Stelter Klaus, Ledderose Georg, Hempel John Martin, Morhard Dominik F B, Flatz Wilhelm, Krause Eike, Mueller Joachim
Department of Otorhinolaryngology, Head and Neck Surgery, Institute for Clinical Radiology, Grosshadern Medical Centre, Ludwig-Maximilians-University, Munich, Germany.
Comput Aided Surg. 2012;17(3):153-60. doi: 10.3109/10929088.2012.668937. Epub 2012 Mar 27.
For successful cochlear implantation in difficult ears, image guided navigation systems can help identify surgical landmarks or confirm the surgeon's anatomical knowledge. In this pilot case study, exact navigation based on intraoperative CT scanning was investigated and helped confirm important and necessary landmarks, such as the facial nerve, cochlea and intracochlear structures, and at least adequate placement of a straight electrode array.
Intraoperative imaging was performed on a 40-slice sliding-gantry CT scanner (Siemens SOMATOM Sensation 40 Open) with an expanded gantry bore (82 cm). Raw image data were reconstructed with a slice thickness and increment of 0.6 mm and were imported to a frameless infrared-based navigation station (BrainLAB VectorVision Sky). In a preoperative accuracy and feasibility study, a phantom skull was scanned and registered five times by the navigation system. Based on the encouraging results, the system was then applied to a male patient with post-traumatic sensorineural hearing loss. The intraoperative target positioning error was measured by a "blinded" colleague who defined the distance of the pointer from different sections of the facial nerve without seeing the intraoperative field.
The average deviation in the phantom skull was 0.91 mm (SD 0.27 mm) on the mastoid, 1.01 mm (SD 0.21 mm) on the round window, and 0.9 mm (SD 0.18 mm) on the inner ear canal. Surgery could be performed without major complications. The distance of the pointer from the facial nerve could be defined exactly using navigation in ten measurements. The cochleostomy and electrode insertion were performed with the aid of navigation. After insertion, direct intraoperative control of the electrode position was achieved by means of a low-dose CT scan. Two months postoperatively, the patient had a satisfactory open-set speech understanding of 85%.
With the use of intraoperative acquisition of CT images (or digital volume tomography devices) and automatic volumetric registration for navigation, surgical precision can be improved, thereby allowing successful cochlear implant surgery in patients with complex malformations or who have undergone multiple previous ear surgeries and consequently lack anatomical landmarks. Our study clearly shows that this high-technology combination is superior to other registration methods in terms of accuracy and precision. Further investigations should aim at developing automatic segmentation and applications for minimally invasive surgery of the lateral skull base.
为了在疑难耳中成功进行人工耳蜗植入，图像引导导航系统有助于识别手术标志或确认外科医生的解剖学知识。在本前瞻性病例研究中，对基于术中CT扫描的精确导航进行了研究，有助于确认重要且必要的标志，如面神经、耳蜗及耳蜗内结构，以及至少将直电极阵列放置到位。
术中成像在一台具有扩展机架孔径（82厘米）的40层滑动机架CT扫描仪（西门子SOMATOM Sensation 40 Open）上进行。原始图像数据以0.6毫米的层厚和层间距进行重建，并导入到一个基于无框架红外线的导航工作站（BrainLAB VectorVision Sky）。在一项术前准确性和可行性研究中，一个仿真头颅被导航系统扫描并配准了5次。基于令人鼓舞的结果，该系统随后应用于一名患有创伤后感音神经性听力损失的男性患者。术中目标定位误差由一位“不知情”的同事测量，该同事在不看术野的情况下确定指针与面神经不同节段的距离。
在仿真头颅中，乳突处的平均偏差为0.91毫米（标准差0.27毫米），圆窗处为1.01毫米（标准差0.21毫米），内耳管处为0.9毫米（标准差0.18毫米）。手术得以顺利进行，未出现重大并发症。在10次测量中，通过导航能够精确确定指针与面神经的距离。耳蜗造口术和电极插入在导航辅助下完成。插入后，通过低剂量CT扫描实现了术中对电极位置的直接控制。术后两个月，患者开放短句言语识别率达到令人满意的85%。
通过术中获取CT图像（或数字容积断层扫描设备）并进行自动容积配准用于导航，可以提高手术精度，从而使复杂畸形或此前接受过多次耳部手术因而缺乏解剖标志患者的人工耳蜗植入手术得以成功。我们的研究清楚表明，这种高科技组合在准确性和精确性方面优于其他配准方法。进一步的研究应致力于开发自动分割技术以及用于侧颅底微创手术的应用。
