Synovial hyperplasia

Synovial hyperplasia refers to an increase in the cellularity of the synovial membrane and leads to synovial thickening, which is a common radiographic feature in the setting of synovitis.

Clinical presentation

Synovial hyperplasia manifests as swelling.

Pathology

Synovial hyperplasia is characterized by an influx of proliferation of different cells which results in synovial thickening ^1-4. Depending on the etiology this might include an influx of immunoreactive and hematopoietic cells such as macrophages and lymphocytes as a reaction to cytokines and other cell mediators ^1,2, a proliferation of mesenchymal stromal cells ³ or synoviocytes ^2,4.

Etiology

Synovial hyperplasia can be found in the following clinical conditions ^1-4:

• osteoarthritis

• inflammatory arthritis

  • pseudogout

  • gout

  • juvenile idiopathic arthritis

  • spondyloarthritis

  • rheumatoid arthritis

• infective synovitis

  • septic arthritis

  • tuberculous arthritis

  • pyogenic tenosynovitis

• reactive synovitis

  • tenosynovitis

  • bursitis

• other arthropathies

  • haemophilic arthropathy

• trauma

• neoplastic

  • synovial hemangioma

  • tenosynovial giant cell tumor

  • synovial sarcoma

Radiographic features

Synovial hyperplasia can be visualized and assessed with ultrasound and MRI ^1,5-9.

Ultrasound

Synovial hyperplasia is pictured as hypoechoic synovial thickening often but not always associated with increased vascularity on power Doppler ^5-7. As opposed to synovial fluid synovial hyperplasia is non-displaceable and hardly compressible ⁷.

Conversely, normal synovium should not be visible and should not show any vascularity on color and power Doppler, not even in the presence of effusion ^5,6.

MRI

Suggested MR imaging for assessment of synovial disease include 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 synovial hyperplasia, the synovium will be thickened and show avid enhancement after contrast administration ¹. For the matter, the inflammatory activity is best reflected by early enhancement.

A correlation between the synovial volume and joint swelling and tenderness or synovial inflammatory activity has been shown ^1,8,9.

Signal characteristics

• T1: hypointense

• T2: hyperintense

• T2FS/PDFS: hyperintense

• T1 C+ (Gd): enhancement

See also

• synovial enhancement

• synovitis

• cystic synovial hyperplasia