Giant Cell Tumor of Tendon Sheath (GCTTS)

Giant cell tumour of tendon sheath (GCTTS) is the second most common hand tumour after the ganglion cyst, accounting for approximately 10% of all hand masses. It is the extra-articular form of tenosynovial giant cell tumour (TGCT), the same pathological process as PVNS arising from tendon sheath rather than joint synovium. Intra-articular disease is PVNS; tendon-sheath disease is GCTTS.

Who. Adults, with a peak incidence at 30-50 years and a 2:1 female predominance. There is no preference for the dominant hand. The classic patient is a middle-aged woman with a painless, slow-growing nodule on the volar aspect of a digit.

Where. Mostly the hand:

• Hand and wrist - 75%. Most lie on the volar aspect of the digits, the index and middle fingers most often, attached to the flexor tendon sheath; the extensor side of the digit is rarely involved. At the wrist, flexor or extensor tendon sheaths.
• Foot - 20%. Toes and plantar aspect.
• Other - 5%. Ankle, and rarely the knee.

Why it matters. The mass can limit finger motion, erode the adjacent phalanx, and sits against the digital neurovascular bundles, which are at risk at excision. The major problem after surgery is recurrence, driven almost entirely by incomplete excision.

The neoplastic cell. GCTTS is a clonal proliferative disorder. The neoplastic component is the mononuclear stromal cell, which expresses CSF1. The multinucleated giant cells that give the lesion its name are reactive, not neoplastic.

The driver. A chromosomal translocation fusing CSF1 to COL6A3, the same driver as in PVNS, leads to CSF1 overexpression and clonal proliferation of the stromal cells. The fusion is not found in every lesion; CSF1 overexpression is.

From signal to mass. CSF1 binds CSF1R and so recruits macrophages and giant cells into the lesion, and it is this inflammatory infiltrate that creates the mass. Recurrent microhaemorrhage deposits haemosiderin, which gives the lesion its dark gross colour and its low signal (blooming) on MRI. The mass also compresses the adjacent bone, scalloping or eroding the cortex of the phalanx.

Histology. Four cell types and a capsule:

• Multinucleated giant cells - the hallmark, but reactive
• Mononuclear stromal cells - the neoplastic, CSF1-expressing component
• Haemosiderin-laden macrophages - from microhaemorrhage
• Xanthoma (foam) cells - lipid-laden macrophages
• Capsule - usually well encapsulated in the localised type

Gross appearance. A well-circumscribed, lobulated nodule arising from the tendon sheath, not from the tendon itself. It is tan to yellow-brown: the xanthoma cells give the yellow, and haemosiderin darkens it.

Differential histology. Four lesions to compare it with:

• PVNS - same histology, different location (joint versus tendon sheath)
• Ganglion - no giant cells; mucinous cyst contents
• Fibroma - no giant cells or haemosiderin
• Giant cell tumour of bone - different location, and more aggressive

The key distinction is between the localised type, which is well encapsulated and makes up 90% of cases, and the diffuse type, which is infiltrative and makes up 10%. It guides the surgical approach and what the patient is told.

Localised. A well-circumscribed, lobulated nodule arising from the tendon sheath, usually a flexor sheath, growing slowly over months to years. On MRI the margins are well defined, the signal is low on T1 and T2, blooming may be seen on gradient-echo sequences, and there is no soft-tissue invasion. Treatment is marginal excision with the capsule intact, and with complete excision the prognosis is excellent.

Diffuse. Infiltrative growth wraps around tendons, vessels and other structures, so the margins are difficult to define clinically. The lesion is larger at presentation, is more likely to erode bone, and may involve a joint capsule as a hybrid with PVNS. MRI shows ill-defined margins, soft-tissue invasion and the lesion wrapping around tendons and vessels. Complete excision is challenging: treatment is wide excision with margins, recurrence is higher despite it, and adjuvant radiation may be required for unresectable recurrence.

Al-Qattan (J Hand Surg Br, 2001) classified localised giant cell tumour of the tendon sheath in the digit by its gross operative morphology and by the integrity of its pseudocapsule, the single feature that best predicts whether excision will be complete.

• Type I (unicapsular) - a single rounded or gently multilobulated mass enclosed by one well-formed pseudocapsule, with no separate satellite nodules. It shells out en bloc, with the lowest margin-positivity and recurrence risk.
• Type II (multicentric or capsule-deficient) - either multilobulated with each lobule carrying its own separate capsule, effectively more than one tumour, or a mass not contained by a single capsule at all. These lesions are the source of the missed satellite nodules that drive recurrence.

Later hand series have refined the scheme into subtypes (for example Ia, Ib, Ic and IIa in Koutserimpas 2018) reflecting lobularity and the relationship to adjacent tendon, joint and bone.

