GENERAL INFORMATION
Benign osteoblastic neoplasm with aggressive growth pattern (considered a benign aggressive tumor)
Histologically it is similar to osteoid osteoma but is a larger size and grows progressively
Consists of well vascularized connective tissue stroma with interconnecting trabeculae of osteoid and woven bone
Osteoblastomas are rare tumors and constitute about 1% of excised primary bone tumors
Osteosarcoma is 20x more common and osteoid osteoma is 4x more common than osteoblastoma
There is a more aggressive form of osteoblastoma in which recurrences are more common. These tumors have a higher chance of coming back after they are removed.
CLINICAL PRESENTATION
Signs/Symptoms: Pain is the most common presenting symptom
Pain is usually less severe and less pronounced at night and may or may not be relieved by aspirin compared to an osteoid osteoma in which night pain is particularly severe and the pain is usually reliable relieved with an aspirin or NSAID
Spinal lesions may be accompanied by muscle spasms, scoliosis and neurological manifestations
Prevalence: Males: Females 2-3:1
Age: Patients are young, Median age 18
80% of patients are between 10 and 30 years old
Sites:
Spine (40% of cases; usually posterior elements)
Long Bones (30%; Most arise from diaphysis or metaphysis; Epiphyseal lesions are rare but may occur more often in the tubular bones of the hands or feet)
RADIOGRAPHIC PRESENTATION
Plain X-rays:
Geographic, circumscribed lesion usually around 5cm in size.
There may be expansion of bone, cortical thinning and cortical breakthrough. A soft tissue mass may accompany this lesion but the soft tissue component is usually contained by the periosteum.
The periosteum remains intact around the soft tissue component. Might need a CT scan to detect the subtle calcification (Egg Shell Rim of Calcification) associated with an intact periosteal reaction
The lesion may be entirely radiolucent but usually shows some degree of mineralization. Mineralization may appear stippled like cartilage but do not see chondroid pathologically. Mineralization is sometimes better detected on a CT scan rather than an x-ray.
Usually less surrounding sclerosis than an osteoid osteoma.
Arise from the Diaphysis (75%) more commonly than Metaphyseal (25%)
4 cm to 6 cm in size
Bone Scan: Increased uptake at the site of the lesion
CT Scan: More useful for detecting mineralization and evaluating extent of bone destruction than plain X-ray
MRI: Also useful in determining extent
There is often extensive edema around the tumor in the surrounding bone and soft tissues that can lead to a misdiagnosis of a malignant tumor.
Plain X-Ray:
Geographic Pattern of Bone Destruction
Eccentric
Sclerotic Margin
Buttressing, Benign Appearing Periosteal Reaction (Cortical Thickening/Bony Expansion)
No clear mineralization on Xray
Plain X-ray: Osteoblastoma of Proximal Humerus
Plain X-Ray: Osteoblastoma of Distal Femur
MRI: T1 Weighted Image of Osteoblastoma of Distal Femur
Geographic Well Circumscribed Lesion
Intermediate Signal on T1
MRI: T2 Weighted of Osteoblastoma of Distal Femur
Geographic Lesion
There is extensive edema around the lesion (high signal in medullary canal)
High signal on T2 with punctate low signal areas consistent with mineralization (Arrows)
MRI: T2 Coronal MRI of Osteoblastoma of Distal Femur
CT Scan of Distal Femur Osteoblastoma
X-ray: Osteoblastoma of Distal Radius
Geographic Lesion
Well Circumscribed
Mineralization may not be detectable on a plain radiograph
MRI: Osteoblastoma of Distal Radius
MRI: Osteoblastoma of Distal Radius
Plain X-Ray: Osteoblastoma of Sternum
CT Scan: Osteoblastoma of Sternum Axial Section
CT Scan Osteoblastoma of Sternum
