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Osteoid Osteoma

  • A small, benign bone tumor that causes intense pain and marked sclerosis
  • The lucent nidus in the bone is 0.5-1.5 cm in diameter.
  • Although the proximal femur is the most common site, followed by the tibia, almost any bone may be affected, including the phalanges.
  • Comprises 10% of all benign bone tumors
  • Occurs primarily in persons 5-25 years old
  • Male:Female ratio, 3:1 (reason unknown)
Risk Factors
No genetic predisposition is known.
The cause is unknown.
Signs and Symptoms
  • Pain is more severe at night and often is relieved by aspirin or other NSAIDs.
  • A limp is common.
  • Mild atrophy or wasting of muscles in the area may occur.
  • The region is tender to palpation.
  • If the osteoid osteoma is near a joint, it may cause stiffness.
    • If it involves the spine, scoliosis may be seen.
  • The presence of osteoid osteoma in >1 site in a patient is unusual.
Physical Exam
  • Mild swelling, erythema, and occasional muscle wasting in the involved area
  • Absence of fever
  • Tenderness and stiffness in the region of the osteoid osteoma
No laboratory findings aid in the diagnosis.
  • In many areas, because the bone is not seen in cross-section, the diagnosis may not be apparent with plain films.
  • CT is the best imaging modality for confirming the lesion, but the lesion’s location must be known to obtain the correct position on the CT scan.
    • Characteristic target appearance of the nidus and its sclerotic rim:
      • An oval radiolucent nidus of ~5-10 mm surrounded by a dense reactive zone
      • Nidus often visible in the bone’s cortex
  • Bone scanning is useful for confirming or localizing an osteoid osteoma if the lesion’s location cannot be determined by plain radiographs.
    • The bone scan is always focally positive.
Pathological Findings
  • On cross-section, the nidus appears as a haphazard arrangement of osteoblasts and trabeculae, which is surrounded by a dense shell of cortical bone.
  • On microscopic examination:
    • The nidus is composed of dense, normally woven bone with osteoblastic rimming, and the reactive shell around it is composed of dense cortical bone.
    • The cells have a normal, benign appearance.
Differential Diagnosis
  • Osteomyelitis
  • Stress fracture
  • Buckle fracture
General Measures
  • Osteoid osteomas may resolve spontaneously in 2-6 years.
  • NSAIDs may be used during this time to control the pain.
  • Because of pain or intolerance to analgesics, many patients request treatment of the lesion.
  • For patients treated nonoperatively, activity may be allowed as tolerated.
  • Return to normal activity is allowed within 2-4 weeks of radiofrequency ablation.
  • After surgical excision, partial weightbearing should be recommended for 6-8 weeks until the bone has had time to remodel and gain strength.
  • Aspirin, regular or enteric-coated
  • Ibuprofen
  • Naproxen
  • Radiofrequency ablation is the preferred method of treatment.
    • Patients are given general anesthesia.
    • The radiofrequency probe is placed into the nidus under CT guidance.
      • The radiofrequency probe must be insulated to prevent soft-tissue necrosis.
    • The nidus is heated to ~80°C for 4-6 minutes.
    • Effective in 90% of patients with 1 or 2 treatments  
  • Surgical resection may be necessary after failed radiofrequency ablation or in sites where the risk of thermal injury is high.
    • En bloc resection is not necessary.
    • Removal of the cortical bone over the lesion and curettage of the nidus is effective.
  • The prognosis is excellent.
  • No risk of malignant transformation exists.
  • Fracture after surgical excision may occur.
  • Gastritis or ulcers from NSAIDs
Patient Monitoring
Frequent monitoring is not needed because these lesions have no malignant potential.
213.9 Osteoid osteoma
Patient Teaching
  • Patients should be counseled about the benign nature of the lesion and its tendency to resolve spontaneously over the years.
  • Patients may be offered medical or surgical treatment and allowed to choose between them.
  • For intensely painful or disabling lesions, or in patients unable to tolerate NSAIDs, an intervention such as radiofrequency ablation or surgical excision often is selected.
Q: Is protected weightbearing necessary after radiofrequency ablation?
A: In general, protected weightbearing is not necessary, and the patient may resume normal activities quickly.
Q: Who performs radiofrequency ablation of osteoid osteomas?
A: Patients should be seen by an orthopaedic oncologist first and then be referred to an interventional radiologist for the procedure.
Q: What is the best imaging modality for detecting an osteoid osteoma?
A: CT scanning (thin cuts, 1 mm) is the best method.

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