Osteoid Osteoma with Night Pain
Osteoid Osteoma with Night Pain
Clinical Scenario
A 15-year-old male presents with an 18-month history of progressive left thigh pain, worse at night, that dramatically responds to aspirin and NSAIDs. He has developed a leg length discrepancy of 2cm (left leg longer). There is no history of trauma.
History:
- 18-month progressive left thigh pain
- Classic nocturnal pain pattern - wakes him from sleep
- Dramatic relief with aspirin/ibuprofen (takes 2 hours to work)
- Pain returns 4-6 hours after medication wears off
- Associated limb overgrowth (left leg 2cm longer)
- No constitutional symptoms
- No family history of bone tumours
- Active teenager, pain limiting sport participation
Examination Findings:
- Localised tenderness over proximal left femur anterolaterally
- 2cm leg length discrepancy (left longer)
- Mild thigh muscle wasting from disuse
- Full hip and knee range of motion
- No mass palpable
- Normal neurovascular examination
- Normal gait (slight limp due to LLD)
- No warmth or erythema
Investigations
Laboratory Results
Imaging
Plain X-ray Left Femur:
- Focal area of cortical thickening in proximal femoral diaphysis
- Dense reactive sclerosis
- Small central lucency (nidus) faintly visible
- No periosteal reaction
- No cortical destruction
CT Left Femur (Thin Slice, Bone Windows):
- 7mm well-defined lucent nidus within sclerotic bone
- Central calcification within nidus ("target sign")
- Marked surrounding cortical sclerosis
- Nidus in anterolateral cortex
- No soft tissue component
- Classic appearances for osteoid osteoma
Bone Scan (Tc-99m MDP):
- Intense focal uptake in proximal left femur
- "Double density" sign - central hot spot within larger area of uptake
- No other skeletal abnormalities
Questions & Model Answers
What is your diagnosis and why has the left leg grown longer?
How do you differentiate osteoid osteoma from osteoblastoma and other differential diagnoses?
What imaging modalities would you use and what are the key features on each?
What are the treatment options for this patient?
What special considerations apply to spinal osteoid osteoma?
What is the prognosis and follow-up protocol for this patient?
Key Teaching Points
| Concept | Detail |
|---|---|
| Classic Triad | Night pain, NSAID response, nidus <1.5cm |
| Mechanism | Prostaglandin (PGE2) production by nidus |
| Imaging | CT gold standard - target sign in nidus |
| Treatment | CT-guided RFA - 90-95% success |
| Spinal Lesion | #1 cause of painful scoliosis |
| Growth Disturbance | Hyperaemia → growth plate stimulation |
| Osteoblastoma | Nidus >1.5cm, different behaviour |
| Recurrence | 5-10% - repeat RFA successful |
Common Examiner Follow-up Questions
-
"What is the difference between osteoid osteoma and osteoblastoma?"
- Size: OO <1.5cm, osteoblastoma >1.5cm
- Location: OO cortical, osteoblastoma medullary/spine
- NSAID response: OO dramatic, osteoblastoma less reliable
- Treatment: OO curettage/RFA, osteoblastoma often en bloc
- Behaviour: OO self-limiting, osteoblastoma may progress
-
"What if the lesion is intra-articular?"
- Hip is most common intra-articular location
- May present as synovitis or unexplained hip pain
- Less surrounding sclerosis (cancellous bone location)
- RFA risky near articular cartilage
- Open surgical excision often required
- Arthroscopic excision for some femoral neck lesions
-
"Why do NSAIDs work so well?"
- Nidus produces prostaglandins (PGE2)
- PGE2 causes vasodilatation and pain
- NSAIDs inhibit cyclooxygenase → block PGE2 synthesis
- Effect takes 2 hours (synthesis blockade, not receptor)
- Aspirin classically used but all NSAIDs effective
-
"What if pain doesn't resolve after RFA?"
- Check CT - was nidus completely ablated?
- May be off-target ablation
- Consider repeat RFA if residual nidus
- Alternative diagnoses if no residual seen
- Surgical excision if RFA fails twice