Stereotactic Approach Combined With 3D Ct Reconstruction On Radiofrequency Thermocoagulation Of The Gasserian Ganglion For Trigeminal Neuralgia

Background: The surgical treatment for trigeminal neuralgia includes craniotomy which is microvascular decompression(MVD) and minimally invasive surgery which is primarily percutaneous radiofrequency thermocoagulation(PRT) recently. Researches have shown that the two methods possess the same postoperative effectiveness and similar recurrence rate. In recent years, PRT is accepted by patients with trigeminal neuralgia increasingly for its favourable surgical safety. However, any procedure for the treatment of TN previously had not make a individual surgical plan and were blind and indefinite, repeated attempts and test for the placement of foramen oval(FO) are necessary. According to the principle that two points determine a straight line in three-dimensional space, the previous methods such as intraoperative radiographic fluoroscopy-guided and computed tomogrphy-guided percutaneous needle penetration of the FO can not define any one of the two points, stereotactic or neuronavigation guided procedure previously can define one point only. Using the treatment methods mentioned to define the puncture trajectory and puncture FO accurately is insufficient. As a result percutaneous needle penetration of the FO for PRT is fairly difficult occasionally, surgeons need repeated attempts to puncture FO which bring great pain and complications to patients. The problem that systematically and objectively assess the surgical difficult factors preoperatively, define the puncture trajectory, improve the surgical success rate of puncture and get rid of the blindness of the previous methods need to be solved urgently.Objectives: To analyze the role of three-dimensional computed tomographic(3D CT) reconstruction of the skull in assessment of surgical difficult factors and making surgical plan. Observe the effectiveness of stereotactic approach combined with 3D CT reconstruction on percutaneous radiofrequency thermocoagulation through foramen ovale on Gasserian Ganglion especially through difficult-to-access foramen ovale for the treatment of trigeminal neuralgia.Methods:(1) The study included 31 patients for whom thin-slice scans(0.625 mm) used for three-dimensional computed tomographic reconstruction of the skull base, maxilla, and mandible was conducted before surgery. On axial CT image, we measure the anatomical data of FO. On the 3D reconstructed image in the direction of the trajectory we measure the data for practical surgery.(2) Analyze the dimensions of FO and anatomical characteristics around the FO: measure the largest transverse diameter and the largest anterior–posterior diameter of the FO and calculate anatomical area of FO(AFO); Observe whether the lateral pterygoid plate obstruct in the direction of the trajectory, for the ones whose trajectory obstructed by the lateral pterygoid plate we calculate available puncture area of FO(APFO); Estimate whether the FO is difficult-to-access foramen ovale; On the 3D reconstructed image in the direction of the trajectory observe whether the mandible obstruct in the trajectory, for the ones whose trajectory obstructed by mandible or with small distance between the mandible and tooth ridge we advise patient to keep the mouth open during preoperative CT scan and surgical procedure.(3) Confirm the target on FO: For V1, the target is located at the inner third of the transverse diameter of the FO; For V2 and V3 the target is located at the half of the transverse diameter of the FO; Target on skull 3D reconstructed image and calculate the coordinates of X, Y, Z axis on corresponding axial CT image.(4) Confirm entry point on face: On the 3D skull reconstructed image in the direction of the trajectory mark a point between maxilla or mandible and adjust the point to coincide with the target on FO, on coronal and sagittal CT image of the trajectory confirm wether the trajectory through the two points be obstructed, if not the point marked was the entry point on face. Measure the spacial angle of the trajectory through the two points and calculate the arc angle and arm angle for stereotactic operation. On corresponding 3D facial reconstructed image measure the distance between the point marked and lateral labial commissure.(5) Stereotactic operation: The surgeons used Komai’s stereotactic instrument and a specially designed 177.5 mm-long radiofrequency probe(diameter, 0.9 mm with 5-mm exposed tip) and a probe holder(diameter, 1.0 mm; length, 43.0 mm) capable of holding the radiofrequency lesioning(RFL) needle for the procedures. Data of surgical plan is used to set stereotaxic apparatus. C-arm fluoroscopy is used to verify placement. Sensory stimulation studies were conducted to confirm the division of paresthesia, after confirming the absence of any adverse effects, radiofrequency thermocoagulation commenced.(6) Visual analogue score(VAS) is used to assess the effectiveness of the method.Result:(1) In all 31 patients, the anatomical largest transverse diameter of FO was 6.5mm(range: 10.4mm to 3.5 mm) in average, the available largest transverse diameter of FO was 6.5mm(range: 10.2mm to 3.7 mm); The anatomical largest anterior–posterior diameter of FO was 3.5mm(range: 1.6 mm to 8 mm) while the available largest anterior–posterior diameter was 3.1mm(range: 1.3 mm to 7.6 mm). Patients with largest transverse diameter<6.0mm have received more punctures than those >6.0mm(P< 0.001); patients with largest anterior–posterior diameter<3.2mm have received more punctures than those >3.2mm(P< 0.05).(2) In this study, 9 of the 31 patients(38.7%) possess the FO obstructed by the lateral pterygoid plate in the direction of the trajectory, 8 of the 9 patients(8/31, 25.8%) have the FO with AFO > 15.0 mm2 while APFO < 15.0 mm2, these FO are practically small FO.(3) 15 patients have the trajectory obstructed by the mandible, all these patients were requested to keep the mouth open during CT scan and operation.(4) The distance between the mandible and tooth ridge of patients was 12.9mm(range: 8.4 mm to 18.8 mm), 7 patients have the small distance(9.0±0.7mm) and were requested to keep the mouth open during CT scan and operation.(5) The number of times of puncture about patients(N=12) with no difficult factors and one difficult factors were 1.4±0.7 while those with multiple difficult factors were 2.6±0.9. Statistic analysis result shows that number of times of puncture about patients with multiple difficult factors was more than those with no difficult factors and one difficult factors(P< 0.001).(6) VAS of all 31 patients was 10 preoperative; 1 patient terminated the operation with the ineffectiveness of treatment; VAS of all 31 patients in first day, third day, tenth day and third month was respectively 1.9±2.1,2.2±2.2,1.8±1.8 and1.7±1.8. The effectiveness was 93.5% one day postoperatively and all 96.8% three days, ten days and three months postoperatively. 4 patients(4/31, 12.9%) underwent recurrence one year postoperatively with the acceptable discomfort and need not another procedure. No severe complication about surgery occurred, 6 patients(6/31, 19.4%) underwent mild numbness of face and improved in 3-6 months.Conclusion:(1) Using 3D CT reconstruction image of the skull to analyze and summarize the difficulty factor of needle penetration of the FO and to make effective individual surgical plan for PRT on Gasserian Ganglion can avoid the uncertainty and blindness of the previous methods.(2) Stereotactic approach combined with 3D CT reconstruction for percutaneous radiofrequency thermocoagulation on Gasserian Ganglion is a safe procedure and make operation on difficult-to-access foramen ovale accurate and effective.(3) Stereotactic approach combined with 3D CT reconstruction on radiofrequency thermocoagulation of the Gasserian Ganglion for trigeminal neuralgia is a new, accurate, effective and safe surgical model and a new idea for PRT.