| Part 1 The Effect of Ablation Parameters on Brain Damage Foci Formation and its Effect on Intracranial Pressure after Radiofrequency Ablation in Normal RatsObjective To study the effect of temperature and duration on coagulation diameter, intracranial pressure(ICP) and neurological function using a rat cerebral radiofrequency ablation(RFA) model.Methods 36 SD rats were were divided randomly into four groups, i.e. Group A, B, C and D. All the rats were treated with an RFA technique at different target temperatures, i.e. 60℃ in Group A, 70℃ in Group B, 80℃ in Group C and 90℃ in Group D. Each group was divided into three subgroups. RFA duration of was 0.5min in Subgroup 1, 1min in Subgroup 2 and 1.5min Subgroup 3 respectively. The target was 3.0mm below the right cortex dura. ICP was monitored preoperatively, 0.5 hour after surgery and 1 hour after surgery. Neurological function of RFA-treated rats was evaluated using the Neurological Severity Score(NSS) scale 1 day after RFA. Then the brain was removed for HE staining,Nissl’s staining and TUNEL staining. Statistical difference was analyzed by t test and multiple linear regression analysis using SPSS 16.0 software.Results ICP of Suburoups B3 and D2 0.5 hours after RFA increased compared with preoperative ICP(P<0.05). ICP increasing occured 1 hour after RFA in Subgroups C1, C2, D1, D2 and D3(P<0.05). Ablation foci area was correlated to ICP 0.5 hour after RFA by multiple regression analysis(P<0.05). Seven rats died within 24 hours, including 4 rats of each Subgroup of C2, C3, D1 and D2, while all the rats of group D3 were dead 24 hours after brain ablation.The mean NSS of Group A and B was below 4. The mean NSS of Group C was 5 ~ 10. The mean NSS of Group D was over 10. HE staining of brain damage showed the damage foci formed 24 hours after RFA. There were three layers in a concentric circle, including the necrotic area in the center, peripheral reaction zone and outside normal brain tissue. In the necrotic area, extensive karyolysis, pyknosis and karyorrhexis were seen. The target temperature and the ablation duration were both positively correlated to the diameter and the area of ablation. Apoptosis was detected in the peripheral reaction zone using Nissl’s staining and TUNEL staining. When the parameters of RFA were 60℃ for 1min, 70℃ for 1min and 80℃ for 1min, the lesion size was close to 2mm, 4mm and 5mm respectively. These parameters will provide important reference for the further study of RFA for brain glioma in rats.Conclusion: The rat brain RFA model is stable and suitable, which may serve as the primary model for preclinical studies. The brain damage foci with the same size could be formed with the same set of ablation parameters. Good repeatability of the pathology and biological effects after radiofrequency ablation can be produced with precise stereotaxy and tight parameters design. Moreover, radiofrequency ablation device is cheap, and the process is easy to master, indicating a good prospect in neurosurgery.Part 2 Guidance and Evaluation of Rat Glioma Radiofrequency Ablation using MRObjective To investigate the guidance and effect evaluation of rat glioma RFA using MR.Methods 27 SD rats with C6 glioma were randomly divided into 3 groups, 2mm, 4mm and 6mm, according to the tumor diameters detected by MR scans once every 3 days since the 7th day after transplantation of C6 cells. Stereotactic RFA of the tumor was done. The parameters of RFA were 60℃ 1min for 2mm Group, 70℃ 1min for 4mm Group, and 80℃ 1min for 6mm Group. Intracranial pressure was monitored peri-RFA. NSS scores and MR scans were performed 3 days, 6 days and 9 days after RFA. Then animals were sacrificed for pathological study. HE staining, Nissl staining and TUNEL staining were performed.Results RFA was successful with the guidance of MR. The volume was significantly reduced in the 2mm Group 6 days after ablation and in the 4mm Group 9 days after ablation. MRI showed a series of tumor signal change after radiofrequency ablation. The location of both the needle tract and tumor necrosis was clear showed on MRI. In 6mm Group, a lot of the tumor cells were still visible with intact morphology, and ablation necrosis was seen with a finger-like arrangement after RFA on HE staining. TUNEL staining showed that a large number of cells were apoptotic.Conclusion RFA could induce suitable range of necrosis on the rat glioma. Positive therapeutic effect of RFA for rat brain glioma was confirmed in Group 2mm and Group 4mm. For the tumors of diameter larger than 4mm, RFA has no positive effect, with a higher mortality rate. Apoptosis may play a role in brain tumor reaction after RFA.Part 3 Ultrasound-guided Intraoperative Radiofrequency Ablation in Surgery of Giant Intracranial MeningiomasObjective To study the value of intraoperative RFA and contrast-enhanced ultrasound(CEUS) in surgery of giant intracranial meningiomas.Methods Between September 2010 and February 2012, 52 giant meningiomas were operated with the intraoperative CEUS. From November 2010 to July 2011, 20 cases of tumor moderately or significantly enhanced on CEUS were chosen as Experimental Group, which were treated with intraoperative RFA before removal. The remaining 32 cases were underwent direct microsurgical resection. 25 cases of tumor moderately or significantly enhanced on CEUS were chosen as Control Group. 7 cases of tumor not enhanced or mildly enhanced on CEUS were chosen as CEUS-Negtive Group. The enhacement degree of the 52 giant meningiomas on CEUS and contrast enhancement MRI was compared.Results In this study, the enhancement patterns of meningiomas can be studied in a similar fashion to contrast enhanced MRI, but in real time and under full control of the ultrasound operator. CEUS of meningiomas showed consistent enhancement patterns with contrast enhancement MRI in most cases. Two of the ultrasound quantitative parameters, increased signal intensity and area under curve, were positively correlated with meningioma microvessel density. Blood loss in the surgery and consuming time of tumor resection, were both lower in Experimental Group than that of Control Group.Conclusions RFA can reduce the bleeding during giant intracranial meningioma surgery, shortening the duration of the operation. Intraoperative CEUS can not only accurately assess the blood supply of giant meningiomas, selecting the cases with rich blood supply suitable for RFA, but also guide positioning and assess its efficacy. Satisfactory devascularization and tumor softening were achieved after RFA without additional complications. |
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