Cell of Origin: Osteoid osteoma is a benign skeletal neoplasm of unknown etiology that is composed of an ovoid or spherical nidus of osteoid-rich tissue and interconnected bone trabeculae superimposed on a background of highly vascularized connective tissue containing large dilated vascular channels.
Synonyms: Osteoid osteoma are named osteoblastoma when they measure greater than 2cm.
Associations/Predisposing Factors: Osteoid osteoma may induce scoliosis, which is initially postural; however, with time, structural changes may occur.
Common Locations: The most common skeletal sites are the metaphysis or diaphysis of long bones, which are affected in 73% of patients. Of the long bones, 50% are found in the femur or tibia. The spine is affected in 10-14% of patients; these predominantly involve the posterior spinal elements. The hands are affected in 8%, and the feet, in 4%. The tumor has been reported in all parts of the skeleton.
Demographics: Most patients with osteoid osteoma are young with three quarters of patients are aged 10-30 years, and more than 90% of patients are aged 5-25 years. Osteoid osteoma more commonly affects males than females. The male-to-female ratio is 2:1. Osteoid osteoma composes 10% of all benign bone tumors.
Gross Morphology:
Gross Appearance: Osteoid osteoma is classified as cortical, cancellous, or subperiosteal. As many as 80% of cases involve the cortical bone; the remainder of the tumors are intramedullary.
Histology: The tumor consists of an ovoid or spherical nidus of osteoid-rich tissue and interconnected bone trabeculae superimposed on a background of highly vascularized connective tissue containing large dilated vascular channels. Multinucleated giant cells and osteoclasts are frequently observed. Neural staining techniques reveal many axons throughout an osteoid osteoma, which probably accounts for the pain. Levels of prostaglandin E2 are markedly elevated in the nidus; this is presumably the cause of pain and vasodilatation.
Special Stains: Neural staining
Radiology: Radiography is the initial examination of choice and may be the only examination required. The lesion initially appears as a small sclerotic bone island within a circular lucent defect. This central nidus is seldom larger than 1.5 cm in diameter, and it may be associated with considerable overlying cortical and endosteal bone sclerosis. Computed Tomography is the ultimate diagnostic tool for the precise localization of the nidus. Computed Tomography is particularly effective in areas with complex anatomy, such as the spinal pedicles, laminae, and femoral neck. On CT examination, the nidus enhances after the intravenous administration of contrast medium and shows a variable degree of mineralization. MRI reliably demonstrates the nidus which is isoechoic to muscle on T1-weighted images and intensity increases with T2-weighted sequences with central area of low signal corresponding to sclerosis. Radionuclide bone scanning of uptake of technetium-99m phosphonates shows intense activity at the site of the tumor. Occasionally, a double-density sign is seen in which a small focus of radioactivity in the nidus is superimposed on a larger area of radioactivity. The sensitivity of radionuclide bone scans is extremely high. A radionuclide bone scan is considered mandatory in patients with painful scoliosis. A radionuclide bone scan can demonstrate the tumor before abnormal radiographic findings are apparent.
Prognosis and Treatment:
The classic presentation includes focal skeletal bone pain, which worsens at night and is frequently relieved with a small dose of aspirin. Pain that increases with activity and at night occurs in 95% of patients with spinal tumors. In 29% of patients, the pain is severe enough to waken the patient. The site of involvement may be tender to touch or pressure. Constitutional symptoms are usually absent. When the spinal column is involved, muscle spasms may cause abnormal alignment. A painful scoliosis may be concave toward the lesion. The onset of scoliosis may be acute and is frequently initiated by physical exertion. Osteoid osteoma has been called the most common cause of painful scoliosis. The tumor has no malignant potential. The tumor usually does not grow, and it occasionally regresses spontaneously or becomes dormant, leaving residual sclerosis.
Treament options for osteoid osteoma include conservative treatment with nonsteroidal antiinflammatory medications, radiofrequency ablation and surgical resection. Long term drug therapy may result in gastrointestinal side effects and is not tolerated well by patients. Surgery is frequently associated with major morbidity and a prolonged period of recovery. Percutaneous RF ablation is performed under CT guidance by using general or spinal anesthesia. After localization of the nidus with 1- to 3-mm CT sections, an osseous access is established with either a 2-mm coaxial drill system or an 11-gauge Jamshidi needle. RF ablation is performed at 90°C for 4-5 minutes by using a rigid RF electrode with a 1-mm diameter. The procedure is successful when the electrode is heated to the desired temperature within the nidus. In one series, clinical success was achieved in 96% of patients. All recurrences were treated with a second procedure, with a secondary success rate of 100%.
Reference(s): 1. Hoffman RT, Jakobs TF, Kubisch CH, Trumm CG, Weber C, Duerr
HR, Helmberger TK, Reiser MF. Radiofrequency Ablation in the
Treatment of Osteoid Osteoma-5-Year Experience. European
Journal of Radiology 2008; 73(2010) 374-379.
2. Khan AN, Chandramohan M, Turnbull I, MacDonald S. Osteoid
Osteoma. Emedicine. September 2009.
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