Triple Sign | Radiology Signs

Answer:

Triple sign is caused by synovial sarcoma, a malignant soft tissue tumor typically arising in the deep soft tissues adjacent to joints or tendon sheaths, most commonly in the lower extremities of young adults; it manifests as a heterogeneous mass with areas of high, intermediate, and low signal intensity on T2-weighted and proton density MRI sequences due to admixture of solid viable tumor, cystic-necrotic or hemorrhagic components, and fibrocollagenous or calcified elements. It has also been reported, less commonly, in other soft-tissue sarcomas such as undifferentiated pleomorphic sarcoma.

Why is it called so?

It is named the triple sign because the mass exhibits three distinct signal intensities (high (hyperintense, from fluid in necrosis or hemorrhage), medium (isointense, from solid tumor components), and low (hypointense, from fibrosis, calcification, or collagen)) on T2-weighted MRI, creating a characteristic tripartite appearance. The finding was first described by Jones et al. in a 1993 AJR series of synovial sarcoma cases.

Pathophysiology

Synovial sarcoma develops from primitive mesenchymal cells with variable epithelial differentiation, leading to heterogeneous tumor composition; high cellularity and myxoid change produce hyperintense areas, solid viable tumor yields intermediate signal, and desmoplastic fibrosis with dystrophic calcifications results in hypointense regions, with prevalence increasing in larger (>5 cm), multilobulated tumors (seen in 35-80% of cases).

Alternative names: None established.

Other associated named signs: Bowl of grapes sign – a distinct related sign describing the multicystic, fluid-fluid-level appearance of synovial sarcoma (a different morphologic pattern from the triple sign, not a synonym); split-fat sign (general soft-tissue-mass sign for intermuscular location).

References

1. Jones BC et al. Synovial sarcoma: MR imaging findings in 34 patients. AJR Am J Roentgenol. 1993.
2. Murphey MD et al. Imaging of synovial sarcoma with radiologic-pathologic correlation. Radiographics. 2006.