Osteoid Osteoma

Osteoid osteoma is a self-limiting benign bone tumor. It’s one of three bone tumors in which tumor cells produce osteoid.

It occurs most often in the long bones, although the spine is the location of 10% of all osteoid osteomas.

The bone tumors which produce osteoid are:

• Osteoid osteoma
• Osteoblastoma
• Osteosarcoma.

See Also: Bone Formation

Epidemiology

Most osteoid osteomas occurs in the second or third decades of life (< 30 years old). With 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.

Osteoid Osteoma Symptoms

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.

Osteoid Osteoma may produce painful non-structural scoliosis in adolescent, where it’s found on the side of concavity. This is thought to result from marked para vertebral muscle spasm.

Imaging Evaluation

Imaging studies usually are diagnostic, these include:

• 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.

	OSTEOID OSTEOMA	OSTEOBLASTOMA
Presentation	– Diurnal pain pattern/night pain – Pain relieved by aspirin/NSAIDs	– Random pain pattern – Pain not relieved by aspirin/NSAIDs
Imaging	– Central radiolucent nidus < 1 cm Large secondary bone reaction – Characteristic “target” appearance	– Central radiolucent nidus > 2 cm – Minimal secondary bone reaction gives lesion a more aggressive appearance
Location	Diaphyseal (typical)	– Diaphyseal or metaphyseal – Posterior spine elements
Growth pattern	Self-limited growth pattern	Unlimited growth pattern
Treatment	– Radiofrequency ablation (RFA) – Surgery if tumor is close to nerve or vessels (e.g., spine)	Intralesional excision

Osteoid Osteoma Treatment

Non-Operative treatment:

• Indications for non-operative treatment:
  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 Contraindication to CT scan guided RFA 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%.

References

1. Azouz EM, Kozlowski K, Marton D, Sprague P, Zerhouni A, Asselah F. Osteoid osteoma and osteoblastoma of the spine in children. Report of 22 cases with brief literature review. Pediatr Radiol. 1986;16(1):25-31. doi: 10.1007/BF02387501. PMID: 2935775.
2. Campbel’s Operative Orthopaedics 12th edition Book.
3. Millers Review of Orthopaedics -7th Edition Book.