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https://upload.orthobullets.com/topic/8012/images/case b - prox humerus - xray - parsons_moved.png
https://upload.orthobullets.com/topic/8012/images/Case B - femur - xray - Parsons_moved.png
https://upload.orthobullets.com/topic/8012/images/Osteoid Osteoma - Xray - proximal fibula_moved.jpg
https://upload.orthobullets.com/topic/8012/images/Osteoid Osteoma - CT scan_moved.jpg
https://upload.orthobullets.com/topic/8012/images/Osteoid Osteoma - Histology_moved.jpg
https://upload.orthobullets.com/topic/8012/images/osteoid17.jpg
  • Summary
    • Osteoid Osteomas are small, benign, osteogenic bone lesions most commonly found in the proximal femur. Patients typically present between ages 5 and 25 with regional pain that is worse at night and improves with NSAIDs.
    • Diagnosis is made radiographically by a characteristic lesion that is less than 1.5 cm in diameter with a sclerotic margin and radiolucent nidus. 
    • Treatment is usually nonoperative with observation and NSAID for pain control. Radiofrequency ablation or surgical resection may be indicated in patients with progressive and severe symptoms.
  • Epidemiology
    • Incidence
      • accounts for 10-14% of all benign bone tumors and 2-3% of all primary bone tumors
      • peak incidence in 2nd decade of life
    • Demographics
      • 2.5:1 male-to-female ratio
      • persons aged 5-25 years (70% present before age of 20)
    • Anatomic location
      • most common
        • lower extremity (>50%)
          • proximal femur > tibia diaphysis
            • usually found within the bone cortex
        • spine (10-15%)
          • thoracic and lumbar regions > cervical and sacral
          • majority involve the posterior elements
          • usually found on the side of concavity in scoliosis
        • hand (5-10%)
          • usually involve scaphoid and proximal phalanx
        • foot (<5%)
          • predominantly involves the talar neck
  • Etiology
    • Pathophysiology
      • pathoanatomy
        • nidus
          • characterized by a central nodule of woven bone and osteoid with osteoblastic rimming
        • reactive zone
          • area of thickened bone and fibrovascular tissue
      • cellular biology
        • pain
          • attributed to increased local concentration of prostaglandin E2 and COX1 & 2 expression
            • explains why pain improved with NSAIDS
          • increased number and size of unmyelinated nerve fibers within the nidus
    • Associated conditions
      • orthopedic manifestations
        • scoliosis with lesion on concave side of the curve
          • thought to result from marked paravertebral muscle spasm
        • growth disturbance
          • epiphyseal involvement could result in elongation of affected limb and resultant limb length discrepancy 
        • flexion contractures
  • Classification
      • Enneking Classification of Benign Lesions
      • Grade
      • Examples
      • Stage 1
      • Latent lesions
      • Enchondroma
      • Non-ossifying fibroma
      • Stage 2
      • Active lesions
      • Osteoid osteoma
      • UBC
      • ABC*
      • Chondroblastoma
      • Chondromyxoid fibroma
      • Giant cell tumor of bone*
      • Stage 3
      • Aggressive lesions
      • Giant cell tumor of bone*
      • ABC*
    • *Giant cell tumor of bone and aneurysmal bone cyst can be either stage 2 (active) or stage 3 (aggressive) lesions depending on the amount of bone destruction, soft tissue, masses, and joint involvement
  • Presentation
    • Symptoms
      • pain
        • constant and progressive
        • worse at night and with drinking ETOH
        • relieved by NSAIDS
        • location may be adjacent to joint and mimic arthritis
      • swelling
        • hand lesions may present with painless swelling
    • Physical exam
      • inspection
        • palpable bone
          • deformity, swelling, erythema, tenderness
        • proximity to a joint
          • effusion, contracture, limp, muscle atrophy
        • spine
          • painful scoliosis due to paravertebral muscle spasm
  • Imaging
    • Radiographs
      • views
        • obtain orthogonal views of affected bone or joint
      • findings
        • intensely reactive bone around a radiolucent nidus
        • because of intensely reactive sclerosis, may be possible to detect nidus only with CT or MRI
    • CT
      • indication
        • considered imaging modality of choice
          • CT provides better contrast between lucent nidus and reactive bone compared to MRI
        • characteristic findings of the nidus
          • usually < 1.5 cm (otherwise think osteoblastoma)
          • the area of reactive bone sclerosis may be greater than the diameter of the nidus
          • target-shaped/bulls-eye appearance, representing calcified center of the nidus   
            • present 50% of the time
    • Bone scan
      • indications
        • concerning features on radiograph or advanced imaging
      • findings
        • intense hot area of focal uptake at the nidus
        • low uptake in reactive zone peripherally
