Osteoid Osteoma and Osteoblastoma Areosteogenic Commonly Bone Seen Neoplasms

Home , Osteoblastoma, Osteoid osteoma

In 6,7 In gen- 8 (Table 1). 4 Other anatomic sites of 6,7 This lesion most commonly 1,5 occurs in persons aged 5with to a 25 male:female years, ratio of 2:1. >50% of cases, thethe lesion metaphysis occurs and in diaphysislong of bones, the particularlyand tibia. the femur involvement include the spine, upper extremity, pelvis,hands, and feet sacrum, ribs, Observed grossly, the lesionally is <1.5 usu- cmtains in a diameter discrete andas central con- the area known nidusdense that sclerotic is bone surrounded tissue. by Gross Structure and Histology mors. eral, osteoid osteoma is a solitary le- 2,3 Journal of the American Academy of Orthopaedic Surgeons Together, these tumors repre- It is the most commonly seen be- steoid osteoma and osteoblastoma are benign bone-forming 4 1 Abstract Osteoid osteoma and osteoblastoma areosteogenic commonly bone seen neoplasms. benign Both tumorssecond are decade typically of seen life, in withHistologically, these the a tumors notable resemble predilection each incharacteristically other, males. increased with osteoid tissue formationvascular surrounded ﬁbrous by stroma and perilesionalosteoblastomas sclerosis. are However, larger than osteoidgreater osteomas, osteoid and production they and exhibit vascularity.osteoma Clinically, most osteoid commonly occurs intibia). The the lesions long cause bones night (eg,nonsteroidal pain femur, anti-inﬂammatory that drugs is (NSAIDs). relieved Osteoblastomamost with is frequently located in theusually axial not skeleton, worse and at the nightNSAIDs. pain and Osteoblastoma is is can less be likely locallyosteoma to aggressive; lacks be osteoid growth relieved potential. with Osteoidnonsurgically osteoma with may NSAIDs. be When managed surgeryinvasive is methods required, (eg, minimally CT-guided excision,are radiofrequency preferred. ablation) Osteoblastoma has adoes higher osteoid rate osteoma, of and recurrence patientsintralesional than must curettage be or treated en surgically bloc with resection. Osteoid Osteoma Review Article Osteoid osteoma was firstin described 1935 by Jaffe, whoterm. also coined the O Osteoid Osteoma and Osteoblastoma nign bone-forming lesion, accounting for 10% to 12% of allmors benign bone and tu- 3% of all primary bone tu- sent approximately 15%nign of skeletal neoplasms, all and they be- commonly are encountered by orthopaedic surgeons in the clinical setting. skeletal neoplasms thatterized are by charac- theor formation mature of bone directly osteoid bycells. the tumor 2011;19: FRCSC FRCSC From the Institute ofScience, Medical University of Toronto, Toronto, ON, Canada (Dr. Atesok), the Division of OrthopaedicThe Surgery, Hospital for SickToronto Children, (Dr. Alman), the DivisionOrthopaedics, of Department of Surgery, St. Michael’s Hospital, University of Toronto, Toronto (Dr. Schemitsch), the DepartmentOrthopedics, of Shaare Zedek Medical Center, Jerusalem, Israel (Dr. Peyser), and theOrthopaedic Department Surgery, of Massachusetts General Hospital, Boston, MA (Dr. Mankin). J Am Acad Orthop678-689 Surg Copyright 2011 by the American Academy of Orthopaedic Surgeons. 678 Emil H. Schemitsch, MD, Amos Peyser, MD Henry Mankin, MD Kivanc I. Atesok, MD, MSc Benjamin A. Alman, MD,

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Table 1 Features of Osteoid Osteoma and Osteoblastoma Osteoid Osteoma Osteoblastoma

