Osteoid osteoma is a painful benign bone lesion most often seen in the adolescent age group. The lesion consists of osteoblastic or growing cell mass called a nidus surrounded by a zone of sclerotic but normal bone. The lesion is generally small and often less than 2 cm in diameter.
Osteoid osteoma accounting for 5% of all primary bone tumors and is a tumor of children and young adults.
It is seen mostly in the age of 10-30 years. It is quite rare after the age of 50 years.
The cases have been reported in children less than one year to 70 years old.
Men are affected about 3 times more than females. There is no racial predilection.
Common Sites of Osteoid Osteoma
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.
Juxta-articular lesions are rare and seen in the elbow, hip, and ankle joints.
Subperiosteal osteoid osteoma is a relatively rare lesion. The lesion is large because the restricting compressive force on side of periosteum is not there.
More than half of the cases are seen in the lower extremity. The proximal femur is the most common site followed by tibial diaphysis. The lesion is usually cortical.
The femoral neck is the single most frequent anatomic site.
Fibular lesions are very rare.
In the upper limbs, the distal humerus is the most frequently involved bone.
The spine is affected in 10-15% of cases. The majority of the lesions are seen in the posterior elements.
Scoliosis may occur. The lesion is usually found on the concave side.
Articular facets, pedicles, the transverse and spinous processes.
A primary tumor in the vertebral body is extremely rare.
Hand and Foot
The hand is affected more than the foot. Commonly affected bones are scaphoid and proximal phalanges in the hand and talar neck in the foot.
Pathophysiology of Osteoid Osteoma
The nidus is the central nodule of woven bone and osteoid with osteoblastic rimming. It is surrounded by a reactive zone which is an area of the thickened bone and fibrovascular tissue. 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 in a highly vascular stroma of connective tissue containing osteoblastic cells.
The nidus is responsible for the pain of the osteoid osteoma. Surrounding sclerosis and nerve endings in reactive fibrous tissue also contribute to the pain.
Chemically, the pain is attributed to the increased local concentration of prostaglandin E2 and COX1 & 2 [That is why osteoid osteoma responds to NSAIDs very well.]. There is also an increased number and size of unmyelinated fibers within the nidus.
The presence of osteoid osteoma can be associated with some conditions which could result as a result of the lesion
- Painful scoliosis in spine osteoid osteoma
- Growth disturbance
- Flexion contractures
Constant dull pain which is often progressive is the main presenting complaint. The pain is worse at night and often decreases in the morning.
About a third of the patients report awakening in the night due to the pain.
The pain may also worsen after drinking alcohol [alcohol is a vasodilator]
The pain is known to be typically and dramatically relieved by nonsteroidal anti-inflammatory agents
The hand lesions may not have pain and just have swelling.
There could be additional symptoms depending on the site of the lesion such as
- Scoliosis and/or radicular pain in the spine.
- Growth disturbances in the lesions near the epiphysis of the long bone
- Joint pain and swelling when lesion is near the joint
- In lower limb lesions, limp may occur
- Small bone lesions may cause bone expansion leading to enlargement of the digit [macrodactyly]
On examination, the involved region may or may not have swelling or deformity. The site is tender in more than half of the patients.
In lesions near joint, joint effusion and contractures may be observed. In intracapsular lesions, the synovial swelling could be present.
Routine Tests usually show normal findings.
Initial x-rays are mostly normal as the changes appear on x-ray quite late.
AP and lateral views are standard. Some authors also add an oblique view to that list.
Over the time, serial x-rays should be done to document bony changes occurring.
The x-rays show a well-demarcated lytic lesion (nidus) surrounded by a distinct zone of sclerosis.
The nidus may show a zone of central opacity [sclerosis].
Spine lesions often so not show nidus and may show just sclerosis.
In small bones, bone expansion is notable.
An intraarticular lesion may lead to decrease in bone density around the joint.
Premature fusion of the epihysis can occur when the lesion is closer to the epiphysis. But it is rare.
CT precisely localizes and identify the nidus. It is the investigation of choice in osteoid osteoma and can tell the extent of bony involvement.
CT is indicated in the following situations
- Nidus not visible on x-rays
- Residual or recurrent tumor
- Lesion at the critical sites 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]
MRI has not been useful in the diagnosis of osteoid osteoma.
MRI is sensitive in detecting peritumoral edema, and soft-tissue abnormalities. It is not done mostly as it can mimic more aggressive lesions.
It is done when the diagnosis cannot be made with certainty especially in children.
It shows nidus as the hot area of focal uptake. There is low uptake in the reactive zone. The sign is known as the ‘double-density sign’
It is also able to diagnose multiple bone involvement.
The investigation as 100% sensitive [picks up all cases of osteoid osteoma] and 100% specificity [ no negative bone-scan findings have been reported in patients with osteoid osteoma]
Differential Diagnoses of Osteoid Osteoma
- Chronic and acute osteomyelitis
- Bone abscess
- Intracortical hemangioma
- Bone island
- Stress fracture
- Ewing’s sarcoma
- Intracortical osteosarcoma
- Aneurysmal bone cyst of spine
- Osteoblastoma of spine
Osteoid Osteoma Treatment
Non-steroidal anti-inflammatory drugs are first line of treatment and often cause dramatic relief of symptoms.
More than half of the patients can be treated with NSAIDs and observation over a period.
Distal tip lesions of the fingers usually do not respond to the NSAIDs.
The pain from the lesions is known to resolve after an average of 3 years and the lesions in about 5-7 years.
But in patients whose pain do not respond to NSAIDs or have secondary issues like deformity [scoliosis in spine] and/or have risk of complications like stress fractures, growth disturbances, early surgery may be considered.
Surgery aims to remove the nidus completely.
Percutaneous Radiofrequency Ablation
Percutaneous radiofrequency ablation involves introducing a thermal probe in the lesion and destroying the lesion. This procedure is indicated in
- When the non-operative management has failed
- Lesions near the joints [surgical removal can injure the cartilage
- ion of failure of medical management periarticular lesions, which increases the risk of cartilage injury
- Selected spinal lesions away from neural tissues
- Lesions close to spinal cord or nerve roots are contraindicated as heat can injure the tissue
Patients may require more than one sitting. 90% of patients are successfully treated with 1-2 sessions.
A recurrence rate of 10-15% has been reported.
Here is a short video on the procedure
Surgical Deroofing and Curettage
In this procedure, overlying bone is removed and the tumor is excised excision with curettes and burrs.
The procedure is chosen when radiofrequency ablation cannot be done due to the site of the lesion i.e. close to skin or nerves or spinal cord.
Spine lesion with painful scoliosis is also a candidate as ablation cannot be done.
En bloc resection
This consists of resection of the lesion totally with a rim of normal bone. The procedure cannot be done in areas that are difficult to reach.
The procedure is contraindicated in patients with lesions in areas difficult to access such as the acetabulum or femoral head and neck.
The drawbacks of this procedure are longer healing times, fractures in the perioperative period, need for bone grafting and internal fixation, joint stiffness etc.
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.
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 reported recurrence rate after open surgery is 9-28%.
Recurrence is typically observed within 1 year after excision.
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