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educational objectives

Osteoid OsteomaPetros J. Boscainos, MD, FRCSEd; Gerard R. Cousins, MBChB, BSc(MedSci), MRCS; Rajiv Kulshreshtha, MBBS, MRCS; T. Barry Oliver, MBChB, MRCP, FRCR; Panayiotis J. Papagelopoulos, MD, DSc

AbstrActOsteoid osteoma is the third most com-mon benign bone tumor. The authors describe the clinical presentation, diag-nostic investigations, differential diagno-sis, histopathology, and treatment options for this condition, including a compre-hensive review of the literature. Osteoid

osteomas have wide variations in presen-tation and tend to present in the second decade of life, with pain that is worse at night and is relieved by salicylates. Plain radiographs and computed tomography scans are the mainstay of imaging; how-ever, bone scintigraphy, single-photon emission computed tomography, magnet-

As a result of reading this article, physicians should be able to:

1. Discuss the clinical presentation of and different imaging modality options for suspected osteoid osteomas.

2. Develop an insight into the histopathology and histochemistry of osteoid osteomas.

3. Use diagnostic processes in the differential diagnosis of suspected osteoid osteomas.

4. Apply current treatment depending on the location and accessibility of the lesion.

The authors are from the Department of Trauma and Orthopaedic Surgery (PJB, GRC, RK), Perth Royal Infirmary, NHS Tayside, Perth, Scotland; Department of Radiology (TBO), Ninewells Hospital, NHS Tayside, Dundee, United Kingdom; and the Department of Orthopaedics (PJP), Athens University Medical School, Athens, Greece.

The authors would like to thank Dr Elaine MacDuff, Western Infirmary, Glasgow, United Kingdom, for providing the image of the hematoxylin-eosin stain.

The material presented in any Keck School of Medicine of USC continuing education activity does not necessarily reflect the views and opinions of OrthOpedics or Keck School of Medicine of USC. Neither OrthOpedics nor Keck School of Medicine of USC nor the authors endorse or recommend any techniques, commercial products, or manufacturers. The authors may discuss the use of materials and/or products that have not yet been approved by the US Food and Drug Administration. All readers and continuing education participants should verify all information before treating patients or using any product.

Correspondence should be addressed to: Petros J. Boscainos, MD, FRCSEd, Department of Trauma and Orthopaedic Surgery, Perth Royal Infirmary, NHS Tayside, Taymount Terrace, Perth, United King-dom, PH1 1NX (petros.boscainos@nhs.net).

doi: 10.3928/01477447-20130920-10

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ic resonance imaging, and sonography are also used. Osteoid osteomas consist of a nidus with surrounding sclerotic bone. The differential diagnosis covers a wide range of conditions due to the vari-able presentation of osteoid osteoma. The natural history is for regression to occur within 6 to 15 years with no treatment; however, this can be reduced to 2 to 3 years with the use of aspirin and non-steroidal anti-inflammatory drugs. Com-puted tomography–guided percutaneous techniques, including trephine excision, cryoablation, radiofrequency ablation, and laser thermocoagulation, are de-scribed.

Osteoid osteoma is a small, dis-tinctive, nonprogressive, be-nign osteoblastic lesion that is

usually accompanied by severe pain. Jaffe1 was the first to report the iden-tification of this osteoblastic lesion in 1935. As the third most common biopsy-analyzed benign bone tumor after osteo-chondroma and nonossifying fibroma, osteoid osteoma is a relatively common lesion. It represents 11% to 14% of be-nign bone tumors. Two percent to 3% of excised primary bone tumors are osteoid osteomas.2,3

clinicAl PresentAtionOsteoid osteoma can manifest at any

age, but the majority of patients are aged between 5 and 20 years, with 50% of pa-tients aged between 10 and 20 years.4,5 Osteoid osteomas are 1.6 to 4 times more prevalent in males.4 In the majority of cas-es, osteoid osteoma occurs in long bones, affecting the metaphysis or diaphysis. The most common loci are the femur and the tibia, with the most characteristic site being the femoral neck and the intertro-chanteric region.4 Rarely, it also involves the epiphyseal and intracapsular aspect of long bones (known as intra-articular os-teoid osteomas). Less commonly affected are the spine and the small bones of the hand and feet. It can involve the talus,

