You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Osteoid OsteomaArticle Last Updated: Apr 24, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Muthusamy Chandramohan, MBBS, DMRD, FRCR, Consultant Radiologist, Bradford Teaching Hospitals, UK; Ian Turnbull, MD, Lecturer, Department of Radiology, University of Manchester; Consulting Neuroradiologist, Hope Hospital, Salford, Manchester and North Manchester Hospital; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute Editors: Leon Lenchik, MD, Director, Densitometry Minifellowship, Assistant Professor, Department of Radiology, Wake Forest University Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Murali Sundaram, MBBS, FRCR, FACR, Consulting Staff, Department of Diagnostic Radiology, The Cleveland Clinic Foundation; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related keywords: sclerotic bone island, benign bone neoplasm, benign skeletal neoplasm, bone lesion, bone neoplasm, skeletal lesion, skeletal neoplasm, cortical bone sclerosis, endosteal bone sclerosis, bone sclerosis, osteoblastic rimming, osteoblastoma, giant osteoid osteoma INTRODUCTIONSection 2 of 12
  BackgroundOsteoid osteoma is a benign skeletal neoplasm of unknown etiology that is composed of osteoid and woven bone. The tumor is usually smaller than 1.5 cm in diameter. Osteoid osteoma can occur in any bone, but in approximately two thirds of patients, the appendicular skeleton is involved. The skull and facial bones are involved exceptionally. Most patients with osteoid osteoma are young. Rarely, an ossification center is affected. The classic presentation is that of focal bone pain at the site of the tumor. The pain worsens at night and increases with activity; it is dramatically relieved with small doses of aspirin. The lesion initially appears as a small sclerotic bone island within a circular lucent defect. This central nidus is seldom larger than 1.5 cm in diameter, and it may be associated with considerable overlying cortical and endosteal bone sclerosis. The tumors may regress spontaneously. The mechanism of this involution is not known, but tumor infarction is a possibility. PathophysiologyFeatures of the tumor The tumor consists of an ovoid or spherical nidus of osteoid-rich tissue and interconnected bone trabeculae superimposed on a background of highly vascularized connective tissue containing large dilated vascular channels. The amount of osseous and osteoid tissue varies within the nidus and is reflected in its radiologic opacity. The average size of the nidus is approximately 1.5 cm, but its size can be 0.5-2 cm. Generally, the amount of osteoid tissue exceeds that of mineralized bone. Multicentric nidi with osteoid osteoma have been reported in 24 cases in the world literature.1 Multinucleated giant cells and osteoclasts are frequently observed. The degree of bone sclerosis varies around the central nidus, but such reactions may be minimal and are sometimes absent. The sclerosis and osteoblastic rimming are indistinguishable from findings in osteoblastoma. Unlike in osteoblastoma, neural staining techniques reveal many axons throughout an osteoid osteoma, which probably accounts for the pain. Levels of prostaglandin E2 are markedly elevated in the nidus; this is presumably the cause of pain and vasodilatation.2, 3 Osteoid osteoma is classified as cortical, cancellous, or subperiosteal. Cortical tumors are the most common. The radiolucent nidus is within the cortical bone, where it is surrounded by a fusiform cortical thickening or solid or laminated periosteal new bone formation. Cancellous osteoid osteoma has an intramedullary location. Intra-articular osteoid osteomas are difficult to identify, and a delay of 4 months to 5 years before diagnosis is not unusual. The most common sites affected by cancellous osteoid osteomas include the juxta-articular region of the femoral neck, the posterior elements of the spine, and the small bones of the hands and feet. Usually, little sclerosis occurs around the nidus. Intra-articular tumors are associated with joint-space widening as a result of joint effusion or synovitis. Subperiosteal osteoid osteoma is a rare form of the disease that usually presents as a rounded soft-tissue mass adjacent to a bony cortex, which it excavates. Surrounding reactive changes are usually absent. The common sites involved include juxta- or intra-articular regions of the medial aspect of the femoral neck and the hands and feet, in particular, the neck of the talus. FrequencyUnited StatesIn a series of 8542 patients with primary bone tumors, investigators from the Mayo Clinic reported that osteoid osteomas accounted for 12.1% of benign tumors and 2.9% of all tumors. The most common skeletal sites are the metaphysis or diaphysis of long bones, which are affected in 73% of patients. The spine is affected in 10-14% of patients; these predominantly involve the posterior spinal elements. The hands are affected in 8%, and the feet, in 4%. The tumor has been reported in all parts of the skeleton. InternationalThe overall incidence in Europe is the same as in the United States, but the international incidence is not known. Mortality/MorbidityThe tumor has no malignant potential. The tumor usually does not grow, and it occasionally regresses spontaneously or becomes dormant, leaving residual sclerosis.
