Synovial sarcoma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Synonyms and keywords: Malignant synovioma

Synovial sarcoma (also known as malignant synovioma) is a very rare form of soft tissue sarcoma, which usually occurs near the joints in upper and lower extremities. Synovial sarcoma was first discovered by Pack and Tabah in 1955. Synovial sarcoma may be classified according to histopathological findings into 4 sub-types: biphasic, monophasic fibrous (most common), monophasic epithelial, and poorly differentiated. The pathogenesis of synovial sarcoma is characterized by the dysregulation of gene expression of SYT-SSX gene. The most common locations for the occurrence of synovial sarcoma include Knee, adjacent to large joints, and Popliteal fossa. The SYT-SSX fusion gene (located in chromosome 18) has been associated with the development of synovial sarcoma. There are no established causes for synovial sarcoma. Synovial sarcoma must be differentiated from other diseases that cause joint pain, mass growth, and limited range of motion, such as malignant fibrous histiocytoma (MFH)–fibrosarcoma, Liposarcoma, Osteosarcoma, and Chondrosarcoma. The prevalence of synovial sarcoma remains unknown. Synovial sarcomas account for 2.5 – 10% of all soft tissue sarcomas. Synovial sarcoma is more commonly observed among patients aged 15 – 40 years old. There is no racial predilection for synovial sarcoma. There are no known risk factors associated with the development of synovial sarcoma. There is insufficient evidence to recommend routine screening for synovial sarcoma. The majority of patients with synovial sarcoma remain asymptomatic for years. If left untreated, patients with synovial sarcoma may progress to develop metastases. Prognosis is generally poor, and the median survival rate of patients with synovial sarcoma is approximately 35% to 60%. The diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18). There are no specific laboratory findings associated with synovial sarcoma. Patients with synovial sarcoma usually are well-appearing. There are no specific laboratory findings associated with synovial sarcoma. There are no ECG findings associated with synovial sarcoma. Plain x-ray can be normal unless the tumor is large in size or has dystrophic calcifications. On ultrasound, characteristic findings of synovial sarcoma include heterogeneity and hypo-echoic mass. On CT scan, characteristic findings of synovial sarcoma include Soft tissue mass, calcifications, and Heterogeneous density and enhancement. MRI is the imaging modality of choice for synovial sarcoma. Medical therapy include Doxorubicin, ifosfamide, and gemcitabine. Surgery is the mainstay of therapy. Surgical resection in conjunction with chemotherapy or radiation is the most common approach to the treatment of synovial sarcoma. There are no established measures for the prevention of synovial sarcoma.

• Synovial sarcoma was first discovered by Pack and Tabah in 1955.^[1]

• Synovial sarcoma may be classified according to histopathological findings into 4 sub-types:^[2]

• Biphasic
• Monophasic fibrous (most common)
• Monophasic epithelial
• Poorly differentiated

• The pathogenesis of synovial sarcoma is characterized by the dysregulation of gene expression of SYT-SSX gene.^[2]
• The most common locations for the occurrence of synovial sarcoma include:^[1]

• Knee
• Adjacent to large joints
• Popliteal fossa

• The SYT-SSX fusion gene (located in chromosome 18) has been associated with the development of synovial sarcoma.
• On gross pathology, characteristic findings of synovial sarcoma include:

• Solid often lobulated
• Grey-yellow
• Pushing border to ill-defined border

• On microscopic histopathological analysis, characteristic findings of synovial sarcoma include:^[2]

• Non-specific appearances
• Well or poorly defined heterogeneous masses
• Frequent areas of hemorrhage
• Necrosis

• There are no established causes for synovial sarcoma.

• Synovial sarcoma must be differentiated from other diseases that cause joint pain, mass growth, and limited range of motion, such as:^[2]

• Malignant fibrous histiocytoma (MFH)–fibrosarcoma
• Liposarcoma
• Osteosarcoma
• Chondrosarcoma

• The prevalence of synovial sarcoma remains unknown.^[2]
• Synovial sarcomas account for 2.5 – 10% of all soft tissue sarcomas.

