Osteoid osteoma is a benign lesion consisting of an active osteoid producing lesion surrounded by a reactive layer of host bone. The lesion is often small, but very symptomatic for the patient.
Osteoid osteoma most often presents as a painful bone lesion in an adolescent or young adult. The classic findings are pain, usually worse at night that is very responsive to non-steroidal anti-inflammatory medications. There is a slight male predominance. The lesions may be periarticular and generate sympathetic joint effusions in the absence of trauma.
The lesion can be present in a number of bones in the body and the symptoms can vary based on the locations. The lesion can be the cause of an olisthetic scoliosis or a radicular pain syndrome when present in the posterior elements of the spine. High cervical spine lesions can cause headache as the primary symptom.
Patients with a large lesion (>1.5cm) radiographically and a histologic diagnosis of osteoid osteoma should have the diagnoses of osteoblastoma and osteosarcoma considered as these lesions can share the same microscopic appearance.
Pain patterns which are predominantly activity related and those not relieved by NSAIDs should have stress reaction included in the differential diagnosis as these are often similar in radiographic appearance (especially when the classic nidus is very small and difficult or impossible to identify on the imaging).
This is the second most common benign bone tumor accounting for 11% of all benign primary bone tumors and 3-5% of all primary bone tumors. As previously mentioned the disease is most common in adolescents and young adults. The majority of cases are diagnosed between the ages of 10 and 20 and it is exceedingly rare is those younger than 5 and older than 40.
Pathology and pathophysiology
This lesion is due to nest of neoplastic bone with a non-infiltrating growth pattern and the host bone’s reaction to the lesion. The neoplasm stimulates a response from the host that attempts to contain the lesion within a sclerotic margin. The benign lesion cannot infiltrate these trabeculae and the osteoclasts in the lesion and the host bone wage a boundary war of resorption and containment. This process is likely responsible for the pain syndrome as the cytokines for both processes are pro-inflammatory. This also explains the ubiquitous relief with NSAIDs.
The cortical hypertrophy around the site of the nidus (the active disease) is the product of the host’s attempt at containment of the lesion. The lesion can mature over years and become less inflammatory and less painful.
- Intramedullary osteomyelits or intracortical abscess
- Stress fracture/reaction
- Arthritis in juxta-articular locations
- Bone island (enostosis)
- Eosinophilic granuloma
As with most neoplasms, there is little known about the exact mechanism of formation of these lesions. Most of the radiographic changes and clinical symptoms are due to the host bone’s containment attempts.
Radiographic and laboratory findings
The radiographic findings in osteoid osteoma are very characteristic. Plain radiographs often show a densely sclerotic lesion in the cortex of a long bone with a smoothly tapered are of hypertrophy to normal host cortex on either side. There may, but most often not be a nidus (central radioluceny – the active neoplastic tissue) visible on plain radiographs.
A scoliosis associated with an osteoid osteoma will often be located on the concave side of the lesion possibly due to unilateral muscle spasm from host mediated factors.
Bone scintigraphy will show increased activity surrounding the lesion.
CT scan will show the reactive surrounding bone and the nidus will generally be lucent or much less dense than the surrounding host bone. When there is a density greater than fibrous tissue in the nidus a relatively less dense margin between the nidus and the host bone can be seen correlating a fibrovascular layer of tissue.
MRI will show low signal in the reactive cortical bone in both fluid and fat sensitive sequences. The fluid sensitive sequences will show perilesional increased signal corresponding to bone marrow edema and edema of the overlying periosteum and muscle.
There are no specific laboratory findings.
Risk factors and prevention
There are no inherent risk factors for development of osteoid osteoma.
Treatment of the symptoms of the disease can often be adequate as many lesions can regress spontaneously over the course of years. NSAIDs are the mainstay of medical treatment. Many patients experience significant pain and discomfort and are desirous to pursue treatment of the disease.
Treatment of the disease adequately requires removal or destruction of the entire lesion in the nidus. Surgical resection has been used extensively with open excision and guided open excision (by tetracycline labelling or CT guided needle/drill placement). The local recurrence rate has been about 10%. This is likely due to the difficulty in finding a sub-centimeter nidus in abundant densely sclerotic reactive bone. Advances in percutaneous treatments like CT guided radiofrequency ablation have resulted in similar local control rates with lower costs associated with surgery and post-operative hospital stay.
Extremity lesions are therefore often treated by an interventional radiologist, who samples the lesion with a CT guided biopsy and then treats the lesion with a radiofrequency probe which heat kills the local tissue in a spherical distribution. The caveats to treatment in this method relate to the lesions proximity to heat intolerant structures. Spinal lesions are not good candidates for RFA. Lesions in the extremities near major neurovascular structures or in subcutaneous locations (anterior tibial cortex) may best be treated in open fashion to avoid thermal necrosis of skin, nerve or blood vessel. Lesions in high stress regions (the medial proximal femur should have consideration of protected weight bearing after treatment to mitigate the risk of pathologic fracture after heat treatment of the calcar.
The primary outcome for osteoid osteoma is local recurrence as the lesion is localized with no potential for metastasis. As mentioned previously, the treatments for the lesion result less than a 10% local recurrence rate.
Recurrent osteoid osteoma is treated in identical fashion; however the differential diagnosis should give careful reconsideration to other items on the differential.
There is minimal need for ancillary support for these patients unless the scope of treatment is large and family support is questionable.
There is a periosteal version of the disease which differs only in location.
Multiple nidus disease can be seen and often has a string of pearls appearance due to the reactive bone.
Osteoblastoma has such a large overlap clinically, radiographically and histologically it was originally called giant osteoid osteoma.
osteoid, osteoma, osteoid osteoma, nidus, radiofrequency ablation, RFA, night pain, NSAIDs, cortical, sclerosis
Skills and competencies
A student should be able to elicit the classic history from a patient with osteoid osteoma and distinguish that from the typical history of a stress fracture.
The student should be able to identify a nidus of osteoid osteoma on plain radiographs when visible and on every CT scan of the disease.