Related eMedicine topics: Related Medscape topics: RaceOsteoid osteomas are uncommon in blacks. SexOsteoid osteoma more commonly affects males than females. The male-to-female ratio is 2:1. AgeThe age range in patients is 5-56 years.
AnatomyAs many as 80% of cases involve the cortical bone; the remainder of the tumors are intramedullary. Clinical DetailsThe classic presentation includes focal skeletal bone pain, which worsens at night and is frequently relieved with a small dose of aspirin. Pain that increases with activity and at night occurs in 95% of patients with spinal tumors. In 29% of patients, the pain is severe enough to waken the patient. The site of involvement may be tender to touch or pressure. Constitutional symptoms are usually absent. When the spinal column is involved, muscle spasms may cause abnormal alignment. A painful scoliosis may be concave toward the lesion. Kyphoscoliosis, torticollis, and exaggerated lordosis may also be seen. The onset of scoliosis may be acute and is frequently initiated by physical exertion. Osteoid osteoma has been called the most common cause of painful scoliosis. Definite neurologic abnormalities are seen in 6.5% of patients with spinal osteoid osteomas. An osteoid osteoma affecting the hip may cause referred pain, simulating that associated with nerve root compression by an intervertebral disc lesion. An intracapsular lesion often provokes a considerable intra-articular inflammatory response, mimicking erosive arthropathy, crystal arthropathy, or infective arthritis. Approximately one half of patients with intra-articular lesions have complications of osteoarthrosis 1.5-22 years after the onset of symptoms. Rarely, marked weakness associated with muscular atrophy may affect the involved limb, particularly when the tumor is long-standing. Preferred ExaminationRadiography is the initial examination of choice and may be the only examination required. CT is used for precise localization of the nidus and may be used for guiding percutaneous ablation.5, 6, 7 MRI is a useful imaging technique, but CT appears superior for precise localization. The roles of conventional and Doppler ultrasonography have not been established. Angiography may be useful in differentiating the tumor from a Brodie abscess. Single-photon emission computed tomography (SPECT) is useful in the localization of the tumor when the spinal arch or spinous process is involved. Radionuclide scanning for technetium Tc 99m diphosphonate uptake shows fairly intense activity at the tumor site. This examination may also be used to localize the tumor preoperatively and to establish complete removal of the nidus by using a hand-held radioactivity detector. Radionuclide scanning is a sensitive technique, and findings may be positive before radiographic changes are apparent.8, 9 Limitations of TechniquesThe nidus in spinal involvement may be difficult to detect by using plain radiographs. Intra-articular tumors are difficult to detect on plain radiographs because of the absent or limited sclerosis around the nidus. CT has the disadvantage of ionizing radiation. On MRIs, tumors are not as conspicuous as they are on CT scans. Angiography is an invasive procedure, and a minor overlap of angiographic features occurs with a Brodie abscess. The specificity of radionuclide bone scanning is low. DIFFERENTIALSSection 3 of 12
Bone Infarct Bone Island Bone Metastases Legg-Calve-Perthes Disease Lymphoma, Bone Osteoblastoma Osteomyelitis, Chronic Stress Fracture Other Problems To Be ConsideredCortical osteoid osteoma Osteoblastoma Intra-articular osteoid osteoma Inflammatory or infective arthritis RADIOGRAPHSection 4 of 12
FindingsRadiographic features depend on the site of involvement, the duration of symptoms, and the age of the patient (see Images 1, 7, 9, 11, 13, 15-16). A circular or ovoid lucent defect is seen in 75% of patients. This defect is usually smaller than 1.5 cm in diameter and is associated with a variable degree of cortical and endosteal sclerosis. The site of the tumor determines the degree of bone sclerosis. In medullary tumors, sclerosis is minimal or absent. Cortical and subperiosteal tumors provoke considerable sclerosis. Long-standing tumors demonstrate more sclerosis. Children also mount more of a sclerotic response than do adults. In subarticular and intracapsular tumors, reactive sclerosis may be absent or minimal, or it may occur relatively distant to the lesion. This sclerosis usually occurs in tumors of the femoral neck because no periosteum covered by articular cartilage is present on the surface. However, whatever periosteum exists beyond the areas covered by