Donald W. Kormos

Use of a frameless, armless stereotactic wand for brain tumor localization with two-dimensional and three-dimensional neuroimaging

Preliminary experience with a frameless, armless stereotactic localization system in brain tumor surgery is presented. The localizing wand emits ultrasonic pulses that are detected by a table-mounted array of microphones--with triangulation of the emitter positions. The wand tip and trajectory are determined by proprietary computer software. Real-time display of this information is presented in multiple, two-dimensional or three-dimensional displays. Forty-eight patients underwent 52 craniotomies for brain tumors. The wand was used to assist in placing a minimal craniotomy in 48 cases, to determine the tumor/brain interface in 27 cases, to localize subcortical tumors in 14 cases, and to correlate the physiological mapping with the surface anatomy in 5 cases. In 12 instances, the wand was used in conjunction with frame stereotaxy and found to be comparable or superior. Triplanar (coronal, sagittal, transverse) two-dimensional images provided sufficient information for the detection of tumor boundaries but proved difficult to use to access a subcortical lesion; two-dimensional or three-dimensional images along the localization axis were more helpful. Frameless stereotaxy with this sonic wand system proved to be a useful adjunct to open-tumor biopsy or resection.

Glioma resection in a shared-resource magnetic resonance operating room after optimal image-guided frameless stereotactic resection.

OBJECTIVEWe describe a shared-resource intraoperative magnetic resonance imaging (MRI) design that allocates time for both surgical procedures and routine diagnostic imaging. We investigated the safety and efficacy of this design as applied to the detection of residual glioma immediately after an optimal image-guided frameless stereotactic resection (IGFSR). METHODSBased on the twin operating rooms (ORs) concept, we installed a commercially available Hitachi AIRIS II, 0.3-tesla, vertical field, open MRI unit in its own specially designed OR (designated the magnetic resonance OR) immediately adjacent to a conventional neurosurgical OR. Between May 1998 and October 1999, this facility was used for both routine diagnostic imaging (969 diagnostic scans) and surgical procedures (50 craniotomies for tumor resection, 27 transsphenoidal explorations, and 5 biopsies). Our study group, from which prospective data were collected, consisted of 40 of these patients who had glioma (World Health Organization Grades II–IV). These 40 patients first underwent optimal IGFSRs in the adjacent conventional OR, where resection continued until the surgeon believed that all of the accessible tumor had been removed. Patients were then transferred to the magnetic resonance OR to check the completeness of the resection. If accessible residual tumor was observed, then a biopsy and an additional resection were performed. To validate intraoperative MRI findings, early postoperative MRI using a 1.5-tesla magnet was performed. RESULTSIntraoperative images that were suitable for interpretation were obtained for all 40 patients after optimal IGFSRs. In 19 patients (47%), intraoperative MRI studies confirmed that adequate resection had been achieved after IGFSR alone. Intraoperative MRI studies showed accessible residual tumors in the remaining 21 patients (53%), all of whom underwent additional resections. Early postoperative MRI studies were obtained in 39 patients, confirming that the desired final extent of resection had been achieved in all of these patients. One patient developed a superficial wound infection, and no hazardous equipment or instrumentation problems occurred. CONCLUSIONUse of an intraoperative MRI facility that permits both diagnostic imaging and surgical procedures is safe and may represent a more cost-effective approach than dedicated intraoperative units for some hospital centers. Although we clearly demonstrate an improvement in volumetric glioma resection as compared with IGFSR alone, further study is required to determine the impact of this approach on patient survival.

Intraoperative Magnetic Resonance Imaging to Determine the Extent of Resection of Pituitary Macroadenomas during Transsphenoidal Microsurgery

