General
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• Also called tenosynovial giant cell tumor, giant cell tumor of tendon sheath, nodular tenosynovitis, xanthogranuloma, benign synovioma
• Ages 20-40's, usually women
• Develops in synovial lining of joints, tendon sheaths and bursae
• Usually knee (80%); also ankle, hip, shoulder or elbow joint and foot
• Almost always monoarticular, painful swelling
• May actually be hyperplastic / reactive, not neoplastic (Hum Pathol 2003;34:65)
• Occasionally invades underlying bone; may cause bone cyst formation, loss of bone and cartilage
• Locally aggressive; often recurs, but only rarely has malignant behavior (see below)
• 15% erode adjacent bone by pressure
• May be related to tendon sheath fibromas

Case reports
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• 9 year old girl with nodule in right index finger (Dermatol Online J 2011;17:9)
• 15 year old boy with swelling in knee (Oncol Lett 2012;3:718)
• 30 year old man with pain in ankle (J Med Case Rep 2009;3:9331)
• 32 year old woman with 2 year history of slowly growing firm, nodular, and nontender thumb mass (Eplasty 2013;13:ic36)
• 73 year old man with mass on thumb (Int J Clin Exp Pathol 2012;5:374)

Treatment
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• Excision (benign), but may recur locally

Gross / clinical images
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Foot

Palmar aspect of middle phalanx of index finger

Firm, nodular, nontender thumb mass

Excised giant cell tumor

Dome-shaped nodule

Well-demarcated yellowish lobulated tumor

Gross description
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• Discrete encapsulated nodule, 1-3 cm on tendon sheath, may be attached to synovium by a pedicle
• Red-brown to orange-yellow, localized, well circumscribed, resembles small walnut; diffuse form may be larger and infiltrative

Micro description
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• Polymorphic infiltrate of small histiocytes, multinucleated giant cells within dense fibrous tissue with hemosiderin and foamy macrophages
• Mitotic figures and focal hyalinized areas; tumor margins are more cellular

Micro images
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2A: H&E with multinucleated giant cells and mononuclear cells; B: mononuclear cells are HAM56+; C: giant cells and some mononuclear cells are TRAP+; 3: differentiation sequence of giant cell tumor

Giant cell

Low power and high power

Circumscribed lobulated nodule

Histiocytes with abundant eosinophilic cytoplasm

Low power view of thumb tumor

High power view of cellular zone

High power view of hypocellular zone

CD68 immunostaining of cellular zone

Ki-67 immunostaining of peripheral zone

CD45 immunostaining of peripheral zone

Electron microscopy description
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• Synovial cells, fibroblasts, histiocytes, lymphocytes

Differential diagnosis
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• Epithelioid sarcoma: granuloma-like formations, necrosis, invasive, epithelioid features, keratin+

General
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• Mean 61 years, no gender preference
• Usually extra-articular, near large joints or extremities
• Most common location is knee joint
• High number of mitotic figures, marked nuclear hyperchromasia, few multinucleated giant cells

Micro images
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Radiological, histologic, and FISH/ISH findings in malignant tumors

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