Incidence ≈12% of all benign bone tumors ≈3% of all benign bone tumors ≈3% of all primary bone tumors ≈1% of all primary bone tumors Age 5to25yr 10to25yr Sex Male:female ratio of 2:1 Male:female ratio of 2:1 Size <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 >35% of lesions in the vertebral column (posterior ele- (ie, femur, tibia). Other common sites: spine, upper ments). Other common sites: long bones, craniofacial extremity, hands, feet, and pelvis bones, hands, and feet Clinical features Local pain that is most severe at night and can be re- Dull, aching, progressive local pain. Due to higher inci- lieved with nonsteroidal anti-inflammatory drugs. De- dence of spinal involvement, patients may experience pending on location, patients may present with bone neurologic symptoms, scoliosis, or torticollis. Local deformity, gait disturbance, limb-length discrepancy, tenderness and swelling may be seen. or synovitis. Imaging findings Plain radiograph is obtained initially, but supportive Plain radiograph obtained initially. Lesions are larger. imaging is required. Supportive imaging is required. Bone scan: Sensitive and valuable in localizing the Bone scan: Sensitive. Shows high uptake of radionu- lesion. Shows high uptake. clide at the lesion site. CT: Imaging method of choice. Shows the low- CT: Imaging method of choice. Larger lesion, central attenuated nidus with surrounding sclerosis. mineralization, expansile bone growth, less reactive MRI is controversial: Nonspecific findings with frequent sclerosis, thin marginal bone shell. misinterpretation. MRI is controversial: Nonspecific findings with overestimation of tumor extent and nature. Histology and Central nidus composed of tiny osteoid islands lined Centrally, lesions demonstrate a less organized osteoid nature by osteoblasts. The area peripheral to the nidus ap- pattern than osteoid osteoma, with greater vascularity. pears clearer because of osteoclastic resorption. Bony trabeculae lined by osteoblasts. Presence of Dense sclerotic bone surrounds the nidus. Benign. epithelioid osteoblasts indicates aggressiveness. Less No growth potential. sclerotic bone with a thin shell of newly formed peri- osteal bone at the margin. Benign. Growth is local- ized, with aggressive potential. sion; in rare cases, however, more gives rise to a clearer area at the pe- Biology and than one nidus may be circumscribed riphery of the circular nidus. The ni- Pathophysiology 9,10 by a single block of sclerotic bone. dus is surrounded by a region of ac- Schulman and Dorfman11 demon- Microscopically, the nidus is com- tive bone formation that appears as strated abundant nerve fibers within posed of thin seams of osteoid or sclerotic dense bone with various the nidus matrix adjacent to areas woven bone lined with osteoblasts, patterns of maturation.1,4 rich in arterioles. High levels of pros- which represents a process of bone Osteoid osteoma does not grow or taglandin synthesis in the nidus of remodelling with osteoblastic activ- behave in a locally aggressive man- osteoid osteoma have been reported ity (Figure 1). Osteoclastic bone re- ner, and it has no potential for malig- in several other studies.12,13 This find- sorption occurs simultaneously and nant transformation.4,6 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 International Society of Arthroscopy, Knee Surgery, and Orthopaedic Sports Medicine and the Orthopaedic Research Society. Dr. Alman or an immediate family member serves as a board member, owner, officer, or committee member of the Pediatric Orthopaedic Society of North America. Dr. Schemitsch or an immediate family member has received royalties from Stryker; serves as a paid consultant to Amgen, Stryker, Synthes, Smith & Nephew, Baxter, Wright Medical Technology, and Kuros; has received research or institutional support from Smith & Nephew; has received nonincome support (such as equipment or services), commercially derived honoraria, or other 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 Trauma Association, Canadian Orthopaedic Association, and Osteosynthesis and Trauma Care Foundation. Neither of the following authors nor any immediate family member has received anything of value from or owns stock in a commercial company or institution related directly or indirectly to the subject of this article: Dr. Peyser and Dr. Mankin.

