Osteoblastoma Treatment & Management


Background

Osteoblastoma is a rare primary neoplasm of bone, categorized as a benign bone tumor that is closely related to osteoid osteoma. It is a bone-forming lesion that may be found within the cortex, medullary canal, or periosteal tissues; multicentric foci within a single bone have also been described. There is a slight predominance of metaphyseal over diaphyseal locations. [1 Osteoblastoma differs from osteoid osteoma in its ability to grow larger than 2.0 cm in diameter and its aggressive behavior in bone. [2345678]

In his original description of osteoblastoma, Lichtenstein termed the lesion an "osteogenic fibroma of bone." [910In 1954, Dahlin and Johnson reported 11 aggressive but benign tumors that appeared to originate within bone and were frequently difficult for the inexperienced pathologist to differentiate from malignancy. [11 They chose to call the tumor a giant osteoid osteoma for its histologic similarity to osteoid osteoma. The current and accepted name, osteoblastoma, was coined by Lichtenstein and Jaffe in their independent and more detailed reports of this neoplasm. [912]

The clinical course of osteoblastoma often makes diagnosis difficult. The tumor may have a slow indolent course or display characteristics that are confused with malignancy, especially if it has an aneurysmal bone cyst component. Other diagnoses that share similar clinical, radiographic, and histologic features with conventional osteoblastoma include osteoid osteoma. Osteoblastomas may also have features that mimic malignant tumors, which often make it difficult for inexperienced surgical oncologists and pathologists to diagnose. Osteoblastoma is about 20 times less common than osteosarcoma is. [21314151617]

Anatomy

Osteoblastoma commonly affects the vertebral column, with approximately 30% of these lesions arising within the posterior elements of the spine. The vertebral body has been reported as the primary origin of these neoplasms in some reports, but these locations may be due to the failure to clearly identify the epicenter of the neoplasms (see the images below). Equally common locations (30%) are the long bones of the appendicular skeleton, typically the femur and the tibia, as is the case with all benign and malignant bony neoplasms.

Standard radiograph of an osteoblastoma with a secStandard radiograph of an osteoblastoma with a secondary aneurysmal bone cyst of the lumbar spine.
(Click image to enlarge.) Osteoblastoma with a sec(Click image to enlarge.) Osteoblastoma with a secondary aneurysmal bone cyst. CT findings are nonspecific but help demonstrate the extent of lesion arising in the vertebral column.

Other documented locations of osteoblastoma include the pelvic bones, the small bones of the hands and feet, the skull/facial bones, the clavicle, the scapula, and the ribs. Osteoblastoma also arises in the talus more frequently than other benign tumors do (see the image below). [1819202122]

Oblique and lateral radiographs of the ankle reveaOblique and lateral radiographs of the ankle reveal a lucent lesion within the talus.

Associated aneurysmal bone cysts (see the image below) may be seen with as many as 10% of osteoblastomas, imparting to these lesions much more aggressive and alarming characteristics.

Standard radiograph of an osteoblastoma with a secStandard radiograph of an osteoblastoma with a secondary aneurysmal bone cyst of the lumbar spine.

Pathophysiology and Etiology

Regardless of where osteoblastomas originate within the musculoskeletal system, they are composed of numerous osteoblasts that produce osteoid and woven bone. When the primary site is within cortical bone, expansion is often present. However, the outer rim of the tumor is always covered by periosteum and a thin rim of reactive bone. In the largest series reported, the size of osteoblastomas ranged from 1 to 11 cm, with a mean of 3.2 cm. [23]

As opposed to more their benign counterparts, aggressive osteoblastomas display aggressive destruction of the adjacent host bone cortex and extends into surrounding soft tissues. This characteristic is thought to be due to a coexisting aneurysmal bone cyst component.

The exact etiology of osteoblastoma is unknown.

Epidemiology

In the United States, osteoblastoma accounts for approximately 1% of all primary bone tumors. The mean age at presentation in the largest series studied was 20.4 years, with a range of 6 months to 75 years. [23The male-to-female patient ratio is 2:1.

Prognosis

Osteoblastoma has a reported recurrence rate of approximately 10-20%. Tumor relapse is associated with inadequate resection of the primary lesion. In some areas (eg, the spine), it might not always be possible to remove the entire lesion.

For stage 2 osteoblastomas (see Workup, Staging), however, the overall recurrence rate after extensive intralesional excision is close to 0%. The recurrence rate after excision through the reactive zone of the bone (marginal excision) is much higher. For an osteoblastoma associated with an aneurysmal bone cyst, the recurrence rate after wide excision in surgically accessible sites is reported as low, but no large-scale studies exist to define what "low" means. The recurrence rate after intralesional excision is higher at any site, as expected.


