Osteoblastoma






  • 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.


Osteosarcoma






  • 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.


Pathology



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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