Osteoid osteoma is a benign [non-cancerous] osteoblastic tumor. It was first described by Bergstrand 1930 but its unique identity was recognized by Jaffe in 1935.
Osteoid osteoma consists of osteoblastic [growing cells] mass called a nidus [very rich in blood supply].
Nidus is surrounded by a zone of sclerotic but otherwise normal bone. It is a reversible secondary change that gradually disappears after the removal of the nidus. The nidus tissue has a limited local growth potential and usually is less than 2 cm in diameter.
Osteoid osteoma accounting for 5% of all primary bone tumors.
Osteoid osteoma is mostly seen 10-30 years of age and about 90% of cases occur in patients younger than 25 years. It has been reported between aged 8 months to 70 years though.
Men are affected more frequently than women and there is no racial predilection.
Pathophysiology of Osteoid Osteoma
Controversy exists whether osteoid osteoma is neoplastic or inflammatory.
Presence of atypical cellular and trabecular components points towards neoplastic nature whereas the small size of the lesion, self-limiting nature and the presence of intracellular viral particles suggest inflammatory nature
The nidus is responsible for the pain of the osteoid osteoma. It is also contributed by surrounding sclerosis and nerve endings in reactive fibrous tissue.
It has been suggested that radially oriented trabeculae of surrounding reactive bone cause increased pressure in the vascular nidus due to vasodilatation and edema is thought to directly stimulate intraosseous nerve endings to cause pain
Prostaglandins have been linked to osteoid osteoma, some even suggesting a fundamental role in the development.
That is why osteoid osteoma responds to NSAIDs very well.
On histopathological examination, the discrete central nidus is a distinct, well-circumscribed cavity, surrounded by a dense reactive bone of varying thickness. It is cherry-red in color and can be shelled out of the surrounding reactive bone. The consistency of nidus is variable from soft vascular to friable and granular to densely sclerotic.
Microscopically, the nidus is typically composed of a mass of irregular lacelike osteoid tissues that in a highly vascular stroma of connective tissue containing osteoblastic cells.
Distribution of Osteoid Osteoma in Body
Osteoid osteoma can occur anywhere in the body. It can involve a single bone or multiple bones.
The cortex of the shafts of long bones is affected 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 osteoma. The femur is the most common bone involved by osteoid osteoma [60% of the cases], followed by tibia.
The femoral neck is the single most frequent anatomic site. The tibia is the second most frequently involved long tubular bone.
Fibular lesions are very rare.
In the upper limbs, the humerus is the most frequently involved bone, and a majority of cases occur around the elbow joint. Involvement of the distal ulna and radius is very rare.
10 percent to 15 percent of Osteoid osteomas occur in the vertebral column. Most frequently, they are located in the lumbar and lower thoracic portions of the spine.
Spinal lesions are difficult to detect on plain radiographs and are known to be responsible for an unexplained backache and painful scoliosis.
In vertebrae, the nidus is most frequently located in the posterior arch.
Magnetic resonance imaging also may facilitate the identification of an inconspicuous nidus.
Other frequent locations include articular facets and pedicles, the transverse and spinous processes.
A primary tumor in the vertebral body is extremely rare.
10 percent of osteoid osteomas occur in the small bones of the hands and feet. The tumor occurs twice more commonly in hands than feet.
In the hands, the phalanges are the most frequently involved sites.
Osteoid osteomas located within the articular capsule are rare. Elbow, hip, and ankle joints are most commonly involved.
Juxtaarticular Osteoid Osteomas are typically associated with nonspecific symptoms similar to other common joint disorders.
Pain is usually less intense when compared to osteoid osteomas of other regions, and so is its response to its response to nonsteroidal anti-inflammatory drugs is also milder.
The intraarticular nidus is difficult to identify, and there is no periosteal reaction.
The diagnosis is often delayed in such cases.
Subperiosteal osteoid osteoma is a relatively rare lesion. Conventional radiographs demonstrate a lucent lesion on the surface of the bone with an adjacent periosteal reaction.
The nidus is typically radiolucent with no evidence of central opacity.
This osteoid osteoma is larger in size because the restricting compressive force on side of periosteum is absent. The subperiosteal lesions are on average less sclerotic and have thinner trabeculae and a greater proportion of stromal tissue compared with intracortical lesions.
Presentation – Osteoid Osteoma Symptoms and Sign
Dull aching pain at the site of the lesion is the main presenting symptom. The pain is usually worse at night and decreases by morning in the majority of patients. Awakening due to pain is reported in about one-third of patients.
