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A young male in his mid-teen years presented with severe back pain for 3 months and was subsequently diagnosed with osteoid osteoma in the left superior articular process of the L4 vertebra. Initial treatment with non-steroidal anti-inflammatory drugs provided temporary relief. Due to concerns about scoliosis progression along with unrelieved pain, a multidisciplinary team recommended endoscopic excision of the osteoid osteoma. The procedure resulted in complete pain relief and an improvement in the scoliosis curve from 22° of Cobb's angle to 12 degrees at the 8-month follow-up., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: Visfatin is currently a cytokine that is extensively researched in the field of bone diseases. In this prospective study, we aimed to investigate the potential of serum visfatin levels as a biomarker for the diagnosis of osteoid osteoma., Patients and Methods: This study included a cohort of 20 patients diagnosed with osteoid osteoma (Group 1) and 30 healthy individuals (Group 2). The age, gender, cyst sizes, and visfatin values of all participants were documented and analyzed., Results: There was a significant difference in visfatin levels between the two groups. The median visfatin level in Group 1 was 6.13 ng/ml (IQR: 4.21-8.08), while in Group 2, it was 15.83 ng/ml (IQR: 11.11-20.6). The difference was statistically significant (p<0.000). The optimal cut-off value for visfatin was found to be 7.74 ng/ml, which had a 93% sensitivity and 78% specificity.  An area under the curve of receiver operating characteristic (ROC) analysis of 0.85 indicates good diagnostic performance., Conclusions: Our study revealed a significant decrease in visfatin levels among patients diagnosed with osteoid osteomas in comparison to the healthy control group. The ROC analysis revealed that visfatin exhibited a commendable diagnostic capacity, indicating its potential utility as a biomarker for osteoid osteoma.

Congenital/neonatal bone neoplasms are extremely rare. We present the case of a patient with a neonatal bone tumor of the fibula that had osteoblastic differentiation and a novel PTBP1::FOSB fusion. FOSB fusions are described in several different tumor types, including osteoid osteoma and osteoblastoma; however, these tumors typically present in the second or third decade of life, with case reports as young as 4 months of age. Our case expands the spectrum of congenital/neonatal bone lesions. The initial radiologic, histologic, and molecular findings supported the decision for close clinical follow-up rather than more aggressive intervention. Since the time of diagnosis, this tumor has undergone radiologic regression without treatment., (© 2023 Wiley Periodicals LLC.)

Osteoid osteomas typically arise in the long bones of extremities. Patients often report pain relieved by NSAIDS, and radiographic findings are often sufficient for diagnosis. However, when involving the hands/feet, these lesions may go unrecognized or misdiagnosed radiographically due to their small size and prominent reactive changes. The clinicopathologic features of this entity involving the hands and feet are not well-described. Our institutional and consultation archives were searched for all cases of pathologically confirmed osteoid osteomas arising in the hands and feet. Clinical data was obtained and recorded. Seventy-one cases (45 males and 26 females, 7 to 64 years; median 23 years) arose in the hands and feet, representing 12% of institutional and 23% of consultation cases. The clinical impression often included neoplastic and inflammatory etiologies. Radiology studies demonstrated a small lytic lesion in all cases (33/33), the majority of which had a tiny focus of central calcification (26/33). Nearly, all cases demonstrated cortical thickening and/or sclerosis and perilesional edema which almost always had an extent two times greater than the size of the nidus. Histologic examination showed circumscribed osteoblastic lesions with formation of variably mineralized woven bone with single layer of osteoblastic rimming. The most common growth pattern of bone was trabecular (n = 34, 48%) followed by combined trabecular and sheet-like (n = 26, 37%) with only 11 (15%) cases presenting with pure sheet-like growth pattern. The majority (n = 57, 80%) showed intra-trabecular vascular stroma. No case showed significant cytology atypia. Follow up was available for 48 cases (1-432 months), and 4 cases recurred. Osteoid osteomas involving the hands and feet follow a similar age and sex distribution as their non-acral counterparts. These lesions often present with a broad differential diagnosis and may initially be confused with chronic osteomyelitis or a reactive process. While the majority of cases have classic morphologic features on histologic exam, a small subset consists solely of sheet-like sclerotic bone. Awareness that this entity may present in the hands and feet will help pathologists, radiologists, and clinicians accurately diagnose these tumors., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Objective: This project evaluates a cranial lesion from a Hellenistic-era individual excavated by the Muğla Archaeological Museum in Gülağzı, Turkey., Materials: An osseous tumor measuring 3.02 × 3.54 × 2.98 cm originating from the occipital bone of a probable young adult male., Methods: The tumor was examined using gross morphological inspection, plain radiography (x-ray), and computed tomography (CT) imaging to identify potential differential diagnoses for the osseous cranial tumor., Results: The lesion in question displays features highly consistent with both osteoid osteoma and osteoblastoma. The tumor had a non-sclerotic, sharply demarcated border, a radiolucent nidus measuring less than 2 centimeters in diameter, and homogeneous sclerotic bone surrounding the nidus., Conclusions: Differential diagnosis determined the osseous tumor to be a benign neoplasm, and in this case the features of the tumor are highly consistent with a diagnosis of either osteoblastoma or osteoid osteoma., Significance: The identification of novel neoplastic cases in paleopathology represents an important contribution to ongoing discussions regarding the temporality and regional variability of neoplastic conditions in the past. Additionally, a rigorous diagnostic study augmented by x-ray, CT scans, and 3D modeling provides data that can be utilized in future paleopathological studies., Limitations: Diagnostic interpretation would be aided by histological examination of the tumor, which was impossible in this case. Histological examination would provide a definitive diagnosis., Suggestions for Further Research: Given the high incidence of benign tumors in the clinical literature but a paucity of reports in the paleopathological record, further research is indicated to better understand the implications of benign neoplasms in antiquity., Competing Interests: Competing Interests The authors have no competing interests to report., (Copyright © 2023. Published by Elsevier Inc.)

