MRI features of three paediatric intra-articular synovial lesions: a comparative study.

AIM: To determine reliable magnetic resonance imaging (MRI) features differentiating three paediatric intra-articular congenital or neoplastic synovial lesions that contain blood products, from post-traumatic or haemorrhagic inflammatory processes.

MATERIALS AND METHODS: This was a retrospective review of MRI findings of 22 paediatric intra-articular congenital or neoplastic synovial lesions, including venous malformation (VM) (n=12), pigmented villonodular synovitis (PVNS; n=8), and synovial sarcoma (SS; n=2). These MRI features were compared with 22 paediatric post-traumatic or inflammatory intra-articular processes containing blood products and producing mass effect. The following imaging features were assessed: presence of a discrete mass, extension, extra-articular oedema, susceptibility, joint effusion, and size. Fisher's exact test was used and results were considered statistically significant when p<0.05.

RESULTS: The three intra-articular synovial lesions, compared with controls, were more likely to directly invade osseous structures when a discrete mass was present (13/16, 81.3% versus 1/9, 11.1%; p<0.002) and extend into extra-articular soft tissues (13/21, 61.9% versus 2/17, 11.8%; p<0.003), but were less likely to show extra-articular oedema (3/22, 13.6% versus 13/22, 59.1%; p<0.004), a joint effusion (10/22,45.5% versus 19/22, 86.4%, p<0.01), susceptibility within a joint effusion (0/22, 0% versus 11/22, 40.9%; p=0.00), osseous oedema (3/16, 18.8% versus 7/9, 77.8%; p<0.009), and synovial enhancement (8/21, 38.1% versus 14/16, 87.5%; p<0.003). VMs had characteristic tubular vessels with internal fluid-fluid levels (11/12) that extended into bone (10/12) and extracapsular soft tissues (11/12).

CONCLUSION: Our study indicates that, despite the overlapping presence of haemorrhagic products, intra-articular VM, PVNS, and SS show MRI features that permit distinction from acquired post-traumatic and haemorrhagic inflammatory lesions.