The Animal Tests And Clinical Applications Of Microwave Ablation Of Osteoid Osteoma

Purpose: To analyze the heat distribution and heat coagulation of osteoid osteoma treating by microwave ablation in vitro animal model and clinic applications to assess the safety and effectivity of the CT-guided percutaneous microwave ablation.Materials and Methods: A hole was drilled in fresh pig's leg to make an in vitro model for osteoid osteoma. The nidus were defined 2mm to the cortical bone lamella and 2cm in depth. Three thermocouples were located at 0, 5, and 10 mm from the periosteum respectively. Before microwave ablation, specimen was heated in a 37℃basin. The microwave ablation was initiated in the nidus of the specimen and conducted for 10min, with a target temperature of 90℃. During microwave ablation, continuous measurements were performed simultaneously with digital thermometers. The heat distribution of the surrounding soft tissue temperatures were analyzed with SPSS. The animal model of the heat coagulation tests were created by drilling a hole in fresh pig's long bone as an in vitro model for osteoid osteoma. The microwave ablation was initiated in the nidus of the specimen and conducted for 10min, with a target temperature of 95℃. MRI were performed 3 times respectively (before drilling hole in long bone, before microwave ablation and after microwave ablation). The MRI images were contrasted. The pathologic specimens were harvested at the places of 0mm, <5mm and <10mm from the nidus. To assess the extent of coagulation necrosis by analyzing the result of MRI-Histopathologic correlation. From July 2007 to February 2008, 3 patients with the osteoid osteomas of the femur were treated with CT-guided percutaneous microwave ablation in clinical applications. There were 2 males and 1 female with an average age of 17.7 years (ranging from 12 to 25 years). The history of local pain was ranging from 2 month to 10 years. The lesion location contained: 1case in the lift neck of femur, 2 cases in the right proximate femur. All patients had the clinical diagnosis of osteoid osteoma with clinical and radiologic evidence. After localization of the nidus with CT, osseous access was established with a "Gallini" puncturatio needle. After scanning the nidus with CT, a trocar was used to obtain specimen for pathological examination. Subsequently, a microwave probe was introduced through the biopsy needle to the nidus. Microwave ablation was performed at 90℃for 4～6 minutes. The resected tumor tissues were taken pathological examination with the formalin fixation.Results: The temperature was 78.5℃, 44.0℃and 34.2℃at 0, 5, and 10 mm from the periosteum, respectively. The extent of coagulation necrosis in the pig's long bone with microwave ablation was a globular-shaped region of approximately 1.5cm diameter. 3 patients were diagnosed as ostetoid osteoma with the pathological confirmation after the operation. The pain of 3 patients was alleviated 24 h after operation. 1 case with history of local pain 10 years retained discomfortableness within 2 weeks, and disappeared after 2 weeks. 1 case with lesion in the right proximate femur retained moderate pain without nonsteroidal antiinflammatory drugs 5 month after operation. No recurrence and complications were observed.Conclusion: CT-guided percutaneous microwave ablation is a simple, minimally invasive, safe, highly effective and economical technique for treatment of osteoid osteoma.