Review Article Osteoid Osteoma and Osteoblastomaupload.orthobullets.com/journalclub/free_pdf/22052644_22052644.pdf · Osteoid Osteoma and Osteoblastoma Abstract Osteoid osteoma and

Osteoid Osteoma andOsteoblastoma

Abstract

Osteoid osteoma and osteoblastoma are commonly seen benignosteogenic bone neoplasms. Both tumors are typically seen in thesecond decade of life, with a notable predilection in males.Histologically, these tumors resemble each other, withcharacteristically increased osteoid tissue formation surrounded byvascular fibrous stroma and perilesional sclerosis. However,osteoblastomas are larger than osteoid osteomas, and they exhibitgreater osteoid production and vascularity. Clinically, osteoidosteoma most commonly occurs in the long bones (eg, femur,tibia). The lesions cause night pain that is relieved withnonsteroidal anti-inflammatory drugs (NSAIDs). Osteoblastoma ismost frequently located in the axial skeleton, and the pain isusually not worse at night and is less likely to be relieved withNSAIDs. Osteoblastoma can be locally aggressive; osteoidosteoma lacks growth potential. Osteoid osteoma may be managednonsurgically with NSAIDs. When surgery is required, minimallyinvasive methods (eg, CT-guided excision, radiofrequency ablation)are preferred. Osteoblastoma has a higher rate of recurrence thandoes osteoid osteoma, and patients must be treated surgically withintralesional curettage or en bloc resection.

Osteoid osteoma and osteoblas-toma are benign bone-forming

skeletal neoplasms that are charac-terized by the formation of osteoidor mature bone directly by the tumorcells.1 Together, these tumors repre-sent approximately 15% of all be-nign skeletal neoplasms, and they arecommonly encountered by orthopae-dic surgeons in the clinical setting.2,3

Osteoid Osteoma

Osteoid osteoma was first describedin 1935 by Jaffe, who also coined theterm.4 It is the most commonly seen be-nign bone-forming lesion, accountingfor 10% to 12% of all benign bone tu-mors and 3% of all primary bone tu-

mors.1,5 This lesion most commonlyoccurs in persons aged 5 to 25 years,with a male:female ratio of 2:1.6,7 In>50% of cases, the lesion occurs inthe metaphysis and diaphysis of thelong bones, particularly the femurand tibia.6,7 Other anatomic sites ofinvolvement include the spine, upperextremity, pelvis, sacrum, ribs,hands, and feet4 (Table 1).

Gross Structure andHistology

Observed grossly, the lesion is usu-ally <1.5 cm in diameter and con-tains a discrete central area knownas the nidus that is surrounded bydense sclerotic bone tissue.8 In gen-eral, osteoid osteoma is a solitary le-

Kivanc I. Atesok, MD, MSc

Benjamin A. Alman, MD,FRCSC

Emil H. Schemitsch, MD,FRCSC

Amos Peyser, MD

Henry Mankin, MD

From the Institute of MedicalScience, University of Toronto,Toronto, ON, Canada (Dr. Atesok),the Division of Orthopaedic Surgery,The Hospital for Sick Children,Toronto (Dr. Alman), the Division ofOrthopaedics, Department ofSurgery, St. Michael’s Hospital,University of Toronto, Toronto(Dr. Schemitsch), the Department ofOrthopedics, Shaare Zedek MedicalCenter, Jerusalem, Israel(Dr. Peyser), and the Department ofOrthopaedic Surgery, MassachusettsGeneral Hospital, Boston, MA(Dr. Mankin).

J Am Acad Orthop Surg 2011;19:678-689

Copyright 2011 by the AmericanAcademy of Orthopaedic Surgeons.

Review Article

678 Journal of the American Academy of Orthopaedic Surgeons

sion; in rare cases, however, morethan one nidus may be circumscribedby a single block of sclerotic bone.9,10

Microscopically, the nidus is com-posed of thin seams of osteoid orwoven bone lined with osteoblasts,which represents a process of boneremodelling with osteoblastic activ-ity (Figure 1). Osteoclastic bone re-sorption occurs simultaneously and

gives rise to a clearer area at the pe-riphery of the circular nidus. The ni-dus is surrounded by a region of ac-tive bone formation that appears assclerotic dense bone with variouspatterns of maturation.1,4

Osteoid osteoma does not grow orbehave in a locally aggressive man-ner, and it has no potential for malig-nant transformation.4,6

Biology andPathophysiologySchulman and Dorfman11 demon-strated abundant nerve fibers withinthe nidus matrix adjacent to areasrich in arterioles. High levels of pros-taglandin synthesis in the nidus ofosteoid osteoma have been reportedin several other studies.12,13 This find-ing was supported by studies demon-

