Bone & joints

Other nonneoplastic

Synovial cysts



Topic Completed: 1 December 2018

Minor changes: 29 December 2020

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: synovial cyst [title]

Vijay Shankar, M.D.
Page views in 2020: 5,740
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Cite this page: Shankar V. Synovial cysts. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/jointssynovialcysts.html. Accessed October 25th, 2021.
Definition / general
  • Herniation of synovium through joint capsule, usually in joint of extremities
  • May bleed and become a mass-like lesion
Terminology
  • Baker cyst: also called popliteal cyst; synovial cyst in popliteal space
  • Cutaneous metaplastic synovial cyst: lined by metaplastic synovial tissue; may be due to local trauma
  • Spinal synovial cyst: cyst in spinal joint
Clinical features
  • Baker cyst: due to herniation of synovial membrane through posterior joint capsule or escape of joint fluid from bursae; associated with degenerative joint disease, neuropathic arthropathy, rheumatoid arthritis
  • Spinal synovial cyst:
    • Soft tissue mass located extradurally along medial border of degenerated facet joint
    • Usually at L4-5, rarely in cervical or thoracic spine
    • Filled with clear or xanthochromic fluid
    • Causes back and radicular pain
    • Rarely results in cauda equina syndrome (Pain Physician 2012;15:435)
Diagrams / tables

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Baker cysts

Radiology images

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Spinal synovial cyst

Case reports
Treatment
  • Baker cyst: treat cause of excess fluid, sclerotherapy (Pain Physician 2008;11:375)
  • Cutaneous metaplastic synovial cyst: surgical excision; recurrence is rare
Clinical images

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Baker cysts

Cutaneous metaplastic synovial cyst

Radiology images

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MRI of Baker cyst

Microscopic (histologic) description
  • Baker cyst: lined by synovium, may have cartilage in cyst wall; palisading histiocytes and fibrinoid necrosis, similar to rheumatoid pericarditis and rheumatoid nodules
  • Cutaneous metaplastic synovial cyst: cystic structure with papillary projections lined by epithelium resembling synovium
Microscopic (histologic) images

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Cutaneous metaplastic synovial cyst with numerous villous-like structures; vimentin+ CD34- CD68-

Hemorrhagic spinal synovial cyst with thin fibrous wall

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