Tumor biology and incidence

  • Benign osteoblastic lesion of bone
  • Accounts for approximately 10% of all benign lesions

Age

  • Typically affects persons 10-35 years of age
  • Has been reported as late as eighth decade

Gender

M:F = 2:1

Presentation

  • Focal pain that is worse at night; may awaken the patient while sleeping
  • Pain relieved by aspirin and low dose NSAIDs, possibly because the tumor has a diurnal production of prostaglandins
  • Vascular tumor; substances that cause vasodilitation such as alcohol may precipitate an acute pain crisis
  • May be vasomotor disturbances in the region (increased skin temperature)
  • May cause scoliosis secondary to muscle spasms
  • Intraarticular lesions can cause synovitis and joint effusions or decreased range of motion, mimicking other intraarticular pathologies
  • May be muscle wasting, which may lead to erroneous diagnosis of neurologic disorder
  • Symptoms usually plateau over time
  • Patients can have accelerated bone growth if nidus is near growth plate, especially in young children
Figure 1a.
Figure 1b.

Physical findings

  • Spinal lesions can present with scoliosis
  • Intracapsular lesions can cause joint effusion

Plain films

Site
  • Predilection for long bones (femur and tibia) as well as the vertebrae (usually posterior elements)
  • May occur in any bone and may be cortical, medullary, subperiosteal, or periarticular (intracapsular)
Size
  • Nidus usually < 1 cm
  • If nidus is greater than 2 cm, lesion usually considered an osteoblastoma
Tumor effect on bone and bone response to tumor
  • Cortical: Intense focal sclerotic reaction around the lucent nidus
  • Medullary: Sclerotic reaction surrounding the lucent nidus; sclerosis may be seen for a considerable distance from the nidus
  • Intracapsular: Radiolucent nidus; usually minimal to no reactive bony sclerosis; can cause effusion
  • Subperiosteal: Periosteal response is minimal, sclerosis is absent, bony scalloping/resorption.
Matrix

Lucent nidus may or may not be partially calcified centrally

Cortex

Intact, may cause marked cortical thickening

Soft tissue mass

None, except in the rare subperiosteal form (small juxtacortical soft tissue mass may be seen immediately adjacent to the bone)

Figure 2a.
Figure 2b.
Figure 2c.

 

Bone scan

  • Hot on bone scan
  • May be difficult to identify nidus due to uptake in surrounding periosteal reaction

CT and MRI

  • Thin section CT is modality of choice for localization of the nidus, often as guided by plain radiographs or a bone scan
  • CT useful :
    • When on plain x-ray there is intense sclerosis and nidus is not visible but suspected
    • To define the exact location of the lesion with respect to the cortex for pre-operative planning
    • In evaluating lesions of the axial skeleton- pelvis and spine
  • May be necessary to obtain thin slices (1-2mm) on CT scan to visualize a small nidus
  • MRI useful for identification of lesions where nidus is of similar density to surrounding bone
Figure 3a.
Figure 3b.
Figure 3c.

 

Differential diagnosis

Figure 5a. Osteoblastoma
Figure 5b. Osteomyelitis
Figure 5c. Stress fracture
Figure 5d. Stress fracture MRI

Natural history

  • Spontaneous regression of clinically and radiologically diagnose osteoid osteomas can occur during an average of 4-6 years
  • Nidus gradually calcifies, ossifies, and finally, blends into the sclerotic surrounding bone
  • Many patients able to tolerate the pain with or without the prolonged use of NSAIDs
    • Those who cannot are candidates for surgical intervention

Pathology

  • Gross: Nidus is small, well circumscribed, red, and granular in appearance
  • Microscopic: Nidus contains osteoid at its center; matures into interconnected trabeculae of bone in a fibrovascular stroma; osteoblasts and osteoclasts rim the trabeculae
  • Bone appears more mature towards periphery of lesion, merges with sclerotic reactive bone
Figure 4a.
Figure 4b.
Figure 4c.
Figure 4d.

Diagnosis and treatment

  • Most osteoid osteomas should be diagnosed by imaging
  • Natural history is to undergo spontaneous resolution after a variable amount of time
  • If pain is unresponsive to anti-inflammatories or if patient cannot tolerate the medication, treat lesion surgically
  • Lesion can be resected or ablated percutaneously under radiographic control, ablated with a radiofrequency technique or toxic substance (for example, alcohol), curetted, or resected en bloc
    • Curettage has higher risk of recurrence than complete resection
    • En bloc resection has lower risk of relapse, but higher likelihood of requiring a reconstructive procedure folowing lesional remova.
  • Specimen can be x-rayed to ensure complete resection.
  • Defect left by removal of lesion should be bone grafted or instrumented if there is risk of fracture
Figure 6a.
Figure 6b.
Figure 6c.
Figure 6d.
Figure 6e.
Absolute contraindications to medical therapy
  • Allergy to medication
  • Uncertainty of diagnosis.
  • Past history of a bleeding ulcer or other bleeding disorders
Relative contraindications to medical therapy
  • Patient preference
  • Breakthrough pain at maximal therapeutic doses
  • Development of adverse reaction to medication

Complications

  • Lesion located close to growth plate in young child may lead to accelerated bone growth in area
  • Lesion in spine may cause scoliosis
  • Intracapsular lesions may produce chronic effusion
  • Full-thickness cortical defect produced after resection of cortical or intramedullary osteoid osteoma may put patient at risk of pathologic fracture

Recommended reading

 

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