Longitudinal US scan of wrist, dorsal side. Patient affected by rheumatoid arthritis.a Gray-scale scan and (b) power Doppler scan.The use of power Doppler allows the amount of synovial proliferation to be assessed more than MR without contrast (spin echo T1 (SET1), short T1 inversion recovery (STIR)) (c, d) or a plain film (e)
Patient with rheumatoid arthritis.a The power Doppler scan shows a high degree of hyperperfusion,an expression of hyperactive pannus.b Follow-up during therapy.A significant reduction in flow signal is shown within the pannus (arrows)
keep in mind that synovial hypertrophy is a nonspecific finding and that the differentiation between a non-specific synovitis and a synovial tumor can be very tricky (hemangioma, synovial sarcoma) [14-16]. A fibrinous exudate can make it difficult to detect the thickened synovial membrane contour, especially when it is abundant, because it may simulate the US pattern of synovial hyperplasia. In these cases, when fluid and hypertrophic synovia cannot be differentiated it is possible to use dynamic and compressive maneuvers. Such a technique allows the fluid to be "squeezed out" from the hypertrophic synovial wall and the differentiation of the two articular contents [1,14,16].
When doubt persists with gray-scale US, power and color Doppler techniques can be applied to differentiate the fluid from the proliferating tissue, with the presence or absence of vascular signals [17-20] (Fig. 4.14 a-e).
The role of Doppler techniques for the assessment of synovial vascularization in rheumatoid arthritis is very important. In rheumatoid arthritis, the formation of pannus is a crucial event in the pathogenesis of articular degeneration. Neoangio-genesis is an important pathological element in rheumatoid synovitis [21,22]. Since hypervascu-
larization is proportional to the degree of inflammation of the synovial pannus, it is fundamental to study and quantify the vascular signals in order to evaluate the aggressiveness of the pannus itself. Power Doppler is able to assess the increased vas-cularization involving synovial hyperplasic tissue and consequently to give information regarding the activity of the synovial pannus [1,18-20] (Fig. 4.15 a,b). Despite attempts at semiquantitative or quantitative evaluation of the vascularization by means of dedicated software, the technique is limited by the poor reproducibility.
Nevertheless, the recent availability of power Doppler techniques in association with the use of contrast agents (Contrast-enhanced Power Doppler - CePD) has allowed a more detailed analysis of the synovial vascularization. It should be considered that the information derived from power Doppler and CePD refer exclusively to the macrovasculature of synovial pannus. Such limits have now been overcome by the introduction of new generation contrast agents (SonoVue) that allow quantitative analysis of the synovial microvascularization to be performed by means of gray-scale US (Contrast-enhanced US - CeUS) [23-25] (Fig. 4.16 a-c).
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