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