Introduction
T1-weighted coronal gadolinium-enhanced magnetic resonance image. This image demonstrates a lesion that enhances slightly, as can be seen in cases with osteoblastomas.
Axial computed tomography scan that was obtained through the tibial diaphysis. This image demonstrates how an osteoblastoma can resemble a large osteoid osteoma, with the typical radiographic features of a central nidus and surrounding reactive bone.
Background
An osteoblastoma is an uncommon primary neoplasm of the bone that has clinical and histologic manifestations that are similar to those of an osteoid osteoma; therefore, some consider the 2 lesions to be variants of the same disease, with osteoblastoma representing a giant osteoid osteoma. However, an aggressive type of osteoblastoma has been recognized, making the relationship between the lesions less clear.1,2,3,4,5,6
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Related eMedicine topics:
Scoliosis, Idiopathic
Idiopathic Scoliosis
Osteoid Osteoma
Osteosarcoma, Classic
Osteosarcoma, Variants
Osteoblastoma (Orthopedic Surgery)
Osteosarcoma (Orthopedic Surgery)
Frequency
United States
Osteoblastomas account for only 0.5-2% of all primary bone tumors and only 3% of benign bone tumors.
Mortality/Morbidity
- Conventional osteoblastomas are benign lesions with little associated morbidity. However, the tumors may be painful, and spinal lesions may be associated with scoliosis and neurologic manifestations.7,8,9,10
- Metastases and even death have been reported with the controversial aggressive variant of osteoblastoma, which can behave in a fashion similar to that of osteosarcoma.11,12,13,14 This variant is also more likely to recur after surgery than is a conventional osteoblastoma.
Race
No racial predilection is recognized for cases of osteoblastoma.
Sex
Osteoblastoma affects males more often than females, with an incidence of 2-3:1.1
Age
Although osteoblastoma can occur in patients of any age, the tumor predominantly affects younger persons, with about 80% of these tumors occurring in those younger than 30 years.15 The mean patient age at presentation is 20 years.
Presentation
Presentation and natural history
Approximately 40% of all osteoblastomas are located in the spine. The tumors usually involve the posterior elements, and 17% of spinal osteoblastomas are found in the sacrum. The long tubular bones are another common site of involvement, with a preponderance in the lower extremities. Osteoblastoma of the long tubular bones is often diaphyseal, and fewer are located in the metaphysis. Epiphyseal involvement is extremely rare. Other reported sites include the bones of the hands, wrists, feet and ankles16 ; the skull and facial bones17,18,19,20,21 ; the ribs22 ; and the sternum, clavicles, scapulae, patellae, and pelvis.23
The etiology of osteoblastoma is unknown. Histologically, osteoblastomas are similar to osteoid osteomas, producing both osteoid and primitive woven bone amidst fibrovascular connective tissue. Although the tumor is usually considered benign, a controversial aggressive variant has been described in the literature, with histologic features similar to those of malignant tumors such as osteosarcomas.11,12,13,14
Patients with osteoblastomas usually present with pain of several months' duration. In contrast to the pain that is associated with osteoid osteoma, the pain of an osteoblastoma is usually less intense, is usually not worse at night, and is not relieved readily with salicylates. If the lesion is superficial, the patient may have localized swelling and tenderness. Spinal lesions can cause painful scoliosis, although this is less common with osteoblastomas than with osteoid osteomas. In addition, lesions may mechanically interfere with the spinal cord or nerve roots, producing neurologic deficits.24,25
Treatment
Unlike osteoid osteomas, which have limited growth potential and may even regress spontaneously, osteoblastomas typically continue to enlarge without intervention. When clinical and radiographic findings are consistent with the diagnosis of osteoblastoma, an excisional biopsy is appropriate. As soon as other diagnoses are included in the differential diagnosis, incisional biopsy should be performed. Percutaneous CT-guided biopsy is an outpatient nonsurgical procedure with minimal complications.26,27,28
Osteoblastomas can be difficult to treat. Curettage and grafting are performed with most active lesions. En bloc resection can also be performed. Larger lesions may require internal fixation. Irradiation is another therapeutic option. The overall recurrence rate is approximately 20%; therefore, close follow-up monitoring of patients is required. Rates of recurrence are lower with wide surgical excision, but the location of the lesion does not always allow for this option. Cementation in conjunction with excision may be helpful in extending the surgical margin.
Preferred Examination
The preliminary radiologic workup should consist of radiography at the site of the patient's pain.1,2 However, computed tomography (CT) scanning is often necessary to support clinical and plain radiographic findings that are suggestive of osteoblastoma and to better define the margins of the lesion for potential surgery.29 CT scans are best used for the further characterization of the lesion with regard to the presence of a nidus and matrix mineralization.9,29
Magnetic resonance imaging (MRI) aids in the detection of nonspecific reactive marrow and soft-tissue edema.29,30,31 This modality best defines soft-tissue extension, although the finding is not typical of osteoblastoma.
Bone scintigraphy demonstrates abnormal radiotracer accumulation at the affected site, substantiating clinical suspicion, but this finding is not specific for osteoblastoma.1 In many patients, biopsy is necessary for confirmation of the diagnosis.
Limitations of Techniques
In most patients, radiographic findings are not diagnostic of osteoblastoma; therefore, further imaging is warranted.
A CT scan examination that is performed with the intravenous administration of a contrast agent poses the risk of a patient's allergic reaction to the contrast material.
The lengthy duration of an MRI examination and a history of claustrophobia in some patients limit the use of MRI.
Although osteoblastomas demonstrate an increased radiotracer accumulation on bone scans, the tumors' appearance is nonspecific, and it is difficult to differentiate these lesions from those due to other etiologies that involve increased radiotracer accumulation in the bone. Therefore, bone scans are only useful in conjunction with other radiologic studies and are best not used alone.
Differential Diagnoses
More on Osteoblastoma |
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Further Reading
Keywords
osteoblastoma, giant osteoid osteoma, bone neoplasm, osteoid osteoma, bone tumor, primary bone tumor, benign bone tumor, benign lesion of the bone, scoliosis, matrix mineralization
