Osteoid Osteoma: Diagnosis and Treatment

Osteoid osteomas are benign, painful osteogenic tumors of small size (<2 cm) with limited or no growth potential.^1-5 In 1930, Bergstrand first described osteoid osteomas and in 1935 Jaffe⁶ differentiated this entity from other variants. Grossly, they are composed of a small “nidus,” measuring from a few millimeters to 1.5 to 2 cm, which exhibits various portions of calcification and is surrounded by reactive sclerosis and periosteal reaction.^2,5,7,8 Osteoid osteomas are relatively common bone lesions accounting for approximately 10% to 12% of all benign bone tumors and 2% to 3% of all primary bone tumors.^1,9,10 Young men in the first 3 decades of life are most commonly affected (5-25 years; 75% of cases).^11,12 Typically, they are located in the subperiosteal region of the diaphysis of the proximal femur and tibia (>50% of cases).¹¹ Generally, it is speculated that all long bone osteoid osteomas grow subperiostealy and through constant bone remodeling, they finally drift into more endosteal positions.⁸

Despite their predilection for the appendicular skeleton, osteoid osteomas may be encountered in any other bone. Ten percent to 25% of all cases occur in the spine, especially in the posterior vertebral elements (70%-100%) and less commonly in the vertebral body.¹³ Additionally, 13% of osteoid osteomas grow intra-articularly, usually within the hip joint.⁸ In long tubular bones, besides diaphyseal location, they can sit in the epiphysis or metaphysis as well, involving not only the cortex but also the medulla and subperiosteal regions.^7,11

Long-term medical treatment is not always well-tolerated and adequately effective especially in cases where the lesion is located intra-articularly or peri-articularly.^7,8 Patient relief from intense pain necessitates the removal or destruction of the nidus. Although surgical resection of osteoid osteomas has been well-established for many years,^14-18 certain drawbacks such as poor lesion localization, extensive tissue damage, and delayed recovery have encouraged the evolvement of other less invasive percutaneous techniques. Computed tomography (CT)-guided core-drill excision with or without ethanol injection,^19-28 arthroscopic removal,²⁹ cryoablation,³⁰ and thermoablation by laser^31-36 or radiofrequency energy^{5,10,12,36-53} have emerged as effective and minimally invasive alternatives to overcome difficulties and potential hazards and avoid the overuse of health care resources.

This article summarizes data concerning the characteristics and behavior of osteoid osteomas and evaluates all standardized and contemporary fashions of management.

Natural Course-Clinical findings

Figure: Histopathologic features of osteoid osteoma. Nidus displaying well mineralized trabeculae of woven bone (asterisk) lined by numerous active osteoblasts (arrow). In addition, multinucleated giant cell-like osteoclasts can be recognized (arrowhead).

Little is known about the natural history of osteoid osteomas. These tumors are self-limiting and exhibit little or no growth potential. Rarely, malignant transformation into aggressive osteoblastomas has been reported.⁵⁴ Nonetheless, cases of spontaneous healing after a 3- to 7-year period have also been observed.^55,56

The clinical presentation of osteoid osteomas usually consists of nonspecific findings, which in many instances confuse the physician and result in delayed diagnosis. The mean duration of symptoms prior to presentation is 16 months.¹⁶ In typical cases, the clinical hallmark is local and intense pain of sudden onset, not related to prior exercise or trauma, presenting nocturnal aggravation. Pain responds to the administration of salicylates and other nonsteroidal anti-inflammatory drugs. Furthermore, elevated skin temperature, local rubor, and tenderness may be observed in superficial lesions.⁵⁰ Patients with long-standing pain usually end up with limping and related muscle atrophy.⁷ Other possible symptoms vary according to tumor location and include bone widening and growth disturbances or even angular deformities, when it rises near an open growth plate.^5,7,50 Spinal lesions may cause painful scoliosis or painful torticollis.⁷ If located within a joint, tenderness, soft tissue swelling, synovitis with restriction of movement, and contracture are commonly encountered.⁸

The aforementioned clinical setting combined with appropriate radiologic and scintigraphic features should raise a substantially high index of suspicion.