Why it predicts recurrence. Cengiz et al. (Medicina, 2025; 44 hand TGCTs) found Al-Qattan type II, alongside bone invasion, interphalangeal-joint proximity and neurovascular involvement, to be an independent predictor of both positive margins and local recurrence, although that model rests on four recurrences. Documenting the Al-Qattan type in the operative note stratifies recurrence risk, and it reminds the surgeon that a type II lesion demands a deliberate search of the whole field for separately encapsulated satellites before closure.

History. A painless nodule that has grown slowly over months to years, usually causing nothing beyond its mass effect, and it may be an incidental finding. Pain is rare unless the lesion compresses a nerve or involves a joint. There is no history of trauma, which helps separate it from other lesions.

Examination. A visible lobulated mass under intact skin, firm, rubbery, well defined and mobile on the tendon sheath. The mass may limit the range of motion. The neurovascular examination is usually normal, although the mass can compress a nerve.

The trap. A bony abnormality beside a digital GCTTS is a classic examiner trap, because it can be mistaken for a primary aggressive bone lesion. How often it occurs is uncertain: 20-30% is the conventional teaching figure, not a cited-cohort measurement, and no source cited on this page gives a proportion.

Recognising the soft-tissue origin. The mass itself gives the lesion away:

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

Why the distinction matters. Recognising extrinsic erosion avoids unnecessary aggressive bone surgery or biopsy for a benign lesion. The erosion is managed by curettage of the defect at the time of soft-tissue excision; the cortex is usually intact despite the scalloping, and true breakthrough is rare. Persistent or expansile lytic change should prompt biopsy to exclude other diagnoses.

How convincing the mimicry can be. De Schepper et al. (Eur Radiol, 2007) found that within 200 consecutive osseous (pseudo)tumours of the hand, six were in fact caused by a neighbouring GCTTS eroding bone, presenting as well-defined cortical defects or a slightly expansile osteolytic lesion, florid enough to be reported as a primary bone tumour. Reading the low T2 signal and the juxta-tendon position of the mass correctly identifies the soft-tissue origin and keeps the operation a soft-tissue excision with curettage rather than a bone resection.

The critical distinction is benign (GCTTS, ganglion, fibroma) versus malignant (epithelioid sarcoma): biopsy if there is any concern for malignancy.

The decision. The presentation points to the type, and the type sets the operation.

Localised disease. The goal is complete marginal excision with the capsule intact, which minimises recurrence. MRI before surgery shows the extent and the relationship to the neurovascular structures. Consent covers recurrence, including how far a positive margin raises it, neurovascular injury and stiffness.

Diffuse disease. The goal is wide excision with margins, but recurrence remains higher than for localised disease. MRI is critical to define the extent and plan the margins, and consent covers the higher recurrence risk and the possibility of staged procedures. Anaesthesia is general or a regional block. The excision:

1. Extensile exposure, which may require zigzag or multiple incisions
2. Wide margins of 5-10mm around the tumour, which may mean sacrificing the involved tendon sheath
3. Protection of the neurovascular bundles, which may need microdissection
4. An aggressive search for satellite lesions
5. Curettage of bone erosions
6. Tendon reconstruction or skin grafting where needed

Diffuse disease requires aggressive surgery and long-term surveillance; the adjuvants for unresectable recurrence are set out under Recurrence and Outcomes.

Early range of motion is critical to prevent finger stiffness after hand surgery. The splint is for comfort, not mandatory.

What drives it. Recurrence comes from disease left behind: an incomplete excision, a capsule ruptured during surgery, satellite lesions not removed, or the diffuse type. A recurrent lesion is harder to excise completely at revision.

Timing. In these series recurrence appeared within the first one to two years, but mean follow-up in Koutserimpas was 21 months, so later recurrences would not have been counted. Surveillance should be long.

Recurrent disease. A first recurrence is re-excised with wider margins, with a search for the satellite lesions missed at the first operation. After multiple recurrences, consider adjuvant external beam radiation (20 Gy) for unresectable disease, or the CSF1R inhibitor pexidartinib (off-label) for extensive recurrent disease.

Overall outcomes are excellent, with low complication rates and high restoration of function, when excision is complete.

GCTTS is a common hand tumour managed routinely by hand and orthopaedic surgeons worldwide, with excellent outcomes after complete excision of localized disease.

GCTTS is biologically benign but locally tenacious, and each of these questions is about how aggressively to treat a non-lethal disease without harming hand function.

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

Where pexidartinib fits. 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.

How wide is wide enough. 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 in diffuse digital disease remains undefined.

Routine postoperative MRI. Surveillance is usually clinical, with MRI reserved for suspected recurrence. Whether routine imaging detects recurrence earlier and improves outcomes, against its added cost and false positives, is unsettled.