging. Magn Reson Imaging 1989; 7:211–216 12. Kleis M, Daldrup-Link H, Matthay K, et al. Diagnostic value of PET/CT for the staging and restag-

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Bixby et al. ing of pediatric tumors. Eur J Nucl Med Mol Imaging 2009; 36:23–36 13. Cadman NL, Soule EH, Kelly PJ. Synovial sarcoma: an analysis of 34 tumors. Cancer 1965;

18:613–627 14. Murphey MD, Gibson MS, Jennings BT, et al. From the archives of the AFIP: imaging of synovial sarcoma with radiologic–pathologic correla-

tion. RadioGraphics 2006; 26:1543–1565 15. Jones BC, Sundaram M, Kransdorf MJ. Synovial sarcoma: MR imaging findings in 34 patients. AJR 1993; 161:827–830

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Fig. 1—Synovial sarcoma mimicking giant cell tumor of tendon sheath. A, Radiograph of ankle in 15-year-old boy who presented with ankle stiffness shows small calcified nodular density (arrow) anterior to ankle joint. B, MR image of same patient as in A shows small well-defined lesion (arrow) deep in relation to extensor tendons that has bright signal on T2-weighted image with intrasubstance low signal corresponding to calcifications. This lesion is synovial sarcoma. C, In contrast, MR image of ankle in 12-year-old girl who presented with palpable ankle mass shows well-defined lesion (arrow) anterior to ankle joint that has moderate, heterogeneously bright signal on T2-weighted image and that enhanced heterogeneously after contrast administration on T1-weighted fat-suppressed image (not shown). This mass is giant cell tumor of tendon sheath. Presence of calcifications on radiographs is important secondary sign of synovial sarcoma in this case.

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Fig. 2—Synovial sarcoma mimicking popliteal cyst. A, Radiograph of knee in 15-year-old boy with lump in back of knee shows coarse soft-tissue calcifications (arrows) in popliteal fossa. B, MR image of knee reveals lobular mass (arrows) within popliteal fossa that has bright signal on fluid-sensitive sequence with areas of interspersed dark signal representing calcifications. C, Lesion (arrows) enhances avidly after contrast administration and evidence of multiple nonenhancing septations is seen on this T1-weighted fat-suppressed image in same patient shown in A and B. This mass is synovial sarcoma. (Figure 2 continues on next page)

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Synovial Sarcoma in Children Fig. 2 (continued)—Synovial sarcoma mimicking popliteal cyst. D and E, In contrast, MR image of knee in 3-year-old boy with palpable popliteal mass shows sharply circumscribed lobular lesion (arrow) within popliteal fossa insinuating between semimembranosus muscle (SM, D) and medial head of gastrocnemius muscle (MG, D) that is bright on T2-weighted image (D) and enhances peripherally after contrast administration with no central enhancement (E). This lesion is popliteal cyst. This case shows several important imaging features of synovial sarcoma including presence of soft-tissue calcifications on radiographs and avid enhancement of mass after contrast administration, features that are both lacking in example of popliteal cyst. (Reprinted with permission from Voss SV. Diagnostic Imaging in the evaluation of childhood cancer. In: Orkin S, Fisher D, Look AT, Ginsburg D, Nathan D, eds. Oncology of infancy and childhood. Philadelphia, PA: Saunders, 2009:1018–1021)

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Fig. 3—Synovial sarcoma mimicking nodular fasciitis. A, MR image of knee in 9-year-old boy who presented with complaint of left knee pain for 9 months’ duration shows large multilobular soft-tissue mass (arrows) that is heterogeneously bright on T2-weighted sequence and has multiple septations and areas of intrasubstance fluid signal (arrowhead). B, Lesion (arrows) enhances heterogeneously after contrast administration as shown on this T1weighted fat-suppressed image, whereas areas of fluid signal (arrowhead) on T2-weighted image (A) do not enhance. C, Ultrasound image reveals lobular, hypoechoic solid mass (arrowheads) with internal vascularity. D, FDG PET image shows mass (arrow) to be highly FDG avid. This mass is synovial sarcoma. E, In contrast, MR image of knee in 12-year-old girl with enlarging mass along medial knee shows round well-circumscribed soft-tissue mass (arrow) in medial soft tissues that is bright on T2-weighted images (not shown) and that enhances rather inhomogeneously after IV contrast administration, as shown on this T1-weighted fat-suppressed image. This mass proved to be nodular fasciitis at biopsy. Although biopsy is ultimately required for diagnosis, multiple septations within lesion and presence of FDG uptake on PET are features of synovial sarcoma that may suggest correct diagnosis.