November 2011, Vol 19, No 11 679 Osteoid Osteoma and Osteoblastoma

Figure 1 Figure 2

A, AP radiograph demonstrating an osteoid osteoma nidus in the base of the Histologic appearance of an area ﬁfth metatarsal (arrows). B, Bone scintigraphy image demonstrating within a nidus in a patient with increased radionuclide uptake by the lesion in the affected foot, at the left, osteoid osteoma. The bony and no abnormal ﬁndings in the contralateral foot at the right. (Panel A trabeculae are rimmed by adapted with permission from Peyser A, Applbaum Y: Radiofrequency osteoblasts (arrow). Capillaries can ablation of bone tumors. Current Orthopaedic Practice 2009;20[6]:616-621.) be detected between the bony trabeculae (arrowhead) (hematoxylin-eosin, high-power view). (Adapted with permission from Zbojniewicz AM, Hartel J, pending on the proximity to a joint, the tumor often leads the clinician to Nguyen T, Wilks K, Mace A, Hogg clinician may note effusion, synovitis, strongly consider a diagnosis of os- JP: Neoplastic disease of the degenerative changes, limitation of teoid osteoma. A combination of vertebral column: Radiologic- movement, and contractures.17 Par- plain radiographs, bone scintigraphy, pathologic correlation. Curr Probl Diagn Radiol 2010;39[2]:74-90. ticularly in pediatric patients, osteoid CT, and occasionally MRI, is usually http://www.sciencedirect.com/ osteoma may present with rapidly sufficient to confirm the diagnosis. science/journal/03630188.) progressive painful scoliosis when the spinal column is involved. In Radiography strating the expression of cyclo- most cases, the concavity of the sco- Conventional radiography is the ini- oxygenase-1 and cyclooxygenase-2 tial examination of choice. A plain liotic curve is ipsilateral to the lesion isozymes by the tumor tissue; both radiograph of osteoid osteoma may as a result of muscle spasm and enzymes are responsible for protein reveal a characteristic oval radiolu- pain.1,6,18 processing in the prostaglandin bio- cency representing the nidus as well 14 Limb-length discrepancy may be synthesis pathway. These reports as a surrounding area of reactive associated with pediatric osteoid os- suggested an important pathophysio- bone sclerosis with or without peri- teoma. Peyser et al7 reported average logic role for prostaglandins both as osteal bone formation (Figure 2, A). mediators of pain and vasodilation limb-length discrepancy of 12 mm in However, these findings are typical that may stimulate the nerve endings four pediatric patients with osteoid of cortical lesions, and they may not by increasing the blood flow within osteoma of the femur and tibia. In be found on a plain radiograph if the the tumor. each case, the involved extremity lesion is located either in the in- was longer than the uninvolved ex- tramedullary cavity or in areas of the Clinical Features tremity. One possible explanation for skeleton that are difficult to assess The most prominent clinical symp- limb overgrowth in children with os- with radiography alone (eg, spine, tom of osteoid osteoma is the pres- teoid osteoma may be the resulting pelvis, small bones of the hands and ence of local pain that is typically inflammatory response and associ- feet).19 more frequent and severe at night ated hyperemia, especially in patients and that is relieved with administra- with lesions located near the open Scintigraphy tion of nonsteroidal anti-inflamma- growth plate. Bone scintigraphy is a highly sensi- tory drugs (NSAIDs).2,4,6,7,15,16 Other tive diagnostic modality for detecting signs and symptoms are local swelling Diagnostic Imaging and localizing osteoid osteoma. and tenderness, bony deformity, gait The typical pain pattern and physical These images demonstrate the classic disturbances, and muscle atrophy; de- findings related to the location of the markedly increased radionuclide

