Osteoid Osteoma : Mnemonic

Epidemiology and Clinical features

Mnemonic: LMNOP

Lower extremity predilection (proximal femur > tibial diaphysis)

Male predilection (2:1 to 3:1)

Night pain relieved by NSAIDs (absent in osteoblastoma)

Osteogenic benign tumor

Prostaglandins (PGE2) and Cyclooxygenase (COX1 and 2) release by nidus (explains night pain and response to NSAIDs)

3 Concentric layers

Mnemonic: 3 R

1. Radiolucent nidus in center (<1.5 cm) – centrally
   • Meshwork of dilated vessels, osteoblasts, osteoid and wove bone
   • Bull’s eye appearance on CT if center is calcified
   • Double density sign on Bone scan (hot uptake in nidus and cold uptake in reactive zone)
   • Size is >2 cm in osteoblastoma
2. Rim of fibrovascular tissue – middle
   • Absent in osteoblastoma and osteosarcoma
3. Reactive bone sclerosis – peripherally

Management

Mnemonic: MRSA

1. MRgFUS (MR guided focused Ultrasound) ablation (new non-invasive and radiation free technique)
2. Radiofrequency ablation (CT guided core biopsy followed by insertion of radiofrequency electrode through the cannula of biopsy needle and temperature of tip is increased to 90 degree celsius for 6 minutes)
   • Not indicated for vertebral lesions (risk of spinal cord injury)
   • Not indicated for small bones of hand and feet (risk of skin injury)
3. Surgery (Curretage or En-bloc resection of nidus)
4. Anti-inflammatory (Spontaneous healing of lesion may be attained in 3-4 years)