predominantly the talar neck. Flat bones in the body and the skull are rarely af-fected. Osteoid osteoma is usually local-ized within the bone cortex. Subcortical, intracortical, and intraperiosteal osteoid osteomas have been described. Osteoid osteomas of the spine account for ap-proximately 6% of cases and almost al-ways involve the posterior arch area close to the pedicles.6,7 The lumbar spine is the most commonly affected region. Multiple osteoid osteoma nidi in the same or dif-ferent bones are rare.8,9

Pain is the most common clinical presentation. Its usual characteristics are dull, unremitting, initially mild and intermittent pain that increases in inten-sity and persistence over time. It tends to become increasingly severe at night and is usually relieved by salicylates and nonsteroidal anti-inflammatory drugs (NSAIDs). The indolent nature of early osteoid osteoma may result in delayed presentation. Swelling, erythema, and tenderness may be present in bones in subcutaneous locations.5 Referred pain and muscular atrophy may result in the misdiagnosis of a neurological disor-der.10 This observation is common in patients who have a painful osteoid os-teoma in posterior elements of the spine, where a postural scoliosis is found due to paravertebral muscle spasm but is revers-ible after treatment.4

Osteoid osteomas in the region of the proximal femur or pelvis may pres-ent with symptoms of knee pain, and the diagnosis may require a bone scan. Intra- or juxta-articular lesions are commonly associated with synovitis.11 Joint pain with flexion contracture, abated range of motion, and antalgic gait can be a clini-cal pattern of an intra-articular osteoid osteoma.5 In children, the most common presenting symptom is nocturnal pain. In a young child with an osteoid osteoma, a limp may be the only symptom. If the lesion is close to an open physis, it can cause lengthening, angular deformity, or both of the extremity.4

imAgingPlain Radiographs

Plain radiographs are the initial imaging study of choice. The osteoid osteoma ap-pears as a small, radiolucent nidus (usually less than 1 cm) surrounded by a variable area of sclerotic bone or cortical thicken-ing (Figure 1). The nidus can be difficult to detect when it is obscured by sclerotic cortical bone or in cases of intra-articular lesions, where bone deposition from the in-tracapsular periosteum is usually less.12,13 In addition, intramedullary-located oste-oid osteomas may not exhibit surrounding bone sclerosis.14 Indirect manifestations of synovial inflammation and joint effusion may be evident, or symptoms that mimic osteoarthritis may be present.13,15 When treatment is delayed, secondary osteopenia and changes in bone morphology may be observed.11 If the nidus is larger than 1.5 cm, the lesion is usually designated as an osteoblastoma.16,17 Osteoblastomas are seen radiologically as lesions with a lucent, slow-growing, expansile area with irregu-lar sclerosis and no definite nidus.18

Computed TomographyThe most common appearance of osteoid

osteoma on computed tomography (CT) is as a small, well-delineated, low-attenuation nidus surrounded by a dense sclerotic reac-tion (Figure 2). Foci of calcification may be visible. A recently described CT finding is the presence of fine, linear, low-density vascular channels that can surround oste-oid osteomas. When present, such vascular grooves have high sensitivity and specificity in the diagnosis of osteoid osteoma.19

A CT scan is useful in diagnosing intra- or juxta-articular osteoid osteomas, and it has been proposed that CT must be used in all patients with suspected osteoid osteomas because it has better diagnos-tic accuracy compared with plain radio-graphs or magnetic resonance imaging in these cases.20,21 Preoperative localization of osteoid osteomas can be facilitated us-ing CT guidance.22,23 Percutaneous abla-tion of lesions under CT guidance is well

