BENIGN TUMORS OF BONE
Osteoma is a benign neoplasm that frequently involves the skull and facial bones. Osteoma can be associated with Gardner syndrome. Malignant transformation doesn’t occur.
Osteoid osteoma is a benign, painful growth of the diaphysis of a long bone, often the tibia or femur. Males are affected more than females, with peak age 5–25. Pain tends to be worse at night and relieved by aspirin. X-rays show central radiolucency surrounded by a sclerotic rim. Microscopically, ostoblasts line randomly connected trabeculae.
Osteoblastoma is similar to an osteoid osteoma but larger (>2 cm) and often involves vertebrae.
Osteochondroma (exostosis) is a benign bony metaphyseal growth capped with car-tilage, which originates from epiphyseal growth plate. It typically presents in ado-lescent males who have firm, solitary growths at the ends of long bones. It may be asymptomatic, cause pain, produce deformity, or undergo malignant transformation (rare). Osteochondromatosis (multiple hereditary exostoses) produces multiple, often symmetric, osteochondromas. Excision is usually curative.
Enchondroma is a benign cartilaginous growth within the medullary cavity of bone, usually involving the hands and feet. It is typically solitary, asymptomatic, and requires no treatment. Multiple enchondromas (enchondromatosis) can occur as part of both Ollier disease (multiple and unilateral) and Maffucci syndrome (with hemangiomas), and carry a risk of malignant transformation.
Giant cell tumor of bone (“osteoclastoma”) is a benign neoplasm containing multi-nucleated giant cells admixed with stromal cells. It is uncommon but occurs more often in females than in males, with peak age 20–50. Clinically, the tumor produces a bulky mass with pain and fractures. X-rays show an expanding lytic lesion sur-rounded by a thin rim of bone, with a possible “soap bubble” appearance. Treatment is surgery (curettage or en bloc resection). Osteoclastoma is locally aggressive with a high rate of recurrence (40–60%). In spite of being considered benign, approximately 2% will metastasize to the lungs.
Grossly, the tumor causes a red-brown mass with cystic degeneration that often involves the epiphyses of long bones, usually around the knee (distal femur and proximal tibia). Microscopically, multiple osteoclast-like giant cells are distributed within a background of mononuclear stromal cells.
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