Dr. Atesok or an immediate family member serves as a board member, owner, officer, or committee member of the InternationalSociety of Arthroscopy, Knee Surgery, and Orthopaedic Sports Medicine and the Orthopaedic Research Society. Dr. Alman or animmediate family member serves as a board member, owner, officer, or committee member of the Pediatric Orthopaedic Society ofNorth America. Dr. Schemitsch or an immediate family member has received royalties from Stryker; serves as a paid consultant toAmgen, Stryker, Synthes, Smith & Nephew, Baxter, Wright Medical Technology, and Kuros; has received research or institutionalsupport from Smith & Nephew; has received nonincome support (such as equipment or services), commercially derived honoraria, orother non-research–related funding (such as paid travel) from the Canadian Institutes of Health Research, BrainLAB, OMEGA, Smith& Nephew, Zimmer, and Stryker; and serves as a board member, owner, officer, or committee member of the Orthopaedic TraumaAssociation, Canadian Orthopaedic Association, and Osteosynthesis and Trauma Care Foundation. Neither of the following authorsnor any immediate family member has received anything of value from or owns stock in a commercial company or institution relateddirectly or indirectly to the subject of this article: Dr. Peyser and Dr. Mankin.

Table 1

Features of Osteoid Osteoma and Osteoblastoma

Osteoid Osteoma Osteoblastoma

Incidence ≈12% of all benign bone tumors≈3% of all primary bone tumors

≈3% of all benign bone tumors≈1% of all primary bone tumors

Age 5 to 25 yr 10 to 25 yrSex Male:female ratio of 2:1 Male:female ratio of 2:1Size <2 cm in diameter (typically <1.5 cm) >2 cm in diameter (average, 3.5 to 4 cm)Location >50% of lesions in the lower extremity long bones

(ie, femur, tibia). Other common sites: spine, upperextremity, hands, feet, and pelvis

>35% of lesions in the vertebral column (posterior ele-ments). Other common sites: long bones, craniofacialbones, hands, and feet

Clinical features Local pain that is most severe at night and can be re-lieved with nonsteroidal anti-inflammatory drugs. De-pending on location, patients may present with bonedeformity, gait disturbance, limb-length discrepancy,or synovitis.

Dull, aching, progressive local pain. Due to higher inci-dence of spinal involvement, patients may experienceneurologic symptoms, scoliosis, or torticollis. Localtenderness and swelling may be seen.

Imaging findings Plain radiograph is obtained initially, but supportiveimaging is required.

Bone scan: Sensitive and valuable in localizing thelesion. Shows high uptake.

CT: Imaging method of choice. Shows the low-attenuated nidus with surrounding sclerosis.

MRI is controversial: Nonspecific findings with frequentmisinterpretation.

Plain radiograph obtained initially. Lesions are larger.Supportive imaging is required.

Bone scan: Sensitive. Shows high uptake of radionu-clide at the lesion site.

CT: Imaging method of choice. Larger lesion, centralmineralization, expansile bone growth, less reactivesclerosis, thin marginal bone shell.

MRI is controversial: Nonspecific findings with overesti-mation of tumor extent and nature.

Histology andnature

Central nidus composed of tiny osteoid islands linedby osteoblasts. The area peripheral to the nidus ap-pears clearer because of osteoclastic resorption.Dense sclerotic bone surrounds the nidus. Benign.No growth potential.

Centrally, lesions demonstrate a less organized osteoidpattern than osteoid osteoma, with greater vascularity.Bony trabeculae lined by osteoblasts. Presence ofepithelioid osteoblasts indicates aggressiveness. Lesssclerotic bone with a thin shell of newly formed peri-osteal bone at the margin. Benign. Growth is local-ized, with aggressive potential.

Kivanc I. Atesok, MD, MSc, et al

November 2011, Vol 19, No 11 679

strating the expression of cyclo-oxygenase-1 and cyclooxygenase-2isozymes by the tumor tissue; bothenzymes are responsible for proteinprocessing in the prostaglandin bio-synthesis pathway.14 These reportssuggested an important pathophysio-logic role for prostaglandins both asmediators of pain and vasodilationthat may stimulate the nerve endingsby increasing the blood flow withinthe tumor.