          • known as the 'double-density sign'
    • MRI
      • indications
        • usually not recommended as bone marrow edema appreciated on MRI can mask typical features of tumors
        • can be useful in illustrating nidus in cases of intra-articular lesions
      • findings
        • must be interpreted with reference to x-ray or CT scan
  • Studies
    • Histology
      • distinct demarcation between nidus and reactive bone
        • nidus
          • contains uniform osteoid seams of immature osteoid trabeculae (woven bone) with a sharp border of osteoblastic rimming
          • uniform plump osteoblasts have regularly shaped nuclei with abundant cytoplasm
        • reactive zone
          • region surrounding the sclerotic border
        • lesion does not infiltrate the surrounding bone
  • Differentials
    • Long bone osteoid osteomas need to be differentiated from
      • stress fx
      • osteomyelitis
      • Ewing's sarcoma
    • Posterior spinal element lesions need to be differentiated from
      • aneurysmal bone cyst
      • osteoblastoma (see table below)
      • Osteoid osteoma vs. Osteoblastoma
      • Osteoid Osteoma
      • Osteoblastoma
      • Incidence
      • 10% of benign tumors
      • 3% of benign 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, partial response to NSAIDS. 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
      • clinical observation and NSAID administration
        • indications
          • first line of treatment for most extremity lesions
            • in 50% of patients treated with NSAIDs, lesions burn out and resolve after several years
            • NSAIDS can be effective for limiting pain
            • not ideal for every patient given the harmful effects of NSAIDs (gastritis, AKI, etc)
          • painful spine lesions without scoliosis
    • Operative
      • percutaneous radiofrequency ablation
        • indications
          • considered standard of care
            • compared to surgery, RFA allows for access to more challenging anatomic sites, decreases procedure time and hospital stay length, and decreases costs
          • spine lesions
            • RFA can be safe and effective for spinal osteoid osteoma based on motor response testing performed during procedure
            • for lesions close to neurovascular structures, a distance of 1-1.5cm should be kept between probe and sensitive anatomy to prevent damage
          • periarticular lesions
            • safe for periarticular lesions if probe is >1cm away from articular surface, otherwise may risk damage to articular cartilage
        • outcomes
          • 90% of patients are successfully treated with 1-2 sessions of RFA
          • 10-15% recurrence rate
      • MR-guided high-intensity focused ultrasound (MR-HIFU)
        • overview
          • based on MR imaging, therapeutic ultrasound energy transferred transcutaneously causing thermal ablation to the periosteal nerves, which penetrates the medullary bone and coagulates the osteoma nidus
        • indications
          • failure of medical management
          • compared with surgery and RFA, MR-HIFU is a non-invasive and non-ionizing treatment option
          • comparable clinical response to RFA 
      • surgical resection with curettage
        • indications
          • location of lesion is not amenable to CT-guided percutaneous radiofrequency ablation
            • e.g. close to skin or nerve
          • en bloc resection indicated in spinal disease if osteoid osteoma is associated with fixed spinal deformity or if RFA unsafe due to proximity to dura/nerve roots
          • lesions that reoccur after RFA
          • digital lesions
            • RFA carries risk of thermal skin necrosis and injury to digital neurovascular bundle
        • outcomes
          • 94% success with local excision
          • associated spinal deformity can resolve spontaneously if the lesion is resected within 15 months of onset of deformity
  • Technqiues
    • Percutaneous radiofrequency ablation 
      • done under CT guidance
      • radiofrequency electrode inserted into the nidus (cad)
      • probe heated to 90 deg C for 4-6 minutes to produce a 1cm zone of necrosis
    • Surgical resection with curettage
      • successful treatment depends on complete marginal resection of nidus (sclerotic bone is normal and can be left behind)
        • percutaneous approach
        • open approach
  • Complications
    • RFA related complications
      • recurrence: 10-15% recurrence rate
      • cellulitis, thrombophlebitis, skin necrosis
        • increased risk if lesion is <1.0 cm from skin
      • neurovascular damage - increased risk if lesion <1.0-1.5cm from neurovascular bundle
    • Limb length discrepancy
      • elongation of affected limb and resultant limb length discrepancy may occur if osteoid osteoma effects the epiphysis
  • Prognosis
    • Pain from lesions usually resolves after an average of 3 years
    • The lesion spontaneously resolves in 5-7 years
    • overall good prognosis, with extremely rare malignant transformative potential
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