Abstract: Intra-articular osteoid osteoma may simulate arthritis, due to the intra-articular presence of prostaglandin, which leads to synovitis, joint effusion, pain, and high local temperature. Also, intra-articular osteoid osteoma may present with minimum or no cortical thickening. Therefore, a high suspicion is needed for a correct and early diagnosis. Perfusion weighted imaging, such as dynamic contrast-enhanced imaging, can aid in the localization of the tumor nidus, seen as an early arterial-phase focal enhancement after the gadolinium injection, with fast washout, as a result of its hypervascularity., Competing Interests: The authors declare no conflict of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Osteoid osteomas of the foot are rare, with a varying and atypical clinical as well as radiological presentation impeding early diagnosis and treatment. The aim of the present multicentre study was to 1) analyze epidemiological, clinical and radiological findings of patients with foot osteoid osteomas and to 2) deduce a diagnostic algorithm based on the findings., Methods: A total of 37 patients (25 males, 67.6%, mean age 23.9 years, range 8-57 years) with osteoid osteomas of the foot were retrospectively included, treated between 2000 and 2014 at 6 participating tertiary tumor centres. Radiographic images were analyzed, as were patients' minor and major complaints, pain relief and recurrence., Results: Most osteoid osteomas were located in the midfoot (n = 16) and hindfoot (n = 14). Painful lesions were present in all but one patient (97.3%). Symptom duration was similar for hindfoot and midfoot/forefoot (p = 0.331). Cortical lesions required fewer x‑rays for diagnosis than lesions at other sites (p = 0.026). A typical nidus could be detected in only 23/37 of x‑rays (62.2%), compared to 25/29 CT scans (86.2%) and 11/22 MRIs (50%). Aspirin test was positive in 18/20 patients (90%), 31 patients (83.8%) underwent open surgery. Pain relief was achieved in 34/36 patients (outcome unknown in one), whilst pain persisted in two patients with later confirmed recurrence., Conclusions: As previously reported, CT scans seem to be superior to MRIs towards detection of the typical nidus in foot osteoid osteomas. In patients with unclear pain of the foot and inconclusive x‑rays, osteoid osteoma should be considered as differential diagnosis., (© 2021. The Author(s).)

Objectives: To analyze the causes of misdiagnosis and missed diagnosis in spinal osteoid osteoma, and to put forward solutions to improve diagnosis accuracy and treatment efficacy in patients., Methods: We performed a retrospective cohort study on patients with spinal osteoid osteoma in Beijing Jishuitan Hospital from January 1983 to September 2019. All patients underwent surgery. The outcome measures were the extent of local pain, nocturnal pain, radicular symptoms of extremities after surgery, and reduction or disappearance of lesions on CT after surgery., Results: Thirty-seven patients with spinal osteoid osteoma were recruited in the study. A total of 27% were female, and the mean (SD) age at diagnosis was 21.3 (8.7) years. A total of 87.0% of patients presented with nocturnal pain, and 94.7% of patients were responsive to NSAIDS treatment. The mean (SD) time from the initial onset of symptoms to the final diagnosis was 14.7 (12.5) months. Only four of 37 (10.8%) patients were correctly diagnosed with spinal osteoid osteoma on the first visit to the local hospital. CT is associated with a higher diagnosis rate than X-ray or MRI on the first visit. Surgical navigation was used in 88.9% of patients who underwent curettage resection, and in 10% of patients who underwent en bloc resection. A total of 37 of 37 patients (100%) reported relief of local pain and radicular symptoms of extremities after surgery, and no recurrence of tumors was found during follow-ups., Conclusions: Spinal CTs are recommended to be performed if osteoid osteoma is suspected based on clinical manifestation, including nocturnal pain and responsiveness to NSAIDS treatment, to avoid misdiagnosis and missed diagnosis of spinal osteoid osteoma., (© 2022 The Authors. Orthopaedic Surgery published by Tianjin Hospital and John Wiley & Sons Australia, Ltd.)

This report describes osteoblastoma of the temporal bone found on a well-child visit. The relevant clinical, radiographic, and histologic features are described. The tumor was completely resected via a transtemporal approach. The differential diagnosis for these tumors include osteoma, giant cell tumor, histiocytosis, aneurysmal bone cyst and sarcoma. Histologic findings are critical for determining the proper diagnosis., (Copyright © 2021, Otology & Neurotology, Inc.)

Bone tumors and tumor-like lesions (pseudotumors) are not uncommonly encountered as asymptomatic findings on imaging, or as symptomatic lesions clinically. Radiographic imaging is the first diagnostic tool for their management strategy, since the symptoms are commonly non-specific, such as pain, swelling, and redness. Image findings must be analyzed with attention to the specific features such as lesion location, margination, zone of transition, mineralization, size and multifocality, soft tissue component and/or loco-regional extent. Cross-sectional imaging including CT and MRI serve as complementary methods, providing additional information with respect to the lesion characterization, mineralization, extent and involvement of the adjoining soft tissues. Clinical and/or key imaging features aid in limiting the differential diagnostic possibilities and serve as a guide in determining the benignity or malignancy of the tumor as well as to exclude pseudotumors. This article reviews the key imaging features of foot and ankle lesions. Benign bone lesions include simple and aneurysmal bone cysts, lipoma, hemangioma, chondroblastoma, enchondroma, osteoid osteoma, osteoblastoma, and giant cell tumor. Locally aggressive intermediate category lesion includes hemangioendothelioma. Malignant lesions include osteosarcoma, Ewing's sarcoma, chondrosarcoma. Pseudotumors such as fibrous dysplasia, hemophilic pseudotumor, gout and Madura foot are also discussed with illustrative case examples., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Purpose: To identify the clinical features of intra-articular osteoid osteoma (OO) of the hip, to evaluate the clinical effect of arthroscopic excision for intra-articular OO, and to summarize the characteristics of revision cases of hip OO and the revision surgery under arthroscopy in these cases., Methods: We retrospectively reviewed the data of 25 patients who underwent arthroscopic excision of hip OO. The case series included 10 patients who underwent revision surgery. Lesion location, presenting symptoms, and symptom duration were analyzed; postoperative improvement was assessed using the modified Harris Hip Score (mHHS) and International Hip Outcomes Tool (iHot-12) score. We examined the reasons for revision surgery and the characteristics of OO progression after the first surgery., Results: The most common presenting symptom was groin pain that was relieved by nonsteroidal anti-inflammatory drugs (NSAIDs). Varying degrees of limitation of range of motion (ROM) were present in all patients. The osteosclerosis around the tumor nest on computed tomography (CT) scan is a characteristic radiographic feature in this disease. However, the classic radiographic feature was apparent on plain x-rays in only 2 of 25 patients. As a kind of efficient radiological method, magnetic resonance imaging (MRI) can help in distinguishing OO from femoroacetabular impingement (FAI), as the latter is characterized by a large effusion and bone marrow edema at the atypical site of impingement. For the patients who had only 1 arthroscopic resection, the mean (± standard deviation) mHHS and iHot-12 scores were 70.30 ± 9.06 (range 51 to 86) and 75.07 ± 7.69 (57 to 88), respectively. At last follow-up, the mean scores were 98.30 ± 2.15 (94 to 100) and 97.76 ± 2.04 (94 to 100). For revision cases, the mean mHHS and iHot-12 scores were 68.55 ± 3.77 (60 to 72) and 67.88 ± 5.39 (56 to 76). At last follow-up, the mean scores were 97.11 ± 2.47 (94 to 100) and 95.22 ± 1.78 (94 to 100). In the present study, 24 of 25 patients (96%) reached the minimal clinically important difference (MCID) of mHHS, and 21 of 22 patients (95.2%) reached the MCID of iHot-12. Among the revision patients, the most common misdiagnosis at first surgery was FAI. Another feature is that a wrong diagnosis or incomplete intra-articular OO resection can stimulate the tumor and cause an inflammatory reaction and rapidly progressive OA, necessitating prompt revision surgery for complete removal. The degree of joint degeneration was related to the time since the first operation., Conclusion: OO of the hip joint typically presents with pain and limited joint activity. Misdiagnosis as FAI or synovitis is common, and CT scan is very helpful for accuracy diagnosis. Arthroscopic excision appears to be an effective method for the treatment of OO of the hip joint., Level of Evidence: IV, case series., (Copyright © 2021 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Competing Interests: Competing interests: None declared.