the articular cartilage cannot be elevated because it is bound down by enhancing Sharpey fibers. Intra-articular tumors may show joint effusion associated with the premature loss of cartilage. Osteoarthrosis affects approximately one half of patients with intra-articular tumors. Rarely, patients experience regional osteoporosis, presumably as a result of disuse. Regional osteoporosis may appear as an area of osteopenia around a joint. With spinal involvement, alignment abnormalities may be obvious, such as scoliosis, kyphosis, or hyperlordosis. In children with a long-standing tumor, the involved bone may demonstrate overgrowth. Supplementary radiographic methods, such as overpenetrated radiographs or thin-section planning radiographs, may be useful in locating tumors in portions of the skeleton with complex anatomy. Degree of ConfidenceRadiographs remain the mainstay of imaging in an orthopedic workup. Usually, radiography is the first examination performed in patients with bone pain. In three quarters of patients, a diagnosis may be suggested on the basis of the plain radiographic findings. However, some areas of the skeleton are difficult to assess by using plain radiographs in patients with a suspected osteoid osteoma. These areas include the spine, the femoral neck, and the small bones of the hands and feet. In the spine, overlapping shadows of the vertebral column can easily obscure the tumor. False Positives/NegativesA long list of conditions may mimic an osteoid osteoma (see Differentials). If excessive, new bone formation can mask the nidus, resulting in a false-negative diagnosis. When the tumor is in a long bone, a periosteal reaction may occur distant to the lesion or in an adjacent bone; these may cause diagnostic problems. However, this difficulty should not deter the radiologist from making the diagnosis. Particular pitfalls include a Brodie abscess and a tumor in the long bones of children where overgrowth may occur. Both osteoblastoma and osteoid osteoma have a propensity for the posterior elements of the spine. Both are osteoblastic tumors; they are differentiated primarily by their sizes. Osteoblastomas become considerably larger than osteoid osteomas and are better depicted on plain radiographs. CT SCANSection 5 of 12
FindingsCT is the ultimate diagnostic tool for the precise localization of the nidus. The nidus enhances after the intravenous administration of contrast medium. The nidus shows a variable degree of mineralization, which may be amorphous, punctate, ringlike, or, in rare cases, uniformly dense. Reactive sclerosis around the nidus varies from being extremely dense to manifesting no reaction at all (see Images 3, 5, 17, 19). Degree of ConfidenceCT is the ultimate tool for the detection and the precise localization of the nidus. It is particularly effective in areas with complex anatomy, such as the spinal pedicles, laminae, and femoral neck. False Positives/NegativesAs a result of the partial volume effect in small lesions, problems can occur with CT scanning. Rarely, osteoid osteoma may be confused with a Brodie abscess. False-negative CT results may occur with extracortical tumors. CT scans may not help in diagnosing osteoid osteoma when the nidus is in a cancellous location because of a lack of changes in attenuation around the nidus. MRISection 6 of 12
FindingsThe nidus is isoechoic to muscle on T1-weighted images. The signal intensity increases with T2-weighted sequences, but it remains low. Bone marrow edema is depicted around the nidus in approximately 60% of patients. Soft tissue edema is depicted adjacent to the tumor in slightly fewer than one half of patients. Perinidal edema is more pronounced in young patients. Intra-articular lesions cause synovial thickening or inflammation and joint effusion, which may be readily apparent on MRIs (see Images 4, 6, 18).10 Degree of ConfidenceMRI reliably demonstrates the nidus, which has a variable appearance related to its position relative to the cortex of the bone. Compared with other techniques, MRI is better in the diagnosis of cancellous osteoid osteomas, whereas difficulty may be encountered by using plain radiography and CT. False Positives/NegativesIn the diagnosis of intracortical tumors, MRI is not as effective as it is in the diagnosis of cancellous bone tumors. ULTRASOUNDSection 7 of 12