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Fig. 4—Synovial sarcoma mimicking desmoid tumor. A and B, MR images of 14-year-old girl who presented with palpable lump on foot shows lobular mass (arrows) along plantar aspect of foot, insinuating between first and second metatarsals. Mass is bright on T2-weighted image (A) and enhances inhomogeneously after contrast administration on T1-weighted fat-suppressed image (B). This mass is synovial sarcoma. C, In contrast, MR image of foot in 3-year-old girl who presented with palpable lump on foot shows lobular mass (arrows) between first and second metatarsals that enhances homogeneously after contrast administration with bright signal on fluid-sensitive images (not shown). This mass is desmoid tumor. These tumors were nearly identical at imaging and biopsy was ultimately required for diagnosis. Location and solid nature of lesions would make both masses concerning for synovial sarcoma.

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Fig. 5—Synovial sarcoma mimicking venous malformation. A and B, MR image of 11-year-old boy with lump on arm for 2 years that has now become painful shows well-circumscribed oblong mass (arrows) deep to superficial fascia that is isointense to muscle on T1-weighted images (A) and bright on T2-weighted image, although not as bright as joint fluid within adjacent elbow (B). No contrast material was administered. This mass is synovial sarcoma. C, In contrast, MR image of arm in 16-year-old boy with long-standing painless mass on arm shows small lobular mass (arrow) within superficial soft tissues along anterior aspect of distal arm that is bright on T2-weighted images (not shown) and that enhances homogeneously after contrast administration on T1-weighted fatsuppressed sequence. This mass is venous malformation. Although not performed in this case, ultrasound may have been helpful in showing solid nature of synovial sarcoma versus cystic and vascular nature of venous malformation.

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Fig. 6—Synovial sarcoma mimicking schwannoma. A, MR image of 3-year-old boy with forearm pain for 3 years shows well-circumscribed lobular mass (arrow) within deep soft tissues that is heterogeneously bright on T2weighted image with focal areas of intermediate and decreased signal intensity. B, Lesion (arrow) enhances inhomogeneously after contrast administration on this T1-weighted fat-suppressed image. C, Color Doppler ultrasound image shows smoothly marginated, hypoechoic soft-tissue mass with internal vascularity. This mass is synovial sarcoma. D, In contrast, MR image of ankle on 6-year-old boy with palpable lump above ankle shows lobular superficial soft-tissue mass (arrow) posteromedial to tibia that is homogeneously bright on T2-weighted images (not shown) and that enhances homogeneously after contrast administration on T1-weighted fat-suppressed image. This mass is schwannoma. Although these lesions appear similar, synovial sarcoma often shows triple-signal pattern on T2-weighted images, as in this case, and tends to be located within deep, rather than superficial, soft tissues.


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Fig. 7—Synovial sarcoma mimicking inflammatory arthritis. A, MR image of knee in 15-year-old girl who presented with knee pain shows large joint effusion that is bright on T2-weighted sequence with intermediate-signal nodularity (arrow) within joint fluid inferior to patella. B, After contrast administration, there is diffuse enhancement of synovium as well as nodular intraarticular masses (arrow) on this fat-suppressed T1-weighted image. This is synovial sarcoma. C, In contrast, MR image of knee in 17-year-old girl with knee swelling shows large joint effusion with diffuse enhancement of thickened synovium with no nodular areas of enhancement on this fat-suppressed T1-weighted image. This is inflammatory arthritis. Although intraarticular synovial sarcoma is rare, presence of solid, enhancing nodular tissue within joint is clue to correct diagnosis.

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Fig. 8—Synovial sarcoma mimicking nodular synovitis. A, Radiograph of knee in 10-year-old boy with lump on knee for 8 months shows soft-tissue mass (arrow) adjacent to lateral femoral condyle with focal calcification. B and C, MR images reveal lobular, well-circumscribed mass (arrow) with multiple septations and bright signal intensity on T2-weighted image (B) and heterogeneous enhancement after contrast administration on T1weighted fat-suppressed image (C). This is synovial sarcoma. D, In contrast, MR image of knee in 17-year-old girl with knee swelling shows oblong lesion (arrows) along lateral joint margin in region of iliotibial band that enhances homogeneously after contrast administration on this fat-suppressed, T1-weighted image. This is nodular synovitis. Presence of soft-tissue calcifications on radiographs and avid, inhomogeneous contrast enhancement of lesion at MRI are important imaging features of synovial sarcoma in this case.