An adult man presented with a 5-month history of anterior right shoulder pain. He denied previous trauma or night pain. On the otherwise normal physical examination, pain was elicited in maximum abduction and external rotation. Radiographs were negative. The primary imaging findings were bone marrow oedema of the inferomedial proximal metaphysis of the humerus on MRI and cortical demineralisation on CT located posteromedially. A superficial elevation was also observed around the lesion. A provisional diagnosis of an osteoid osteoma was made based on these imaging findings. Arthroscopic excision of the lesion was performed, and histopathological examination confirmed the diagnosis of an osteoid osteoma. Diagnosis of intra-articular osteoid osteomas may be challenging due to atypical symptomatology and lack of pathognomonic imaging findings. Arthroscopic excision of such lesions in the shoulder is a safe and reliable option and should be considered as the treatment of choice., Competing Interests: Competing interests: None declared., (© International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Enchondromas originating in the epiphyses of long bones are rare and epiphyseal osteoid osteomas are also uncommon. Diagnosis can become elusive when enchondromas or osteoid osteomas occur in atypical locations and present with nonspecific clinical and imaging characteristics., Case Presentation: We report a case of epiphyseal enchondroma of the left proximal femur in a 15-year-old girl with a 2-month history of left lower extremity pain. Preoperative CT displayed thickened cortex in the anterior surface of the left proximal femur with specks of calcification and inhomogeneity of the adjacent bone marrow cavity. She was diagnosed with osteoid osteoma. Postoperative pathological examination of surgically excised specimens revealed a diagnosis of enchondromas., Conclusions: Our case highlights that enchondroma should be considered in lesions of the epiphysis.

Purpose: To assess efficacy and safety of imaging-guided radiofrequency ablation (RFA) of Osteoid Osteoma (OO) in both typical and atypical sites., Methods and Materials: Between January 2014 and March 2019, 102 consecutive percutaneous RFA were performed and retrospectively reviewed. The procedures were performed using a RFA bipolar ablation system (Covidien, exposed tip of 0.7-1cm), under Computed Tomography (CT) guidance or using a navigation system (Masmec) under CT and Cone Beam CT (CBCT) guidance. Patients were followed up over 24 months. Clinical success and recurrences were considered on the base of established criteria. In patients with clinical failure and/or imaging evidence of relapse, retreatment was considered., Results: Administered power per-procedure was ≤8 W (mean temperature, 90°C). The pre-procedure average value of visual analog scale (VAS) was 8.33+/-0.91. Primary and secondary success rate 96.08% (98/102) and100% (102/102), respectively. No major complication was described. Technical success was proved in every patient by CT scan acquisition after needle positioning. Relapse and tumour location were significantly correlated (p-value = 0.0165). The mean dose-length product was 751.55 mGycm2. Advanced bone healing was noted in 68 lesions after 1y-follow up and in 86 lesions after 2y-follow up., Conclusion: Imaging-guided percutaneous RFA is a highly effective technique for OO, both in typical and atypical sites. CT or CBCT guidance, navigation systems and operator experience grant the technical success, which is the most crucial parameter affecting outcome., Competing Interests: The authors have declared that no competing interests exist.

A 22-year-old man is referred to the orthopaedic surgeon. He has pain, mostly at night, in his proximal right tibia that greatly reduces with NSAIDs. The CT scan shows a focal lucent zone, called a nidus, in the tibia cortex, surrounded by reactive, sclerotic bone. This is typical for an osteoid osteoma, a benign bone tumour.

Objectives: CT-guided radiofrequency ablation (CT-RFA) is considered to be the gold standard for treatment of osteoid osteoma (OO) yet treatment failures (TFs) continue to be reported. This systematic review was conducted to evaluate factors associated with TF, such as ablation time, lesion location, and patient age as well as evaluating how TF has trended over time., Methods: Original studies reporting on patients undergoing CT-RFA of OO published between 2002 and 2019 were identified. TF was defined as patients with (1) recurrent or persistent pain +/- (2) imaging evidence of persistent OO. TFs were subdivided into those occurring after the index procedure (primary TF) or those occurring after repeat RFA (secondary TF). Subgroup analysis was performed for TF based on the study date (2002-2010 or 2010-2019), time duration of ablation at 90 °C (6 min or > 6 min), patient age, and tumor location (spinal vs. appendicular)., Results: Sixty-nine studies were included for a total of 3023 patients. The global primary TF rate was 8.3% whereas the secondary TF rate was 3.1%. The TF rate reported in studies published after 2011(7%) was about half that during the earlier time period 2002-2010 (14%). There was no statistical difference in TF corrected for age, OO location, or duration of ablation (respectively p = 0.39, 0.13, and 0.23). The global complication rate was 3%, the most frequent being skin burns (n = 24; 0.7%)., Conclusions: A decrease in TF observed between 2011-2019 compared to 2002-2010 may reflect improvements in operator technique or advancements in equipment. Duration of ablation, patient age, or location of OO failed to significantly correlate with TF., Key Points: • CT-guided radiofrequency ablation of osteoid osteomas is a safe technique with a low rate of treatment failure (8.3% failure rate after the primary radiofrequency reducing to 3.1% following a secondary treatment). • The treatment failure rate has decreased over time, possibly due to an improved understanding of the disease process, better technique, and advances in equipment. • Duration of ablation, patient age, or lesion location did not significantly correlate with treatment failure.