FindingsA limited study of the use of duplex color Doppler ultrasonography has shown promising results. The technique has also been used to guide percutaneous localization and biopsy. Duplex color Doppler studies clearly demonstrated the highly vascular nidus and its feeding artery in one patient and the feeding artery in a second patient. Ultrasonography has also been used to aid in the diagnosis of intra-articular osteoid osteomas. Some have suggested that the sonographic findings of a cortical irregularity and focal synovitis suggests the possibility of intra-articular osteoid osteoma, prompting the search for characteristic findings on correlative imaging studies.11, 12 Degree of ConfidenceSufficient experience has not been accumulated to assess the degree of confidence with ultrasonography. NUCLEAR MEDICINESection 8 of 12
FindingsRadionuclide bone scanning of uptake of technetium-99m phosphonates shows intense activity at the site of the tumor. Occasionally, a double-density sign is seen in which a small focus of radioactivity in the nidus is superimposed on a larger area of radioactivity (see Images 2, 8, 10, 12, 14). SPECT may be useful in areas with complex anatomy, such as the posterior elements of the spine. Radionuclide imaging also may be used preoperatively and intraoperatively to localize the tumor and to establish complete removal of the nidus by using a hand-held radioactivity detector. Recently, positron-emission tomography with 18-fluorodeoxyglucose has been used in the diagnosis of osteoid osteoma.13 Degree of ConfidenceThe average time from the onset of symptoms to diagnosis is reported to be 28 months with spinal tumors. Radionuclide bone scanning reduced the time to diagnosis in 66% of patients. The sensitivity of radionuclide bone scans is extremely high. A radionuclide bone scan is considered mandatory in patients with painful scoliosis. A radionuclide bone scan can demonstrate the tumor before abnormal radiographic findings are apparent. False Positives/NegativesNo false-negative results have been recorded in osteoid osteoma. However, the specificity of isotope bone scans does not match its sensitivity, and a variety of infective, neoplastic, metabolic, and traumatic lesions show increased activity. ANGIOGRAPHYSection 9 of 12
FindingsAn osteoid osteoma is highly vascular, a feature that can be demonstrated angiographically. The nidus is the most vascular part of the tumor, with an intense circumscribed blush that appears in the early arterial phase and that persists into the venous phase. Degree of ConfidenceBlush persisting into the venous phase during angiography is believed to be diagnostic of osteoid osteoma. False Positives/NegativesA Brodie abscess may be difficult to distinguish from osteoid osteoma radiologically. Hypervascularity may also be observed with a Brodie abscess, but the characteristic blush seen in the venous phase in osteoid osteoma usually does not occur in a Brodie abscess. INTERVENTIONSection 10 of 12
Several techniques are available for ablation of osteoid osteoma. The tumor can be percutaneously ablated by using radiofrequency (RF), ethanol, laser, or thermocoagulation therapy under CT guidance. In spinal tumors, complete ablation or resection of the tumor is desirable but not always feasible.14, 15, 16, 17, 18, 19, 20 Percutaneous RF ablation is performed under CT guidance by using general or spinal anesthesia.21 After localization of the nidus with 1- to 3-mm CT sections, an osseous access is established with either a 2-mm coaxial drill system or an 11-gauge Jamshidi needle. RF ablation is performed at 90°C for 4-5 minutes by using a rigid RF electrode with a 1-mm diameter. The procedure is successful when the electrode is heated to the desired temperature within the nidus. In one series, clinical success was achieved in 96% of patients. All recurrences were treated with a second procedure, with a secondary success rate of 100%. CT-guided percutaneous drilling of the nidus with subsequent ethanol injection to cause sclerosis in the remnants of the nidus has been achieved in a small series of patients. Percutaneous thermocoagulation under CT guidance has been performed to achieve ablation of a spinal osteoid osteoma. Frequently, lesions are located near the joint surface, involve the vertebral body, or are close to major nerves. To determine whether RFA can safely be used in these cases, a study on an animal model was conducted.22 The study revealed the insulative effect of cortical bone. The authors showed that RFA always respected cortical bone, and therefore, articular cartilage was not damaged. RFA can therefore can be safely performed close to the joint surface without damaging the cartilage. There were no significant differences in lesion size, probe type, and the duration of the procedure. Medical/Legal Pitfalls
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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