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established and is discussed later (Figure 3).24-28 Computed tomography–guided ab-lation of osteoid osteomas has also been described in technically challenging loca-tions, such as the spine.29,30

Bone ScintigraphyDue to the correlation between osteo-

blastic activity and the intensity of radio-pharmaceutical uptake, bone scintigraphy

usually shows intense uptake in the arterial phase within the richly vascular nidus and in the delayed phase within surrounding re-active bone (Figure 4).31 Usually, an intense area of radiotracer uptake is found in the region of the nidus and less in the reactive bone. This pattern, which is known as the double-density sign, is diagnostic of osteoid osteoma.32 The area of uptake may be wide. Historically, a pinhole collimator has been

used to demonstrate the nidus because the reactive bone uptake may obscure it.14

In children, increased uptake by active growth plates can obscure an adjacent os-teoid osteoma. In this situation, compari-son with the contralateral unaffected site is helpful to identify the tumor.13 In situa-tions where radiofrequency ablation is not available, intraoperative radionucleotide imaging may be used to confirm complete resection of the tumor.14,33

Single-photon Emission Computed Tomography

Although in most cases a conventional bone scan followed by thin-section CT scan is sufficient, single-photon emission computed tomography (SPECT) can be helpful in diagnosing osteoid osteomas in cases in which bone scintigraphy up-take is subtle.34 A SPECT scan can detect smaller lesions by improved spatial reso-lution of overlying normal tissue uptake and has been advocated as helpful in de-picting osteoid osteomas of the spine.14,35 Transaxial anatomic imaging of SPECT can further enhance its diagnostic ability in positioning suspicious lesions.36

Magnetic Resonance ImagingThe appearance of osteoid osteoma is

variable with magnetic resonance imaging

Figure 1: An 11-year-old girl presented with chronic midtibial pain and localized warmth on examination. Lateral radiograph showing diffuse anterior cortical thickening (arrow) centered on a subtle lucency, which was diagnosed as an osteoid osteoma (A). Axial proton-density fat-saturated magnetic resonance image showing diffuse high-signal medullary edema and periostitis surrounding a markedly thickened low-signal cortex, within which a 3-mm osteoid osteoma lies (B). Axial computed tomography scan obtained during radiofrequency ablation showing the densely thickened cortex and an ablation needle completely occupying the nidus (C).1A

1B 1C

Figure 2: A 23-year-old man presented after 18 months of knee pain due to medullary osteoid osteoma. Axial computed tomography scan from a treatment planning study showing the lucent osteoid osteoma, subtle central calcification, and surrounding medullary sclerosis. Note the vascular channel entering the medial aspect of the lesion (A). Coronal proton-density fat-saturated magnetic resonance image showing a zone of marrow edema centered on a high-signal nidus adjacent to the physeal scar (B).

2A 2B

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(MRI). A primarily cellular nidus will dem-onstrate low to intermediate signal inten-sity on T1-weighted images that increases on T2-weighted images (Figure 1B). A heavily calcified nidus appears as low to intermediate signal intensity on both T1- and T2-weighted images.37A more striking finding is the presence of surrounding bone marrow edema or periostitis, best demon-strated on fluid-sensitive sequences (Figure 2B). Areas of densely sclerotic medullary or cortical bone may retain low signal in-tensity on all sequences. In some cases, the bone marrow and soft tissue edema is florid and can mimic an aggressive process, such as infection or malignancy. Reactive soft tissue mass with myxomatous change, cell-depleted juxtanidal bone marrow, and proteinaceous material may be confused with those of a malignant tumor or osteo-myelitis.38,39

It has been suggested that MRI must not be interpreted without reference to plain radiographs and CT scans because the appearance of osteoid osteomas on MRI can mimic that of an aggressive le-sion.25 Correlation with clinical infor-mation is the most important aspect of diagnosing osteoid osteomas. Following

intravenous gadopentate dimeglumine, both the central nidus and surrounding edema show enhancement. This technique is not always necessary, but occasion-ally it may assist the differential diagnosis along with other modalities.