Aim: To assess the clinical success rate of percutaneous radiofrequency and laser ablation of osteoid osteomas in older adults., Materials and Methods: Percutaneous radiofrequency or laser ablation was performed in 43 patients (35 years and older) with osteoid osteoma to achieve definitive cure in this retrospective study. The clinical success rate was defined as complete pain relief determined by numeric rating scale (NRS) scores (pre-procedural and post-procedural at 1-week, 6-week, and 2-year intervals). Tumour characteristics, technical success, procedural details, biopsy results, and complications were documented., Results: Forty-four osteoid osteomas were ablated in 43 patients, and all procedures were technically successful. The clinical success rates were 95.2% (41/43), 93% (40/43), and 93.2% (41/44) at 1-week, 6-week, and 2-year post-procedural intervals. The acute complication rate was 2.3% (1/44; meningeal perforation following epidural anaesthesia). No delayed complication was documented., Conclusion: Osteoid osteomas are not unique to the paediatric and young population, and safe and effective definitive treatment of these benign tumours in older adults can be achieved by percutaneous radiofrequency and laser ablation with excellent patient outcomes., (Copyright © 2020 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.)

Purpose: Osteoid osteomas are benign and nonprogressive lesions. The clinical presentation of osteoid osteoma is typical with night pain responsive to nonsteroidal anti-inflammatory agents. The typical radiological appearance is lucent nidus and adjacent reactive sclerosis. The most traditional management of osteoid osteoma is surgical removal which is associated with significant morbidity. This article aims to demonstrate our single-center experience of 55 patients with osteoid osteoma treated with percutaneous radiofrequency ablation (RFA)., Methods: Fifty-five symptomatic patients who were seen at our orthopedics outpatient clinics, diagnosed with osteoid osteoma, and referred to interventional radiology department between May 2015 and April 2019 were enrolled. The nidus size, pain numeric rating scale score, and intramedullary edema diameter before and after RFA were compared. Clinical and technical success, intervention-related complications, and need for subsequent ablation were recorded., Results: Of the 55 patients, including 12 pediatric cases, 6 had atypical locations such as metatarsal, vertebra, and scapula, while 1 case had osteoid osteoma with multiple nidus. The mean age was 18.5 ± 9.6 years. Preintervention maximum nidus diameter, pain score, and edema diameter were significantly lower in postintervention measurements ( p < 0.001). Technical success rate was 98.1%, and clinical success was 96.36%. Severe complication occurred in one patient with soft tissue burn and osteomyelitis., Conclusion: This is one of the largest series of osteoid osteoma treated with RFA done in a single center with atypical cases. In conclusion, RFA is safe and effective in both pediatric and adult patients with rare complications even in challenging cases with atypical locations.

Competing Interests: Competing interests: None declared.

Primary benign bone tumors are uncommon and most often affect children and young adults. They typically are detected incidentally on imaging, though some patients present with pain, swelling, or other symptoms. The four main categories of benign bone tumor are: bone-forming (eg, osteoid osteoma, osteoblastoma, fibrous dysplasia, enostosis), cartilage-forming (eg, osteochondroma, enchondroma), connective tissue, and vascular; the latter two are rare. A fifth category is idiopathic (eg, giant cell tumor, aneurysmal bone cyst, simple bone cyst). Osteochondromas are the most common, accounting for 30% to 35% of benign bone tumors. Giant cell tumors account for 20%, osteoblastomas for 14%, and osteoid osteomas for 12%. All others are less common. Diagnosis mainly is via imaging; biopsy rarely is required. Management varies with tumor type, location, symptoms, and risk of recurrence. Some (eg, enchondroma, osteochondroma, fibrous dysplasia, enostosis) typically are asymptomatic, and generally require no intervention. Others (eg, osteoid osteoma, aneurysmal bone cyst, simple bone cyst) can cause symptoms and require percutaneous ablation or surgery. Still others (eg, giant cell tumor, osteoblastoma) can be aggressive and require surgery and other therapies. Malignant transformation is rare for all benign bone tumors, but patients with these tumors should be monitored with serial imaging., (Written permission from the American Academy of Family Physicians is required for reproduction of this material in whole or in part in any form or medium.)

Osteoid osteoma is a benign bone lesion that accounts for approximately 10% to 12% of all benign bone tumors. More than 80% of lesions occur in patients between 5 to 25 years old; males are more commonly affected with a ratio of 3:1. The foot is rarely involved: its involvement is less than 4% in the foot and of 1.7% in the metatarsals. In this paper we discuss the case of a 27-years-old woman with a 12 months follow-up, presented with an osteoid osteoma of the proximal phalanx of the great toe that underwent an en-bloc excision of the lesion and subsequent filling with cancellous autograft from the ipsilateral calcaneus.

Osteoid osteoma and osteoblastoma are bone-forming tumors shown to harbor FOS (87%) and FOSB (3%) rearrangements. The aim was to evaluate the immunohistochemical expression of FOS and FOSB in these tumors in comparison to other bone tumors, to evaluate the influence of decalcification, and to correlate immunohistochemical findings with the underlying genetic alteration using fluorescence in situ hybridization (FISH). Immunohistochemistry using whole sections was performed on osteoid osteoma (n=23), osteoblastoma (n=22), osteoblastoma-like osteosarcoma (n=3), reactive (n=3), and proliferative (n=11) bone lesions. Immunoreactivity in giant cell tumor of bone (n=74), aneurysmal bone cyst (n=6), chondromyxoid fibroma (n=20), osteosarcoma (n=85), chondroblastoma (n=17), and clear cell chondrosarcoma (n=20) was assessed using tissue micro arrays. Strong nuclear expression of FOS in > 50% of the tumor cells was observed in all osteoid osteomas (22/22), in 57% of osteoblastomas (12/21) and in 3/197 control cases. FOS immunoreactivity disappeared after > 3 days decalcification. FOS rearrangements were present in 94% of osteoid osteomas and osteoblastomas, with a concordance of 86% between FISH and immunohistochemistry. Two osteoblastomas (5%) were positive for FOSB, as opposed to 8/177 control cases. Additional FISH revealed no FOSB rearrangements in these cases. To conclude, in short decalcified biopsies, FOS immunohistochemistry can be used to diagnose osteoid osteoma and osteoblastoma, as overexpression is seen in the majority, being rare in their mimics. FOS immunohistochemistry should not be used after long decalcification. Moreover, low level of focal expression found in other lesions and tissues might cause diagnostic problems, in which case FISH could be employed.