• Synovial sarcoma is more commonly observed among patients aged 15 – 40 years old.
• Synovial sarcoma is more commonly observed among adolescents and young adults.

• Males are more commonly affected with synovial sarcoma than females.
• The male to female ratio is approximately 1.2 to 1.

• There is no racial predilection for synovial sarcoma.^[2]

• There are no known risk factors associated with the development of synovial sarcoma.^[1]

• There is insufficient evidence to recommend routine screening for synovial sarcoma.

• The majority of patients with synovial sarcoma remain asymptomatic for years.
• Early clinical feature includes a soft palpable mass.
• If left untreated, patients with synovial sarcoma may progress to develop metastases.
• The most common complication of synovial sarcoma is pulmonary cannonball metastases.
• Prognosis is generally poor, and the median survival rate of patients with synovial sarcoma is approximately 35% to 60%.
• The table below demonstrates the good and poor prognostic factors for patients with synovial sarcoma.^[2]

Poor prognosis	Good prognosis
Large size (> 5 cm): most important factor Located in the trunk or head and neck Older patients Cystic/hemorrhagic components Marked heterogeneity Histology Poorly differentiated histology Extensive tumor necrosis High nuclear grade p53 mutations High mitotic rate (> 10 mitoses per 10 high-power field)	Small size Located in extremity Younger age < 20 years of age Solid homogenous mass Presence of calcification Biphasic histology (controversial)

• The diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18).^[2]

• Synovial sarcoma is usually asymptomatic.
• Symptoms of synovial sarcoma may include the following:^[2]

• Soft tissue mass
• Localized pain
• Limited range of motion

• Specific areas of focus when obtaining the history include:

• Localized pain
• Accompanying local swelling or mass, progressive pain that is not relieved with rest, night pain
• Recent weight loss (or failure to thrive)
• Personal history of cancer
• Family history of bone tumors

• Patients with synovial sarcoma usually are well-appearing.
• Physical examination may be remarkable for:

• Tenderness to palpation
• Soft tissue swelling
• Decreased range of motion
• Muscle atrophy
• Joint effusion

• There are no specific laboratory findings associated with synovial sarcoma.

• There are no ECG findings associated with synovial sarcoma.

• Plain x-ray can be normal unless the tumor is large in size or has dystrophic calcifications.^[3]

• There are no echocardiography findings associated with synovial sarcoma.
• On ultrasound, characteristic findings of synovial sarcoma include:^[2]

• Non-specific
• Heterogeneous
• Hypoechoic mass

• On CT scan, characteristic findings of synovial sarcoma include:

• Non-specific
• Soft tissue mass
• Heterogeneous density and enhancement
• Calcifications

• MRI is the imaging modality of choice for synovial sarcoma.
• On MRI, characteristic findings of synovial sarcoma include:^[2]

• T1: iso- (slightly hyper-) intense to muscle/heterogeneous
• T2: mostly hyperintense, markedly heterogeneous appearance of synovial sarcomas on fluid sensitive sequences result in so called “triple sign” which is due to areas of necrosis and cystic degeneration with very high signal, relatively high signal soft tissue components, and areas of low signal intensity due to dystrophic calcifications and fibrotic bands, due to high tendency of lesions to bleed.
• T1 C + (Gd): ​enhancement is usually prominent and can be diffuse (40%) heterogeneous (40%) or peripheral (20%)

• The image below demonstrates an MRI image of synovial sarcoma.

There are no other imaging findings associated with synovial sarcoma.

There are no other diagnostic studies associated with synovial sarcoma.

• The mainstay of therapy for synovial sarcoma includes:^[2]

• Doxorubicin
• Ifosfamide
• Gemcitabine

• Surgery is the mainstay of therapy for synovial sarcoma.^[1]
• Surgical resection in conjunction with chemotherapy or radiation is the most common approach to the treatment of synovial sarcoma.^[2]

• There are no established measures for the primary prevention of synovial sarcoma.

There are no established measures for the secondary prevention of synovial sarcoma.