====== Osteoid osteoma ====== 

Osteoblastoma is a rare, benign, locally recurrent tumor with a predilection for the spine that may rarely undergo sarcomatous change (to [[osteosarcoma]],
((Amacher AL, Eltomey A. Spinal Osteoblastoma in Children and Adolescents. Childs Nerv Syst. 1985; 1:29–32)) 
only a handful of known cases of this). 
More vascular than Osteoid osteoma
((Lichtenstein L, Sawyer WR. Benign Osteoblastoma. J Bone Joint Surg. 1964; 46A:755–765)).

===== Key concepts =====

● [[Osteoid osteoma]] and [[osteoblastoma]] are benign [[bone tumor]]s

● histologically identical, differentiation depends on size ≤ 1 cm = osteoid osteoma > 1 cm = osteoblastoma

● can occur in the [[spine]] and may cause neurologic symptoms (esp. osteoblastoma)

● high cure rate with complete excision

===== Classification =====

see [[Intracranial osteoma]].

see [[Spinal osteoid osteoma]].

Characteristically cause night pain and pain relieved by aspirin.

===== Clinical features =====

[[Tenderness]] confined to the vicinity of the lesion occurs in ≈ 60%. 28% of patients with BOB presented with myelopathy. OO presented with a neurologic deficit of only 22%.

===== Evaluation =====

[[Bone scan]]s are a very sensitive means for detecting these lesions. Once localized, CT or MRI may better define the lesion in that region.

Caution regarding needle biopsy: if the lesion turns out to be [[osteosarcoma]], the contaminated needle tract can result in a worse prognosis.

===== Differential diagnosis =====

Lesions with similar symptoms and increased uptake on [[radionuclide]] [[bone scan]]:

1. benign osteoblastoma

2. osteoid osteoma: more pronounced sclerosis of adjacent bone than BOB

3. osteogenic sarcoma: rare in spine

4. aneurysmal bone cyst: typically trabeculae in central, lucent region

5. unilateral pedicle/laminar necrosis

==== Osteoid osteoma ====

A radiolucent area with or without surrounding density, often isolated to pedicle or facet. May not show up on tomograms.

==== Osteoblastoma ====

Most are expansile, destructive lesions, with 17% having moderate sclerosis. 31% have areas of ↑ density, 20% surrounded by a calcified shell. 

Often a contralateral [[spondylolysis]]
((Amacher AL, Eltomey A. Spinal Osteoblastoma in Children and Adolescents. Childs Nerv Syst. 1985; 1:29–32)).

===== Treatment =====

In order to obtain a cure, these lesions must be completely excised. The role of radiation therapy is poorly defined in these lesions, but is probably ineffective
((Amacher AL, Eltomey A. Spinal Osteoblastoma in Children and Adolescents. Childs Nerv Syst. 1985; 1:29–32)).

The cortical bone may be hardened and thickened, with a granulomatous mass in the underlying cavity.