Osteoid osteoma is a relatively common benign tumor of bone, typically presenting in the diaphysis of long bones during the second or third decades of life. This tumor is rarely reported in the hand and wrist, making up only approximately 10% of cases. When reported in the hand, osteoid osteoma tends to occur more frequently in the proximal phalanx of the index and middle fingers. We present the case of an osteoid osteoma in an adolescent male in the distal phalanx of the thumb. The presentation of this osteoid osteoma was atypical owing to its location and lack of characteristic clinical features, making the initial work-up and final diagnosis challenging and pointing to the importance of considering this diagnosis on a differential for painful bony tumors in the hand., (Copyright © 2019 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

Objective: To explore the incidence and significance of intra- and extra-osseous edema associated with benign tumors and tumor-like diseases., Methods: Magnetic resonance imaging (MRI) data from 300 benign osseous tumors and tumor-like diseases diagnosed by pathology were retrospectively reviewed. Borderline tumors, cases associated with pathological fractures, and skull lesions were excluded from the study. Bone marrow and soft tissue edema were defined on T2WI with fat suppression on MRI in all cases. The incidence rate of edema in benign tumors and tumor-like diseases was determined using the χ 2 test. The preoperative diagnoses were reviewed, and the effect of edema on the differential diagnosis of benign and malignant tumors was analyzed., Results: The incidence rate of bone marrow and soft tissue edema associated with benign tumors and tumor-like diseases was 35.7% (107/300), including 84.4% (27/32) Langerhans cell histiocytosis, 86.4% (19/22) osteoblastoma, 93.9% (31/33) osteoid osteoma, and 85.2% (23/27) chondroblastoma cases. There was no statistically significant difference in the incidence of edema among the four diseases ( χ 2 = 1.7, P > 0.05). Of 107 cases associated with edema, 49 (45.8%) were misdiagnosed as malignant tumors by MRI preoperatively., Conclusion: Bone marrow and soft tissue edema are a common finding associated with benign bone tumors and tumor-like diseases, and they are frequently detected in Langerhans cell histiocytosis, osteoblastoma, osteoid osteoma, and chondroblastoma., Competing Interests: The authors declare that they have no conflicts of interests., (Copyright © 2019 Sai Gao et al.)

Objective: The aim of this prospective study was to evaluate pre- and post-treatment MRI and CT findings of osteoid osteoma (OO) patients treated with radiofrequency thermo-ablation (RFTA) and to compare these findings with visual analog scale (VAS) scores., Methods: Sixteen patients (4 females and 12 males; mean age of 18.87 ± 8.75 years (range: 8-37)) with OO were examined with CT and MRI, at baseline and at an average of 3 months following the procedure. On pre- and post-procedural CT and MRIs, OO-related findings were recorded. Treatment success was evaluated with VAS scores., Results: Baseline VAS scores were 8 or 9 and follow-up scores were 0 or 1, indicating no early recurrences. Nidus diameters decreased significantly after the procedure (p = 0.027, p = 0.002, and p = 0.002; and p = 0.001, p = 0.001, p = 0.001 for AP, ML and CC nidus diameters for CT and MRI, respectively). The mean nidus volume were significantly decreased after the procedure (p = 0.001, for CT and MRI). On post-procedural images, cortical thickening, the signal intensity and contrast enhancement of the nidus and the extent of periostitis were significantly decreased (p = 0.019, p = 0.001, p = 0.001 and p = 0.034, respectively). There was no significant change in nidus calcification, perinidal cortical and intramedullary sclerosis, periosteal reaction, bone deformity, bone marrow and soft tissue edema, joint effusion and synovitis after the procedure (p = 0.253, p = 0.062, p = 0.245, p = 1, p = 1, p = 0.429, p = 0.371, p = 0.625, p = 1)., Conclusion: Although the changes in imaging findings may be helpful in early follow-up of OO patients treated with RFTA, these changes alone cannot be used with accuracy in predicting treatment response., Level of Evidence: Level IV, Therapeutic Study., (Copyright © 2019 Turkish Association of Orthopaedics and Traumatology. Production and hosting by Elsevier B.V. All rights reserved.)

Aim: The aim was to present the surgical technique and clinical outcome in a series of patients treated with gamma-probe-assisted arthroscopic removal of osteoid osteoma in the hip joint., Methods: The case series consisted of 10 patients diagnosed with osteoid osteoma of the hip, who were treated by arthroscopic nidus removal. An endoscopic gamma probe was used intraoperatively to locate the nidus and to control the extent of its removal. Residual osteoma cavities were additionally treated with an arthroscopic radiofrequency ablator. Microfracturing was performed when the osteochondral defect was in the weight-bearing area and osteochondroplasty was done in cases of concomitant cam deformity. Nonarthritic Hip Score (NAHS), Tegner activity score, quality of life questionnaire (EQ-5D) and postoperative magnetic resonance imaging (MRI) were used for evaluation before and post-surgery, with a minimum follow-up of 2 years., Results: The relative reduction of the gamma irradiation count immediately after removal of the nidus was 44.9% (range 33.3-54.5%). Postoperatively, all patients experienced prompt pain relief and a significant improvement according to all patient reported outcomes. Control MRI revealed fibro-cartilaginous tissue repair of post-osteoma osteochondral defects in the weight-bearing area; 1 patient showed signs of early degeneration., Conclusions: The results of this case series demonstrated the safety and high efficacy of gamma-probe-assisted arthroscopic removal of the osteoid osteoma from the hip joint. Endoscopic gamma probe was recognised as a very useful device for locating the nidus of the osteoid osteoma exactly and preventing incomplete or excessive removal of the bone.

