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 - Case B prox. femur - - Case C prox. femur - - Case D spine Case E calcaneus -
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