Coronal Section
CT Scan Osteoblastoma of Sternum
Sagittal Section
CT 3 Dimensional Reconstruction of Osteoblastoma of Sternum
MRI: T2 Weighted Image of Osteoblastoma of Sternum with Surrounding Edema
MRI: T1 Weighted Image Osteoblastoma of Sternum
Sagittal MRI of Osteoblastoma of Sternum
X-ray: Osteoblastoma of Proximal Phalanx
Osteoblastoma
Radiology of Spine Lesions:
Well defined, expansile, geographic, osteolytic lesion that is partially or extensively calcified or ossified
Posterior elements alone (>60% of cases)
Posterior elements with extension into vertebral body (25%)
Vertebral body alone (15%)
More likely to contain ossification and a soft tissue mass
Sclerosis less likely than long bones
Scoliosis less characteristic than osteoid osteoma
Osteoblastoma of Spine
Geographic Lesion
Posterior Elements of Spine
Bone is Expanded
The lesion (soft tissue component) is surrounded by an “Egg Shell” rim of calcification indicating the periosteum is intact
Mineralization present in lesion
Osteoblastoma of Spine Posterior Elements
MRI: Osteoblastoma of Spine Posterior Elements
MRI: Osteoblastoma of Spine Posterior Elements
CT Scan Osteoblastoma of Spine Posterior Elements
Osteoblastoma
Differential between Osteoid Osteoma and Osteoblastoma
Osteoblastoma
Size: >1.5-2cm
Growth: Benign Aggressive Lesion: Continues to grow and destroy bone (osteoid osteoma has a limited growth potential--indolent)
Soft Tissue Mass with an Osteoblastoma
Scoliosis and classical symptoms absent with Osteoblastoma
Matrix is multifocal in an osteoblastoma and not central
GROSS PATHOLOGY
The gross pathology of an osteoblastoma is indistinguishable from an osteoid osteoma except larger
Nidus is well demarcated
Granular, friable, reddish hemorrhagic tissue
May bleed significantly when curetted
Cortex is thinned, possibly destroyed
MICROSCOPIC PATHOLOGY
Interlacing network of bone trabeculae in a loose fibrovascular stroma
Prominent vessels
Osteoblasts are plump, active, scattered mitotic figures
Osteoblasts line up around periphery of trabeculae (Osteoblastic Rimming)
Soft tissue component usually surrounded by shell of reactive bone or periosteum (Egg Shell Rim of Calcification)
No cartilage production (as opposed to osteosarcomas that may contain areas of cartilage)
Osteoblastoma
Osteoblastoma
Osteoblastoma
Osteoblastoma
Osteoblastoma
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Osteoblastoma High Power View
Osteoblastoma
Trabeculae of Immature, Woven Bone
Osteoblasts Line Trabeculae (Osteoblastic Rimming)
Fibrovascular Stroma
Low Power View
Osteoblastoma
Low Power View
Osteoblastoma
Osteoblastoma
Aggressive Osteoblastoma
Aggressive osteoblastoma is a distinct rare type of osteoblastoma that has a much more aggressive local behavior than a conventional osteoblastoma. They have a higher chance for local recurrence after removal.
There has been controversy about the true existence of this type of tumor and whether these tumors are actually low grade osteosarcomas.
They have a similar appearance microscopically as a conventional osteoblastoma except the osteoblasts are twice as large and have an epithelioid quality with abundant eosinophilic cytoplasm (Epithelioid Osteoblasts).
Aggressive osteoblastoma is a borderline lesion lesion between osteoblastoma and osteosarcoma. It is not a precursor to osteosarcoma. It does not metastasize.
Aggressive osteoblastomas usually occur in an older age group than conventional osteoblastoma.
Most patients are older than age 30. It affects a broad variety of bones.
Aggressive osteoblastomas are usually larger than a conventional osteoblastoma and have been reported to be up to 8.5 cm in diameter.
