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https://upload.orthobullets.com/topic/8013/images/Case B - xray - Parsons_moved.png
https://upload.orthobullets.com/topic/8013/images/Case B - CT - Parsons_moved.png
https://upload.orthobullets.com/topic/8013/images/Case B - bone scan - Parsons_moved.png
https://upload.orthobullets.com/topic/8013/images/Case C - xray - Parsons_moved.png
https://upload.orthobullets.com/topic/8013/images/Histology C - parsons_moved.png
https://upload.orthobullets.com/topic/8013/images/osteoblastoma ct.jpg
  • summary
    • Osteoblastomas are benign, aggressive osteogenic bone lesions commonly found in the posterior elements of the spine. Patients typically present between ages 10 and 30 with regional pain with only partial response from NSAIDs.
    • Diagnosis is made radiographically by a characteristic lesion that is > 2 cm in diameter with a sclerotic margin and radiolucent nidus. 
    •  Treatment is usually curettage or marginal excision with bone grafting.
  • Epidemiology
    • Incidence
      • relatively rare: 1% of all primary bone tumors and 10% of all osseous spinal neoplasms
      • less common than osteoid osteoma
    • Demographics
      • males > females (2:1)
      • majority of patients 10-30 years of age
    • Anatomic location
      • most common in posterior elements of spine and sacrum (30-40%)
      • other locations include diaphysis or metaphysis long bones (lower > upper extremities) and mandible
  • Etiology
    • Genetics
      • Rearrangements of FOS (Chr 14) and FOSB (Chr 19) are reported
    • Associated conditions
      • oncogenic osteomalacia
      • secondary ABC
        • 10%-40% associated with secondary ABC
  • Presentation
    • Symptoms
      • pain
        • slowly progressive dull aching pain
        • night pain is not typical
        • partial response to 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 2-10cm in size with occasional intralesional densities
        • reactive sclerotic bone
        • 66% cortically based, 33% medullary based; rarely periosteal 
        • often expansile with or without characteristic reactive bone formation seen in osteoid osteoma
          • 25% appear very aggressive and often mistaken for malignant lesion given minimal secondary bone reaction
    • CT
      • Indicated to fully evaluate lesion
      • Specifically helpful in characterizing the size, exact location, presence and extent of cortical disruption, and presence of a soft tissue component
    • MRI
      • identifies reactive soft tissue edema and often better evaluates the soft tissue component if present
      • low to intermediate T1 signal intensity and intermediate to high T2 signal intensity 
    • Bone scan
      • hot with intense focal uptake despite the pathologically benign features
  • 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
      • irregular seams of osteoid/woven bone spicules separated by loose fibrovascular stroma
      • rim of osteoblasts surrounds osteoid
      • numerous mitotic figures, but not atypical
      • rich vascularity often with extravasated erythrocytes
  • Differential
    • Radiographic differential for osteoblastoma includes
      • osteosarcoma
      • ABC
      • osteomyelitis
      • osteoid osteoma
    • Differentiating from ABC
      • cross sectional imaging for ABCs demonstrate air-fluid levels and internal septations
      • on histopathology, ABCs will demonstrate multiple blood filled sinusoidal spaces with fibrous walls
    • Differentiating from osteosarcoma
      • osteoblastoma does not demonstrate periostitis unless in the setting of acute pathologic fracture 
      • soft tissue component more common with osteosarcoma
      • osteoblastoma does not infiltrate or permeate preexisting lamellar bone structures 
      • osteoblastoma is characterized by nuclear beta-catenin staining, whereas cytoplasmic or membranous staining of beta-catenin suggests osteosarcoma
    • 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 less likely to be relieved by NSAIDs
        • larger
        • more giant cells
    • Differential for lesions of the posterior spinal elements includes
      • aneurysmal bone cyst
      • osteoid osteoma
      • osteoblastoma
      • Osteoid osteoma vs. Osteoblastoma
      • Osteoid Osteoma
      • Osteoblastoma
      • Incidence
      • 10% of benign bone tumors
      • 3% of benign bone tumors
      • Size
      • < 2 cm (typically <1.5cm)
      • > 2 cm (average, 3.0-3.5 cm)
      • Site
      • > 50% in long bone diaphysis
      • > 35% in posterior elements of the spine
      • Location
      • Proximal femur > tibia diaphysis > phalanges > spine
      • Vertebral column > long bone diaphysis/metaphysis
      • 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 that is not self-limiting. Central lesion less organized with greater vascularity.
      • Symptoms
      • Nocturnal pain, relieved by NSAIDS. If spine involvement, presents 75% of the time with painful scoliosis with lesion on concave side of curve
      • Dull ache which is less likely to be relieved by NSAIDS (partial response). Neurologic symptoms common if spine involvement.
      • Management of Spine Lesions
      • Nonsurgical management is indicated as first-line treatment, definitive treatment is percutaneous RFA/surgical resection 
      • Surgery is always indicated as they do not respond to nonsurgical treatment.
  • Treatment
    • Nonoperative
      • observation
        • rarely indicated as the lesion will continue to grow
    • Operative
      • curettage or marginal excision with bone grafting
        • aqedeuate in most cases to achieve local control
        • can be combined with cryotherapy and chemical cauterization with phenol as adjuncts
      • En bloc resection
        • typically perfomed for locally aggressive, large, or recurrent lesions
        • occasionally required for lesions in the spine
        • lower risk of recurrence compared to curettage
  • Prognosis 
    • excellent prognosis with most patients disease free after the initial surgical treatment. 
    • most common complication is local reoccurrence, with rates as high as 15-25%
    • recurrence is most common in initial 2 years following treatment but is rare after 2 years
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