Osteoid osteoma is a benign tumor that consists of osteblastic mass called a nidus that is surrounded by a distinct zone of reactive bone sclerosis. The zone of sclerosis represents a secondary reversible change that gradually disappears after the removal of the nidus.
The nidus tissue has a limited local growth potential and usually is less than 1 cm in diameter.
Osteoid osteomas account for about 10 percent to 12 percent of all benign bone tumors. The males are three times more commonly affected than females. More than 80 percent of the patients are between 5 and 25 years age, and the peak incidence is in the second decade of life. Half all osteoid osteomas occur in the long bones of the lower extremities.
The femoral neck is the single most frequently affected site anatomically.
In the long bones, osteoid osteoma is usually located near the end of the shaft, are often present in the small bones of the hands and feet.
In vertebrae, they are nearly exclusively located in the posterior arch. The primary location in the vertebral body is very rare. Osteoid osteomas occur very rarely in flat bones and almost never occur in craniofacial bones.
The most frequently reported symptom is pain of increasing severity that is worse at night, relieved by aspirin and other nonsteroidal anti-inflammatory agents.
If the involved bone is superficial, painful swelling of the adjacent soft tissue may be present. This often occurs in the small bones of the hands and feet.
Scoliosis may occur with vertebral osteoid osteoma.
The radiographic features of osteoid osteoma are characteristic and diagnostic. Conventional radiographs reveal a well-demarcated lytic lesion (nidus) surrounded by a distinct zone of sclerosis. A zone of central opacity that represnts a more sclerosis. A zone of central opacity that represents a more slecrotic portion of the nidus and is surrounded by a lucent halo may be present within the nidus.
The intracortical lesions of long bones produce extensive fusiform thickening of the cortex with dense radiopacity that sometimes obscures the nidus.
In many cases, nidus may not be visible, so additional imaging techniques, such as computed tomography, radioisotope scanning, and magnetic resonance imaging, may be necessary to document the lesions.
In vertebral locations, conventional radiographs show increased density of the pedicle, loss of a distinct contour, or both features. The nidus is often not seen on conventional radiographs. Exact anatomic localization of the nidus usually requires computed tomography. Most frequently, the nidus is present in the area of the posterior arch or at the base of a pedicle. In very unusual instances, it is present within the transverse or spinous process.
- Chronic and acute osteomyelits
- Bone abscess
- Intracortical hemangioma
- Bone island
- Stress fracture
- Ewing’s sarcoma
- Intracortical osteosarcoma.
Osteoid osteomas has limited growth potential. The majority of lesions are about 0.5 cm in diameter. Some may even spontaneously regress.
The primary treatment is surgical removal of the nidus and some of the surrounding bone by enbloc excision after precise localization of the nidus.
Some of these patients can be managed with prolonged treatment with nonsteroidal anti-inflammatory durgs.
Ablation of the nidus with a percutaneously placed radiofrequency electrode has also been advocated as an alternative approach. This could prove to be valuable where it is difficult to surgically remove the tumor.