Ganglion Cysts

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  • Usually in close proximity to joints and tendon sheaths
  • Extremely rare in veterinary medicine c.f. humans
  • No consensus as to genesis
  • Cysts contain mucinous/yellow fluid


More about ganglion cysts:


[Ganglion cysts in a juvenile dog. Cho K-O et al. Vet Path (2000) 37 340-3]

Ganglion cysts:

  • Usually in close proximity to joints and tendon sheaths
  • Extremely rare in veterinary medicine c.f. humans
  • No consensus as to genesis
  • Cysts contain mucinous/yellow fluid
  • Wall composed of: inner myxomatous and outer
    • Inner myxomatous areas
      • Pleomorphic stellate and spindle cells within an abundant myxoid stroma
      • Lined by fibroblasts on the inner aspect (although no true lining cells)
    • Outer fibromatous areas
      • Similar to granulation tissue
    • Mitoses rare
  • The base of all ganglion cysts in contact with the bone, with no boney destruction
  • Mucin in the cavities stains blue with acid mucin and with AB-PAS
  • EM
    • Abundant rough ER and golgi and few mitochondria in the inner myxomatous cells and various stages of myxoid metaplasia
    • Cells resemble both synovial cells and fibroblasts
    • Small numbers of degenerative ganglion cells in the inner myxomatous lesions – marked dilation of rER and golgi; filopodia, multiple small vacuoles containing a dense granular material in the cytoplasm
    • ECM – bundles of collagen fibrils adjacent in the fibroblasts in the initial phase of the mucinous lesions -> collagen fibrils broken and shortened and haphazardly arranged
  • No communication with the synovial cavity and no synovial lining so not synovial cysts or adventitious bursa
  • Cysts develop within the mucinous lesions surrounding a central collagenous core
  • Synovial cells have two appearances on EM:
    • Type A cells – phagocytic, contain numerous vacuoles, branched aperiodic fibrils, filopodia, vesicles, mitochondria
    • Type B cells – adapted for protein production and contain abundant rER, few mitochondria, occasional vesicles and vacuoles
  • Cells in the ganglion walls are similar to type B cells and fibroblasts
  • Mucin probably produced by metaplastic fibroblasts