Osteoblastoma

Osteoblastomas are rare and benign primary bone tumours. They may be locally aggressive and tend to affect the axial skeleton more often than their histologic relative, osteoid osteoma.

Epidemiology

They account for 1-3% of all primary bone tumours ^2-3. Patients typically present around the second to third decades of life. There is a recognised male predilection with a male to female ratio of approximately 2.5:1.

Clinical presentation

With spinal lesions a painful scoliosis is a common presenting symptom. Otherwise there is ait presents with an insidious onset of dull pain which tends to present slowly,worse at night and only with a response to salicylates in only 7% of patients (unlike osteoid osteoma). The area will characteristically be swollen and tender with a decreased range of motion.

Pathology

ItOsteoblastoma is histologically similar to an osteoid osteoma except that it is much larger. The tumour is bone and osteoid forming and is comprised of osteoblasts. There is high associated vascularity.

Location

• spinal column: ~40% (range 32-46% ²); often involves the posterior column
  • cervical spine: 9-39% of all spinal lesions ² 
  • sacrum: 17% of all spinal lesions ³
• usually located in the metaphysis and distal diaphysis of the long bones

Variants

• aggressive (malignant) osteoblastoma: has a high of number epitheloid osteoblasts with nuclear atypia

Radiographic features

TheyOsteoblastomas can have a wide range of radiographic patterns. Lesions are typically larger than 2 cm in size ^4-5. 

Plain filmConventional radiography

• lesions are predominantly lytic, with a rim of reactive sclerosis
• tend to be expansatileexpansile
• internal calcification may sometimes be present
• an associated soft tissue mass may also be present at times
• these rapidly increasedemonstrate a rapid increase in size with associated cortical expansion in the vast majority  and sometimes of patients, sometimes with cortical destruction
• there may be surrounding sclerosis or periostitis in up to 50%
• there may be a secondary aneurysmal bone cyst in 20%

CT 

• as with plain filmsimilar to the radiograph, lesions are often demonstrated as predominantly lytic 
• internal matrix mineralisation is better appreciated on CT

MRI

MRI features tend to be non specific and often over estimatesoverestimates the lesion ⁹:

• T1 - typically hypo to isointense on T1 with areas of decreased intensity that correspond to the foci of calcification
• T2 - typically isointense to hypointense on T2 with foci of decreased intensity corresponding to the foci of calcification
• C+ (Gd) - this is a highly vascular tumor and therefore typically avidly enhances, with associated enhancement of the surrounding soft tissues ⁹

Nuclear medicine

• Tc⁹⁹m MDP or HMDP- often shows intense uptake although this is non specific and is typical in all lesions exhibiting increased bone turnover

Treatment and prognosis

Radical surgical excision is often the treatment of choice. Pre-operative embolisation is commonly carried out to reduce bleeding risk although surgery needs to be performed at the very short time interval in order to avoid reconstitution of collateral blood supply. Percutaneous ablation is an emerging modality for treatment of these lesions (as well as osteoid osteoma) ¹⁰.

Complications

Lesions are prone to extensive intra-operative bleeding due to intrinsic vascularity.