History and Physical Examination

Osteoblastomas most commonly occur during the first three decades of life. The primary symptom is pain, and patients often characterize it as dull and achy. Unlike the pain of osteoid osteoma, the pain of osteoblastoma is unlikely to be relieved by salicylates.

Osteoblastoma may affect any bone, but it most frequently arises within the posterior elements of the vertebral column and long tubular bones. When these tumors develop in the spine, patients may present with neurologic symptoms due to spinal cord or nerve root compression. [24252627 A report of osteoblastomas and osteoid osteomas of the spine showed that 9 of 13 patients had neurologic disorders before treatment and 8 of 13 had an associated structural deformity (ie, scoliosis, torticollis, or both). [28 Therefore, scoliosis and torticollis are frequently associated presenting signs.

According to the Musculoskeletal Society Tumor Staging (MSTS) system for benign bone tumors, [2930 most osteoblastomas are stage 2 lesions (see Workup, Staging).



Approach Considerations

Lucas reported that "distinguishing osteoblastoma from osteosarcoma is one of the most challenging and important problems in orthopaedic pathology and ... is sometimes impossible." [23 The histologic diagnosis requires a meticulous microscopic examination for cellular atypia, nuclear atypia, abnormal mitoses, and a permeative (penetrating) pattern. If any of these characteristics are found, osteosarcoma should be considered the likely diagnosis.

Immunohistochemical analysis may also aid in the diagnosis. The cells of osteoblastoma may show a different reactivity pattern for the expression of cyclooxygenase (COX)-2 than atypical osteoblastic cells in osteosarcoma. [31]

The diagnosis and treatment of osteoblastoma frequently requires the coordinated participation of an experienced radiologist, a pathologist, and a surgeon with expertise in orthopedic oncology. Once the diagnosis is made, the outcome is generally good.

Laboratory Studies

No serum or blood studies are helpful in the diagnosis of osteoblastoma. Histologic analysis of an appropriate, representative biopsy specimen is required to make the diagnosis. The representative sample must be at least 1.0 cm in volume and from the body of the mass; taking a piece of irritated, reactive periosteum adjacent to the lesion or from the aneurysmal component of such tumors will result in an inappropriate diagnosis.

Imaging Studies

Radiography

Standard plain films are the most helpful radiographs for making the diagnosis of osteoblastomas. These tumors typically possess several general characteristics on standard radiographs. [93233]

First, osteoblastomas tend to occur in particular locations, and an awareness of their typical, most frequent locations must be kept in mind.

The radiographic presentation shows a well-circumscribed radiolucent lesion in the bony cortex, with a thin shell of peripheral new bone separating it from the surrounding soft tissue (see the images below).

Radiograph of the cervical spine of a 15-year-old Radiograph of the cervical spine of a 15-year-old girl.
Radiograph of the cervical spine reveals an expansRadiograph of the cervical spine reveals an expansile lesion in the posterior elements of the cervical spine in this 15-year-old girl.

The lesion is typically larger than 2.0 cm in diameter, and does not have a surrounding, intense, reactive zone of bone surrounding it, as is characteristic of osteoid osteoma.

Approximately two thirds of osteoblastomas in tubular bones occur within the cortex, and the remaining one third appear within the medullary canal.

Within the vertebral column, radiographs most commonly display the tumor in the posterior elements. It is usually a well-defined destructive process within the cortical bone but may bulge into the surrounding soft tissues and spinal column. This is probably because the limited bony volume of the posterior element cannot contain the over two centimeter volume of tumor growth at this site.

Within the long bones, the radiographic presentation of osteoblastoma is usually a rounded or oval, lucent tumor arising within the diaphysis.

In general, reactive bone formation is seen more frequently in cortical bone lesions than in those arising within the spongy bone of the spine, ilium, or talus.

Osteoblastoma may have features similar to those of malignancy, such as cortical destruction and extraosseous soft-tissue expansion but, as noted above, this is usually due to the associated aneurysmal bone cyst component.

Computed tomography

Computed tomography (CT) is a useful imaging tool for the diagnosis, and management planning of these tumors. During the preoperative evaluation, CT can provide information about the size and extent of the lesion in cortical bone. It is most helpful with vertebral column lesions that are difficult to clearly localize on plain radiographs (see the image below). CT often results in smaller and more accurate surgical resections.

Computed tomography of the cervical spine reveals Computed tomography of the cervical spine reveals an expansile lesion in the posterior elements.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is most helpful in depicting the extent of lesions that extend into the surrounding soft tissues, bone marrow, and spine. Like CT findings, MRI findings alone are not diagnostic (see the images below).

T1-weighted sagittal MRI of the left foot demonstrT1-weighted sagittal MRI of the left foot demonstrates a lesion in the talus with low signal intensity. MRI findings are not specific enough to suggest the diagnosis of osteoblastoma but aid in determining the extent of the lesion.
T2-weighted sagittal MRI of the left foot demonstrT2-weighted sagittal MRI of the left foot demonstrates a lesion in the talus with high signal intensity.