Clinical FeaturesThe most prominent clinical symp-tom of osteoid osteoma is the pres-ence of local pain that is typicallymore frequent and severe at nightand that is relieved with administra-tion of nonsteroidal anti-inflamma-tory drugs (NSAIDs).2,4,6,7,15,16 Othersigns and symptoms are local swellingand tenderness, bony deformity, gaitdisturbances, and muscle atrophy; de-

pending on the proximity to a joint, theclinician may note effusion, synovitis,degenerative changes, limitation ofmovement, and contractures.17 Par-ticularly in pediatric patients, osteoidosteoma may present with rapidlyprogressive painful scoliosis whenthe spinal column is involved. Inmost cases, the concavity of the sco-liotic curve is ipsilateral to the lesionas a result of muscle spasm andpain.1,6,18

Limb-length discrepancy may beassociated with pediatric osteoid os-teoma. Peyser et al7 reported averagelimb-length discrepancy of 12 mm infour pediatric patients with osteoidosteoma of the femur and tibia. Ineach case, the involved extremitywas longer than the uninvolved ex-tremity. One possible explanation forlimb overgrowth in children with os-teoid osteoma may be the resultinginflammatory response and associ-ated hyperemia, especially in patientswith lesions located near the opengrowth plate.

Diagnostic ImagingThe typical pain pattern and physicalfindings related to the location of the

tumor often leads the clinician tostrongly consider a diagnosis of os-teoid osteoma. A combination ofplain radiographs, bone scintigraphy,CT, and occasionally MRI, is usuallysufficient to confirm the diagnosis.

RadiographyConventional radiography is the ini-tial examination of choice. A plainradiograph of osteoid osteoma mayreveal a characteristic oval radiolu-cency representing the nidus as wellas a surrounding area of reactivebone sclerosis with or without peri-osteal bone formation (Figure 2, A).However, these findings are typicalof cortical lesions, and they may notbe found on a plain radiograph if thelesion is located either in the in-tramedullary cavity or in areas of theskeleton that are difficult to assesswith radiography alone (eg, spine,pelvis, small bones of the hands andfeet).19

ScintigraphyBone scintigraphy is a highly sensi-tive diagnostic modality for detectingand localizing osteoid osteoma.These images demonstrate the classicmarkedly increased radionuclide

Histologic appearance of an areawithin a nidus in a patient withosteoid osteoma. The bonytrabeculae are rimmed byosteoblasts (arrow). Capillaries canbe detected between the bonytrabeculae (arrowhead)(hematoxylin-eosin, high-powerview). (Adapted with permissionfrom Zbojniewicz AM, Hartel J,Nguyen T, Wilks K, Mace A, HoggJP: Neoplastic disease of thevertebral column: Radiologic-pathologic correlation. Curr ProblDiagn Radiol 2010;39[2]:74-90.http://www.sciencedirect.com/science/journal/03630188.)

Figure 1

A, AP radiograph demonstrating an osteoid osteoma nidus in the base of thefifth metatarsal (arrows). B, Bone scintigraphy image demonstratingincreased radionuclide uptake by the lesion in the affected foot, at the left,and no abnormal findings in the contralateral foot at the right. (Panel Aadapted with permission from Peyser A, Applbaum Y: Radiofrequencyablation of bone tumors. Current Orthopaedic Practice 2009;20[6]:616-621.)

Figure 2

Osteoid Osteoma and Osteoblastoma


uptake by the nidus (Figure 2, B).Nuclear medicine bone scans usetechnetium Tc-99m-labeled diphos-phonates, which have avidity for ar-eas with increased osteoblastic activ-ity and bone turnover. In addition,portable gamma cameras can be usedas radiotracer detectors intraopera-tively to localize the nidus during re-section.20 Despite its increased sensi-tivity, scintigraphy is not a specificimaging method for determining thedistinctive features of the lesions.

CTCT is considered to be the imagingmethod of choice for visualizing theanatomic position of the nidus andaiding in the differential diagno-sis.1,6,19 The characteristic appearanceof osteoid osteoma on thin-slice CTscan is of a low-attenuation niduswith central mineralization and vary-ing degrees of sclerosis surroundingthe nidus21 (Figure 3). CT imaging isparticularly useful when the nidus isin an intra-articular location or isnot apparent radiographically be-cause of the presence of complex an-atomic features.

MRIThe effectiveness of MRI in diagnos-ing osteoid osteoma is controversial.The appearance of the lesion may behighly variable, and the presence ofassociated soft-tissue changes andbone marrow edema may result indiagnostic errors. Davies et al22 ret-rospectively reviewed the MRI find-ings of 43 patients with osteoid os-teoma and compared the accuracy ofMRI localization with that of otherimaging modalities. Six tumors werenot seen on MRI, and nine werepoorly visualized. The potential for amissed diagnosis was 35% basedsolely on the MRI findings.

