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Tenosynovial Giant Cell Tumors (TGCTs) are a group of benign but potentially locally aggressive tumors that arise from the synovium of joints, bursae, or tendon sheaths. They are characterized by synovial proliferation, hemosiderin deposition, and infiltration of multinucleated giant cells, foamy histiocytes, and mononuclear cells.

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Classification

Type	Old terminology	New terminology (WHO 2020)	Features
Diffuse intra-articular form	‣	Localized TGCT	Small, discrete nodular lesion, typically extra-articular (e.g., fingers)
Localized form	Giant Cell Tumor of Tendon Sheath (GCTTS)	Diffuse TGCT	Involves entire synovial lining of a joint; large, infiltrative intra-articular mass

Epidemiology

Most common in 20–50 years.
Slight female predominance.
Localized TGCT: most common in digits (flexor tendon sheath).
Diffuse TGCT: most often affects the knee (~70%), followed by hip and ankle.

Etiopathogenesis

Neoplastic nature supported by:
- CSF1 gene overexpression in most cases.
- Local overproduction of colony-stimulating factor 1 (CSF1) recruits inflammatory cells and giant cells.
May result from previous trauma, but exact cause remains unclear.

Clinical Features

Localized TGCT

Painless, slow-growing mass near a joint (commonly fingers).
May cause mechanical restriction or swelling.

Classification

Epidemiology

Etiopathogenesis

Clinical Features

Localized TGCT

Diffuse TGCT