Bone scanning

Bone scintigraphy is a sensitive tool but not a specific one. It reveals intense focal activity of the radionuclide at the tumor site but, by itself, is not diagnostic. Many bone tumors (eg, osteoid osteoma, aneurysmal bone cyst, fibrous dysplasia) show a similar type of focal activity (see the image below).

Increased radionuclide activity in the talus correIncreased radionuclide activity in the talus corresponds to the site of the lesion.

Angiography

In the past, angiography was commonly used to determine the vascularity of the lesion, but at present, with the availability of more definitive studies, it is not considered to be helpful or cost-effective in most situations. It can, however, be helpful if adjacent major vessel locations/involvement information is needed.

Biopsy

Biopsy of the lesion is necessary to provide an appropriate, representative tissue sample for histologic diagnosis.

Fine-needle biopsy usually is not indicated for obtaining a tissue sample for this tumor, because the amount of tissue is usually too small to make any diagnosis other than benign versus malignant and primary versus metastatic disease. This tool has up to a 25% false-negative/false-positive outcome in most hands. A core-needle biopsy is more useful to obtain a representative specimen for diagnosis.

Open biopsy may also be performed. The use of this type of biopsy depends on the anatomic location of the lesion, the experience of the person performing the biopsy, and any associated defects (eg, aneurysmal bone cyst) present with the mass.

Histologic Findings

Osteoblastoma has been characterized as having a cellular osteoblastic tissue with active intercellular production of osteoid material and primitive woven bone (see the images below).

Photomicrograph of an osteoblastoma (original magnPhotomicrograph of an osteoblastoma (original magnification, X40). Special thanks to Dr. Ronald Burns, Palmetto Richland Department of Pathology, for his assistance in obtaining these slides.
Photomicrograph of an osteoblastoma (original magnPhotomicrograph of an osteoblastoma (original magnification, X100). Special thanks to Dr. Ronald Burns, Palmetto Richland Department of Pathology, for his assistance in obtaining these slides.

General histologic findings of osteoblastoma include the following:

  • Most important, immature bony trabeculae are lined by osteoblasts; some of these trabeculae may have extensive ossification, whereas others may be without mineralization
  • Highly vascularized connective tissue - The stroma contains widely dilated capillaries and areas of large dilated blood sinusoids
  • Mitotic activity - Mitotic activity is nil to minimal in 89% of cases

Histologic findings are very important in making the diagnosis of osteoblastoma versus osteosarcoma, but the differentiation is often difficult. Histologic hints in separating the two diagnoses include the following:

  • Osteoblastoma has a very low rate of mitosis and minimal cytologic atypia
  • Osteoblastoma has a tendency for peripheral maturation and does not permeate surrounding bone and soft tissue as osteosarcoma does
  • Osteoblastoma rarely has the cartilaginous matrix that is often present with osteosarcoma

Staging

The Enneking system, now known as the Musculoskeletal Society Tumor Staging System, categorizes benign tumors into the following three levels [2930:

  • Latent (stage 1) - These tumors are asymptomatic and are usually discovered incidentally; they may be active in adolescence but become latent after adulthood

  • Active (stage 2) - These tumors usually enlarge slowly, are always surrounded by a rim of normal bone, and are usually discovered during an investigation of bone for other reasons (eg, after an associated pathologic fracture or mechanical dysfunction); they usually grow slowly but steadily, have benign cytologic characteristics, remain intracapsular, and do not metastasize

  • Aggressive (stage 3) - These tumors grow rapidly, destroy surrounding bone, and are symptomatic (eg, a giant cell tumor of bone); they are usually associated with an aneurysmal bone cyst that destroys bone aggressively and extends extracapsularly, though the histologic architecture and cell structure of the osteoblastoma remains benign in these instances

In most cases, osteoblastoma is a stage 2 lesion.


Approach Considerations

There are two primary indications for surgical management of an osteoblastoma within the musculoskeletal system. The first is obtaining a tissue sample that firmly establishes the diagnosis. "When tumor is the rumor, tissue is the issue" is a good rule to remember. It is frequently the case, however, that even with an appropriate, representative tissue sample, it may be very difficult to differentiate the aggressive (stage 3) lesions from osteosarcoma.

The second reason for surgical management is to eliminate the continued structural destruction of bony architecture by this aggressive tumor. It is important to emphasize that repairing the structural bony defect is the secondary consideration, in that it cannot be planned and implemented until diagnosis of the lesion is established.