Hosalkar et al23 prospectively com-pared the diagnostic accuracy ofMRI and CT for osteoid osteoma inchildren. Preoperative magnetic reso-nance images and CT scans of pa-tients with biopsy-confirmed diagno-sis of osteoid osteoma wererandomly reviewed by three radiolo-gists who were blinded to the diag-nosis. The radiologists were asked toclassify lesions as benign-latent,benign-aggressive, or malignant de-

pending on features seen on MRIand CT. The lesions were correctlyclassified as benign-latent in 19% ofmagnetic resonance images, com-pared with 81% of CT scans. Theprimary diagnosis was correctlyidentified as osteoid osteoma in 3%of magnetic resonance images and in67% of CT scans. Based on their re-sults, the authors recommended CTscanning with thin sectioning as thepreferred advanced imaging modal-ity for the diagnosis of osteoid os-teoma. They also stated that “MRI,especially without clinical or CT cor-relation, may not be reliable, can bemisinterpreted, and can lead to mis-diagnosis.” The main limitation ofthis study was the small sample size(12 magnetic resonance images and 7CT scans of patients with osteoid os-teoma), which may have been asource for bias with regard to intra-and interobserver variability.

Management and Prognosis

NonsurgicalNonsurgical management with sali-cylates or NSAIDs is a justifiabletherapeutic option because thesedrugs can effectively relieve pain,which is typically the presenting andmost striking patient complaint1,4,24

(Figure 4). However, few publishedstudies have evaluated the results ofprolonged medical management andreported complete resolution ofsymptoms with discontinuation ofNSAIDs.24,25 Kneisl and Simon24

noted an average time of 33 monthsto resolution of symptoms in six pa-tients treated with NSAIDs. Sporadiccase reports in the literature describethe probability of the evolution ofosteoid osteoma into osteoblastomaafter prolonged nonsurgical manage-ment with NSAIDs.26

SurgicalSurgical management is warranted incases in which the pain is severe and

Axial CT scan of distal femurs. The nidus is located in the left distal femuranterior metaphysis within the cortex (arrowhead). Increased sclerotic boneformation is seen around the lesion (arrows).

Figure 3



unresponsive to medication. Surgeryis also warranted for patients whoare unwilling to endure pain and ac-cept long-term medical treatment be-cause of potential gastrointestinalcomplications associated with theuse of NSAIDs. Prolonged presenceof osteoid osteoma lesions, especiallyin skeletally immature patients, maylead to complications such as growthdisturbances, scoliosis, and osteoar-throsis.27 The most commonly used

surgical management techniques in-clude open excision of the lesion,CT-guided percutaneous excision,and CT-guided radiofrequency (RF)ablation.

Open ExcisionUntil the late 1990s, open excisionwas the only surgical option.1,6 Enbloc excision of the tumor, and corti-cal shaving and curettage of the ni-dus cavity, are frequently used con-

ventional techniques with successfuloutcomes.24,27 However, these tech-niques can be unexpectedly challeng-ing for both surgeon and patient.The tumor may be difficult to iden-tify intraoperatively, and incompleteremoval may result in recurrence.Additionally, resection of weight-bearing bone may necessitate pro-longed hospital stay as well as re-strictions on activities and weightbearing.15,28,29 Advances in imaging

Treatment algorithm for osteoid osteoma and osteoblastoma.a This is an option only at institutions equipped to perform minimally invasive procedures.b CT-guided excision, image-guided cryotherapy, drill trepanation with or without ethanol injection, thermal destructionby means of laser photocoagulation, and arthroscopic excision. All can be an alternative minimally invasive surgicalmethod depending on the availability of each technique and the preference of the operating surgeon.c All locations in which en bloc resection of the tumor may cause significant morbidity.d Includes the bones in which en bloc resection of osteoblastoma does not cause significant morbidity (eg, ribs, fibula,clavicle, sternum).NSAIDs = nonsteroidal anti-inflammatory drugs, RF = radiofrequency

Figure 4



technology have made it possible toaddress the disadvantages of openexcision by providing real-time CTguidance and percutaneous manage-ment of osteoid osteoma.