680 Journal of the American Academy of Orthopaedic Surgeons Kivanc I. Atesok, MD, MSc, et al

Figure 3 pending on features seen on MRI and CT. The lesions were correctly classified as benign-latent in 19% of magnetic resonance images, compared with 81% of CT scans. The primary diagnosis was correctly identified as osteoid osteoma in 3% of magnetic resonance images and in 67% of CT scans. Based on their results, the authors recommended CT scanning with thin sectioning as the preferred advanced imaging modality for the diagnosis of osteoid osteoma. They also stated that “MRI, especially without clinical or CT correlation, may not be reliable, can be misinterpreted, and can lead to misdiagnosis.” The main limitation of Axial CT scan of distal femurs. The nidus is located in the left distal femur anterior metaphysis within the cortex (arrowhead). Increased sclerotic bone this study was the small sample size formation is seen around the lesion (arrows). (12 magnetic resonance images and 7 CT scans of patients with osteoid osteoma), which may have been a uptake by the nidus (Figure 2, B). MRI source for bias with regard to intra- Nuclear medicine bone scans use The effectiveness of MRI in diagnos- and interobserver variability. technetium Tc-99m-labeled diphos- ing osteoid osteoma is controversial. phonates, which have avidity for ar- The appearance of the lesion may be Management and Prognosis eas with increased osteoblastic activ- highly variable, and the presence of ity and bone turnover. In addition, associated soft-tissue changes and Nonsurgical portable gamma cameras can be used bone marrow edema may result in Nonsurgical management with sali- cylates or NSAIDs is a justifiable as radiotracer detectors intraopera- diagnostic errors. Davies et al22 ret- therapeutic option because these tively to localize the nidus during re- rospectively reviewed the MRI find- 20 drugs can effectively relieve pain, section. Despite its increased sensi- ings of 43 patients with osteoid os- tivity, scintigraphy is not a specific which is typically the presenting and teoma and compared the accuracy of imaging method for determining the most striking patient complaint1,4,24 MRI localization with that of other distinctive features of the lesions. (Figure 4). However, few published imaging modalities. Six tumors were studies have evaluated the results of not seen on MRI, and nine were CT prolonged medical management and CT is considered to be the imaging poorly visualized. The potential for a reported complete resolution of method of choice for visualizing the missed diagnosis was 35% based symptoms with discontinuation of anatomic position of the nidus and solely on the MRI findings. NSAIDs.24,25 Kneisl and Simon24 23 aiding in the differential diagno- Hosalkar et al prospectively com- noted an average time of 33 months sis.1,6,19 The characteristic appearance pared the diagnostic accuracy of to resolution of symptoms in six pa- of osteoid osteoma on thin-slice CT MRI and CT for osteoid osteoma in tients treated with NSAIDs. Sporadic scan is of a low-attenuation nidus children. Preoperative magnetic reso- case reports in the literature describe with central mineralization and vary- nance images and CT scans of pa- the probability of the evolution of ing degrees of sclerosis surrounding tients with biopsy-confirmed diagno- osteoid osteoma into osteoblastoma the nidus21 (Figure 3). CT imaging is sis of osteoid osteoma were after prolonged nonsurgical manage- particularly useful when the nidus is randomly reviewed by three radiolo- ment with NSAIDs.26 in an intra-articular location or is gists who were blinded to the diag- not apparent radiographically be- nosis. The radiologists were asked to Surgical cause of the presence of complex an- classify lesions as benign-latent, Surgical management is warranted in atomic features. benign-aggressive, or malignant de- cases in which the pain is severe and

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Figure 4

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 destruction by means of laser photocoagulation, and arthroscopic excision. All can be an alternative minimally invasive surgical method 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 unresponsive to medication. Surgery surgical management techniques in- ventional techniques with successful is also warranted for patients who clude open excision of the lesion, outcomes.24,27 However, these tech- are unwilling to endure pain and ac- CT-guided percutaneous excision, niques can be unexpectedly challeng- cept long-term medical treatment be- and CT-guided radiofrequency (RF) ing for both surgeon and patient. cause of potential gastrointestinal ablation. The tumor may be difficult to iden- complications associated with the tify intraoperatively, and incomplete use of NSAIDs. Prolonged presence Open Excision removal may result in recurrence. of osteoid osteoma lesions, especially Until the late 1990s, open excision Additionally, resection of weight- in skeletally immature patients, may was the only surgical option.1,6 En bearing bone may necessitate pro- lead to complications such as growth bloc excision of the tumor, and corti- longed hospital stay as well as re- disturbances, scoliosis, and osteoar- cal shaving and curettage of the ni- strictions on activities and weight throsis.27 The most commonly used dus cavity, are frequently used con- bearing.15,28,29 Advances in imaging