Background: Osteoid osteoma is a benign bone-forming tumour, which very unfrequently has multifocal or multicentric presentation. We report the first known case of a multicentric, multifocal and recurrent osteoid osteoma treated using radiofrequency ablation., Case Presentation: A 39-year-old man with two-year history of left hip pain was admitted at our Institution. The pain was more intense during the night and partially relieved by salicylates. Pelvis CT demonstrated two lytic lesions (8 and 7 mm, respectively) with surrounding sclerotic reactive bone, both with a central focal area of high attenuation, located in the femoral neck and along the anterior portion of the acetabulum, respectively. Both lesions had clinical and imaging findings consistent with multicentric osteoid osteoma. Thus, the two lesions were biopsied - with pathologic confirmation of osteoid osteoma - and treated using radiofrequency ablation. Hip pain decreased but did not disappear, actually increasing a few months after treatment. CT and MRI were performed showing a smaller lesion (5 mm) with the same imaging features, surrounded by marrow oedema, along the posterior column of the acetabulum. The lesion was considered suspicious for osteoid osteoma, overlooked on previous examinations. Therefore, a diagnosis of multicentric and multifocal osteoid osteoma was established. The new lesion was again treated with radiofrequency ablation with symptom disappearance. However, hip pain relapsed after 18 months, and CT and MRI showed an osteoid osteoma recurrence on the posterior column of the acetabulum, which was biopsied and successfully treated using radiofrequency ablation., Conclusions: To our knowledge, this is the first reported case of multicentric, multifocal, recurrent osteoid osteoma. Our case report highlights the importance of considering a diagnosis of multifocal osteoid osteoma when dealing with multifocal lytic lesions of the bone and with pain persistence after treatment. It also emphasises the combined role of CT and MRI in this setting.

Background: The etiology of hip pain in pediatric and adolescent patients can be unclear. Osteoid osteoma (OO) about the hip in children has only been described in case reports or small studies. The present study assessed the clinical presentation and diagnostic course, imaging, and treatment approaches in a large cohort of pediatric cases of OO about the hip., Methods: Medical record and imaging results were reviewed for all cases of OO identified within or around the hip joint in patients <20 years old between January 1, 2003, and December 31, 2015, at a tertiary-care pediatric center. Demographic, clinical, and radiographic data were analyzed., Results: Fifty children and adolescents (52% female; mean age, 12.4 years; age range, 3 to 19 years) were identified. Night pain (90%) and symptom relief with nonsteroidal anti-inflammatory drugs (NSAIDs) (88%) were common clinical findings. Sclerosis/cortical thickening was visible in 58% of radiographs, although a radiolucent nidus was visible in only 42%. Diagnostic imaging findings included perilesional edema and a radiolucent nidus on 100% of available magnetic resonance imaging (MRI) and computed tomography (CT) scans, respectively. Initial alternative diagnoses were given in 23 cases (46%), the most common of which was femoroacetabular impingement (FAI). Delay in diagnosis of >6 months occurred in 43% of patients. Three patients underwent operative procedures for other hip diagnoses, but all had persistent postoperative pain until the OO was treated. Of the 41 patients (82%) who ultimately underwent radiofrequency ablation (RFA), 38 (93%) achieved complete post-RFA symptom resolution., Conclusions: Initial misdiagnosis, the most common of which was FAI, and delayed correct diagnosis are common in pediatric OO about the hip. Presenting complaints were variable and nonspecific MRI findings were frequent. Night pain and relief with NSAIDs were present in the vast majority of cases. CT scans provided definitive diagnosis in all patients who received them. As increasing numbers of young, active patients are being evaluated for various causes of hip pain, such as FAI, OO should not be overlooked in the differential diagnosis., Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Osteoid Osteoma (OO) is a benign tumor that can affect any age, but it occurs mostly in adolescents. Only few cases are reported in early infancy but very rare in advanced age. From our series of OO of the spine, we selected a rare case that combines many unusual features that makes diagnosis very difficult. A case of a painful thoracic syndrome in an old female patient due to an OO localized in the inferior edge of the left pedicle of T11 with engagement of the foramen was reported. The age of the patient, the absence of any typical clinical and diagnostic signs, such as nocturnal pain or side effects to NSAIDs administration, are unusual at presentation of OO. She presented instead, a type of pain to the chest that was stabbing, fulminating and radiating. The interest of the case is due to the association of a variety of clinical aspects that stimulate discussion as well as to the role of the modern investigative diagnostic process.

Background: OO (osteoid osteoma) is a common, osteoblastic, benign bone tumor but rarely seen in the hand region. There is still some debate about the diagnosis and treatment of hand OOs. In the present study, we aimed to evaluate the epidemiology, radiologic features, surgical treatment options and functional outcomes., Methods: Between January 2003 and December 2014, surgically treated and pathologically verified 9 hand OO cases were investigated retrospectively. The preoperative and postoperative clinical outcome scores were calculated using the M2-DASH (Manchester-Modified Disabilities of Arm Shoulder and Hand) Score., Results: Lesion locations were as follows: middle phalanx in 2/9 (22%) patients (2nd and 4th digit), proximal phalanx in 6/9 (67%) patients (one 4th, two 2nd and three 5th digits) and metacarpal (2nd) in 1/9 (11%) patient. Incidence of nidus formation was 6/9 (67%) on X-ray, 7/9 (78%) on CT imaging and 2/9 (22%) on MR imaging. The mean time to diagnosis was 13.22 ± 5.44 months. Preoperative mean M2-DASH score was 41 ± 6 and postoperative was 7.4 ± 8.6., Conclusion: Osteoid osteoma is usually seen below 25 years, and rarely found over 40 years of age. There is male dominance with a male to female ratio of 3:1. Delay of diagnosis may be encountered because of many differential diagnoses. When OO is suspected, CT imaging should be taken before the MR imaging. Because of superiority in soft tissue imaging, MR imaging should be an alternative tool in complex cases.