SonographyHistorically, the use of preoperative

Doppler duplex color localization of os-teoid osteomas has been reported as a means of assessment of the vascularity of the nidus or the nidus’ feeding artery.40 Color Doppler sonography may show in-creased blood supply and demonstrate the entering vessel at the site of the lesion.41 Sonography is limited by its inability to penetrate bone and has been replaced by other imaging modalities.

HistopathologyOsteoid osteomas consist of a nidus

that is surrounded by sclerotic bone, the density of which usually varies with time from the onset of the lesion.42 Macroscop-ically, the nidus is a distinct round or oval reddish area with little contact with its surrounding sclerotic bone. Depending on the degree of calcification, the nidus’ con-

sistency may vary from soft and granular to hard and sclerotic. Older lesions dem-onstrate formation of defined trabeculae.

Intraoperatively, the tumor can be visu-alized protruding from the bone surface, or it may be hidden under a thick cortical lay-er of hyperostotic reactive bone. Intracorti-cal and subperiosteal lesions are often as-sociated with hyperemia and edema of the surrounding soft tissues.4 In tubular bones specifically, osteoid osteomas that present subperiosteally tend to become intracorti-cal due to continuous bone remodeling and subperiosteal new bone apposition.43

Histologically, the nidus appears as a small, well-defined area consisting of interlacing, irregular bone trabeculae of varying mineralization (Figure 5). Size, thickness, and mineralization diversity of trabeculae are evident among different le-sions, as well as in different areas of the same lesion. The nidus may demonstrate a zonal arrangement of trabecular architec-ture, with the central part being more scle-rotic and the periphery less mineralized and with more cells. Osteoid trabeculae are surrounded mainly by osteoblasts.44

Osteoclast-like, multinucleated giant cells have also been reported to be pres-

Figure 3: An 11-year-old boy presented with an osteoid osteoma in the right medial femoral neck that was treated with radiofrequency ablation. Computed tomography (CT) scanogram image showing the lucent osteoid osteoma surrounded by medullary sclerosis and overlying cortical thickening. An ablation needle has been placed in the lesion under CT guidance (A). Axial CT scan showing the needle traversing the osteoid osteoma. A lateral approach was used to avoid the grossly thickened cortical bone (B).

3A 3B

Figure 4: A 16-year-old boy presented with a 1-year history of knee pain but normal clinical ex-amination. Radionuclide bone scan image showing a wide zone of increased uptake in the proximal tib-ia due to increased osteoblastic activity provoked by an osteoid osteoma.

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ent.45 A reactive bone-formation zone with thickened trabeculae and a loose fibro-vascular stroma surrounds the nidus. The surrounding zones of soft tissue, skeletal muscle, and bone show increased vascular-ity, with vessels becoming smaller closer to the nidus.46 In chronic lesions, the fibro-vascular stroma may be dense with chronic inflammatory cell infiltration.

Pain commonly induced by osteoid os-teomas is attributed to unmyelinated nerve fibers found within the nidus.47 Immunohis-tochemical analysis has detected peripheral nerve fibers in the reactive zone and the ni-dus, with the greatest number being at the interface between the reactive zone and the edge of the nidus.44 Increased local concen-tration of prostaglandins (PGE2, PGI2, PGF2-alpha) and increased urinary excretion of 6-keto-PGF1 (the major urinary metabolite of PGI2) have been discussed in the literature in cases of osteoid osteoma.48,49 Pain medi-ated by prostaglandins has been attributed to the vasodilatory and vascular proliferation effect causing increased local pressure and thus stimulating the peripheral nerve fibers of the reactive zone, or through activation of the bradykinin system.50 Increased prosta-glandin values are reversible after osteoma removal.49 Although the remodeling and os-teolytic effect of prostaglandins is still under consideration, prostaglandins of the E series stimulate osteoclastic bone resorption in vi-tro and may contribute to the formation of osteoid osteoma.51