CT-guided Percutaneous ExcisionIn this technique, a cannulated curetis inserted into the lesion over aKirschner wire under CT image guid-ance to excise the nidus. Fenichel etal30 used this technique in a series of18 patients with osteoid osteoma ofthe pelvis, femur, and tibia. Sixteenpatients experienced immediate andpermanent pain relief after the firstprocedure. In two patients, the niduswas missed because of misinterpreta-tion of the CT scan, and no clinicalimprovement was observed postop-eratively. In these patients, the proce-dure was repeated successfully, re-sulting in prompt postexcisionalcessation of typical osteoid osteomapain. There were two complications(femoral neurapraxia, skin abra-sion), both of which resolved. Otherauthors have reported similar resultswith a high clinical success rate andminimal complications.31

CT-guided RadiofrequencyAblationIn CT-guided RF ablation, heat is ap-plied locally to destroy the nidus(Figure 5). The RF probe is intro-duced into the nidus through a can-nulated needle under CT-guided im-aging, and the temperature at the tipof the probe is increased to approxi-mately 90°C and maintained at thatlevel for 5 to 6 minutes.32 The tip ofthe probe must be insulated to pre-vent injury to the soft tissues adja-cent to the osteoid osteoma.

Rosenthal et al29 performed CT-guided RF ablation on 263 patientswith a mean age of 19 years. In total,271 ablation procedures were per-formed: 249 for initial tumor treat-ment, 14 for recurrence after conven-tional surgery, and 8 for recurrenceafter prior RF ablation. All the pro-cedures were technically successful,and two minor procedure-relatedcomplications were observed. Afterthe procedure, all daily activitieswere resumed immediately. The onlyrestriction involved avoidance ofstrenuous sports for 3 months forpatients with lesions in weight-bearing bones. Of the 126 patientsfor whom 24-month follow-up datawere available, 112 were pain-freeand did not require additional proce-dures. The procedure was unsuccess-ful in nine patients, and the outcomewas indeterminate in five. The au-thors suggested RF ablation as “thetreatment of choice with high clinicalsuccess rate (91%), brief recovery,and gratifyingly low complicationrate.”

Peyser et al7 reported the results ofCT-guided RF ablation in 22 pediat-ric patients with osteoid osteoma(mean age, 13 years 6 months). Theprocedure was technically successfulin all patients, and all were dis-charged from the hospital within 24hours postoperatively with no re-strictions in weight bearing. At anaverage follow-up of 38.5 months,

clinical recovery was achieved in allbut two patients. These two patientsunderwent a second ablation, afterwhich they remained symptom-free.The only procedure-related compli-cation was observed in a patient witha nidus located in the tibial diaphy-sis. This patient experienced superfi-cial skin infection of the ablationarea that resolved with outpatientantibiotic treatment. The authorsstated, “RF ablation in pediatric os-teoid osteoma patients is a safe andeffective technique.” Several otherrecent case series and cohort studieshave demonstrated the effectivenessof RF ablation as a safe and mini-mally invasive method for the man-agement of osteoid osteoma.33,34

In a series of 125 patients, Rosen-thal et al15 retrospectively comparedthe outcomes of RF ablation (38 pa-tients) and surgical excision (87 pa-tients). They found no significant dif-ference between the two groups withregard to rate of recurrence (P =0.725) and clinical success (P =0.722). The average length of hospi-tal stay was 0.18 day for the RFgroup and 4.7 days for the open ex-cision group. No complications wereassociated with the percutaneousmethod. Two patients in the openexcision group experienced compli-cations, requiring a total of five sec-ondary procedures.

No studies to date have comparedCT-guided percutaneous excisionwith CT-guided RF ablation; how-ever, clinical outcomes are known tobe similar with both techniques.Higher success rates in tissue diagno-sis have been reported with CT-guided excision than with RF abla-tion (69% to 77% and 47% to 50%,respectively), possibly because theentire nidus can be removed in theexcision procedure.2,30,31 However,CT-guided excision of the nidusalong with cortices may act as astress riser and may predispose thepatient to pathologic fracture or

Axial CT scan demonstrating thefemoral metaphysis duringradiofrequency (RF) ablation ofosteoid osteoma. The nidus islocated cortically, with increasedsclerotic bone formation (arrows).The RF probe (P) was introducedinto the nidus to ablate the lesion.

Figure 5



activity-related restrictions postoper-atively.