682 Journal of the American Academy of Orthopaedic Surgeons Kivanc I. Atesok, MD, MSc, et al

Figure 5 CT-guided Radiofrequency clinical recovery was achieved in all Ablation but two patients. These two patients In CT-guided RF ablation, heat is ap- underwent a second ablation, after plied locally to destroy the nidus which they remained symptom-free. (Figure 5). The RF probe is intro- The only procedure-related compli- duced into the nidus through a can- cation was observed in a patient with nulated needle under CT-guided im- a nidus located in the tibial diaphy- aging, and the temperature at the tip sis. This patient experienced superfi- of the probe is increased to approxi- cial skin infection of the ablation mately 90°C and maintained at that area that resolved with outpatient level for 5 to 6 minutes.32 The tip of antibiotic treatment. The authors the probe must be insulated to pre- stated, “RF ablation in pediatric os- vent injury to the soft tissues adja- teoid osteoma patients is a safe and Axial CT scan demonstrating the cent to the osteoid osteoma. effective technique.” Several other femoral metaphysis during Rosenthal et al29 performed CT- recent case series and cohort studies radiofrequency (RF) ablation of guided RF ablation on 263 patients have demonstrated the effectiveness osteoid osteoma. The nidus is located cortically, with increased with a mean age of 19 years. In total, of RF ablation as a safe and mini- sclerotic bone formation (arrows). 271 ablation procedures were per- mally invasive method for the man- The RF probe (P) was introduced formed: 249 for initial tumor treat- agement of osteoid osteoma.33,34 into the nidus to ablate the lesion. ment, 14 for recurrence after conven- In a series of 125 patients, Rosen- tional surgery, and 8 for recurrence thal et al15 retrospectively compared after prior RF ablation. All the pro- the outcomes of RF ablation (38 pa- technology have made it possible to cedures were technically successful, tients) and surgical excision (87 pa- address the disadvantages of open and two minor procedure-related tients). They found no significant dif- excision by providing real-time CT complications were observed. After ference between the two groups with guidance and percutaneous manage- the procedure, all daily activities regard to rate of recurrence (P = ment of osteoid osteoma. were resumed immediately. The only 0.725) and clinical success (P = restriction involved avoidance of 0.722). The average length of hospi- CT-guided Percutaneous Excision strenuous sports for 3 months for tal stay was 0.18 day for the RF In this technique, a cannulated curet patients with lesions in weight- group and 4.7 days for the open ex- is inserted into the lesion over a bearing bones. Of the 126 patients cision group. No complications were Kirschner wire under CT image guid- for whom 24-month follow-up data associated with the percutaneous ance to excise the nidus. Fenichel et were available, 112 were pain-free method. Two patients in the open al30 used this technique in a series of and did not require additional proce- excision group experienced compli- 18 patients with osteoid osteoma of dures. The procedure was unsuccess- cations, requiring a total of five sec- the pelvis, femur, and tibia. Sixteen ful in nine patients, and the outcome ondary procedures. patients experienced immediate and was indeterminate in five. The au- No studies to date have compared permanent pain relief after the first thors suggested RF ablation as “the CT-guided percutaneous excision procedure. In two patients, the nidus treatment of choice with high clinical with CT-guided RF ablation; how- was missed because of misinterpreta- success rate (91%), brief recovery, ever, clinical outcomes are known to tion of the CT scan, and no clinical and gratifyingly low complication be similar with both techniques. improvement was observed postop- rate.” Higher success rates in tissue diagno- eratively. In these patients, the proce- Peyser et al7 reported the results of sis have been reported with CT- dure was repeated successfully, re- CT-guided RF ablation in 22 pediat- guided excision than with RF abla- sulting in prompt postexcisional ric patients with osteoid osteoma tion (69% to 77% and 47% to 50%, cessation of typical osteoid osteoma (mean age, 13 years 6 months). The respectively), possibly because the pain. There were two complications procedure was technically successful entire nidus can be removed in the (femoral neurapraxia, skin abra- in all patients, and all were dis- excision procedure.2,30,31 However, sion), both of which resolved. Other charged from the hospital within 24 CT-guided excision of the nidus authors have reported similar results hours postoperatively with no re- along with cortices may act as a with a high clinical success rate and strictions in weight bearing. At an stress riser and may predispose the minimal complications.31 average follow-up of 38.5 months, patient to pathologic fracture or

