Osteoblastoma
Synonyms and keywords:Osteogenic fibroma of bone; giant osteoid osteoma

# Overview
Osteoblastoma is a rare benign neoplasm of the bone, which constitutes for almost 1% of all primary bone tumors and 3% of all benign tumors in the United States. One-third of patients have lesions in the posterior elements of the spine, most often the lumbar and sacral regions. In 1952, Lichtenstein first termed the lesion as osteogenic fibroma of bone. In 1956, Lichtenstein and Jaffe in their independent detailed studies of this neoplasm renamed the lesion as osteoblastoma. Osteoblastoma might be conventional benign or aggressive and malignant. The exact etiology of osteoblastoma is unknown. The osteoblastomas are more aggressive compared to the other benign tumors of the musculoskeletal system. Histologically osteoblastoma is similar to osteoid osteoma and is differentiated on the basis of its large size. Osteoblastoma is a benign tumor of the musculoskeletal system and is associated with little morbidity. The risk factors are not yet established and there is insufficient evidence to recommend routine screening for osteoblastoma. If not treated, it may grow and damage the bone and adjacent structures. If the untreated osteoblastoma invades the spinal canal or neural foramina, it may lead to progressive neurologic deficits. Once the tumor expands outside the bone, the recurrence rate of osteoblastoma reaches to nearly 20%. Biopsy is the diagnostic study of choice for the diagnosis of osteoblastoma which shows similar features to that of osteoid osteoma. The majority of patients with osteoblastoma have a positive history of pain which is dull and achy in nature, and the pain is not relieved by salicylates. There are no diagnostic laboratory, ECG, echocardiography or ultrasound findings associated with osteoblastoma. X-ray is a useful diagnostic tool in the diagnosis of osteoblastoma and may reveal a well circumscribed radiolucent lesion in the bony cortex. CT scan may be helpful in the diagnosis and management of osteoblastoma and may provide the size and extent of osteoblastoma. MRI may be helpful in determining the extent of osteoblastoma that has invaded the surrounding soft tissues, bone marrow, and spine. The most sensitive radiographic examination for the evaluation of osteoblastoma is bone scan. The angiography is performed if the information about the adjacent major ve sel locations or its involvement is needed. Surgery is the mainstay of treatment for osteoblastoma and the treatment with chemotherapy and radiation therapy are still controversial.

# Historical Perspective
- In 1952, Lichtenstein was the first physician who termed the lesion as osteogenic fibroma of bone.
- In 1954, Dahlin and Johnson, were able to identify 11 tumors of bone origin that shared aggressive but nonetheless benign qualities. Therefore, this made these tumors notoriously difficult to diagnose as benign or malignant.
- In 1954, Dahlin and Johnson, were the first to notice that an osteoid osteoma and osteoblastoma had many histological characteristics in common and they named it giant osteoid osteoma.
- In 1956, Lichtenstein and Jaffe in their independent detailed studies of the neoplasm termed the lesion as osteoblastoma.
- In 1977, Jackson published a review of 181 osteoblastomas from the literature and reported that spine is the location of 36% of the osteoblastomas.
- In 1984, Dorfman and Weiss reported on the aggressive osteoblastoma and termed it as a borderline osteoblastic tumor entity.

# Classification
- Osteoblastoma may be classified into two subtypes:
Conventional or benign osteoblastoma
Aggressive or malignant osteoblastoma
- Conventional or benign osteoblastoma
- Aggressive or malignant osteoblastoma
- A controversial aggressive tumor is reported which is malignant in nature as compared to the conventional or benign osteoblastomas.

# Pathophysiology
- The exact etiology of osteoblastoma is unknown.
- The osteoblastomas are composed of several osteoblasts that produce osteoid and woven bone regardless to their origin in the musculoskeletal system.
- The expansion usually occurs when the primary site of osteoblastoma is within the cortical bone.
- Typically the external rim of the osteoblastoma is concealed by the covering of periosteum and a thin rim of reactive bone.
- In a clinicopathologic study conducted at Mayo clinic, the reported sizes of osteoblastomas ranged from 1 to 11 cm, with a mean of 3.2 cm.
- The osteoblastomas are more aggressive as compared to the other benign tumors of the musculoskeletal system.
- Due to their aggressive nature, the osteoblastomas may mimic malignancy on radiographic studies.

# Causes
The cause of osteoblastoma has not been identified.

# Differentiating Osteoblastoma from Other Diseases
- Osteoblastoma must be differentiated from following bone disorders:

# Epidemiology and Demographics
- In the United States, osteoblastoma constitutes for almost 1% of all primary bone tumors and 3% of all benign tumors.
- Patients of all age groups may develop osteoblastoma.
- The mean age reported in a literature study conducted by Lucas DR at the time of diagnosis is 20.4 years, but it may be seen at any age.
- Males are more commonly affected by osteoblastoma than females.
- The male to female ratio is 2 to 1.
- One-third of patients have lesions in the posterior elements of the spine, most often the lumbar and sacral regions.
- Osteoblastoma is a benign tumor of the musculoskeletal system and is associated with little morbidity.

# Risk Factors
There are no established risk factors for osteoblastoma.

# Screening
There is insufficient evidence to recommend routine screening for osteoblastoma.

# Natural History, Complications, and Prognosis
- If left untreated, osteoblastoma may progress to grow and it may damage the bone and adjacent structures.
- If the untreated osteoblastoma invades the spinal canal or neural foramina, it may lead to progressive neurologic deficits.
- If the lesion expands outside the bone, the recurrence rate of osteoblastoma is nearly 20%.
- Secondary aneurysmal bone cyst (ABC) occurs in approximately 15 % of lesions. 
- Recurring osteoid osteoma can rarely evolve to osteoblastoma.
- Since osteoblastoma is a benign tumor, the prognosis is generally good.

