Synovitis refers to any inflammatory process affecting the synovium of joints, tendon sheaths and bursae. It can take many morphological forms and occur from many etiologies. It may not necessarily be infective.
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Pathology
Specific subtypes
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degenerative conditions
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common
associated with the degree of cartilage loss
associated with increasing symptoms and disease progression
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foreign bodies, e.g. foreign body induced synovitis
Syndromes associated with synovitis include:
Chronic synovitis causes pannus formation which is characterized histologically by hypervascular masses of villous hyperplasia, cellular infiltration and fibroblastic proliferation. Fibrosis is often the end result.
Radiographic features
Synovitis can be well-visualized and assessed with ultrasound and MRI.
Broad general features include synovial thickening (can take many forms), synovial enhancement and increased vascularity (e.g. on color Doppler ultrasound). An effusion may be present.
Ultrasound
Ultrasound will usually show hypoechoic synovial thickening with increased vascularity on color or power Doppler in different graduations 7.
MRI
Suggested MR imaging for assessment of synovial disease includes T1 weighted images before and after intravenous contrast as well as T2 weighted fat saturated or STIR images in at least two different planes.
In the setting of synovitis, the synovium will be thickened and irregular, sometimes frond-like, and show avid enhancement after contrast administration 8,11. Inflammatory activity is best reflected by early enhancement during dynamic imaging 8.
A relation between synovial inflammatory activity and the synovial volume and early enhancement has been shown 8-10.
Signal characteristics
T1: hypointense
T2: hyperintense
T2/PD FS: hyperintense
T1 C+ (Gd): homogeneous early enhancement