Histopathology

Osteoid osteomas were first described in 1935 by Jaffe⁵⁷ as independent benign neoplasms, distinct from inflammatory processes occurring in bone. They are small-sized bone-forming tumors, with limited growth potential, primarily located within the cortex. Histologically, these lesions consist of a central area of vascularized connective tissue, nidus, that is largely occupied by active, differentiated osteoblasts that produce osteoid or bone. Multinucleated osteoclast can also be encountered as part of active bone remodeling (Figure). Cartilage, bone marrow elements, and mitotic figures are usually absent.^58,59 The nidus is characterized by more abundant mineralization centrally (reflecting a central sclerosis on radiographs) and separation from host bone by a fibrovascular core that is located in the periphery of the sclerotic bone. It is usually surrounded by a distinct zone of reactive sclerotic bone that is not an integral component of the tumor, since it represents a secondary reversible change induced by the exerted pressure of the highly vascular neoplastic tissue on the surrounding trabeculae bone.⁵⁵ The nidus is usually <1 cm in its greatest diameter. Lesions measuring >2 cm should raise the possibility of osteoblastoma.

The pathogenesis of osteoid osteomas remains elusive. Several in vivo and in vitro studies have demonstrated the presence of high levels of prostaglandin E2 and prostacycline directly in nidus tissue, causing local inflammation and vasodilatation. These mediators are considered responsible for reactive sclerosis, nonspecific soft tissue reactive changes and pain that occur in osteoid osteomas. In parallel, the stimulation of unmyelinated neurofibers, accompanying the vessels in the nidus and the surrounding reactive zone, has been also thought to play a significant role in the mediation of pain.^7,55,59-61

Its self-limiting course along with the report of sporadic cases of spontaneous remission represents another clinical feature needing interpretation. It is suggested that like other benign vascular osseous lesions, such as benign bone angiomas, spontaneous thrombosis of the contained blood vessels of osteoid osteomas may be a possible explanation.^55,62

Imaging features

On plain radiographs, the osteoid osteomas “nidus” is typically depicted as an oval or round radiolucent area of approximately 1 cm, surrounded by dense radio-opaque osteosclerosis or periosteal reaction. The amount of the reactive bone may vary from subtle to considerably dense completely obscuring the visualization of the “nidus.”⁷ Intramedullary lesions, which account for 20% of cases, do not present with prominent reactive sclerosis.^11,55 In addition, when the “nidus” is <3 mm it cannot be easily demonstrated.⁸ In 15% of cases, the “nidus” may be overlooked on radiographs.¹¹ Occasionally, the radiolucent nidus may contain various portions of mineralization, appearing as areas of radiodensity on plain radiographs, hence resulting in the formation of the “Jaffe sequestrum.”⁶ This calcification is associated with the maturity of the tumor and becomes more prominent with age.^8,55 Owing to the lack of periosteum, intra-articular lesions are not associated with periosteal reaction, which usually occurs in adjacent bones along with regional peri-articular osteopenia.⁸

Thin-section CT scan (≤2 to 3 mm), adequately reconstructed with a bony algorithm is the ideal imaging modality for delineating a small nidus, especially in the spinal pedicles, laminae, and femoral neck or when intense reactive sclerosis and accompanying periosteal reaction may obscure the lesion. Additionally, dynamic contrast-enhanced CT greatly assists in differentiating osteoid osteomas from chronic osteomyelitis by exhibiting the intense nidus enhancement in contrast with the relatively avascular Brodie’s abscess.^5,11 Other differentials include osteoblastomas, stress fractures, arthritis, etc. In intra-articular lesions, osteophytes, muscle atrophy, local osteopenia, and sclerosis on both sides of the joint may be seen.⁸ Computed tomography scan can be also used as an excellent guidance modality while performing percutaneous therapeutic interventions.⁷ Osteoid osteomas in cancellous bone and joints are often difficult to diagnose by CT alone owing to the lack of perinidal sclerosis.¹¹

