General
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• Benign neoplasm characterized by proliferating histiocytes containing lipid and hemosiderin intermingled with multinuclear giant cells

Terminology
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• Synovial-type giant cell tumor, pigmented villonodular synovitis

Epidemiology
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• Usually adults over 30 years old

Sites
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• Frequently tendon sheaths in hand, rarely axial skeleton (thoracic vertebrae, lumbar or cervical spine)

Pathophysiology
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• Most tumors appear to be clonal neoplastic proliferations driven by CSF1 production (Arch Pathol Lab Med 2012;136:901)

Clinical features
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• Mechanical derangement of joint; with knee joint, meniscal symptoms and locking are often present
• May have joint effusion without previous trauma
• Vertebral involvement presents with pain localized to spinal region or radicular pain

Case reports
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• 7 year old Thai girl with back pain, progressive paraparesis (J Med Case Rep 2013;7:178)
• 18 year old man with 2 year history of mild knee pain (Orthopedics 2012;35:e1116)
• Malignant synovial giant cell tumor (Hum Pathol 1989;20:765)

Treatment
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• Complete surgical resection

Gross description
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• 1-6 cm, circumscribed, solid or diffuse

Micro description
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• Polyhedral stromal cells with numerous multinucleated giant cells
• Stroma can be hyalinized
• Siderophages, xanthoma cells, lymphocytes, and some spindled fibroblast-like cells
• Rarely classic villiform architecture of pigmented villonodular synovitis is noted

Micro images
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Histiocytes, foam cells, and multinucleated giant cells

Histiocyte-like tumor cells, lymphocytes,
hemosiderin-laden macrophages and
osteoclast-like giant cells

Positive stains
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• CD68, CD163, vimentin
• Rarely muscle actin (HUC1-1)

Differential diagnosis
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• Other primary bone lesions such as aneurysmal bone cyst, osteoblastoma and osteoclastoma should be considered in differential diagnosis of lesion involving posterior vertebral elements

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