Osteoma

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 the third most common benign bone tumor, with well-known clinical presentation and radiological features. Although surgical excision has been the only therapeutic option for a long time, to date it has been replaced by minimally invasive techniques, which proved satisfactory success rates and low complication occurrence. Therefore, the purpose of this literature review was to describe the main updates of these recent procedures in the field of interventional radiology, with particular attention paid to the results of the leading studies relating to the efficacy, complications, and recurrence rate. Nevertheless, this study aimed to analyze the peculiarities of each reported technique, with specific focus on the possible improvements and pitfalls. Results proved that all mininvasive procedures boast a high success rate with slight number of complications and a low recurrence rate. Radiofrequency ablation is still considered the gold standard procedure for percutaneous treatment of osteoid osteoma, and it has the possibility to combine treatment with a biopsy. Interstitial laser ablation's advantages are the simplicity of use and a lower cost of the electrodes, while cryoablation allows real-time visualization of the ablated zone, increasing the treatment safety. Magnetic resonance-guided focused ultrasound surgery is the most innovative non-invasive procedure, with the unquestionable advantage to be radiation free.

Bone tumours are difficult to diagnose and treat, as they are rare and over 60 different subtypes are recognised. The emergence of next-generation sequencing has partly elucidated the molecular mechanisms behind these tumours, including the group of bone forming tumours (osteoma, osteoid osteoma, osteoblastoma and osteosarcoma). Increased knowledge on the molecular mechanism could help to identify novel diagnostic markers and/or treatment options. Osteoid osteoma and osteoblastoma are bone forming tumours without malignant potential that have overlapping morphology. They were recently shown to carry FOS and-to a lesser extent-FOSB rearrangements suggesting that these tumours are closely related. The presence of these rearrangements could help discriminate these entities from other lesions with woven bone deposition. Osteosarcoma is a malignant bone forming tumour for which different histological subtypes are recognised. High-grade osteosarcoma is the prototype of a complex karyotype tumour, and extensive research exploring its molecular background has identified phenomena like chromothripsis and kataegis and some recurrent alterations. Due to lack of specificity, this has not led to a valuable novel diagnostic marker so far. Nevertheless, these studies have also pointed towards potential targetable drivers of which the therapeutic merit remains to be further explored.

ObjectivePercutaneous CT-guided radiofrequency ablation (CT-RFA) is a widely accepted procedure for treatment of osteoid osteomas. However, the application of CT-RFA was restricted as a result of some drawbacks, such as radiation exposure, and inconvenience in general anesthesia. The primary aim of this study is to evaluate the safety and efficacy of intra-operative TiRobot-assisted percutaneous RFA of osteoid osteomas.MethodsWe retrospectively reviewed 21 medical files of patients who were treated with percutaneous RFA of osteoid osteomas guided by the TiRobot system in our institution between March 2021 and April 2022. The three-dimensional images obtained by a 3D C-arm intra-operatively were sent to the TiRobot system. The puncture point and trajectory were designed. Then the guide pin was positioned to the lesion with the assistance of TiRobot and the biopsy sheath was inserted into the lesion through the guide pin. The tumor was biopsied for pathological examination. Then the RFA needle was inserted into the nidus through the biopsy sheath for thermal ablation. Data were extracted on the associated complications, the reduction in pain at 1 month and 1 year postoperatively assessed by the visual analogue scale (VAS). A paired t-test was used to compare the pre-operative and post-operative VAS scores.ResultsThe patients included 17 males and four females with a mean age of 19.5 ± 10.4 years (range 3-45 years). Lesions were located on the femur in nine cases, on the tibia in nine cases, on the humerus in one case, on the calcaneus in one case, and on the acetabulum in one case. TiRobot-assisted percutaneous RFA was successfully performed on all 21 patients. There was no intra-operative or post-operative complications observed. Pathological diagnosis of osteoid osteoma was obtained in 11 patients, but the other 10 cases were not pathologically diagnosed. The mean follow-up time was 18.8 months (range: 12-26 months).Post-operative VAS scores were reduced significantly in all cases. The mean VAS score decreased from 6.5 pre-operatively to 0.5 at 1 month post-operatively and to 0.1 at 1 year post-operatively.ConclusionAs a reliable technique for localizing and resection of nidus, TiRobot-assisted percutaneous RFA is a safe and effective option for the treatment of osteoid osteomas.