On magnetic resonance imaging (MRI), the nidus appears with variable signal intensity depending on size, age vascularity, and the portion of mineralization contained.⁸ Most commonly, it is demonstrated as isointense to the muscle on T1-weighted sequences while on T2-weighted and STIR sequences its signal intensity varies from hypointense to hyperintense or exhibits marked heterogeneity.⁶³ Long-standing lesions may form, with time, low-signal intensity on all pulse sequences.⁶⁴ Gadolinium-enhancement is more prominent in cases of osteoid osteomas with less mineralization, especially on T1-weighted fat suppressed sequences.⁶⁵ Although MRI can identify cancellous osteoid osteomas better than other techniques because of the lack of perinidal alterations, in total, compared with CT, MRI is inferior in demonstrating the nidus and may easily lead to nondiagnostic results.^61,65,66 Assoun et al⁶⁶ comparing the conspicuity of CT and MRI in 19 patients with osteoid osteomas, failed to recognize the lesion in 26% of cases (5/19) with an overall potential for misdiagnosis of 63% (12/19). Accordingly, Davies et al⁶³ recently reported a 35% (15/43) potential for misdiagnosing osteoid osteomas solely with MRI.

However MRI is sensitive in depicting useful but still nonspecific characteristics of the tumor such as bone marrow and soft tissue edema (64% and 47%, respectively).¹¹ These reactions usually subside following medical therapy and relate strongly with the maturity of the lesion; detecting more edema in newer lesions and less in older lesions.⁸ However, these nondiagnostic features can, not infrequently, result in diagnosing more aggressive osseous pathologies such as malignancies or infections and stress fractures, jeopardizing thus the therapeutic outcome.^11,67 For all the above reasons, a consensus has been established supporting that radiologists should take into consideration the variation of appearances of osteoid osteomas and correlate the whole clinical and radiologic setting (radiographs, scintigraphy, and CT scans) with the MRI findings before making a diagnosis. When the suspicion of dealing with an osteoid osteomas is considerably high, the MRI can then be used to localize rather than characterize the nature of the lesion, provided that extra caution is taken regarding the MRI technique performed.⁶³

The latest comparative retrospective study of Liu et al⁶⁷ supported that, in contrast to unenhanced MRI, dynamic gadolinium-enhanced MRI increases the conspicuity in detecting osteoid osteomas and assists greatly in their accurate localization to an equal or even better degree than thin-section CT. Furthermore, Cioni et al⁴⁵ highlighted the usefulness of dynamic contrast-enhanced MRI in detecting residual nidi contrast uptake and persisting marrow edema during the follow-up of post radiofrequency ablation patients with persistent or recurrent pain indicating the need for an additional percutaneous intervention. In the future, open MRI may facilitate, as an effective guiding system, the real-time monitoring of tissue response during radiofrequency ablation while providing extra space for technical maneuvering, with no ionizing irradiation.⁴⁵

Bone scintigraphy is usually positive by showing increased uptake of technetium-99m phosphonates at the tumor site. This intense activity is maintained both at immediate and delayed acquisitions and is usually defined as the “double density sign” composed of a small focus of uptake, representing the nidus, superimposed on a larger area of radioactivity peripherally indicating the reactive sclerosis.^{2,5,7,8,12,50} A bone scan can exhibit radioactivity at the lesion site before radiographic abnormalities become evident. Furthermore it can provide the physician with useful information in patients with painful scoliosis. Although, scintigraphy is sensitive, a negative bone scan does not exclude the diagnosis of an osteoid osteoma especially in the presence of highly suggestive clinical and CT findings.⁵¹ In the past, nuclear medicine was used to confirm intraoperatively the complete eradication of the nidus; however currently, along with radiographs, CT and MRI scans are useful, especially in cases with subtle appearance.^7,11

Treatment Options

Owing to the self-limited nature of osteoid osteomas and their potential of resolving spontaneously after several years, patients are initially prompted to undergo medical treatment. However the vast majority usually continue to report intense pain or can no longer tolerate long-term medication, due to undesirable side effects.⁴⁵ As a result, other therapeutic alternatives have emerged.

Treatment aims at the removal or destruction of the nidus, either in the traditional surgical manner by curettage and en-bloc resection or by other variable percutaneous methods. Current trends have pointed towards the evolution of less invasive and substantially more time and cost-effective therapeutic techniques with radiofrequency ablation being the cornerstone. In 1992, Rosenthal et al³⁷ reported the first clinical successful application of radiofrequency ablation in the treatment of osteoid osteomas. Since then numerous retrospective and comparative studies have established the role of radiofrequency ablation in the treatment armamentary of small but painful benign bone tumors like osteoid osteomas.^{5,10,12,36-53} Nonetheless radiofrequency ablation has been recently used for the treatment of painful bone metastases as well as for recurrences of chordomas, rhabdomyomas, and chondroblastomas.^47,68,69