The current trend toward minimallyinvasive therapies has resulted in theuse of many other less commonly em-ployed percutaneous techniques for themanagement of osteoid osteoma. Theseinclude image-guided cryotherapy, drilltrepanation with or without ethanol in-jection, thermal destruction by meansof laser photocoagulation, and ar-throscopic excision of juxta-articularlesions.2,31,35

Osteoblastoma

Osteoblastoma was first described in1932 by Jaffe and Mayer36 as “anosteoblastic-osteoid tissue formingtumor.” In 1956, Jaffe and Lichten-stein further characterized the lesionand independently proposed theterm “benign osteoblastoma.”37 Os-teoblastoma is a rare tumor that ac-counts for 3% of all benign bone tu-mors and approximately 1% of allprimary bone tumors.1,38 Osteoblas-toma most commonly arises in patientsaged between 10 and 25 years, with amale:female ratio of 2:1; this is similarto the age and sex characteristics of pa-tients with osteoid osteoma.27,38 Un-

like osteoid osteoma, however, os-teoblastoma is most often located inthe posterior elements of the verte-bral column and the sacrum. Thispresentation accounts for approxi-mately one third of cases. Othercommonly involved sites are the longbones (eg, femur, tibia), particularlywithin the medullary cavity and di-aphysis. Osteoblastoma is also seenin the craniofacial bones (15%) andthe hands and feet (14%) and, to alesser extent, in sites such as the ribs,clavicle, and sternum.6,27,38

Gross Structure andHistologyGrossly, osteoblastoma is consider-ably larger than osteoid osteoma,with an average diameter of approxi-mately 4 cm.4,37 The tumor containsa larger and structurally less orga-nized central area and a less densesclerotic reaction circumscribing thelesion (Figure 6). The presence ofmore than one central zone per le-sion (ie, multifocal osteoblastoma) isseen in 4% to 14% of cases, which ishigher than in osteoid osteoma.27,37,39

The microscopic features of osteo-blastoma are similar to those of os-teoid osteoma. Centrally, the lesion

consists of an interlacing network ofbony trabeculae within a loose fibro-vascular stroma that is rimmed by asingle row of benign osteoblasts thatare responsible for osteoid formation(Figure 7). The lesions show a vari-able number of osteoclasts at the sur-faces of the bony trabeculae; theseosteoclasts are involved in bone re-sorption. The stroma of osteoblas-toma demonstrates a less organizedpattern of osteoid and trabecularbone distribution than does that ofosteoid osteoma as well as greatervascularity. The lesion may showsecondary aneurysmal bone cyst de-generation as a result of increasedvascularity. The tumor is surroundedby a thin shell of newly formed peri-osteal bone tissue, which appears lesssclerotic than that of osteoid os-teoma and matures toward its pe-riphery.1,4,27

Osteoblastoma is a benign but lo-cally aggressive tumor, with a clinicalcourse ranging from slow, indolentprogression to rapid aggressivegrowth. Aggressive osteoblastomasare associated with large epithelioidosteoblasts that rim the bony trabec-ulae, and they are more mitoticallyactive than the cells in osteoid os-teoma and conventional benign os-teoblastoma.1,4,6,27,38 Zon Filippiet al39 demonstrated that a predomi-nance of epithelioid osteoblasts iscommonly seen in multifocal osteo-blastomas (Figure 8).

Osteoblastoma has neither malig-nant nor metastatic potential. Histo-logically, the lesion has benign fea-tures even when it appears aggressiveradiographically.40 Osteoblastomathat is reported to have malignantpotential should be meticulously dif-ferentiated from other malignantbone tumors, in particular, from theosteoblastoma-like variant of osteo-sarcoma. Bertoni et al41 reported aseries of 11 patients withosteoblastoma-like osteosarcomaand noted that the lesions histologi-

Schematic illustration demonstrating the spectrum of changes in lesion sizeand amount of sclerotic bone surrounding the lesion in osteoid osteoma andosteoblastoma. (Adapted with permission from Dorfman HD, Czerniak B:Benign osteoblastic tumors, in Dorfman HD, Czerniak B, eds: Bone Tumors.St. Louis, MO, Mosby, 1998, pp 85-127.)

Figure 6



cally resembled osteoblastoma, withperipheral infiltration into surround-ing tissues. The tumors had charac-teristic features of low-grade osteo-sarcoma, with moderate cellularatypia under high-power micro-scopic examination.

Biology andPathophysiologyThe unique pathophysiologic rela-tionship between the presence ofnerve endings and vessels, and in-creased production of prostaglandinsin osteoid osteoma, has not beensimilarly documented for osteoblas-toma. Local pain associated with os-teoblastoma is most likely caused bylocal expansion of the tumor and thepressure of its mass on surroundingstructures.40

Clinical FeaturesClinically, osteoblastoma does notexhibit the typical presenting symp-toms and signs seen in patients withosteoid osteoma. In patients with os-teoblastoma, the most common pre-senting complaint is pain, which isusually described as dull, aching, and

often progressive in intensity. Typi-cally, pain does not respond dramati-cally to NSAIDs and is not generallymost severe at night.38,40

