Giant Cell Tumor of Tendon Sheath (GCTTS)

• Age: Peak incidence 30-50 years (adults)
• Gender: Female predominance 2:1
• Location: Hand and wrist 75%, foot 20%, other 5%
• Laterality: No dominant hand preference

• Functional impairment: Mass effect limits finger motion
• Bone erosion: Pressure erosion of phalanx (20-30% of cases)
• Recurrence: 10-20% overall (higher for diffuse type)
• Neurovascular risk: Close proximity to digital neurovascular bundles

• Multinucleated giant cells: Hallmark (but reactive)
• Mononuclear stromal cells: Neoplastic component (CSF1 expressing)
• Hemosiderin-laden macrophages: From microhemorrhage
• Xanthoma (foam) cells: Lipid-laden macrophages (yellow color)
• Capsule: Usually well-encapsulated (localized type)

• vs PVNS: Same histology, different location (joint vs tendon sheath)
• vs Ganglion: No giant cells, mucinous cyst contents
• vs Fibroma: No giant cells or hemosiderin
• vs Giant cell tumor of bone: Different location, more aggressive

• Single mass enclosed by one complete pseudocapsule
• Rounded or gently lobulated - shells out en bloc
• No separate satellite nodules
• Lowest margin-positivity and recurrence risk

• Multiple distinct nodules each with its own capsule, OR no single containing capsule
• The source of the missed satellite lesions that drive recurrence
• Independently predicts positive margins and local recurrence
• Demands a deliberate search of the whole field before closure

• Mass: Painless slow-growing nodule (months to years)
• Location: Volar digit (index and middle finger most common)
• Symptoms: Usually asymptomatic, mass effect only
• Pain: Rare unless nerve compression or joint involvement
• Trauma: No history of trauma (helps differentiate from other lesions)

• Inspection: Visible lobulated mass, skin intact
• Palpation: Firm, rubbery, well-defined, mobile on tendon sheath
• Range of motion: May be limited by mass effect
• Neurovascular: Usually intact (but mass may compress nerve)
• Transillumination: Negative (solid, not cystic like ganglion)

• Polylobular ("cauliflower") mass sitting against the tendon sheath
• Low T2 signal with GRE blooming from hemosiderin
• High CT attenuation from dense collagen and hemosiderin-laden macrophages
• Marked gadolinium enhancement from proliferative capillaries

• Avoids unnecessary aggressive bone surgery or biopsy for a benign extrinsic lesion
• Erosion is managed by curettage of the defect at the time of soft-tissue excision
• Cortex is usually intact despite scalloping - true breakthrough is rare
• Persistent or expansile lytic change should prompt biopsy to exclude other diagnoses

• No dedicated implant registry (GCTTS is a soft-tissue excision, not arthroplasty)
• Evidence base is retrospective series and systematic reviews, plus one phase 3 RCT (ENLIVEN) for advanced TGCT
• Recurrence reporting is heterogeneous: ~10-15% localized, ~30-40% diffuse across pooled series
• Histology is the diagnostic gold standard in every setting

• High-resource: MRI mapping, microsurgical excision, pexidartinib for refractory diffuse disease, radiosynoviorthesis for joint disease
• Limited-resource: Diagnosis often clinical plus ultrasound or radiograph; marginal excision under loupe magnification with tourniquet
• Outcomes for localized digital GCTTS are excellent globally with complete excision
• Systemic CSF1R inhibitors are costly and not universally available

Low-dose external beam radiotherapy is proposed for diffuse or repeatedly recurrent disease, but evidence is limited to small series. Benefit must be weighed against radiation morbidity in the hand (skin, joint stiffness, theoretical late malignancy). Most authors reserve it for unresectable recurrence rather than primary use.

ENLIVEN proved efficacy in advanced TGCT, but the trial was dominated by large-joint diffuse disease, hepatotoxicity is significant, and there is no EMA approval. Its role in digital GCTTS is off-label and confined to recurrent disease not amenable to surgery.

Positive margins are the strongest predictor of recurrence, yet aggressive margins in the digit threaten nerves, vessels and tendons. The optimal balance between oncological clearance and functional preservation for diffuse digital disease remains undefined.

Surveillance is usually clinical, with MRI reserved for suspected recurrence. Whether routine imaging detects recurrence earlier and improves outcomes (versus added cost and false positives) is unsettled.