Radiofrequency ablation is a procedure based on inducing irreversible thermal damage to tissues by using alternating current in the form of high-frequency radioimpulses produced by a generator and dissipating their energy as heat via a needle-electrode, adequately positioned inside the selected area.^1,4 The majority of investigators support that while treating osteoid osteomas, the optimum level for the heating temperature and duration of each radiofrequency ablation session is 85°C to 90°C for approximately 4 to 6 minutes.^4,11,70

Larger osteoid osteomas (>1 cm) or osteoblastomas are advocated to be treated with multiple overlapping radiofrequency ablation sessions by repositioning the needle-electrode.^4,11,70 However, Peyser et al¹ and Martel et al,⁴⁶ in contrast with the results of other experimental and clinical studies,^70,71 exhibited excellent success rates with minimal complications by using water-cooled tip electrodes in larger lesions. Recently, bipolar radiofrequency-technology has gained interest in the management of osteoid osteoma. The efficacy of monopolar radiofrequency ablation is most commonly hampered by the incidence of skin burns at the site of neutral electrodes and the formation of aberrant currents resulting in irregular shape of necrosis or inducing heat at metallic implants. These drawbacks can be overcome by using bipolar probes.⁷² Another innovative approach with promising results was introduced by Cioni et al,⁷³ who successfully performed radiofrequency ablation by using probe needles with expandable electrodes in osteoid osteoma with medium to large size (9.7±4.4 mm) lesions.

The steps of the radiofrequency ablation procedure per se have been scrupulously described.⁴ In the present study, the authors prefer to highlight special technical considerations. In general, when peripheral lesions and younger patients are treated percutaneously, general anesthesia should be preferred to attain patient’s stability and sufficient control of anxiety.^2,11,49 Exceptionally, in spinal lesions extra care should be taken for the early detection of impending damage to neural structures so, conscious sedation or local anesthesia should be performed.¹¹

The access route should be designed in the CT-suite, usually preferring the nonaffected, opposite cortex side, hence avoiding immediate contact with adjacent neurovascular bundles and unwanted positioning of the probe-electrode close to the skin.⁴⁵ Thermal skin damages can also be avoided by using specially designed insulating sheaths or by slightly withdrawing the penetrating cannula.^4,7,45 Although potentially effective alternatives exist, most investigators prefer the surgical access for lesions in proximity (<3 cm) with the skin and neurovascular bundles (≤1.5 cm).^11,45 However, lesions of the femoral neck or closely sited to an open growth plate can be successfully approached by adequately rotating the affected limb and angulating the access penetrating systems.⁴

Radiofrequency ablation of spinal lesions remains a challenging but still controversial field. In 1998, Osti and Sebben³⁸ were the first to successfully use this technique in the management of spinal osteoid osteomas. According to Dupuy et al,⁷⁴ radiofrequency ablation can be safely applied in the spine provided that the lesion’s size is <12 mm and it is surrounded either by cortex or a thick sclerotic “insulating” rim. In this experimental study no cytotoxic alterations were recorded in the spinal canal. The so called “heat sink” effect, due to the presence of the rich epidural venous plexus and the cerebrospinal fluid circulation, served as the theoretical rationale for this observation.⁷⁴ However, for the past decade several reports have tried to assess clinically radiofrequency ablation’s effectiveness and safety at this complex anatomic site, coming up with inconsistent results.^{12,38,44,51-53} Vanderschueren et al¹² in 2002, reported their experience with a few cases that resulted in a success rate not >50%, with surgery being the only option in cases of failure. In view with a substantial risk of harming noble spinal structures, lesions located closer than 1 cm to neural elements are not good candidates for radiofrequency ablation and should be referred for surgical excision.^5,42,44,53

In contrast to open surgery, lack of histological proof is a major concern regarding radiofrequency ablation and other percutaneous methods. Although biopsy specimens can be obtained through the initial access procedure, it is not routinely performed and it is not always feasible to obtain sufficient specimen of hard osteoid tissue given the small caliber of the needles used.⁴⁴ The latter justifies the relative low percentage of diagnostic results (≤50%) yielded from most percutaneous biopsies of osteoid osteomas.^5,12,21,47 In a wide review of the literature, osteoid osteoma tissue sampling is rarely performed and usually provides nondiagnostic information; however paradoxically post-radiofrequency ablation clinical outcomes are excellent.⁷ The combination of multiple imaging modalities and clinical symptoms seem to improve greatly the diagnostic confidence and assist physicians with the correct patient selection.⁵ As suggested by Campanacci et al,¹⁴ biopsy should be reserved only in cases where imaging and clinical findings are not in accordance, or when the imaging profile is unusual.