No specific contraindications to the treatment of osteoblastoma have been documented. General precautions include avoiding harm to a growth plate when operating near one in the skeletally immature patient. When these tumors are removed from the spinal elements, meticulous care to protect the spinal cord during the procedure is mandatory. Similar precautions must be considered for the urinary bladder, the sacral plexus, and other associated pelvic organs when lesions are removed in these locations. Because all patients need some form of surgery in the management of this tumor, they must be able to tolerate anesthesia.

Medical Therapy

The use of radiation or chemotherapeutic measures to treat osteoblastoma has been controversial. Most authorities have maintained that neither treatment has any therapeutic effect on this lesion and that each has more risks than benefits. For instance, postirradiation sarcoma is a well-documented outcome in the management of benign tumors and makes this method of treatment inappropriate for benign, destructive surgically accessible tumors such as osteoblastoma.

Surgical Therapy

The appropriate surgical treatment goal for osteoblastoma is complete excision of the lesion. For stage 2 lesions, the recommended treatment is extensive intralesional curettage followed by management of the resulting structural defect. After curettage of macroscopic material, a high-speed burr can be used to remove microscopic tumor back to a circumferential margin of normal appearing bony tissue. Curettage alone is usually inadequate.

In a study of 99 cases of osteoblastoma over 30 years (1974-2006), the local recurrence rate was approximately 24% after curettage alone and bone reconstruction of the resulting defect. The authors concluded that in select cases, recurrence can be minimized by more aggressive surgery. [34]

For stage 3 lesions, wide resection is recommended to ensure removal of all tumor-bearing and any associated tumor (eg, aneurysmal bone cyst). Wide excision is defined as the excision of the tumor with a circumferential cuff of normal bone and soft tissue around the entity. Such excisions are usually curative for osteoblastoma with an associated aneurysmal bone cyst. [3435]

Weber et al compared the clinical success and costs of computed tomography (CT)-guided radiofrequency ablation (RFA) with those of open surgical resection for osteoblastoma as well as spinal osteoid osteoma (OO). [36They found RFA to be an efficient method for treating osteoblastoma, with results comparable to those of open surgery.

Preparation for surgery

Surgical excision of osteoblastomas must be carefully planned. For instance, embolization 24 hours before definitive surgery may be indicated to help control bleeding of an associated aneurysmal bone cyst; it can also be used to reduce intraoperative bleeding and facilitate complete excision in surgically difficult sites. A study of a small cohort of patients did not show any evidence of tumor relapse when preoperative embolization was used before surgical resection and reconstruction of cervical spine lesions. [37]

Planning for reconstruction of any critical defect (ie, one in which bony stability is lost) also must be carried out before one may proceed with definitive surgery. For example, those lesions necessitating wide resection for adequate removal of the osteoblastoma may require facet resections that can create an unstable spine. Appropriate preoperative planning for stabilization of such a defect is required for this eventuality.

Preoperative embolization as an adjunct to surgical management of osteoblastoma may lead to reductions in intraoperative blood loss and blood transfusion volume. [38]

Operative details

Aggressive lesions must be removed by means of wide resection. If required, internal fixation must be planned for stabilization as noted above (see the images below).

Surgical stabilization with internal fixation was Surgical stabilization with internal fixation was used after wide resection of osteoblastoma of the cervical spine (this image depicts the same 15-year-old patient shown above).
Surgical stabilization with internal fixation was Surgical stabilization with internal fixation was used after wide resection of osteoblastoma of the cervical spine (this image depicts the same 15-year-old patient shown above).

Regardless of the method of resection, the surgical margins must be tumor-free if complete excision of the tumor is expected.

Postoperative Care

The application of external bracing, rehabilitation modalities, home healthcare, postoperative pain control, muscle relaxants, pulmonary and urinary tract care must be monitored and adequately managed during the postoperative period. Providing the patient and family with written expectations of healing times for the reconstructed site, as well as expected temporary and permanent functional limitations, is also appropriate in this period.

Complications

The most frequent immediate postoperative complications are as follows:

  • Wound, urinary tract, and lung infections
  • Hemorrhage at the operative site
  • Loss of bony stability of the surgical stabilization construct

Tumor recurrence occurs "late" (months to years) after the procedure, and planning for this eventuality must be done for a scheduled period after the definitive procedure. However, there are no universally accepted time intervals for the period within which such follow-up should occur, so the range is highly variable. A good rule is to continue these studies until the reported likelihood of regrowth of this tumor is small. It is also important to include chest films; giant cell tumor, osteoblastoma, and chondroblastoma have been reported to metastasize to the lungs.

Long-Term Monitoring

Monitoring for signs and symptoms of infection and bleeding of the operative site, as well as for systemic signs of urinary tract and pulmonary complications, are important during the immediate postoperative period.

Scheduling appropriate studies to reevaluate the patient for local and distant spread after the definitive procedure is necessary at specific postoperative intervals and must be planned and discussed with the patient and family.



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