One-third in spine: In vertebrae, osteoblastoma tends to involve the posterior elements. Most common locations in the spine are, by frequency, cervical, lumbar, thoracic, and sacral.
One-third in tubular bones: Predilection for proximal and distal femur, proximal tibia, and proximal humerus.
Appendicular lesion bone location: metaphyseal, 45 %; diaphyseal, 35 %; and epiphyseal, 20 %.
Osteoblastoma may have medullary, cortical, or periosteal location.
Less frequent in craniofacial and foot and ankle bones.
In maxillary bones, most lesions are cementoblastomas.
Clinical Symptoms and Signs
Pain in 87 % of patients, usually of long duration without the features of osteoid osteoma.
Local swelling, tenderness, and warmth.
In the lower extremities the patient may present with a limp.
When in spine: numbness and tingling. Paraparesis and paraplegia due to compression of the cord or nerve roots may appear. Scoliosis or atrophy of regional muscle groups in the area.
Osteoblastoma has been associated with systemic “toxic” symptoms in a small number of patients, which cure with the excision of the tumor.
The radiographic appearance is quite variable and often nonspecific.
The lesion is oval and expansile but usually well defined.
It may be radiolucent, radiodense, or mixed.
It may have medullary, cortical, or periosteal location.
Osteoblastoma in the vertebral column tends to involve the posterior elements, 57 %, and almost never involves the vertebral body alone, less than 3 %. It can involve two or more adjacent segments. It produces scoliosis similar to that of osteoid osteoma due to a unilateral spasticity of spinal muscles. Half the lesions show radiodense ossifications.
On the basis of radiographic features, the lesions are thought to be:
Benign: 70 %
Indeterminate: 20 %
Malignant: 10 %
In jaw bones, lesions that are ossified and located in the periapical region of a tooth and surrounded by a radiolucent halo are, probably, cementoblastomas.
In some cases osteoblastoma presents ill-defined margins with erosion of the cortex and involvement of surrounding soft tissues.
Some cases may show periosteal reaction.
Osteoblastoma in spine is best visualized by a CT scan.
Well-circumscribed expansile lesion.
Low signal in T1
High signal intensity in T2
May present dark spots corresponding to mineralized deposits
Peripheral edema best shown by using contrast
Useful for appreciation of cystic degeneration
The lesion is hot.
Image Differential Diagnosis
Nidus – less than 2 cm – is round and osteolytic. Some lesions present mineralization of the central area, “target pattern.”
The nidus is surrounded by sclerosis.
Three types of location: cortical, subperiosteal, and medullary.
Extensive sclerosis may mask the nidus in nearly 25 % of cases.
CT scan is the most useful method to show the nidus, especially when a heavy surrounding sclerosis masks the nidus.
Some osteoblastomas are locally aggressive and may destroy the cortex, mimicking a malignant neoplasm.
More than 10 % of osteoblastomas show an aggressive appearance on x-ray.
On the other hand, there are some osteosarcomas that appear indolent in the roentgenograms.
Conventional osteosarcoma is a metaphyseal permeative and destructive lesion.
Osteosarcoma is a poorly defined lesion without a sclerotic rim.
Osteosarcoma usually destroys the cortex and develops a soft tissue mass.
Periosteal reaction is common in osteosarcomas, with a Codman triangle, onionskin, or sunburst pattern.
ABC: When in Spine
Area of lucency situated eccentrically in the medullary cavity in the metaphysis of a long bone.
Most ABCs are completely lytic, but a few contain traces of mineral.
Frequently presents a multiloculated appearance.
Later, a “ballooned” or “aneurysmal” cystic expansion of the affected bone – “blow out” – is evident. Usually forms a thin sclerotic rim of ossification due to periosteal new bone formation.
When in spine, more than one vertebral segment is commonly affected.
In other bones, ABC may cross joints and involve an adjacent bone.
CT and MRI highlight the internal septation, the cystic nature, and the fluid-fluid levels.
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The lesions are reasonably well circumscribed and delineated from the surrounding bone tissue.
Reddish, hemorrhagic, friable, and granular.
A small percentage of lesions may show cystic changes.
Sometimes the vascularity is so great that hemostasis may be problematic at surgery.
Average diameter: 3–6 cm.
Histologically, the lesion is similar to the “nidus” of osteoid osteoma.
Osteoblastoma is usually very well circumscribed.
The edge may show parallel well-formed bone trabeculae and tends to show maturation or zonation, appearing well limited, with no tendency to permeate the surrounding bone.
The lesion does not infiltrate the surrounding native bone tissue.
The lesion is composed of anastomosing immature osteoid and bone trabeculae embedded in a loose fibrovascular stroma – vessels with wide lumina – usually associated with few benign multinucleated giant cells of osteoclastic type.
Osteoblasts lining the trabeculae are uniform and do not fill the intertrabecular bone marrow spaces.
Lace-like osteoid may be present.
Rarely, mitotic figures may by numerous. Lacks atypical mitoses.
Areas of secondary aneurysmal bone cyst are seen in approximately 10 % of osteoblastomas.
Clear-cut chondroid matrix differentiation is seen in a small percentage (6 %) of typical osteoblastomas.
Epithelioid osteoblasts – larger than conventional osteoblasts – with large nuclei and prominent nucleoli are found in a small number of cases.
In rare instances, large osteoblasts with bizarre and degenerative nuclei are seen.
Necrosis is usually not present.
Histological features that may be misinterpreted and lead to an overdiagnosis are:
Presence of lace-like osteoid
Foci of cartilage
Numerous mitotic figures
A rare type of osteoblastoma is the multifocal sclerosing osteoblastoma, which can be medullary, central, or endosteal and peripheral or juxtacortical:
Presents a multifocal growth pattern.
Roentgenological and gross features: more than one circumscribed lesion with the appearance of the central “nidus” of osteoid osteoma – “multifocal osteoid osteoma” – enclosed in a block of reactive sclerotic bone.
Histologically defined by multiple small foci of typical osteoblastoma separated by a proliferating bone and fibrous tissue.
A few may have a predominant proliferation of epithelioid cells.
Eventually, a nodule composed exclusively by epithelioid cells can mimic metastatic carcinoma.
“Out of the average” findings:
These findings do not represent a different clinical behavior and are not sufficient to consider, when they are present, different variants of osteoblastoma.
Pathologic Differential Diagnosis
Less than 2 cm in diameter
Sclerotic peripheral reactive area
ABC: In Vertebral Location
Less sclerotic lesion
Woven trabeculae in a fibrogenic stroma with haphazardly distributed multinucleated giant cells
Cavernomatous spaces filled with blood
Lace-like or powdery calcifications with a basophilic blue appearance (“blue bone”), peculiar chondroid-like zones, and pink parallel seams of fibrillary osteoid beneath the lining of the septum are typical and relatively specific features of ABC.
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