Background: Osteoid osteoma is a painful benign skeletal tumour of unknown aetiology. Most often it occurs in the long bones of extremities and responds well to nonsteroidal anti-inflammatory medications. However, unusual localization and atypical presentation of this tumour might present a diagnostic challenge, especially if symptoms mimic that indicative of juvenile spondyloarthritis., Case Presentation: A misdiagnosed ten-and-a-half-year-old girl with osteoid osteoma involving the distal phalanx of a little finger is presented. Her initial symptoms were pain and swelling of the little finger resembling dactylitis, while various imaging modalities showed signs of tenosynovitis, indicating a possible development of juvenile spondyloarthritis. Several trials of different non-steroid anti-inflammatory drugs gave no satisfactory results and ultrasound guided triamcinolone-hexacetonide injection provided only a short relief. Finally, almost three years after initial presentation, persistent clinical symptoms warranted repeated imaging that raised suspicion of an osteoid osteoma. Directed treatment with surgical intervention led to almost immediate and complete resolution of her symptoms., Conclusions: Osteoid osteoma should be suspected in case of a tender swelling of a digit in children and adolescents, regardless of initial imaging findings and clinical presentation. Early diagnosis and treatment of this benign condition can have a substantial impact on quality of life of patients and their families and protect them from many unnecessary diagnostic procedures and treatment.

Background/aim: Osteoid osteoma (OO) is a benign tumor characterized by the excessive formation of unmineralized bone matrix. It is mostly located in the long bones of the lower extremities or the spine, but can also occur in atypical locations., Patients and Methods: Here we report on a rare case of OO in the mandible in an 18-year-old male patient with a simultaneous finding of a pilomatrixoma in the parietal region. Initially, a biopsy had been taken due to an unclear tumor mass and non-specific pain adjacent to tooth 46., Results: The detailed radiographic and histopathological analysis revealed the diagnosis of OO in terms of a characteristic radiolucent nidus and structurally disorganized woven bone with osteoid, respectively. The tumor was subsequently completely resected resulting in a complete recovery of symptoms., Conclusion: As we demonstrate an infrequent finding of OO in the mandible, it is important to diagnose and treat this condition appropriately., (Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

PURPOSE OF THE STUDY Osteoid osteoma (OO) of the upper extremity is a rare pathology representing a major diagnostic challenge. The patients are often times incorrectly treated due to a misdiagnosis and therefore the final management of symptoms is delayed by several months. During this time the pain, which is the main symptom, increases. The surgical treatment is a fast and efficient solution. This paper aims to highlight the specificity of the OO of the upper extremity, evaluate our study group, the time to diagnosis and the benefits of individual imaging techniques. MATERIAL AND METHODS In the period 2007-2017, a total of 8 patients with a histologically verified OO of the upper extremity were consulted and treated at the authors departments. The group of patients was retrospectively evaluated based on the medical reports, surgical protocols, imaging examinations, histology results of preoperative samples and a postoperative questionnaire. Pain was assessed on the Visual Analogue Scale (VAS) preoperatively, at 2 weeks, 2 months and at one year postoperatively and in January 2018. The mean follow-up period was 48 months (range 16-78). The presence of swelling, synovitis and a limited range of motion were clinically assessed. The removed tissue was tested in an accredited biopsy laboratory. RESULTS 8 patients with OO of the elbow, wrist and hand were treated in the period 2007-2017. In 5 cases the OO was located in the wrist (scaphoid, 2x trapezoid, hamate and capitate) and in 2 cases in finger phalanges (middle and distal phalanx). The mean age of the patients was 24.5 years (median 21.5, range 18-42). The male to female ratio was 7:1. The mean interval between the onset of symptoms and the final diagnosis was 16.25 months (median 15.5, range 12-25). The CT examination proved to be the most beneficial imaging techniques. A plain radiograph led to a diagnosis in 1 case only. The preoperative mean pain VAS value 9.25 dropped to VAS 1 at two weeks after the surgery. No recurrence was reported. DISCUSSION The main challenge in treating the OO of the upper extremity is the diagnosis. Despite of the availability of advanced imaging techniques, the interval from the onset of symptoms to correct diagnosis did not change over the past decades. As to the treatment, despite the development of new procedures the method of choice continues to be the surgical excochleation. CONCLUSIONS Osteoid osteoma of the upper extremity is a rare pathology which shall be considered in case of an increasing pain, especially in young men. A plain radiograph of the anatomically complex terrain of the hand and wrist is mostly not useful in diagnosis, whereas the CT examination can visualise even a small size nidus. The surgical excochleation results in pain relief and early functional recovery with swelling disappearance. To diagnose the OO is not difficult provided we take it into consideration. Key words:osteoid osteoma, upper extremity, hand, wrist, diagnosis.

Foot and ankle osteoid osteomas (OOs) are often cancellous or subperiosteal and rarely present with a periosteal reaction. Additionally, the large number of disorders included in the differential diagnosis and the nonspecific findings on radiographs complicate the diagnosis. We performed a manual search of the senior surgeon's hospitals' operating room records for the terms "benign bone tumor," "foot," "ankle," and "osteoid osteoma" from January 2003 until December 2014. Of 87 surgically treated patients with lower extremity OOs, 9 patients (11%) with foot or ankle OOs were included. The mean age at presentation was 21 (range 6 to 30) years; all 9 (11%) patients were male. The patients were evaluated for swelling, pain, trauma history, night pain, response to pain relievers, duration of complaints, and interval to diagnosis. The mean follow-up period was 48 ± 24 months, and no recurrences had developed. The mean American Orthopaedic Foot and Ankle Society scale score was 59.04 ± 11 before surgery and 91.56 ± 6 after surgery. The difference was statistically significant at p ≤ .0003. Most previous studies have been limited to case reports. The need for findings from a case series was an essential determinant of our decision to report our results. Patients usually have been treated conservatively, often for a long period. However, delays in treatment cause social, economic, and psychological damage. In conclusion, the presence of atypical findings on radiographs has resulted in a preference for magnetic resonance imaging instead of computed tomography; however, the diffuse soft tissue edema observed on MRI can lead to the use of long-term immobilization and a delay in the diagnosis., (Copyright © 2017 The American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.)

Bone tumors are relatively rare in the foot and ankle region. Many of them present as cystic lesions on plain films. Due to the relative rarity of these lesions and the complex anatomy of the foot and ankle region, identification of such lesions is often delayed or they get misdiagnosed and mismanaged. This review discusses the most common cystic tumors of the foot and ankle including their radiographic features and principles of management., (© 2018 Wiley Periodicals, Inc.)

