musculoskeletal and connective tissue disorders
Benign Bone Tumors and Cysts
Osteoid osteoma
Osteoid osteoma, which tends to affect young people (commonly aged 10 to 35), can occur in any bone but is most common in long bones. It can cause pain (usually worse at night, reflecting increased nocturnal prostaglandin-mediated inflammation). Pain is typically relieved by mild analgesics (particularlyaspirinor other nonsteroidal anti-inflammatory drugs [NSAIDs]) that target prostaglandins. In growing children, the inflammatory response and associated hyperemia, if close to the open growth plate, may cause overgrowth and limb length discrepancy. Physical examination may reveal atrophy of regional muscles because the pain causes muscle disuse. Characteristic appearance on imaging studies is a small radiolucent zone surrounded by a larger sclerotic zone. If a tumor is suspected, a total body technetium-99m bone scan should be done; an osteoid osteoma appears as an area of increased uptake, although many other bone lesions do so as well. CT with fine image sequences or MRI is also done and is most helpful in distinguishing the lesion. Plain films or fine cut CT scan may show a classic "bull's eye" appearance of the true nidus of the tumor surrounded by reactive bone. Ablation of the small radiolucent zone with percutaneous radiofrequency energy provides permanent relief in most cases. Most osteoid osteomas are treated by an interventional musculoskeletal radiologist using percutaneous techniques and anesthesia. Less often, osteoid osteomas are surgically curetted or excised. Surgical removal may be preferred when the osteoid osteoma is near a nerve or close to the skin (eg, spine, hands, feet) because the heat produced by radiofrequency ablation may cause damage. Axial CT image of the proximal femur (adjacent bone is pelvic ramus) shows typical lucent nidus with central calcification (arrow) in child aged 6 with left hip pain. This CT shows the classic bullseye lesion. Image courtesy of Michael J. Joyce, MD, and Hakan Ilaslan, MD. This lateral x-ray of the left tibia shows a lucent posterior osteoid osteoma (red arrow). Note the chronic-appearing, smooth periosteal thickening around the tumor (blue arrows). Image courtesy of Michael J. Joyce, MD, and Hakan Ilaslan, MD. This axial T2-weighted fat-suppressed MRI shows an intracortical osteoid osteoma (arrow) and adjacent subtle intramedullary bone marrow edema. Image courtesy of Michael J. Joyce, MD, and Hakan Ilaslan, MD. 