Most commonly involves the diaphysis of long bones especially femur and tibia, and the proximal femur is the most common site.
50% of tumours involve the lower extremity
Osteoid osteoma may have a unique ‘pathogenic’ nerve supply
Three types have been described: Intracortical (80%), cancellous and subperiosteal
The pain may be referred to an adjacent joint and when the lesion is intracapsular it may simulate arthritis with effusions ,spasms and contractures
Occasionally pain precedes the appearance of radiographic changes, and leads to multiple incorrect diagnoses including neurosis
In the spine, posterior elements of the lumbar spine is most commonly involved (next common thoracic spine). An associated scoliosis is often present
If the nidus is in proximity to a nerve root, root irritation can develop.
In the lumbar spine, this pain can present as sciatica and suggest the diagnosis of a herniated intervertebral disc
Torticollis may be seen if the cervical spine is involved.
Aspirin or nonsteroidal anti-inflammatory agents relieves pain secondary to a high concentration of prostaglandins in the nidus
• There is a distinct demarcation between the nidus and the reactive bone
• The nidus consists of an interlacing network of osteoid trabeculae with variable mineralisation.
• The trabecular organization is haphazard and the greatest degree of mineralisation is in the centre of the lesion
• X rays: Central lytic nidus with extensive reactive sclerosis. The nidus is always less than 1.5 cm although the area of the reactive bone sclerosis may be larger.
• The radiolucent nidus may be obscured by dense sclerotic bone
• When the lesion is intramedullary there is less sclerotic bone
• CT scan is the investigation of choice
• Double density sign on bone scan (Focal areas of increased uptake with a second smaller area of increased uptake)
• MRI scans will show extensive edema, which may be confused with a marrow-replacing neoplasm and is therefore not recommended if osteoid osteoma is the suspected lesion
Bone island (enostoses):
‣ Mimic osteoid osteoma on X-rays but MRI changes are different from an Osteoid osteoma.
Treatment: If surgery is undertaken, it is important to eradicate the entire symptomatic nidus.
Removal of a large amount of the surrounding sclerotic bone should be avoided because it can severely weaken the bone and may result in a pathologic fracture
Intralesional resection by simple curettage of the nidus followed by high-speed burring is done often (Burr down technique).
Intraoperative localization of the lesion may be done by technetium labeled methylene diphosphonate and detection by a Geiger counter
If block excision is performed, intraoperative roentgenograms of the specimen are advised to document complete removal of the nidus
CT-guided percutaneous resection for small tumours is becoming popular.
Percutaneous Radiofrequency ablation is being tried. Under CT Guidance a radiofrequency probe is placed into the lesion and the nidus is heated upto 80degree C. This induces ionic agitation and frictional heat to cause tumor necrosis
The patient may be also treated nonoperatively using NSAIDS. About 50% of the patients treated with NSAIDs will have their lesions burnt out with no further medical or surgical treatment necessary
1. Cantwell CP et al: Current trends in treatment of osteoid osteoma with an emphasis on radiofrequency ablation. Eur Radiol 2004; 14(4):607.