Most have a similar radiographic appearance as a conventional osteoblastoma and have well defined margins, variable amounts of mineralization and peritumoral sclerosis. They occasionally have radiographic characteristics consistent with malignancy.
Aggressive osteoblastomas are locally aggressive but never metastasize.
Plain X-Ray: Aggressive Osteoblastoma of a Hand Metacarpal
Pathology of Aggressive Osteoblastoma
Osteoblast cells are uniform
Cells line trabeculae
Trabeculae are usually more thickened than conventional osteoblastoma
Osteoblasts are larger than normal osteoblasts and have an epithelioid shape (Epithelioid Osteoblasts)
Pathology of Aggressive Osteoblastoma
Pathology of Aggressive Osteoblastoma
Epithelioid Osteoblasts
Aggressive Osteoblastoma
Differential Diagnosis:
Osteoid Osteoma
Conventional Osteoblastoma
Osteosarcoma
The differential between osteoid osteoma, conventional osteoblastoma and aggressive osteoblastoma is based on size and the presence of epithelioid osteoblasts. Can have epithelioid osteoblasts in osteoid osteoma and conventional osteoblastoma but they do not occur in cohesive sheets that fill intertrabecular spaces
Aggressive Osteoblastoma vs. Osteosarcoma
Osteosarcoma:
Cellular atypia
High mitotic rate
Atypical mitotic figures
Abundant lacelike osteoid
Permeative growth into adjacent bone and soft tissue
Presence of neoplastic cartilage
No peripheral shell of reactive bone
Pathology:
Differentiation from osteosarcoma
Osteoblastomas that are greater than 4 cm and that show prominent periosteal new bone formation may present problems in differentiation from osteosarcoma
May have foci of lace-like osteoid, high cellularity and more than a few scattered mitotic figures but these characteristics usually occur independently in an osteoblastoma vs all these atypical characteristics being present in an osteosarcoma
Osteoblastoma vs. Osteosarcoma
Osteoblastoma
Osteosarcoma
Osteosarcoma
Lace-like Osteoid laid down in between cells
No trabeculae
Cells are crowded
High degree of cellular pleomorphism
Cells do not resemble osteoblasts
High mitotic rate with atypical mitoses
Aggressive Osteoblastoma
Cells are more uniform
Less atypical cells
Cells tend to line trabeculae
Less pleomorphism
Cells look more like osteoblasts and are less cigar and bizarre shaped
Xray: Conventional Osteosarcoma of Distal Femur
Classic radiographic example of a conventional osteosarcoma of the distal femur
Distal Femur is most common site for a conventional osteosarcoma
Permeative lesion with mixed lysis and sclerosis (sclerosis is calcified osteoid)
Metaphyseal Origin
There is a Codman's triangle interrupted type of periosteal reaction
Tumor extends into soft tissue and the soft tissue component is ossified
Xray: Osteosarcoma of Proximal Tibia
Proximal tibia is second most common site for conventional osteosarcoma
Permeative lesion with mixed lysis and sclerosis (ossification)
Metaphyseal origin
Soft tissue extension
Hair on End periosteal reaction
Osteoblastoma:
Natural History
Benign, aggressive tumors
Propensity for local recurrence
Grow locally within the bone and destroy bone as they grow
Grow slowly and do not metastasize
TREATMENT
Extremity Lesions:
Intralesional Curettage Resection and Cement Fixation vs. Bone Grafting
Local adjuvant may be considered such as cryosurgery to reduce the risk of local recurrence
En-bloc excision for massive tumors
Spine lesions:
En-bloc resection (recurrence may be as high as 25%)
Radiotherapy may be recommended after inadequate removal
Rarely—malignant transformation after radiation
PROGNOSIS
Majority of patients are cured by initial therapy
Recurrences usually occur within 2 years from initial surgery from regrowth of microscopic cells
Recurrences after 2 years is very rare
Recurrences in spine are more common and occur in approximately 25% of cases
