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. High resolution CT scan distinguishes osteoid osteomas from other radiolucent bone lesions Treatment is usually nonoperative with observation and NSAID for pain control. Radiofrequency ablation (RFA) 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%) login to view 2 more bullets spine (10-15%) login to view 3 more bullets hand (5-10%) login to view 1 more bullet foot (<5%) login to view 1 more bullet Etiology Pathophysiology pathoanatomy nidus login to view 1 more bullet reactive zone login to view 1 more bullet cellular biology pain login to view 3 more bullets Associated conditions orthopedic manifestations scoliosis with lesion on concave side of the curve login to view 1 more bullet growth disturbance login to view 1 more bullet 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* 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 or within posterior spinal elements and cause scoliosis swelling hand lesions may present with painless swelling Physical exam inspection palpable bone login to view 1 more bullet proximity to a joint login to view 1 more bullet spine login to view 1 more bullet 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 login to view 5 more bullets characteristic findings of the nidus login to view 5 more bullets Bone scan indications concerning features on radiograph or advanced imaging findings intense area of focal uptake at the nidus low uptake in reactive zone peripherally login to view 1 more bullet 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 login to view 2 more bullets reactive zone login to view 1 more bullet 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 login to view 5 more bullets MR-guided high-intensity focused ultrasound (MR-HIFU) overview login to view 1 more bullet indications login to view 3 more bullets Operative percutaneous radiofrequency ablation indications login to view 7 more bullets outcomes login to view 2 more bullets surgical resection with curettage indications login to view 6 more bullets outcomes login to view 2 more bullets Techniques 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