Osteoid Osteoma

• Osteoid osteoma is a self-limiting benign bone tumor.
• It’s one of three bone tumors in which tumor cells produce osteoid:
  1. Osteoid osteoma
  2. Osteoblastoma
  3. Osteosarcoma.

Epidemiology

• Most osteoid osteomas occurs in the second or third decades of life (< 30 years old).
• Male > female (3:1).
• The tumor usually found in cortical bone, (It can also be found in cancellous bone).
  • Common locations include diaphyseal bone, proximal femur, tibia, and spine.

Clinical Evaluation

• The patient with an osteoid osteoma has pain that is worsen at night and is relieved by aspirin or other nonsteroidal anti-inflammatory medications (NSAIDs).
  • Maybe due to increased levels of cyclooxygenases and prostaglandins that have been found in the lesion.
• When the tumor is near a joint, swelling, stiffness, and contracture may occur.
• May produce painful non-structural scoliosis in adolescent.
  • The Osteoid osteoma found on the side of concavity.
  • This is thought to result from marked para vertebral muscle spasm.

Imaging Evaluation

• Imaging studies usually are diagnostic.
• Plain radiographs often are sufficient to make the diagnosis.
  • The lesion consists of a small (<1.5 cm) central radiolucent nidus with surrounding bony sclerosis.
• Computed tomography CT is the best study to identify the nidus and confirm the diagnosis.
  • It demonstrates better contrast between the lucent nidus and reactive bone.
• Technetium bone scans always show intense focal uptake.
  • Double density sign which if present is highly specific and helpful in distinguishing it from osteomyelitis.
• Ultrasound: focal cortical irregularity with adjacent hypoechoic synovitis may be present at the site of intra-articular lesions.
• MRI usually shows extensive surrounding edema.

The double density sign, also sometimes referred to as the hotter spot within hot area sign. It refers to a central focus of intense uptake (the nidus) within a surrounding lower, but nonetheless increased uptake(the rim).

Histology Findings

• Fibrovascular tissue with immature bony trabeculae that are rimmed by
  prominent osteoblasts, and surrounded by a sclerotic rim.
• It’s appears similar to osteoblastoma (osteoblastomas are larger).

The osteoid osteoma is composed of three concentric parts:
1. Nidus
2. Fibrovascular rim
3. Surrounding reactive sclerosis

Differential Diagnosis

• Long bones lesions differential diagnosis are:
  1. Enostoses (bone island)
  2. Stress fracture.
  3. Osteomyelitis (Brodie abscess).
  4. Cortical desmoid
  5. Osteochondroma
  6. Osteosarcoma
• Posterior spinal lesions differential diagnosis are:
  1. Aneurysmal bone cyst.
  2. Osteoblastoma.

Treatment

Non-Operative treatment:

• Indications:
  1. The patient’s symptoms are adequately controlled.
  2. The patient is willing to undergo long term medical management.
• Anti-inflammatory medication can be used as the definitive treatment.
• Patients treated in this manner usually experience spontaneous healing of the lesion within 3 to 4 years.

Operative treatment:

1. CT scan–guided RFA:
   • It’s the dominant method of treatment.
   • Indications:
     • Failure of medical management
     • Most patients with lesions of the pelvis or long bones of the extremities.
   • Contraindication:
     • A lesion close to a critical structure (i.e., neurovascular bundle or spinal cord) is a to RFA.
   • A radiofrequency probe is placed into the lesion, and the nidus is heated to 80-90°C.
   • It usually is done as an outpatient procedure, and patients usually can return immediately to full activity.
   • Recurrence rates are less than 10%.
2. Open surgical removal:
   • Indication:
     • Failure of medical management
     • A lesion close to a critical structure (i.e., neurovascular bundle or spinal cord).
   • Removal of the entire nidus, this can be accomplished by curettage or en bloc resection.
   • Recurrence rates with this technique are less than 10%.

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