• 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.

Image Diagnosis

Radiographic Features

  • 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.

CT Features

  • Osteoblastoma in spine is best visualized by a CT scan.

  • Well-circumscribed expansile lesion.

MRI Features

  • 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

Bone Scan

  • The lesion is hot.

Image Differential Diagnosis

Osteoid Osteoma

  • 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.


Gross Features

  • 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.

Histological Features

  • 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

    • High cellularity

    • 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:

    • Cystic change

    • Chondroid matrix

    • Epithelioid osteoblasts

    • Pseudomalignant osteoblasts

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

Osteoid Osteoma

  • Less than 2 cm in diameter

  • Sclerotic peripheral reactive area

ABC: In Vertebral Location

Jan 2, 2017 | Posted by in ORTHOPEDIC | Comments Off on Osteoblastoma
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