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

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