Joint tumors

Fibrous histiocytoma of tendon sheath

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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

Solitary, slow-growing, painless nodule on tendon sheaths of flexor surfaces of wrists/fingers, ankle/toes

15% erode adjacent bone by pressure

May be related to tendon sheath fibromas

Unclear if reactive or neoplastic

Treatment: excision (benign), but may recur locally

Gross: 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: polymorphic infiltrate of small histiocytes, multinucleated giant cells within dense fibrous tissue with hemosiderin and foamy macrophages; mitotic figures and focal hyalinized areas

Micro images: 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

EM: synovial cells, fibroblasts, histiocytes, lymphocytes

DD: epithelioid sarcoma (granuloma-like formations, necrosis, invasive, epithelioid features, keratin+)

Malignant variant of fibrous histiocytoma of tendon sheath

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High number of mitotic figures, marked nuclear hyperchromasia, few multinucleated giant cells

Synovial giant cell tumor

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Axial skeleton tumor; often cervical spine

<50 cases reported

Mean age 32 years, range 17-44 years

Xray: mass of posterior aspect of adjoining vertebrae, often involving facet joints, with bone abnormalities present

Treatment: resection; may persist if incompletely excised; no metastases reported

Case reports: malignant synovial giant cell tumor (Hum Path 1989;20:765)

Gross: 1-6 cm

Micro: epithelioid cells with mixed osteoclast-like giant cells, hemosiderin containing macrophages, xanthoma cells, fibroblasts, lymphocytes; often with infiltrative growth; variable mitotic activity

Positive stains: CD68, CD163, vimentin

DD: giant cell tumor of bone (10% involve spine, usually sacrum, giant cells have abnormally large number of nuclei), osteoblastoma (well circumscribed, surrounded by cortical bone or periosteum, osteoblastic rimming with scattered osteoclasts), aneurysmal bone cyst (younger patients, well demarcated, lytic lesion bordered by thin rim of new bone, cavernous blood filled spaces), schwannoma

References: Hum Path 2003;34:670

Tenosynovial chondromatosis

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Rare; may be extraarticular counterpart of synovial chondromatosis

Mean age 46 years, range 20-86 years

Painless mildly tender mass present for median 2 years

Usually recurs, perhaps due to subclinical micronodules

Sites: fingers (50%), feet (20%); also wrists, ankles, palm, knee, forearm

Treatment: complete excision in a conservative, function-preserving fashion

Micro: multinodular cartilaginous proliferation arising from tenosynovial membranes; often mild or moderate atypia similar to chondroma of soft parts or synovial chondromatosis; occasionally has prominent mineralization; often minute cartilaginous nodules; cartilaginous matrix more intensely basophilic than chondroma of soft parts

DD: chondroma of soft parts (not multinodular, younger patients overall although overlap exists)

References: AJSP 2003;27:1260