Other common manifestations ofosteoblastoma are local swelling andtenderness, especially when the tu-mor is near the surface. Gait distur-bance can be seen in children withlower extremity involvement. Be-cause of its size and predilection forthe vertebral column, osteoblastomafrequently presents with neurologicsymptoms resulting from spinal cordor nerve root compression, such asnumbness, tingling, radicular pain,paresthesias, and paraparesis. Scolio-sis and torticollis may be observedsecondary to muscle spasm associ-ated with osteoblastoma.27,37,38,40

In a series of 306 patients with os-teoblastoma, Lucas et al37 found pro-gressive pain to be the most frequentcomplaint (87%). Local swelling,tenderness, warmth, and gait distur-bance were also mentioned fre-quently. The average duration ofthese complaints prior to diagnosiswas 2 years. Ten patients presentedwith neurologic complaints second-

ary to spinal tumors, and four hadscoliosis.

Diagnostic ImagingBecause of the nonspecific signs andsymptoms associated with osteoblas-toma, radiologic studies are impera-tive to establish the diagnosis. Insporadic cases, the patient may be

Histologic appearance of the microscopic features of osteoblastoma. A, Low-magnification image demonstrating a well-circumscribed tumor with a thick fibrous capsule (arrows) and irregular woven bony trabeculae with differing degrees ofmineralization (box) embedded in a loose fibrovascular stroma (asterisks) (hematoxylin-eosin). B, High-magnificationimage demonstrating plump and mildly pleomorphic spindle cells (arrows) and osteoclastic giant cells (asterisks)(hematoxylin-eosin). C, High-magnification image demonstrating bony trabeculae lined by a single layer of osteoblasts(arrow) (hematoxylin-eosin). (Adapted with permission from Chakrapani SD, Grim K, Kaimaktchiev V, Anderson JC:Osteoblastoma of the spine with discordant magnetic resonance imaging and computed tomography imaging featuresin a child. Spine [Phila Pa 1976] 2008;33[25]:E968-E970.)

Figure 7

High-power histologic imagedemonstrating epithelioid cells andirregular blue-staining matrix inaggressive multifocalosteoblastoma (hematoxylin-eosin).(Reproduced with permission fromZon Filippi R, Swee RG, KrishnanUnni K: Epithelioid multinodularosteoblastoma: A clinicopathologicanalysis of 26 cases. Am J SurgPathol 2007;31[8]:1265-1268.)

Figure 8



pain-free or asymptomatic, and thediagnosis can be obtained inciden-tally.1,42

RadiographyThe radiographic appearance of os-teoblastoma depends on the locationand maturity of the tumor.27,37 Ingeneral, these tumors appear as ir-regularly shaped radiolucent lesionssurrounded by a thin shell of reactivebone.40 The interior of the tumormay show various degrees of ossifi-cation, which tends to increase as thelesion matures.1,37,39 Compared withosteoid osteoma, osteoblastoma le-sions appear larger in diameter, withless reactive bone sclerosis and morecortical expansion (Figure 9, A).

Plain radiographs may be useful inestablishing the diagnosis. However,radiographic appearance is usuallynot distinctive, and additional imag-ing studies are required for diagnos-tic accuracy. Based solely on radio-graphs, Lucas et al37 reported

diagnostic accuracy of 43% in 116patients with appendicular osteo-blastomas and 64% in 66 patientswith vertebral osteoblastomas. Theauthors noted that the radiographicappearance was not completely reli-able in distinguishing osteoblastomafrom osteosarcoma; lesions weremisinterpreted as malignant in ap-proximately 15% of cases. The ra-diographs of 17% to 33% of pa-tients were considered to beindeterminate.

ScintigraphyOsteoblastomas exhibit marked up-take of bone-seeking radionuclide onbone scintigraphy because of in-creased osteoblastic activity withinthe tumor (Figure 9, B). Scintigraphyis sensitive to but not specific for os-teoblastoma. It may be helpful in lo-calizing the lesion, as in cases of os-teoid osteoma. However, it may bethat the larger size of the tumor maymake it relatively easier to localize

the lesion without the need for bonescintigraphy.

CTCT is the imaging method of choicefor osteoblastoma.6,43 It can providethe most specific information aboutthe location, size, extent, and natureof the tumor. Areas of mineralizationwithin the lesion as well as corticaldestruction and soft-tissue extensioncan be well-delineated on CT sec-tions.1,38,42 Characteristically, the le-sion tends to demonstrate areas ofmineralization centrally, expansilebone remodeling, and signs of reac-tive sclerosis toward the peripherywith a thin marginal bone shell6 (Fig-ure 10).

