Nauta H J
Division of Neurosurgery, University of Texas Medical Branch, Galveston 77555-0517.
Comput Med Imaging Graph. 1994 Jul-Aug;18(4):279-87. doi: 10.1016/0895-6111(94)90052-3.
The mechanical accuracy of several available stereotactic instruments is extremely high as measured in tests with rigid phantoms. The author's experience with stereotactic-guided resection by craniotomy using both "frameless" and framed methods simultaneously is that neither the image accuracy nor the mechanical accuracy of the instrument is the limiting factor in the usefulness of the guidance. Rather, it appears that the errors encountered in actual use have to do with tissue position changes which occur during the procedure. The accuracy may be better for extrinsic lesions rigidly attached to the skull, but for intrinsic lesions, tissue position changes occur following the release of cerebrospinal fluid, air entry into the subdural spaces, tumor debulking, or cyst drainage. The potential error appears to be worse with hydrocephalus, intraoperative dehydration, collapse of larger cysts, and debulking of large tumors. Even with very small intrinsic tumors in young, not atrophic patients, the error may be 5 mm. The need for intraoperative update of the guidance image is obvious if greater accuracy is required. The advantages of such "imaging-interactive" stereotactic surgery have long been apparent from stereotactic biopsy procedures performed in the CT scanner where errors such as needle deflection or hemorrhage can be appreciated and corrected promptly. With intraoperative scanning it is also possible to monitor the progress of a cyst aspiration and confirm the site of a biopsy to avoid unnecessary sampling in cases where the pathology is inherently equivocal.
在对刚性体模的测试中，几种现有立体定向器械的机械精度极高。作者同时使用“无框架”和有框架方法通过开颅手术进行立体定向引导切除的经验是，器械的图像精度和机械精度都不是引导有效性的限制因素。相反，实际使用中遇到的误差似乎与手术过程中发生的组织位置变化有关。对于牢固附着于颅骨的外在病变，精度可能更高，但对于内在病变，在脑脊液释放、空气进入硬膜下间隙、肿瘤减瘤或囊肿引流后会发生组织位置变化。在脑积水、术中脱水、较大囊肿塌陷和大肿瘤减瘤的情况下，潜在误差似乎更大。即使在年轻、无萎缩的患者中存在非常小的内在肿瘤，误差也可能达到5毫米。如果需要更高的精度，术中更新引导图像的必要性显而易见。这种“影像交互式”立体定向手术的优势长期以来在CT扫描仪中进行的立体定向活检程序中就已显现，在这些程序中，诸如针偏转或出血等误差能够被及时察觉并纠正。通过术中扫描，还可以监测囊肿抽吸的进展情况，并确认活检部位，以避免在病理本质上不明确的情况下进行不必要的采样。