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Figure 6 consists of an interlacing network of bony trabeculae within a loose fibrovascular stroma that is rimmed by a single row of benign osteoblasts that are responsible for osteoid formation (Figure 7). The lesions show a variable number of osteoclasts at the sur- faces of the bony trabeculae; these osteoclasts are involved in bone resorption. The stroma of osteoblastoma demonstrates a less organized pattern of osteoid and trabecular bone distribution than does that of osteoid osteoma as well as greater Schematic illustration demonstrating the spectrum of changes in lesion size vascularity. The lesion may show and amount of sclerotic bone surrounding the lesion in osteoid osteoma and osteoblastoma. (Adapted with permission from Dorfman HD, Czerniak B: secondary aneurysmal bone cyst de- Benign osteoblastic tumors, in Dorfman HD, Czerniak B, eds: Bone Tumors. generation as a result of increased St. Louis, MO, Mosby, 1998, pp 85-127.) vascularity. The tumor is surrounded by a thin shell of newly formed peri- osteal bone tissue, which appears less activity-related restrictions postoper- like osteoid osteoma, however, os- sclerotic than that of osteoid os- atively. teoblastoma is most often located in teoma and matures toward its pe- The current trend toward minimally the posterior elements of the verte- riphery.1,4,27 invasive therapies has resulted in the bral column and the sacrum. This Osteoblastoma is a benign but lo- use of many other less commonly em- presentation accounts for approxi- cally aggressive tumor, with a clinical ployed percutaneous techniques for the mately one third of cases. Other course ranging from slow, indolent management of osteoid osteoma. These commonly involved sites are the long progression to rapid aggressive include image-guided cryotherapy, drill bones (eg, femur, tibia), particularly growth. Aggressive osteoblastomas trepanation with or without ethanol in- within the medullary cavity and di- are associated with large epithelioid jection, thermal destruction by means aphysis. Osteoblastoma is also seen osteoblasts that rim the bony trabec- of laser photocoagulation, and ar- in the craniofacial bones (15%) and ulae, and they are more mitotically throscopic excision of juxta-articular the hands and feet (14%) and, to a active than the cells in osteoid os- lesions.2,31,35 lesser extent, in sites such as the ribs, teoma and conventional benign os- clavicle, and sternum.6,27,38 teoblastoma.1,4,6,27,38 Zon Filippi et al39 demonstrated that a predomi- Osteoblastoma Gross Structure and nance of epithelioid osteoblasts is Histology Osteoblastoma was first described in commonly seen in multifocal osteo- 1932 by Jaffe and Mayer36 as “an Grossly, osteoblastoma is consider- blastomas (Figure 8). osteoblastic-osteoid tissue forming ably larger than osteoid osteoma, Osteoblastoma has neither malig- tumor.” In 1956, Jaffe and Lichten- with an average diameter of approxi- nant nor metastatic potential. Histo- stein further characterized the lesion mately 4 cm.4,37 The tumor contains logically, the lesion has benign fea- and independently proposed the a larger and structurally less orga- tures even when it appears aggressive term “benign osteoblastoma.”37 Os- nized central area and a less dense radiographically.40 Osteoblastoma teoblastoma is a rare tumor that ac- sclerotic reaction circumscribing the that is reported to have malignant counts for 3% of all benign bone tu- lesion (Figure 6). The presence of potential should be meticulously dif- mors and approximately 1% of all more than one central zone per le- ferentiated from other malignant primary bone tumors.1,38 Osteoblas- sion (ie, multifocal osteoblastoma) is bone tumors, in particular, from the toma most commonly arises in patients seen in 4% to 14% of cases, which is osteoblastoma-like variant of osteo- aged between 10 and 25 years, with a higher than in osteoid osteoma.27,37,39 sarcoma. Bertoni et al41 reported a male:female ratio of 2:1; this is similar The microscopic features of osteo- series of 11 patients with to the age and sex characteristics of pa- blastoma are similar to those of os- osteoblastoma-like osteosarcoma tients with osteoid osteoma.27,38 Un- teoid osteoma. Centrally, the lesion and noted that the lesions histologi-

