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 cause of painful scoliosis in the adolescent population Demographics 3:1 male to female ratio persons aged 5-25 years (>80% present before age of 30) 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%) scaphoid and proximal phalanx foot (<5%) predominantly involves the talar neck Etiology Pathophysiology pathoanatomy nidus 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 increased number and size of unmyelinated nerve fibers within the nidus Associated conditions orthopaedic manifestations painful scoliosis growth disturbance 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 Stage 3 Aggressive lesions Giant cell tumor of bone Symptoms Symptoms pain constant and progressive worse at night and with drinking ETOH relieved by NSAIDS may be adjacent to joint and mimic arthritis 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 postural scoliosis, paravertebral muscle spasm Imaging Radiographs recommended views 3 views of affected bone or joint findings intensely reactive bone around radiolucent nidus CT indication cross-sectional imaging is the study of choice findings to help identify the location and size of nidus usually < 1.5 cm (otherwise think osteoblastoma) Bone scan indication concerning features on radiograph or advanced imaging findings intense hot area of focal uptake at the nidus low uptake in reactive zone known as the 'double-density sign' MRI indications usually not recommended as it can mimic aggressive lesions findings must be interpreted with reference to x-ray or CT scan Histology 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 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, 3.5 - 4.0 cm) Site > 50 % in long bone diaphysis > 35% in posterior elements of the spine Location Proximal femur > tibia diaphysis > spine Vertebral 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, partial response to 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 clinical observation and NSAID administration indications NSAIDS are 1st line and will lead to a dramatic decrease in symptoms ~50% can be treated with NSAIDS alone also indicated for painful spine lesions without scoliosis fingertip lesions (distal phalanx) may not respond to NSAIDS Operative percutaneous radiofrequency ablation relative indications failure of medical management periarticular lesions, which increase the risk of cartilage injury and premature degenerative disease. spinal lesions (controversial) - depends on the location of the lesion and proximity to neural elements contraindications lesions in the fingers lesions close to nerves technique done under CT guidance probe at 80-90 deg C for 6 minutes to produce a 1cm zone of necrosis 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) indications failure of medical management contraindications any contraindication to anesthesia lesions in anatomic area which could not be directly accessed by ultrasound energy (ex. vertebrae) technique 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 outcomes less invasive than other modalities significant and persistent decreases in pain with low risk for adverse events improvements in quality of life scores decreased need for NSAID in treatment population improvement in follow-up imaging showing decrease or total absence in osteoid osteoma nidus vascularity surgical resection with curettage indications location of lesion is not amenable to CT guided percutaneous radiofrequency ablation e.g. close to skin or nerve spine lesion associated with painful scoliosis digital lesions RFA carries risk of thermal skin necrosis and injury to digital neurovascular bundle technique successful treatment depends on complete marginal resection of nidus (sclerotic bone is normal and can be left behind) percutaneous approach open approach outcomes 94% success with local excision associated scoliosis rarely requires treatment Complications Recurrence 10-15% recurrence rate with percutaneous radiofrequency ablation Prognosis Pain from lesions usually resolves after an average of 3 years The lesion spontaneously resolves in 5-7 years In the spine, early resection (within 18 months) leads to resolution of scoliosis in young children (<11years)