Nidus osteoblasts also display strong diffuse staining for COX-2, a key enzyme in the production of prostaglandins and in particular of prostaglandin E2.52 This enzyme appears to be a major factor in osteoid osteoma pain, and inhibition of COX-2 production enables control of symptoms.53

DifferentiAl DiAgnosisThe differentiation of osteoid osteomas

from other benign bone-forming lesions is based on the difference in size, location, pathology, and clinical symptoms, pathol-ogy, and clinical symptoms.5 In particular, osteoblastomas are larger in size (usually more than 1.5 to 2 cm) and tend to expand instead of regress.45 Osteoblastomas are also painful but generally without charac-teristic night exacerbation seen with oste-oid osteomas, and pain does not respond dramatically to salicylates or NSAIDs. Osteoblastomas have a predilection for vertebrae and can be accompanied more frequently with neurological symptoms or paravertebral muscle spasm.6,7 Instances of osteoid osteoma transition to osteo-blastoma have been reported, although they are rare.54,55 Radiographically, osteo-blastomas appear larger with less reactive sclerosis.5 Plain radiographs alone may not be distinctive enough to establish the diagnosis, and CT scans can give more in-formation on the expansive nature of the lesion.

When small in size, a Brodie’s abscess may appear similar to an osteoid osteoma on plain radiographs.9 Imaging using MRI, CT, and scintigraphy can help dif-ferentiate between osteoid osteomas and osteomyelitis, as well as other types of tumors, including nonossifying fibromas, chondroblastomas, enchondromas, eosin-ophilic granulomas, and malignant bone tumors.32,39,56

In children, infantile cortical hyperos-tosis, osteomyelitis, Perthes’ disease, leg-length discrepancy, healing stress frac-tures, tuberculosis, and neuromuscular conditions should be considered.57 Imag-

ing using CT, bone, and SPECT scans are useful in delineating the nature of the le-sion. Patients with unexplained low-back pain and sciatic pain in the second decade of life should be carefully examined to rule out osteoid osteoma.58

treAtmentMoberg59 suggested that the natural

history of osteoid osteoma is that of spon-taneous healing. In various studies, it has been noted that if the osteoid osteoma is not excised, complete resolution of symp-toms occurs within 6 to 15 years.42,59 Ad-ministering aspirin or other NSAIDs can reduce this time period to 2 to 3 years.50,53 Kneisl and Simon60 reported permanent relief of symptoms and regression of the nidus after prolonged NSAIDs treatment for 30 to 40 months. Strict selection cri-teria should be applied if nonoperative treatment is considered, given the poten-tial side effects of prolonged NSAIDs ad-ministration. Nonoperative management should be considered in patients where osteoid osteoma is not easily accessible by surgery.

Various techniques have been de-scribed for the preoperative localization of osteoid osteomas, such as angiography and placing wires and needles dipped in methylene blue over the nidus while un-der CT guidance.23 Radioisotope imaging with scintimetric guidance for intraop-erative localization and excision has been reported.61-63 Historically, in cases of in-tracortical lesions, preoperative oral tetra-cycline administration and examination of nidus’ fluorescence under ultraviolet light has been used to demonstrate the lesion and to verify excision, but such techniques are not currently considered practical.64,65

Osteoid osteoma was traditionally treated with excision of the nidus.6,16 Al-though the nidus needs to be removed completely to achieve symptomatic relief, complete removal of the sclerotic bone is not necessary. A well-planned surgical approach is essential. Radiographs or CT scans confirm identification of the nidus

Figure 5: Hematoxylin-eosin stain (original magni-fication 3200) showing trabeculae of woven bone lined by osteoblasts surrounded by a loose vascu-lar connective tissue stroma.