684 Journal of the American Academy of Orthopaedic Surgeons Kivanc I. Atesok, MD, MSc, et al

Figure 7

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 of mineralization (box) embedded in a loose fibrovascular stroma (asterisks) (hematoxylin-eosin). B, High-magnification image 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 features in a child. Spine [Phila Pa 1976] 2008;33[25]:E968-E970.)

cally resembled osteoblastoma, with often progressive in intensity. Typi- Figure 8 peripheral infiltration into surround- cally, pain does not respond dramati- ing tissues. The tumors had charac- cally to NSAIDs and is not generally teristic features of low-grade osteo- most severe at night.38,40 sarcoma, with moderate cellular Other common manifestations of atypia under high-power micro- osteoblastoma are local swelling and scopic examination. tenderness, especially when the tumor is near the surface. Gait distur- Biology and bance can be seen in children with Pathophysiology lower extremity involvement. Be- The unique pathophysiologic rela- cause of its size and predilection for High-power histologic image tionship between the presence of the vertebral column, osteoblastoma demonstrating epithelioid cells and nerve endings and vessels, and in- irregular blue-staining matrix in frequently presents with neurologic aggressive multifocal creased production of prostaglandins symptoms resulting from spinal cord osteoblastoma (hematoxylin-eosin). in osteoid osteoma, has not been or nerve root compression, such as (Reproduced with permission from similarly documented for osteoblas- numbness, tingling, radicular pain, Zon Filippi R, Swee RG, Krishnan toma. Local pain associated with os- Unni K: Epithelioid multinodular paresthesias, and paraparesis. Scolio- osteoblastoma: A clinicopathologic teoblastoma is most likely caused by sis and torticollis may be observed analysis of 26 cases. Am J Surg local expansion of the tumor and the secondary to muscle spasm associ- Pathol 2007;31[8]:1265-1268.) pressure of its mass on surrounding ated with osteoblastoma.27,37,38,40 40 structures. In a series of 306 patients with osteoblastoma, Lucas et al37 found pro- ary to spinal tumors, and four had Clinical Features gressive pain to be the most frequent scoliosis. Clinically, osteoblastoma does not complaint (87%). Local swelling, exhibit the typical presenting symp- tenderness, warmth, and gait distur- Diagnostic Imaging toms and signs seen in patients with bance were also mentioned fre- Because of the nonspecific signs and osteoid osteoma. In patients with os- quently. The average duration of symptoms associated with osteoblas- teoblastoma, the most common pre- these complaints prior to diagnosis toma, radiologic studies are impera- senting complaint is pain, which is was 2 years. Ten patients presented tive to establish the diagnosis. In usually described as dull, aching, and with neurologic complaints second- sporadic cases, the patient may be

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Figure 9 the lesion without the need for bone scintigraphy.

CT CT is the imaging method of choice for osteoblastoma.6,43 It can provide the most specific information about the location, size, extent, and nature of the tumor. Areas of mineralization within the lesion as well as cortical destruction and soft-tissue extension can be well-delineated on CT sec- tions.1,38,42 Characteristically, the lesion tends to demonstrate areas of mineralization centrally, expansile bone remodeling, and signs of reactive sclerosis toward the periphery with a thin marginal bone shell6 (Fig- ure 10).

