Age group: 20-40 years.Most common in lower extremities, particularly around knee.Histopathology: not related to synovium, being typically located in an intermuscular location near to a joint.MRI features: Usually located within 5cm of a synovial joint. Typically oval and nodular with heterogeneous intermediate SI on T1W (A) and hyperintense on T2W (B) images, shows heterogeneous contrast enhancement (C). Cystic areas, calcification, haemorrhage and fluid-fluid levels (D) are common.Features suggestive of high-grade tumour: proximal distribution, tumour size >10cm, absence of calcification, presence of cystic areas and haemorrhage.
MRI OF SYNOVIAL SARCOMA
Tumors tend to be large, averaging approximately 8 cm in largest dimension. The largest dimension is usually parallel to the long axis of the body. Approximately 91% of patients have a well-defined ovoid lesion with rounded or gently lobulated margins. The effect on adjacent structures is usually displacement, rather than invasion or destruction. Most tumors display heterogeneous intermediate signal-intensity on T1-weighted images.
Lesions smaller than 5 cm are more likely (40%) to have predominantly homogeneous signal intensity similar to that of adjacent muscle. Larger lesions are most often heterogeneous secondary to extensive areas of hemorrhage and necrosis. On T2-weighted images, lesions are usually hyperintense, with signal intensity similar to or lower than that of fatty tissue. Considerable inhomogeneity is demonstrated in 82% of lesions, with cystic components seen in 77%. Cystic components with striking fluid-fluid levels are demonstrated in 18% of tumors. Approximately one third of lesions demonstrate the so-called triple signal pattern on T2-weighted images.
This pattern consists of the following:
- mixtures of hyperintense fluid with or without fluid levels
- intermediate signal similar to muscle
- slightly hypointense signal similar to that of fibrous tissue.
Apposition to bone surfaces without a clear plane of separation is seen in 50-59% of cases with clear bone erosion or destruction in 22%. Calcifications are not easily seen on MRIs, and they are usually hypointense on images obtained with all sequences. The use of gadolinium-based contrast agents has limited value in theevaluation of synovial sarcomas. On dynamic imaging, malignant soft-tissue masses have been shown to enhance earlier, faster, and more predominantly peripherally than benign lesions. These findings are believed to be secondary to the effects of tumor angiogenesis.
Synovial sarcomas usually demonstrate heterogeneous contrastenhancement, with early enhancement of tumor within 7 seconds of arterial enhancement. Gadolinium-based agents may be helpful in posttreatment MRIs, on which mild, diffuse, nonfocal contrast enhancement is a typical finding. With recurrent disease, focal nodules with homogeneous enhancement and high signal intensity without cystic components are typically seen on T2-weighted images.