Osteoid osteomas are benign bone tumors which rarely occur in the hand and impose severe diagnostic problems. The course of the disease is often protracted before the patient receives an adequate surgical treatment. The case of an osteoid osteoma in the scaphoid bone of a 15-year-old patient is presented, who was completely symptom free after a true diagnostic odyssey by resection of the nidus and reconstruction by crest bone graft and spongiosaplasty.

BACKGROUND Osteoid osteomas are benign bone-forming tumors characterized by local inflammation and pain. They are also characterized by a small osteolytic lesion (nidus). Spondylolysis is a defect of the pars interarticularis, which may lead to stress fractures, and is a common cause of low back pain in adolescence. Osteoid osteoma occurs predominantly in the posterior elements of the spine. Magnetic resonance imaging (MRI) signal abnormality suggesting bone marrow edema is a common finding in osteoid osteoma and early-stage spondylolysis without prominent defect. CASE REPORT An 18-year-old male was suffering from low back pain. He was diagnosed with lumbar spondylolysis on initial MRI and computed tomography (CT). Subsequent thin-slice CT demonstrated a nidus at the pars interarticularis, and variously-sliced MRI could detect widespread bone marrow edema. On the diagnosis of an osteoid osteoma, the nidus and surrounding osteosclerosis were resected. The patient's pain disappeared after surgery. CONCLUSIONS Osteoid osteoma in the pars interarticularis can be difficult to diagnosis, because MRI and CT findings for osteoid osteoma at the pars interarticularis are similar to those of the lumbar spondylolysis. The possibility of osteoid osteoma should be kept in mind when examining adolescents with low back pain.

Clinically, it is difficult to differentiate osteoid osteoma, more than 50% of which occur in the fibia or tibia, from other diseases, i.e. spinal degenerative diseases, inflammatory and noninflammatory arthritis. In this case report, we presented an unusual case of lumbar osteoid osteoma in a 38-year-old male, who experienced low back pain and sciatica as initial symptoms. The patient was initially misdiagnosed as lumbar disc herniation for more than 10 years. With the usage of computed tomography (CT) and magnetic resonance imaging (MRI), the patient was finally diagnosed as osteoid osteoma in L5. To our knowledge, spinal osteoid osteoma with sciatica as initial symptoms has never been reported. Although lumbar vertebra osteoid osteoma is clinically uncommon, it should be taken into consideration especially when patients experience long duration of pain in lumbar.

Bone-forming tumors are defined by neoplastic cells that differentiate along the lines of osteoblasts that deposit neoplastic bone. The morphology and biological spectrum of bone-forming tumors is broad, and their accurate diagnosis requires the careful correlation of their clinical, morphologic, and radiologic characteristics. Immunohistochemical and molecular analyses have an important role in select instances. At present, the identification of neoplastic bone largely depends on histologic analysis, which can be subjective. The major types of osteosarcoma are defined according to their morphology, origin within or on the surface of the bone, and their histologic grade., (Copyright © 2017 Elsevier Inc. All rights reserved.)

An osteoid osteoma is a rare, small, benign and painful tumour occurring in the extra-articular portion of long bones seen most commonly in the lower extremities. This is a case report of a 23-year-old female patient who underwent arthroscopic resection of an intra-articular osteoid osteoma. The nidus was completely removed by arthroscopic excision. The diagnosis was confirmed by postoperative histopathological analysis. In the case presented we have shown that intra-articular arthroscopy can be successful in the surgical management of benign bony lesions involving the elbow joint. We also present a review of the literature which reports on similar cases or intra-articular disease, preferred methods of surgical management and limitations in histopathological specimen acquisition for diagnosis., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Ltd (unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

The foot is rarely the focus of osteoid osteoma, and only a few of those cases are related to the fifth metatarsal. The present case demonstrates that atypical symptoms with suspicious findings on plain radiographs that are not associated with trauma must be analyzed carefully to determine the nature of the lesion and perform the precise treatment to obtain and sustain the cure. A 29-year-old man presented to the outpatient clinic with a 2-year history of chronic pain in the lateral aspect of his left forefoot. The onset was not related to trauma, surgery, local infection, osteomyelitis, or another entity regarding the proximal fifth metatarsal. The patient noted that the pain was aggravated at night and typically subsided with the use of salicylates or other nonsteroidal anti-inflammatory drugs. Initial plain radiographs demonstrated cortical thickening and a lytic lesion at the proximal diaphysis of the fifth metatarsal. Because the pain relief was transient, we suspected an osteoid osteoma lesion, and subsequent magnetic resonance imaging manifested pathognomonic signs of subperiosteal osteoid osteoma. Diagnosis was followed by planning of the surgery that ended the patient's symptoms.

The trapezium is rare site of osteoid osteoma development. The diagnostic challenge lies in its rare occurrence, and requires differentiation from various disease entities causing thumb basal joint pain. We report the case of a 29-year-old male who presented with severe thumb basal joint pain. He was initially treated for calcific periarthritis because of concomitant calcifications around the thumb basal joint, but had undiscovered osteoid osteoma. A high index of suspicion to a patient with wrist pain unresponsive to prior treatment is necessary for diagnosis of osteoid osteoma.

Background: Osteoid osteoma is the third most common benign bone tumor and typically induces pain that is worse at night., Objective: To identify the epidemiological, pathogenetic, histological and radiological characteristics of osteoid osteoma and to present the broad variety of treatment options., Material and Methods: This review article summarizes relevant clinical studies and meta-analyses on this topic., Results: Osteoid osteoma is characterized by a central nidus smaller than 1.5 cm in diameter with surrounding bone sclerosis. In the majority of cases, the tumor occurs in the long bones of the lower extremities and is predominantly manifested in patients aged between 5 and 25 years. Pain is mediated by prostaglandins, which stimulate afferent peripheral nerve fibers. Besides plain radiographs, thin-section computed tomography represents the gold standard of diagnostics but should be complemented by magnetic resonance or nuclear medicine imaging modalities. The conservative treatment consists of long-term therapy with non-steroidal anti-inflammatory drugs. Minimally invasive radiofrequency ablation of the nidus is the current operative treatment of choice., Conclusion: Success rates of radiofrequency ablation and other minimally invasive procedures are high while treatment costs and length of hospital stay are low. Thus, open surgical curettage is reserved for rare indications and en bloc excision of the nidus should only be performed in cases of recurrent lesions.