The pain responds dramatically to NSAIDs. This also goes in favor of the inflammatory nature of this lesion.
Spinal lesions may present with scoliotic deformities of the spine. Radicular pain may be present.
When the lesion is around the growth plate of the bone, growth disturbances may also occur.
Joint pain and swelling may occur in juxta-articular lesions.
In lower limb lesions, limp may occur.
Diaphyseal regions of bone may present with swelling
Lesions of the small bones may lead to an expansion of the bone and may present protuberance or swelling of the region, macrodactyly [enlarged digit]
Tenderness is present in more than 50% of patients and usually occurs with subperiosteal lesions and is relatively uncommon with medullary lesions.
Local warmth and redness is also a less common finding. Joint swelling and synovitis may be found in intracapsular lesions. Soft-tissue swelling, contractures, and a soft-tissue mass can be an associated finding.
In cases of intracapsular lesions, synovium is generally edematous and thickened. Synovial changes spontaneously subside after removal of the nidus.
Usually normal findings.
The radiographic changes are noticeable after a long period. Initial x-rays are normal in most of the cases.
Therefore, repeat radiographs should be obtained from time to time to document osseous manifestations.
Radiographs reveal a well-demarcated lytic lesion (nidus) surrounded by a distinct zone of sclerosis. A zone of central opacity that represents a more sclerosis.
A zone of central opacity that represents a more sclerotic portion of the nidus and is surrounded by a lucent halo may be present within the nidus.
In many cases, nidus may not be visible on x-ray, thus necessitating additional images like computed tomography, radioisotope scanning, and magnetic resonance imaging may be necessary.
In vertebral locations, the nidus is often not seen. The x-rays may show an increased density of the pedicle, loss of a distinct contour, or both.
Better imaging may be needed for localization of nidus.
Expansion of the bone contour can be found in the small bones.
An intraarticular osteoid osteoma may lead to periarticular osteoporosis and induce joint destruction
Lesions near the physis may induce premature fusion of the epiphysis in rare cases.
Radionuclide scans are indicated when radiographic findings are either normal or unable to diagnose.
It is a very useful investigation in such situations, especially in pediatric patients.
The scans show nonspecific but intense, well-defined uptake of activity on bone scans. This focus of intense uptake is correlated with the nidus.
Radionuclide scans also help the surgeon in resection of tumor and also suggests multiple bone involvement.
The investigation as 100% [picks up all cases of osteoid osteoma] and 100% specificity [ no negative bone-scan findings have been reported in patients with osteoid osteoma]
CT is the primary investigator for the definitive diagnosis of osteoid osteoma
CT is helpful in precisely define localization and delineation of the nidus. It is able to determine the extent of bony involvement.
CT is indicated
- Nidus is not visible on routine x-rays
- Residual or recurrent tumor
- The tumor is located in a critical area like the spine or femoral neck
On CT, osteoid osteoma appears as a circumscribed annular lesion with a double-attenuating sign [lesion within a lesion]
Magnetic resonance imaging
MRI has not been useful in the diagnosis of osteoid osteoma. It is reserved for equivocal cases and sensitive in detecting bone marrow, peritumoral edema, and soft-tissue abnormalities.
Localization of lesion
Localization of osteoid osteoma is important because exact localization of the lesion is the most important determinant of successful surgical treatment.
Preoperatively, radionuclide scanning and CT are the most important investigations for preoperative localization.
Intraoperative localization can be done by tetracycline labeling and frozen section examination.
Multiplanar fluoroscopy and intraoperative radioisotope scanning are radiological measures for localization during surgery.
Differential Diagnoses of Osteoid Osteoma
Underlying osteoid osteoma is ruled out in virtually all cases of unexplained back pain and painful scoliosis that occur in children and young adults.
In some patients, clinical symptoms may suggest a neurologic disorder, lumbar disc disease, or both conditions.
In small bones of hand and foot, osteoid osteoma can mimic an inflammatory process. It is not unusual for a patient with osteoid osteoma of the hands and feet to be treated initially for chronic osteomyelitis or other inflammatory conditions.
Other conditions which might appear similar in symptoms and signs
- Chronic and acute osteomyelitis
- Bone abscess
- Intracortical hemangioma
- Bone island
- Stress fracture
- Ewing’s sarcoma
- Intracortical osteosarcoma.
