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Osteoblastoma

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Topic updated on 06/09/16 5:19pm
  
Introduction
  • Aggressive benign osteoblastic tumor of bone 
    • "big brother" of osteoid osteoma (nidus > 2cm)
  • Epidemiology
    • incidence
      • relatively rare
      • less common than osteoid osteoma
    • demographics
      • males > females (2:1)
      • majority of patients 10-30 years of age
    • location
      • most common in posterior elements of spine
  • Genetics
    • unknown
  • Associated conditions
    • oncogenic osteomalacia
    • secondary ABC
      • 10%-40% associated with secondary ABC
Presentation
  • Symptoms
    • pain
      • slowly progressive dull aching pain
      • not relieved by NSAIDS
    • may see neurologic symptoms with spine involvement
  • Physical exam
    • swelling
    • muscle atrophy
    • limp
Imaging
  • Radiographs
    • recommended views
      • AP and lateral of symptomatic area
    • findings
      • lytic or mixed lytic-blastic lesion with radiolucent nidus > 2cm   
      • reactive sclerotic bone
      • 66% cortically based, 33% medullary based
      • often expansile with extension into soft tissues with rim of reactive bone
        • 25% appear very aggressive and often mistaken for malignant lesion
  • CT
    • indications
      • necessary to fully evaluate lesion
  • Bone scan
    • hot with intense focal uptake 
Studies
  • Histology
    • similar to osteoid osteoma but with more giant cells
    • distinct demarcation between nidus and reactive bone   
      • nidus of immature osteoid and osteoblasts with abundant cytoplasm and normal nuclei  
    • fibrovascular stroma that merges with normal trabeculae of bone
    • rim of osteoblasts surrounds osteoid 
    • numerous mitotic figures, but not atypical
Differential
  • Radiographic differential for osteoblastoma includes
    • osteosarcoma
    • ABC
    • osteomyelitis
    • osteoid osteoma
  • Differentiating from osteoid osteoma
    • characteristics specific to osteoblastoma
      • rare and locally aggressive but benign (not self limiting)
      • over 40% occur in posterior elements of spine or sacrum 
      • dull pain unresponsive to NSAIDs 
      • larger
  • Differential for lesions of the posterior spinal elements elements includes
    • aneurysmal bone cyst
    • osteod osteoma (see table below)
    • osteoblastoma

Osteoid Osteoma
Osteoblastoma
Incidence 10% of benign tumors 3% of benign tumors
Size

< 2 cm (typically <1.5cm)

>2 cm (average, 3.5 - 4.0 cm)
Site > 50 % in long bone diaphysis
> 35% in posterior elements of the spine
Location Proximal femur > tibia diaphysis > spine vetebral column > proximal humerus > hip
Natural History Self-limited Progressive
Histology

Benign appearance. No growth potential. Central nidus composed of more organized osteoid and lined by osteoblasts. 

Benign appearance. Localized growth, with aggressive potential. Central lesion less organized, with greater vascularity. 
Symptoms Nocturnal pain, relieved by NSAIDS Dull ache, not relieved by NSAIDS. >50% of spine tumors have neurologic symptoms.
Management of Spine Lesions Nonsurgical management is indicated as first-line treatment.  Surgery is always indicated as they do not respond to nonsurgical treatment.

 
Treatment
  • Nonoperative
    • observation
      • indications
        • rarely, if ever, indicated as the lesion will continue to grow
  • Operative
    • curettage or marginal excision with bone grafting
      • indications
        • standard of care
      • recurrence 10-20%
Image Bank
  Location
Xray
CT
Bone scan
MRI
Histology
Case A prox. humerus
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Case B prox. femur
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Case C prox. femur
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Case D spine
Case E calcaneus
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