MRI A, Lateral plain radiograph in a patient with osteoblastoma of the spinous process of C5. Mild kyphosis is seen at the level of the lesion (arrow), The usefulness of MRI in the diagno- resulting from the mass effect of the enlarged spinous process. B, Bone sis of osteoblastoma is questionable. scintigraphy image demonstrating remarkable radionuclide uptake by the The features are nonspecific and tumor. sometimes confusing, and there may be an overestimation of the extent pain-free or asymptomatic, and the diagnostic accuracy of 43% in 116 and nature of the tumor as a result diagnosis can be obtained inciden- patients with appendicular osteo- of increased local inflammatory reac- tally.1,42 blastomas and 64% in 66 patients tion and extensive marrow 6,42-44 with vertebral osteoblastomas. The edema. However, MRI may be a Radiography authors noted that the radiographic valuable tool in cases in which the The radiographic appearance of os- appearance was not completely reli- tumor has extensive effects on the teoblastoma depends on the location able in distinguishing osteoblastoma spinal canal and cord. MRI also may and maturity of the tumor.27,37 In from osteosarcoma; lesions were be useful in the evaluation of intra- general, these tumors appear as ir- misinterpreted as malignant in ap- and extraosseous reactive changes regularly shaped radiolucent lesions proximately 15% of cases. The ra- and the presence of soft-tissue infil- surrounded by a thin shell of reactive diographs of 17% to 33% of pa- tration associated with osteoblas- bone.40 The interior of the tumor tients were considered to be toma. The lesion generally appears may show various degrees of ossifi- indeterminate. as low or intermediate signal density cation, which tends to increase as the on T1-weighted images and interme- lesion matures.1,37,39 Compared with Scintigraphy diate to high signal density on T2- 6,38,45 osteoid osteoma, osteoblastoma le- Osteoblastomas exhibit marked up- weighted images (Figure 11). sions appear larger in diameter, with take of bone-seeking radionuclide on less reactive bone sclerosis and more bone scintigraphy because of in- Management and Prognosis cortical expansion (Figure 9, A). creased osteoblastic activity within Osteoblastoma must be managed Plain radiographs may be useful in the tumor (Figure 9, B). Scintigraphy surgically because of its potential for establishing the diagnosis. However, is sensitive to but not specific for os- aggressive behavior and bone de- radiographic appearance is usually teoblastoma. It may be helpful in lo- struction (Figure 4). The selection of not distinctive, and additional imag- calizing the lesion, as in cases of os- surgical procedure depends largely ing studies are required for diagnos- teoid osteoma. However, it may be on the location and aggressiveness of tic accuracy. Based solely on radio- that the larger size of the tumor may the tumor. Intralesional curettage graphs, Lucas et al37 reported make it relatively easier to localize and en bloc resection are the most

686 Journal of the American Academy of Orthopaedic Surgeons Kivanc I. Atesok, MD, MSc, et al commonly performed surgical proce- Figure 10 dures.

Intralesional Curettage Intralesional curettage is sufficient in most 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 bone grafting should be performed as indi- cated.27,38 Although curettage may have lower morbidity than en bloc resection, this procedure may leave behind microscopic tumor, which is a source for recurrence.40

En Bloc Resection En bloc resection is an effective surgical approach for locally aggressive Sagittal (A) and axial (B) CT images of an osteoblastoma of the spinous process of C5. An enlarged spinous process (arrow) with irregular borders is and large tumors in appropriate visible on the sagittal image. The axial view demonstrates a partially cases. In particular, recurrent lesions destroyed cortex as well as central areas of mineralization (circle). following intralesional curettage are most successfully managed with en Figure 11 bloc resection. This is also the preferred method for lesions located in expendable bones such as the ribs, clavicle, and fibula.38,42 Berry et al40 reported on 99 osteoblastoma patients treated surgically with curettage and bone grafting or en bloc resection. They noted that “23% of the patients treated with curettage required further surgery for recurrence compared to 14% of the patients who underwent en bloc resection.” Five patients had two or more subsequent recurrences. Pa- tients who required more than one reoperation were ultimately treated Magnetic resonance images of a patient with osteoblastoma at C3. A, T2- definitively with en bloc resection. weighted sagittal image demonstrating an enhancing mass with expansile features (arrow). B, T1-weighted axial image demonstrating involvement of the right side of C3 and extension into the spinal canal (dashed circle). Summary (Adapted with permission from Burn SC, Ansorge O, Zeller R, Drake JM: Management of osteoblastoma and osteoid osteoma of the spine in Osteoid osteoma and osteoblastoma childhood. J Neurosurg Pediatr 2009;4[5]:434-438.) are distinct benign bone-producing tumors with certain similar features. vent confusion and misdiagnosis. option for osteoid osteoma. Surgical It is crucial to recognize the typical The differences in management are management is considered when clinical presentation and imaging considerable. Nonsurgical manage- nonsurgical methods fail or are not findings of both types tumor to pre- ment with NSAIDs may be a valid feasible for or desirable by the pa-

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