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before and after en bloc removal, and then the nidus undergoes histological examina-tion for confirmation. En bloc resection has the disadvantages of a large surgical exposure and excision of a large part of sclerotic bone. Bone grafting or internal fixation may be necessary, depending on the size of the bone defect left by the re-section.5 Unroofing and curettage has a role in structurally critical locations, such as the neck of femur because the central sclerotic structure is not disrupted.4 Mul-tiple articles report arthroscopic removal of intra-articular osteoid osteomas.66-69

Several methods have been described whereby osteoid osteomas may be treated percutaneously using CT guidance. These include trephine excision, cryoablation, radiofrequency ablation, and laser thermo-coagulation.24-28 The use of 3-dimensional C-arm radiographs during percutaneous excision in the long bones of children has also been reported.70 However, most patients in the literature undergoing per-cutaneous ablation or resection required general anesthesia for pain control. The need for a general anesthetic increases the invasive nature and the cost of these procedures and reduces the advantages of percutaneous treatment over surgical resection. Furthermore, these techniques require equipment not commonly avail-able in all hospitals.

Fine drills, bone trephine, or Tru-Cut needles (Medline Industries, Inc, Mun-delein, Illinois) have been described for use in precise and bone-sparing resec-tion. With smaller instruments, the need for a general anesthetic is also reduced, and the procedure can be performed in the outpatient setting, reducing the overall cost. Roger et al26 reported 16 patients who were treated using per-cutaneous CT-guided excision and had satisfactory results in 14 patients. The 2 failures were attributed to the proximity of the lesion to the articular margin and excessive periosteal reaction preventing access. The authors concluded that in-traoperative CT guidance and immediate

postoperative scintigraphy were effective in localizing and confirming removal of the nidus in an outpatient setting.26 In a series of 38 patients, Sans et al71 reported a cure rate of 84% at 3.7 years postopera-tively and 2 instances of femoral fracture at 2 months. Muscolo et al72 reported su-perior outcomes of CT-guided minimally invasive surgery rather than open sur-gery. Overall, percutaneous CT-guided procedures have profoundly modified the treatment of osteoid osteoma. Rosenthal et al73 reported a statistically significant reduction in hospital stay over the past 20 years by using more conservative and intralesional procedures.

Gangi et al74 reported laser interstitial photocoagulation as a successful mini-mally invasive procedure. In their case series of 114 patients, 112 patients had a visual analog score of 0 at 1 week postop-eratively. Six patients had recurrence and were successfully treated at the second attempt.74 A recent retrospective study re-ported 26 patients treated by percutaneous trephine resection and 100 by percutane-ous interstitial laser ablation.75 Percutane-ous trephine resection had a success rate of 95% at 24 months. Two patients sus-tained skin burns and 1 reported meralgia. Interstitial laser ablation had a success rate of 94% at 24 months, with compli-cations including infection, tendonitis, hematoma, and common peroneal nerve injury. The outcome was worse regardless of treatment method in patients younger than 18 years and in instances where the nidus was 12 mm or larger.75

Percutaneous thermocoagulation of the nidus has been used by de Berg et al,76 who reported 17 patients treated success-fully with this method. Percutaneous ra-diofrequency ablation has been proposed as an alternative to the operative treatment of osteoid osteomas.77 The newer technol-ogy radiofrequency probes allow thermo-coagulation of a region as large as 5 cm using a single probe (Figure 1C). Gener-ally, osteoid osteoma nidus size is up to 1 cm; consequently, the conventional mono-

polar radio frequency probe is adequate. A series of 21 patients with osteoid osteoma in atypical locations (eg, hip, radioulnar joint, phalanx) showed radiofrequency ablation to be successful, albeit with only short-term follow-up data available.78 A 5-year review of radiofrequency ablation confirmed cure in 38 of 39 patients, with 1 case of a broken drill and 1 of infection as the only reported complications.79 Simi-larly, a 5-year case series of 21 patients confirmed a primary cure rate of 89.6% that increased to 93% if a second treat-ment was required.80

With osteoid osteoma affecting the spine, the efficacy and safety of this pro-cedure has been assessed, especially con-sidering the effect of increased temperature in the spinal canal. Dupuy et al81 reported that this technique has no cytotoxic ef-fects into the spinal canal, especially with internally cooled radiofrequency probes. Recently, Peyser et al82 and Neumann et al83 also concluded that CT-guided percu-taneous radiofrequency ablation of osteoid osteomas is a safe, effective, and minimally invasive procedure with a high success rate and no recurrence. Rimondi et al84 reported a series of 557 patients and recommended modifications to electrode parameters, du-ration of ablation with regard to the size, and morphology of the lesion.