Radiofrequency ablation of osteoid osteomas has advanced in parallel with surgical interventions. A literature search of radiofrequency ablation articles yielded approximately 789 cases of osteoid osteomas, of all locations, treated with percutaneous radiofrequency ablation since 1992 (Table 1). Series with a sufficient number of patients (n>20) and mean follow-up (>22 months) included a total of 535 patients of whom 463 (86.5%) were successfully treated with initial radiofrequency ablation. In the remaining 72 patients (13.4%), initial radiofrequency ablation failed and a subsequent radiofrequency ablation session was performed with success in 49 (68%) of these initially failed cases resulting thus in a total secondary success rate of 95.7% (512/535). The remaining 23 patients (32%) were either treated surgically (8/23) or left with residual but tolerable pain or eventually were scheduled for a third radiofrequency ablation session. When biopsies were performed, histological verification was available in 8.3% to 75% of cases treated with radiofrequency ablation (Table 1). Nonetheless, the method was not associated with any major complications, except for 1 case of pyogenic arthritis. The overall incidence of complications remains satisfactorily low (10 complications/535 cases: 1.8% [Table 1]). In agreement with published data, the authors have also experienced positive clinical response by performing radiofrequency ablation to 26 consecutive patients with appendicular osteoid osteomas, from 2002 until 2007. Reported primary and secondary clinical success was 88.5% and 92.3%, respectively, in a follow-up period of 6 to 50 months. Finally, 1 (3.8%) of the 2 untreated patients underwent curettage and the other patient (3.8%) refused further treatment and had persistent, but not restrictive, tolerable pain. Two cases of arthritis, 1 of which was complicated with infection and cutaneous fistula, were encountered in the knee and the hip joint, respectively.

In an attempt to identify impending risk factors that jeopardize the clinical importance of radiofrequency ablation and favor recurrence, most authors agree that lesion size (≥10 mm) matters. It is well known that radiofrequency ablation induces overlapping spherical areas of coagulative necrosis measuring approximately 10 mm^4,50; therefore, it is possible that parts of the tumor outside these spheres are not totally ablated, especially when its shape is more elongated or oval. Multiple needle positions or the use of cooled-tip electrodes represent the recommended alternatives.^1,4,46,68,70 Additionally, Rosenthal et al⁴⁴ and Vanderschueren et al¹² support that history of prior treatment (radiofrequency ablation or surgery) with a pain-free interval followed by relapse is related to a poor-post second radiofrequency ablation clinical outcome but this conviction is not uniformly accepted as other investigators presented with different results.⁴⁸ There is variety in the duration of follow-up periods among several studies that should be extended beyond 24 months to meet with orthopedic standards and produce reliable results.⁴⁴ However, Cribb et al⁴⁸ found in a series of 45 patients that nondiaphyseal location is strongly related (P<.01) to recurrence. A possible explanation for this is that diaphyseal lesions are more “contained” by the surrounding cortical thickening and thus, it is easier to be treated effectively with radiofrequency ablation. Apart from size and shape, recurrences occurring within the first year post treatment are most commonly attributed to inaccurate needle placement owing either to poor visualization of the nidus or to complex anatomy with difficulties in access.^12,35 However, for recurrences that present after a prolonged symptom-free interval (≥12 months), it is speculated that they are stimulated by the regeneration of a new tumor.³⁵ If the latter proves to be true along with the difficulty in localizing the lesion, it may justify the occurrence of post surgical recurrences as well.