# Diagnosis

## Diagnostic Study of choice
- Biopsy is the diagnostic study of choice for the diagnosis of osteoblastoma.
- Biopsy features of the osteoblastoma are similar to osteoid osteoma. Osteoblastoma lesions are larger than osteoid osteoma.
- Biopsy demonstrates the following features:
Nidus
Network of interconnecting bone, widened vessels, osteoblasts, and bone matrix
Fibrinoid margin with areas of angiogenesis
Adjacent sclerosis
- Nidus
- Network of interconnecting bone, widened vessels, osteoblasts, and bone matrix
- Fibrinoid margin with areas of angiogenesis
- Adjacent sclerosis
- On histological examination the aggressive or malignant osteoblastomas contain:
An osteoid nidus with rimming epitheloid osteoblasts surrounded by a fibrovascular stroma with osteoclasts.
More aggressive lesions tend to have large epitheloid-like osteoblasts that are mitotically active.
- An osteoid nidus with rimming epitheloid osteoblasts surrounded by a fibrovascular stroma with osteoclasts.
- More aggressive lesions tend to have large epitheloid-like osteoblasts that are mitotically active.

## Enneking (MSTS) Staging System
- The Enneking surgical staging system (also known as the MSTS system) for benign musculoskeletal tumors based on radiographic characteristics of the tumor host margin.
- It is widely accepted and routinely used classification.

## History and Symptoms
- The majority of patients with osteoblastoma have a positive history of pain which is dull and achy in nature.
- The pain is not relieved by salicylates.
- Neurological conditions occur often due to compression of either the spinal cord or nerve roots, and lead to:
Paralysis
Spinal stiffness
- Paralysis
- Spinal stiffness

## Physical Examination
- Common physical examination findings of osteoblastoma include:
Scoliosis
Torticollis
- Scoliosis
- Torticollis

## Laboratory Findings
Some patients with osteoblastoma may have elevated  concentration of  para-neoplastic beta-human chorionic gonadotropin (-hCG) , which is usually suggestive of aggressive osteoblastoma.

## Electrocardiogram
There are no ECG findings associated with osteoblastoma.

## X-ray
- An x-ray may be helpful in the diagnosis of osteoblastoma.
- Findings on an x-ray suggestive of osteoblastoma include:
A well-circumscribed radiolucent lesion in the bony cortex
A thin shell of peripheral new bone separating the tumor from the surrounding soft tissue
Typically > 2.0 cm in diameter
No reactive zone surrounding the lesion
- A well-circumscribed radiolucent lesion in the bony cortex
- A thin shell of peripheral new bone separating the tumor from the surrounding soft tissue
- Typically > 2.0 cm in diameter
- No reactive zone surrounding the lesion
- Cortical bone lesions often present with reactive bone formation, more so than those lesions in the spongy bone of the spine, ilium, or talus.
- Osteoblastoma may have features similar to those of malignancy, such as:
Cortical destruction
Extraosseous soft-tissue expansion
Left acetabular fossa pubic bone expansile predominantly lytic lesion with a rim of reactive sclerosis. Case courtesy of Dr Amr Farouk, Associated aneurysmal bone cyst component
- Cortical destruction
- Extraosseous soft-tissue expansion
- Left acetabular fossa pubic bone expansile predominantly lytic lesion with a rim of reactive sclerosis. Case courtesy of Dr Amr Farouk, Associated aneurysmal bone cyst component
- The usual sites of osteoblastoma and their plain radiographic features are described below:

## Echocardiography or Ultrasound
There are no echocardiography or ultrasound findings associated with osteoblastoma.

## CT scan
- CT scan may be helpful in the diagnosis and management of osteoblastoma.
- CT scan may provide information during the preoperative evaluation of osteoblastoma in cortical bone, such as:
Size of the tumor
Extent of the tumor
- Size of the tumor
- Extent of the tumor
- CT scan is best beneficial for the vertebral column lesions, which are hard to clearly localize on plain radiographs.
- CT scan generally results in smaller and more precise surgical resections.

## MRI
- MRI may be helpful in determining the extent of osteoblastoma that has invaded the surrounding soft tissues, bone marrow, and spine.

## Other Imaging Findings
- The most sensitive radiographic examination for the evaluation of osteoblastoma is bone scan.
- The typical appearance of an osteoblastoma on a technetium bone scan is:
A hot spot
- A hot spot

## Other Diagnostic Studies
- Angiography is performed if the information about the adjacent major vessels locations or its involvement is needed.

# Treatment

## Medical Therapy
- The treatment of osteoblastoma with chemotherapy and radiation therapy is controversial.
- The radiation therapy may lead to post-irradiation sarcoma.

## Surgery
- Surgery is the mainstay of treatment for osteoblastoma.
- The total  removal of the tumor is the treatment of goal in osteoblastoma.
- Extensive intra-lesional excision with a use of a high-speed burr is the recommended treatment for enneking stage 1 and 2 lesions.
- Wide resection for the removal of all tumor-bearing tissue is the recommended treatment for enneking stage 3 lesions, which is considered curative for osteoblastoma.

## Recurrence
- The recurrence risk is related to the adequacy of resection and is about at 1024 %.

## Primary Prevention
There are no established measures for the primary prevention of osteoblastoma.

## Secondary Prevention
There are no established measures for the secondary prevention of osteoblastoma.