MRIThe usefulness of MRI in the diagno-sis of osteoblastoma is questionable.The features are nonspecific andsometimes confusing, and there maybe an overestimation of the extentand nature of the tumor as a resultof increased local inflammatory reac-tion and extensive marrowedema.6,42-44 However, MRI may be avaluable tool in cases in which thetumor has extensive effects on thespinal canal and cord. MRI also maybe useful in the evaluation of intra-and extraosseous reactive changesand the presence of soft-tissue infil-tration associated with osteoblas-toma. The lesion generally appearsas low or intermediate signal densityon T1-weighted images and interme-diate to high signal density on T2-weighted images6,38,45 (Figure 11).

Management and PrognosisOsteoblastoma must be managedsurgically because of its potential foraggressive behavior and bone de-struction (Figure 4). The selection ofsurgical procedure depends largelyon the location and aggressiveness ofthe tumor. Intralesional curettageand en bloc resection are the most

A, Lateral plain radiograph in a patient with osteoblastoma of the spinousprocess of C5. Mild kyphosis is seen at the level of the lesion (arrow),resulting from the mass effect of the enlarged spinous process. B, Bonescintigraphy image demonstrating remarkable radionuclide uptake by thetumor.

Figure 9



commonly performed surgical proce-dures.

Intralesional CurettageIntralesional curettage is sufficient inmost cases. To minimize recurrence,curettage should be extended to nor-mal bone with a high-speed burr.Cryotherapy and chemical cauteriza-tion with phenol are valuable ad-juncts, and cementation or bonegrafting should be performed as indi-cated.27,38 Although curettage mayhave lower morbidity than en blocresection, this procedure may leavebehind microscopic tumor, which is asource for recurrence.40

En Bloc ResectionEn bloc resection is an effective sur-gical approach for locally aggressiveand large tumors in appropriatecases. In particular, recurrent lesionsfollowing intralesional curettage aremost successfully managed with enbloc resection. This is also the pre-ferred method for lesions located inexpendable bones such as the ribs,clavicle, and fibula.38,42

Berry et al40 reported on 99 osteo-blastoma patients treated surgicallywith curettage and bone grafting oren bloc resection. They noted that“23% of the patients treated withcurettage required further surgery forrecurrence compared to 14% of thepatients who underwent en bloc re-section.” Five patients had two ormore subsequent recurrences. Pa-tients who required more than onereoperation were ultimately treateddefinitively with en bloc resection.

Summary

Osteoid osteoma and osteoblastomaare distinct benign bone-producingtumors with certain similar features.It is crucial to recognize the typicalclinical presentation and imagingfindings of both types tumor to pre-

vent confusion and misdiagnosis.The differences in management areconsiderable. Nonsurgical manage-ment with NSAIDs may be a valid

option for osteoid osteoma. Surgicalmanagement is considered whennonsurgical methods fail or are notfeasible for or desirable by the pa-

Sagittal (A) and axial (B) CT images of an osteoblastoma of the spinousprocess of C5. An enlarged spinous process (arrow) with irregular borders isvisible on the sagittal image. The axial view demonstrates a partiallydestroyed cortex as well as central areas of mineralization (circle).

Figure 10

Magnetic resonance images of a patient with osteoblastoma at C3. A, T2-weighted sagittal image demonstrating an enhancing mass with expansilefeatures (arrow). B, T1-weighted axial image demonstrating involvement ofthe right side of C3 and extension into the spinal canal (dashed circle).(Adapted with permission from Burn SC, Ansorge O, Zeller R, Drake JM:Management of osteoblastoma and osteoid osteoma of the spine inchildhood. J Neurosurg Pediatr 2009;4[5]:434-438.)

Figure 11



tient. Minimally invasive methodssuch as CT-guided excision and RFablation are the new trend in man-agement of osteoid osteoma, withhighly successful outcomes.

Osteoblastoma must be managedsurgically because of its locally de-structive and aggressive growth po-tential. Intralesional curettage is per-formed effectively in many patients;however, the recurrence rate is rela-tively high. When feasible, en blocresection is the preferred method fordefinitive management of large andaggressive osteoblastomas as well asfor recurrent lesions following curet-tage.

References

Evidence-based Medicine: Levels ofevidence are described in the table ofcontents. In this article, references15, 23, and 24 are level III studies.References 2, 7, 11, 13, 14, 16-18,20-22, 28-31, 33, 34, and 37-41 arelevel IV studies. References 1, 6, 8,19, 27, 32, 43, and 45 are level V ex-pert opinion. References 3, 5, 9, 10,12, 25, 26, 35, 36, 42, and 44 arecase reports.

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