Surgical interventions of osteoid osteomas require wide exposure of the bone surrounding the nidus and use gross features for localization.¹⁴ They include mainly en-bloc resection, wide excision, and the less invasive method of unroofing with intralesional excision-curettage of the nidus. With the latter, less aggressive approach, the sclerotic–reactive bone is gradually removed in thin layers, by using gouges or high speed rotating burrs. As a result, the reddish, punctiform nidus is revealed and subsequently curetted out of its bed and sent to pathology. The walls of the nidus are burred out for 1 to 2 mm in all directions and the remaining cavity is occasionally filled with the pieces of the removed reactive bone.¹⁴

Surgical success occurred in 376 of 396 reviewed cases (94.9%), with a sufficient mean follow-up period of 30 to 156 months (Table 2). Despite these results, the method bears the criticism of causing extensive tissue damage, thus resulting in considerable morbidity, delayed recovery, and further cost for the patient and the institutions. The intraoperative difficulty of precise lesion localization requires, even with the improved less invasive curettage techniques, substantial bone removal, resulting in consecutive structural bone weakness that, not unusually, necessitates internal fixation, bone grafts and prolonged postoperative immobilization, additional physical therapy, and restriction of activity.

Osteoid osteomas have a propensity for long tubular, weight-bearing bones, especially the femur, where open resections may impair not only the vascular supply of the femoral head but also the integrity of the related articular and epiphyseal surfaces.^10,11 It is noteworthy that despite its aggressive style, surgical efficacy is not infrequently hampered by failures as well (20 of 396; 5%; Table 2). Among several published studies, related complications are not negligible with the rate of minor complications ranging from 7% to 45.5% combined, in most studies, with fractures and other complications (Table 2). The Rosenthal et al⁷⁵ comparative study has also shown that radiofrequency ablation is essentially equivalent to surgery (primary success radiofrequency ablation: 88% versus 91% and secondary success radiofrequency: 100% versus 90%) and is preferred for the treatment of osteoid osteomas in the extremities due to its less invasive nature.

In agreement with the recommendation of most authors surgery should be reserved for either spinal or appendicular lesions in proximity with neurovascular elements, for cases where the histology is unclear and also after repeated failures of percutaneous ablation or resection.^5,11,42,44 Additionally, orthopedic surgeons favor the use of the less invasive curettage for subperiosteal lesions that are easily accessible and percutaneous methods do not offer any significant advantage.^17,18

Computed tomography-guided percutaneous resection requires large skin incisions extending deep into the soft tissues and uses various trephines and drilling systems with relative large caliber, ranging from a 14 G cutting needle to a 9-mm drill bit, so as to achieve complete eradication of the nidus.¹¹ As a result, the term “minimally invasive” should be used with caution and skepticism when comparing this technique with radiofrequency ablation and the other percutaneous ablative methods. Curative rates reach up to 89.5%, 129 successfully treated cases of 144 reviewed cases with a mean follow-up period from 9.8 to 44 months (Table 3) for initial percutaneous resection. The method can be performed either on inpatient or on outpatient basis but procedural duration is longer than other ablative techniques.¹¹

The drilling process usually demands more aggressive manipulations and can lead to fractures with considerably longer restriction of activity and weight bearing for up to 3 months⁷ compared with a maximum 6 weeks of limitation of strenuous sports, in cases of radiofrequency ablation.¹¹ Owing to the heat produced by the high rotation speed of the drilling instruments, especially when powered drills are used without cooling, more extensive tissue damage is caused in the form of skin burns, bone weakening, osteonecrosis, and muscle hematomas.^5,42 Further complications include irritation of adjacent nerves and osteomyelitis, and although the method provides larger tissue specimens for definite histological diagnosis,^5,42 reported overall complication rates may reach up to 24% (Table 3). As a result, CT-guided percutaneous resection is not uniformly accepted as a minimally invasive method for the management of osteoid osteomas and further technical optimization is necessitated.

Taking advantage of the augmentation of cellular desiccation induced by ethanol, several investigators have combined its use with percutaneous resection with promising preliminary results.^27,28 These outcomes refer to small case studies with short follow-up and further workup is needed, taking into account the nonspecific effects of ethanol instillation on the surrounding soft tissues and the fact that drill ablation per se can successfully destroy the nidus.^7,11 Ethanol injection has also been used post-radiofrequency ablation,² but it is similarly questionable whether the addition of ethanol increases the effectiveness when compared with the use of radiofrequency alone. Likewise, because limited data are available future randomized comparative studies are needed.

