Practice Essentials
Osteoid osteoma [1] is a benign osteoblastic tumor that was first described in 1930 by Bergstrand. Jaffe described it in 1935 and was the first to recognize it as a unique entity. Osteoid osteomas are usually smaller than 1.5-2 cm and characterized by an osteoid-rich nidus in a highly loose, vascular connective tissue. The nidus is well demarcated and may contain a variable amount of calcification. Surrounding the nidus is a zone of sclerotic but otherwise normal bone.
Osteoid osteoma is commonly classified according to its location, as follows [2] :
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Intracortical (75%)
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Medullary (20%)
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Subperiosteal (4%)
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Endosteal (4%)
Osteoid osteoma can occur anywhere and can involve either a single bone or several bones. Osteoid osteoma is reported to occur in the cortex of the shafts of long bones in 80-90% of cases. It is also reported in the epiphyseal and metaphyseal regions of both small and large bones of the axial and appendicular skeletons, especially the femur, tibia, and humerus.
The lower extremities are the most common sites of osteoid osteomas. The femur, particularly the intertrochanteric or intracapsular regions of the hip, is affected in two thirds of cases. [3] The diaphyseal part of the tibia and the humerus are other common sites. Barei et al reported that in 50-60% of cases, osteoid osteoma occurs in the femur and tibia. [4]
Approximately 7-20% of osteoid osteomas involve the spine. Involvement here most commonly manifests as painful scoliosis, but painless conditions can also occur. Pettine et al noted that 50% of lesions occur in the cervical spine, and as many as 78% of osteoid osteomas in the lumbar spine are associated with scoliosis. [5, 6, 7, 8]
The tumor has a predilection for the posterior elements, most commonly affecting the cancellous lamina, spinous process, and pedicle but sparing the vertebral bodies. Wells et al observed this predilection in 75% of cases, with 33% involving the lamina, 20% involving the articular facets, and 15% involving the pedicles. [9] About 59% of spinal osteoid osteomas affect the lumbar spine. Rates for other areas are 27% in the cervical spine, 12% in the thoracic spine, and 2% in the sacrum.
Other areas that may be involved include the hand, [10] talus, [11] foot, and joints. Osteoid osteomas of the hand and wrist are rare, most commonly involving the phalanges, and often result in atypical clinical and radiologic characteristics. The findings are similar to those of tumors involving the foot and ankle. Intra-articular osteoid osteoma occurs in 10% of cases and can involve the hip, elbow, and ankle.
Certain characteristic manifestations (eg, night pain and the presence of a nidus) are well known; however, osteoid osteoma is capable of mimicking, or being mimicked by, various other conditions, and this may result in prolonged diagnostic and therapeutic process, along with associated complications. [12]
Initial treatment of osteoid osteoma remains nonoperative, with medications consisting of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs). Surgical intervention is generally indicated for patients whose pain is unresponsive to medical therapy, those who cannot tolerate prolonged use of NSAIDs, and those who are not amenable to activity restrictions. Open surgical treatment of osteoid osteoma has included wide en-bloc resection and unroofing and excision. Minimally invasive approaches are effective and have come to be preferred to open surgery. [13]
Pathophysiology
Whether the pathophysiology of osteoid osteoma is neoplastic or inflammatory has been controversial. The presence of atypical cellular and trabecular components support the view that osteoid osteoma is a neoplasia; however, the relatively small size of the lesion, its self-limited nature, and the presence of intracellular viral particles (as observed on electron microscopy) may suggest an inflammatory process.
Pain in osteoid osteoma has been typically attributed to the nidus, with its associated hyperostosis and neural elements in the reactive fibrous tissue.
Golding described radially oriented trabeculae of surrounding reactive bone, which implied an increased pressure in the vascular nidus. [14] This arrangement of the bony trabeculae was attributed to the stresses placed on them. This increased pressure due to vasodilatation and edema is thought to directly stimulate intraosseous nerve endings, generating pain.
Schulman et al supported this observation, finding increased amounts of unmyelinated nerve fibers, with greatest abundance next to arterioles. These fibers were believed to be sensitive to changes in vascular pressure. [15]
Prostaglandins have been implicated and linked to osteoid osteoma. Several authors have suggested that they may play a fundamental role in the development of osteoid osteoma. Support is derived from reports of a 100- to 1000-fold increase in levels of prostaglandins, particularly prostaglandins E2 and I2 (prostacyclin), in the nidus that was reversible on extirpation of the tumor.
These prostaglandins and other mediators of bone formation and inflammation are believed to provide the final common pathway for pain generation. Furthermore, the dramatic response to salicylates or NSAIDs, which affect prostaglandin synthesis, supports the suggested role of prostaglandins in the pathophysiology of pain.
Healey et al described two pathways of pain generation due to prostaglandins. [16] The first involved permeability and vasodilatory effects, which increase the size and flow of vessels in the bony lesion, increasing pressure and pain. The second involved its effect in the bradykinin system, which potentiates pain akin to injured soft tissues.
Epidemiology
Osteoid osteoma is the third most common benign bone tumor, accounting for approximately 10-14% of all benign bone tumors and 2-3% of all primary bone tumors. [13]
Age-, sex-, and race-related demographics
Osteoid osteoma is generally a condition of the young, but it can affect a wide range of individuals aged 8 months to 70 years. The literature reports that people aged 10-30 years are most susceptible. As many as 90% of cases have been found to occur in patients younger than 25 years. Barei et al noted that 70% of osteoid osteomas occurred in patients younger than 20 years. [4] The tumor is less common in patients older than 30 years, who account for 13% of cases. About 3% of cases occur in children younger than 5 years. [17, 18]
Men are affected more frequently than women. The male-to-female ratio is in the range of 2-3:1.
No racial or ethnic predilection is noted for osteoid osteoma.
Prognosis
The natural history of osteoid osteoma is controversial. The literature suggests a history of resolving pain and healing of the lesions, but no histologic confirmation of the diagnosis has been reported. The course of this disease is unpredictable and protracted, with intervals of resolution of pain that sometimes last 6-15 years.
Atar et al (1992) described two stages of the disease. [19] The first is an acutely painful stage that lasts 18-36 months, during which patients require steady use of analgesics. The second is the recovery stage, which includes healing of the nidus and which usually takes 3-7 years. Barei et al noted that healing involves ossification of the untreated nidus, which cannot be readily distinguished from surrounding bone and which resembles a localized zone of cortical hypertrophy. [4]
Direct visualization and intralesional excision of the nidus is associated with a primary cure rate of 100%. Successful excision substantially eliminates tumor-related pain within hours to days after surgery. Assenmacher et al described immediate relief of pain in their patients, with a mean symptom-free duration of 6.6 years after surgery. [20]
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Anteroposterior (AP) and lateral radiographs of osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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Axial CT scan shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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Reconstructed axial CT scan shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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Coronal CT scan shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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Sagittal CT scan shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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MRI shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
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MRI shows osteoid osteoma. Courtesy of Cincinnati Children's Hospital Medical Center, Department of Pediatric Orthopaedics.
