= GIANT CELL REACTION = GIANT CELL GRANULOMA

Cause: ? reactive inflammatory process to trauma / infection (not a true neoplasm)

Histo: numerous giant cells in exuberant fibrous matrix arranged in clusters around foci of hemorrhage + commonly exhibiting osteoid formation (unusual in giant cell tumor); indistinguishable from brown tumor of HPT; cystic degeneration + ABC components distinctly uncommon

Peak age: 2^nd + 3^rd decade (range, childhood to 76 years); 74% <30 years of age; M÷F = 1÷1

May be associated with: enchondromatosis, Goltz syndrome, fibrous dysplasia, Paget disease

Location:

• Gnathic (1–7% of all benign oral tumors):
  • gingiva + alveolar mucosa of mandible, maxilla
    1. central type = in bone
    2. peripheral type = in gingival soft tissue
  • M÷F = 1÷2
  • nonspecific pain + swelling (increasing during pregnancy)
  • expansile bone remodeling with multilocular appearance
  • thinned usually intact cortex
  
  DDx: indistinguishable from odontogenic cyst, ABC, ameloblastoma, odontogenic myxoma, odontogenic fibroma
• Small bones of hand + feet (less common): phalanges of hand >metacarpals >metatarsals >carpal bones >tarsal bones >phalanges of foot
  M÷F = 1÷1
  • nonspecific pain + swelling for months to years
  
  Site: metaphysis ± extension into diaphysis; extension into epiphysis is UNCOMMON
  • expansile lytic defect of 2–2.5 cm in diameter with internal trabeculations
  • thinning of overlying cortex
  • matrix mineralization may be seen (DDx to GCT)
  • periosteal reaction is unusual (as in GCT)
  • extension beyond cortex is unusual
• Other locations (rare):
  • ethmoid sinus, sphenoid sinus, temporal bone, skull, spine, clavicle, tibia, humerus, ribs, femur

Cx: pathologic fracture

Prognosis: may recur; NO malignant transformation

Rx: curettage (22–50% recurrence rate) / local excision

DDx:

1. Enchondroma (same location, matrix calcification)
2. Aneurysmal bone cyst (rare in small bones of hand + feet, typically prior to epiphyseal closure)
3. Giant cell tumor (more aggressive appearance)
4. Infection (clinical)
5. Brown tumor of HPT (periosteal bone resorption, abnormal Ca + P levels)