Th. Czech

Frameless stereotactic guided neurosurgery: Clinical experience with an infrared based pointer device navigation system

SummaryAn infrared based frameless stereotactic navigation device (Easy Guide Neuro) was investigated for its clinical applicability, registration/application accuracy and limitations in a standard operating room set-up.In a five-month period 40 frameless stereotactic procedures (23 female, 17 male, mean age 46.4, yrs range 10–83) including 36 craniotomies and 4 spinal surgery procedures were performed. Image registration, data transfer and operation planning using skin fixed fiducials (between 5–10, mean 6.6) and CCT in 12 patients/MRI in 28 patients, generally was done the day before surgery.Clinical applicability was proven in all procedures with an additional time for pre-operative imaging and system application in the OR of 50 min mean (35–120 range). A useful registration was achieved in 39/40 patients (97.5%) with a registration accuracy of 3.4 mm (range 1.8–6.7) for brain surgery cases and 14.4 mm (6.8–25) for spine cases. This resulted in intra-operative application accuracy values for brain surgery of 4.2 mm mean (range 1–12). Enhanced registration/application accuracy values over the test period from 4.2/3.8 mm mean (Cases 1–20) up to 3.2/2 mm mean (Cases 21–40) was observed. In spinal surgery an application accuracy of 11.3 mm mean (range 5–20) was found. An intra-operative re-calibration because of system-head drift was necessary in none of the patients, nevertheless, application accuracy degradation due to brain shift was detected in every case.In conclusion, the system allowed a time sufficient accurate frameless intra-operative localisation guidance in cavernoma, meningioma, glioma, and brain metastasis surgery. In spinal surgery, the application accuracy exceeded clinical usefulness due to high registration inaccuracy using skin markers.

Direct surgical approach to infraclinoidal aneurysms

SummaryA loose connective tissue layer covering the intracavernous portion of the internal carotid artery makes the exposure of the anterior syphon knee possible without opening the cavernous sinus. The approach leads by a fronto-latero-basal craniotomy to the anterior part of the cavernous sinus roof (transversal plate). The anatomical relationships are discussed. By means of surgical cases, both the ipsilateral and the contralateral approach to infraclinoidal aneurysms are demonstrated.

Improvement of presurgical patient evaluation by generation of functional magnetic resonance risk maps.

Recent functional magnetic resonance imaging (FMRI) replication studies show a high variability of active voxels within subjects and across runs - a potentially harmful situation for clinical applications. We tried to reduce these uncertainties inherent in current presurgical FMRI. For this, a new high quality head fixation device was used to detect reliably activated voxels over repeated measurements. In addition high correlation thresholds were applied to define the areas with highest probability of activation. The results show a focussing of such functional high risk areas to only a few voxels which localized close to intraoperative cortical stimulation. The generation of such FMRI risk maps may improve validity of clinical localization and facilitate the development of currently missing standards for maximized but still safe tumor resection.

Contour-guided brain tumor surgery using a stereotactic navigating microscope.

OBJECTIVE The benefit of intraoperative radiological data integration in approach planning and resection of brain tumors using a computer navigating microscope (MKM Zeiss) was investigated. METHODS Since February 1995, out of 86 MKM-guided surgical procedures, 53 contour-guided tumor cases (24 females, 29 males, mean age 51.6) including 16 metastasis, 14 glioblastomas, 10 low-grade gliomas, 6 anaplastic gliomas, 3 meningiomas and 4 others were performed. The preoperative planning was based on CT in 42 cases and Magnetic Resonance Tomography (MRT) in 11 cases using skin markers (4-9, mean 6). Neuroradiologically defined tumor contours were transferred into the ocular of the microscope and projected into the operating field during the procedure. RESULTS The advantages of the system were: (1) preoperative approach planning; (2) minimal, accurate skin incision and craniotomy; (3) intraoperative detection of deep seated lesions or lesion components; (4) determination of lesion boundaries; (5) minimized traumatization in/near eloquent areas. Mean registration accuracy improved from 5.3 mm for the first 10 cases up to 2 mm for the last 18 cases. In glioma surgery, the system provided exact definition of radiologically planned resection borders. In meningioma surgery, it allowed a tailored craniotomy, dura opening and resection, lowering the risk of recurrence. In metastasis surgery, it provided a safe approach to deep and eloquent located lesions. CONCLUSION Contour-guided operation planning and resection guidance using the investigated navigating microscope provides additional security to avoid some potential risks in brain tumor surgery.

Clinical evaluation of a new epidural pressure monitor

SummaryComparative measuring of epidural pressure using the Spiegelberg probe 1 and ventricular fluid pressure was carried out in 15 neurosurgical intensive-care patients. Deviations in both directions were established, with a trend toward overestimating ventricular pressure in epidural pressure measuring (r=0.77). Individual pulsations, spontaneous wave courses and therapy-induced pressure changes were reflected without delays. There were no complications observed with probe implantation periods for up to 6 days. The system has been shown to be mechanically stable and easy to implant. We believe the device to be fit for trend monitoring of intracranial pressure. As with other epidural pressure monitoring systems, false assessments of ventricular pressure may lead to wrong decisions as to the required therapy.

Para- and infraclinoidal aneurysms. Anatomy, surgical technique and report on 22 cases

The internal carotid artery in its intracavernous portion is covered by a soft connective tissue layer. At the entrance of the artery into the subarachnoid space there is a very dense fibrous ring fixing the artery wall at the roof of the cavernous sinus. After cutting the fibrous ring it is possible to dissect along the artery wall without opening the cavernous sinus. The anatomical details are described.

Intra-Operative Marking of Neuroanatomical Details — Helpful for Radiosurgery?

This report is a list of simple but effective techniques for marking important structures intra-operatively. During the last 2 years in 52 patients intra-operative marking techniques have been used. In 37 cases a small piece of fat has been taken. In 10 patients it was done by a radiopaque Barium impregnated silicon sphere and in 5 patients with a piece of a monofilament suture. Postoperative checks were done by conventional X-ray, computer tomography and Magnetic Resonance Imaging. The indication in all cases was to offer landmarks helpful for planning postoperative radiosurgery. In case of fat and radiopaque Barium impregnated silicone spheres the markings were always well defined and clear in contrast. In those cases where a piece of monofilament suture was used it was impossible to get clear postoperative information. In general there were no intra- or post-operative complications. All markers were well tolerated and no side effects have been observed so far. The advantages and disadvantages of each of these possibilities are described and discussed.