Osteoid Osteoma Treatment
Initial treatment of osteoid osteoma remains nonoperative, with medications. Some of these patients can be managed with prolonged treatment with nonsteroidal anti-inflammatory drugs. Salicylates and naproxen are most used nonsteroidal anti-inflammatory drugs.
Sequential radiographs at 3- 6-months may suggest healing of the lesion.
Some patients have good pain relief and are continued with this. However, the effect may diminish in others and surgery may be chosen.
Osteoid osteomas are known to regress with time in some cases.
Surgical Treatment of Osteoid osteoma
In patients whose pain does not respond to drug treatment or there is a problem with nonsteroidal anti-inflammatory drugs, surgery should be considered. Patients who find difficult to restrict activity are also candidates for surgery.
Surgery, whether conventional or minimally invasive, seeks complete excision of the nidus.
En bloc resection
En bloc resection is the resection of the lesion in toto to ensure complete removal of the nidus.
Disadvantages of this procedure include excessive resection of normal bone in the effort to completely excise the lesion.
The procedure is contraindicated in patients with lesions in areas difficult to access, such as the acetabulum or femoral head and neck.
En bloc surgical resection of the tumor is associated with longer healing times, prolonged hospital stay, fractures in the perioperative period, need for bone grafting and internal fixation, joint stiffness etc.
Unroofing and curettage
In this procedure, overlying bone is removed and the tumor is excised excision with curettes and burrs. It can achieve a cure rate of 75-100%.
Unroofing and curettage is especially helpful in treating lesions in a structurally vital location, such as the femoral neck where much bone loss cannot be afforded without disturbing structural support for the area.
Prophylactic internal fixation where needed may be done if the treatment weakens the remaining bone.
Similarly, spinal fusion is recommended if instability results from the treatment.
Recurrence after Open Surgery
Reported recurrence rate after open surgery is 9-28%.
Recurrence is typically observed within 1 year after excision; hence, the patient should be monitored for a minimum of 1 year.
Failure to relieve pain indicates incomplete removal of the tumor and bad prognosis
Minimally Invasive Surgery
Three hours before surgery, the radionuclide [technetium-99m-labeled hydroxymethylene diphosphonate (HMDP) and dichloromethylene diphosphonate (DMDP)] is given to the patient. Scanning after one hour localizes the hot spot.
A detector probe is then used to locate the hot spot during surgery. The method is reported to localize the nidus with a precision of 2 mm enabling the excision of lesions with minimal damage to the normal bone. The same probe can also determine completeness of removal.
False positive results during surgery or for completion assessment are a problem.
CT Guided Percutaneous Excision
In this method, under CT guidance, a needle is inserted in the nidus. This reduces the amount of bone removed during surgery. Postoperative CT scan and pathologic examination are done for the confirmation. The reported success rate is 83-100%.
Percutaneous Laser Photocoagulation
An optical fiber or fibers are inserted directly into the target tissue, followed by treatment with laser energy for several minutes. The cure rate of 93% and 96% are reported after the second ablation.
Percutaneous Radiofrequency Ablation
An electrode is placed in the lesion which is coupled to a radiofrequency generator. This would lead to that produces local tissue destruction by converting radiofrequency into heat. This method can treat a smaller lesion in a single application. Larger lesions may require a second application.
The patients can be sent home the same day and it is the method of choice in suitable patients. The procedure is most suited for treatment if the location of the osteoid osteoma should permit a safe access and a safe heating procedure without risking to damage nerves, major blood vessels, and the skin.
[ If the tumor nidus is more than 1 cm away from these structures the procedure can usually be safely performed.]
Complete or nearly complete relief of pain often occurs within 3 days. Younger patients and lesion of 10 mm are associated with increased risk of treatment failure.
Primary cure rates are 83-94%. Cure with a second ablation procedure is approximately 100.
Patients may return to work, school and other normal activities usually within the first week after the procedure. Athletic activities are prohibited for 3 months.
It should be considered that recurrence rates of 10-20% have been described and a second procedure may sometimes be required especially in large lesions.
Percutaneous radiofrequency coagulation is currently the preferred treatment for osteoid osteoma because it does not require hospitalization, is not associated with complications, and is associated with rapid convalescence.
Here is a short video outlining the procedure
- CT Osteoid Osteoma – Case courtesy of Dr Maulik S Patel, Radiopaedia.org. From the case rID: 10262
- Osteoid Osteoma of Femur – Case courtesy of Dr Angela Byrne, Radiopaedia.org. From the case rID: 7592
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