Laser technology was first used in the treatment of tumors by Bown in the 1980s.¹¹ Gangi et al^31,32 introduced laser energy in the management of osteoid osteomas in the late 1990s and since then it has been applied to approximately 153 patients (Table 4). Laser energy can be transmitted through optic fibers (400 µm) into selected tissues and cause direct cellular thermal injury and producing thus controlled areas of coagulative necrosis. Like radiofrequency ablation, the extent of necrosis is limited by the cooling effect of local blood flow.¹¹

Laser interstitial thermal therapy compared to radiofrequency ablation ensures, in proportion to the energy delivered, better predictability and control of the size of produced necrosis.^11,35 Laser technology has been used successfully in the spine as well. Gangi et al,³¹ after treating 3 cases of spinal osteoid osteomas with laser photocoagulation, initially supported its use with the condition that the laser needle should be positioned centrally into the nidus, at least 8 mm away from neural elements. Recently, the same author successfully treated, with laser ablation, 5 cases of osteoid osteomas that were located closer than 8 mm to adjacent nerve roots by slowly infusing normal saline into the epidural or periradicular space so as to avoid thermal injury.³⁵ By inference, its use has been proposed for all osteoid osteomas, even those located in the spine where accuracy is needed.³⁵ It can be also performed on an outpatient basis, uses a less invasive approach, favors rapid recovery, does not interact with pacemakers, and can safely be repeated, like radiofrequency, in cases of initial failure but with a higher, yet secondary success rate of 100% in all reported series (Table 4).^11,35 Primary success rate is also slightly superior and it is estimated at 92.8% with an overall of 142 initial successes of 153 reviewed cases with a mean follow-up period ≤58.5 months (Table 4). Although the results are promising, this technique is still evolving, has a higher cost, is not oblivious to potential failure (7.2%; 11 failures of 153 reviewed cases; Table 4), requires specialized personnel, cannot provide reliable histological results,¹¹ and presents with higher, in total, than radiofrequency ablation minor complication rates (Table 4).

Conclusion

The results of this review article suggest that radiofrequency ablation should be considered as the preferred percutaneous technique for the treatment of deeply cited or inaccessible, preferably nonspinal, osteoid osteomas with excellent initial clinical response and acceptable failure and complication rates. Owing to its minimally invasive nature, it can be safely and effectively repeated for the management of persistent or recurrent lesions, without jeopardizing prognosis. Opinion exists that the efficacy of the method will be further increased with the introduction of new technical advances such as bipolar technology, cooled-tip, and expandable probes. Moreover, it does not necessitate prolonged hospital stay and favors rapid recovery, reducing thus considerably not only the economical but also the social costs due to restriction or potential impairment of activity.

However, clinical experience with surgical interventions is not negligible and, according to the established consensus their use should be reserved for readily accessible subperiosteal lesions and lesions in proximity with neurovascular structures, when the histology is unclear and where percutaneous methods have repeatedly failed.

However, serious concerns should be raised when CT-guided resection is considered as a safe alternative owing to the relatively high associated morbidity rates presented in some series.

Laser interstitial thermal therapy as an exciting and upcoming alternative, creates new horizons in the treatment of all osteoid osteomas regardless of location, especially in spinal lesions where accuracy and safety are most needed; by exhibiting more than promising primary and secondary success rates.

References

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Authors

Drs Papathanassiou, Petsas, Nilas, and Siablis are from the Department of Radiology and Dr Megas is from the Orthopedic Clinic, University Hospital, Patras, Greece; and Dr Papachristou is from the Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.

Drs Papathanassiou, Megas, Petsas, Papachristou, Nilas, and Siablis have no relevant financial relationships to disclose. Dr Morgan, CME Editor, has disclosed the following relevant financial relationships: Stryker, speakers bureau; Smith & Nephew, speakers bureau, research grant recipient; AO International, speakers bureau, research grant recipient; Synthes, institutional support. Dr D’Ambrosia, Editor-in-Chief, has no relevant financial relationships to disclose. The staff of Orthopedics have no relevant financial relationships to disclose.

The material presented at or in any Vindico Medical Education continuing education activity does not necessarily reflect the views and opinions of Vindico Medical Education or Orthopedics. Neither Vindico Medical Education or Orthopedics, nor the faculty endorse or recommend any techniques, commercial products, or manufacturers. The faculty/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 utilizing any product.

Correspondence should be addressed to: Zafiria G. Papathanassiou, MD, Department of Radiology, University Hospital, Patras, Rio 26504, Greece.