Recently, bipolar radiofrequency tech-nology has gained interest in the manage-ment of osteoid osteoma. Some drawbacks of monopolar radiofrequency ablation include skin burns at the site of neutral electrode and aberrant currents causing ir-regular areas of necrosis or inducing heat at metallic implants.85 Another innovative approach with promising results, particu-larly for inaccessible lesions, has been described by Mylona et al,29 who success-fully performed radiofrequency ablation using a probe needle with expandable electrodes. A retrospective review of 81 patients treated either by conventional surgery or minimally invasive techniques for osteoid osteoma of the spine found no difference in outcome.86

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In its 2004 issue, the National Institute of Clinical Excellence stated that “Current evidence on the safety and efficacy of CT-guided thermocoagulation of osteoid osteoma appears adequate to support its use, provided that the normal arrangements are in place for consent, audit and clinical governance.”87

Regardless of the technique used, it is imperative that a biopsy be taken at the time of intervention to confirm the diagnosis. Various methods have been used to determine the complete removal of the nidus. These include immediate radiographs of the patient, tomogram or bone scan of the resected specimen, pre-operative tetracycline labeling and use of intraoperative ultraviolet light, microra-diography, specimen autoimaging on un-derdeveloped film, intraoperative use of bone scintigraphy, and immediate post-operative scintigraphy.26,65,88-92

conclusionOsteoid osteomas are the third most

common benign bone tumor and have a wide variation in presentation. They tend to present in the second decade of life with pain that is worse at night and is relieved by salicylates. Plain radiographs and CT are the mainstays of imaging. Osteoid osteomas consist of a nidus with surrounding sclerotic bone. The natural history of an untreated osteoid osteoma is natural regression, which occurs with-in 6 to 15 years but can be reduced to 2 to 3 years with treatment with aspirin or NSAIDs.59

Various surgical techniques have been discussed in the literature. With the ad-vancement of radiological techniques, percutaneous procedures with less mor-bidity have been introduced. Surgery is still performed in instances where the lo-cation of the lesion precludes percutane-ous techniques. If a complete excision or ablation of the nidus is achieved, the reac-tive bone sclerosis regresses and patients become asymptomatic. In the future, iden-tification of factors that control the local

production of prostaglandins may lead to further treatment modalities.53

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blastic tumor composed of osteoid and atypi-cal bone. Arch Surg. 1935; 31:709-728.

2. Unni KK. Osteoid osteoma. In: Unni KK, ed. Dahlin’s Bone Tumors: General Aspects and Data on 11,087 Cases. 5th ed. Philadelphia, PA: Lippincott Raven Publishers; 1996:121-130.

3. Campanacci M. Osteoid osteoma. In: Cam-panacci M, ed. Bone and Soft Tissue Tu-mours. Padova, Italy: Piccin Nuova Libraria S.p.A.; 1999:391-414.

4. Frassica FJ, Waltrip RL, Sponseller PD, Ma LD, McCarthy EF Jr. Clinicopathologic fea-tures and treatment of osteoid osteoma and osteoblastoma in children and adolescents. Orthop Clin North Am. 1996; 27(3):559-574.

5. Gitelis S, Schajowicz F. Osteoid osteoma and osteoblastoma. Orthop Clin North Am. 1989; 20(3):313-325.

6. Pettine KA, Klassen RA. Osteoid osteoma and osteoblastoma of the spine. J Bone Joint Surg Am. 1986; 68(3):354-361.

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