OBJECTIVEWell-established surgical goals for pituitary macroadenomas include gross total resection for noninvasive tumors and debulking with optic chiasm decompression for invasive tumors. In this report, we examine the safety, reliability, and outcome of intraoperative magnetic resonance imaging (iMRI) used to assess the extent of resection, and thus the achievement of preoperative surgical goals, during transsphenoidal microneurosurgery. METHODSOur magnetic resonance operating room contains a Hitachi AIRIS II 0.3-T, vertical-field open magnet (Hitachi Medical Systems America, Inc., Twinsburg, OH). A motorized scanner tabletop moves the patient between the imaging and operative positions. For transsphenoidal surgery, the patient is positioned directly on the scanner tabletop so that the surgical field is located between 1.2 and 1.6 m from the magnet isocenter. At this location, the magnetic field strength is low (<20 G), thus permitting the use of many conventional surgical instruments. Thirty consecutive patients with pituitary macroadenomas underwent tumor resection in our magnetic resonance operating room by use of a standard transsphenoidal approach. After initial resection, the patient was advanced into the scanner for imaging. If residual tumor was demonstrated and deemed surgically accessible, the patient underwent immediate re-exploration. RESULTSiMRI was performed successfully in all 30 patients. In one patient, iMRI was used to clarify the significance of hemorrhage from the sellar region and resulted in immediate conversion of the procedure to a craniotomy. In the remaining 29 patients, initial iMRI demonstrated that the endpoint for extent of resection had been achieved in only 10 patients (34%) after an initial resection attempt, whereas 19 patients (66%) still had unacceptable residual tumor. All 19 of these latter patients underwent re-exploration. Ultimately, re-exploration resulted in the achievement of the planned endpoint for extent of resection in all of the 29 completed transsphenoidal explorations. Operative time was extended in all cases by at least 20 minutes. CONCLUSIONiMRI can be used to safely, reliably, and objectively assess the extent of resection of pituitary macroadenomas during the transsphenoidal approach. The surgeon is frequently surprised by the extent of residual tumor after an initial resection attempt and finds the intraoperative images useful for guiding further resection.

Intraoperative, real-time 3-D digitizer for neurosurgical treatment and planning

Summary form only given. An easy-to-use interface has been developed that allows real-time image localization and 3-D volume data set reformatting for use with computed-tomography (CT) and magnetic-resonance-imaging (MRI) images. As the basis for an intraoperative armless and frameless means of head stereotaxis, the surgeon uses a 3-D digitizer and an ultrasonic neurowand intraoperatively to register fiducials located on a patients head with image voxels stored in a workstation. Once this registration step is performed, the tip of the wand can be located in both the image and patient coordinate systems. In near real-time, coronal, sagittal, and axial sections (triplanar display) of the patients anatomy located by the wand are displayed on a graphics workstation. The neurowand has been used to chart and record the positions of scalp and intradural electroencephalography electrodes in 3-D MRI volume data sets. Three-dimensional rendering of these data reveals the precise location of the electrodes with respect to the gyral and sulcal anatomy of the brain.<<ETX>>

Registration of EEG electrodes with three-dimensional neuroimaging using a frameless, armless stereotactic wand.

A technique of image and electrode registration has been developed that allows electroencephalogram electrode location to be merged with 2-D or 3-D MRI or CT. An armless, frameless stereotactic localization system that may be used in or out of the operating room is used to generate spatial data for surface and accessible intracranial electrodes. Acquisition of electrode position data may be obtained before or after neuroimaging and the locations of additional electrodes added at any time. The methodology of this system and representative cases with MRI imaging are presented.

Frameless stereotaxis for the insertion of lumbar pedicle screws.

Spinal instrumentation and frameless stereotaxy are two separate fields in neurosurgery that have rapidly advanced in recent years. The application of stereotaxis to spinal surgery has previously been limited by the inaccuracy of surface mounted reference points. The development of frameless stereotaxy using anatomical registration techniques has overcome this problem and has allowed stereotactic techniques to be successfully applied to spinal surgery at our institution. We tested our frameless spinal stereotactic technique in cadaver studies with optimal screw placement. The technique is currently undergoing preliminary clinical evaluation. We review the technique and its application to spinal instrumentation.

Astrocytoma resection using an interactive frameless stereotactic wand: an early experience

18 patients with varying grades of astrocytoma had tumour resection using a new frameless, interactive sterotactic localizing wand. The system enables localizing information to be presented to the operator in multiple two-dimensional or three-dimensional displays in real time. In all cases the wand was used to help outline tumour boundaries in an attempt to resect solid tumour completely. Other uses included placing a minimal craniotomy or modifying an existing craniotomy in 17 (94%) patients, for intraoperative physiologic mapping in 2 (11%) and electrode placement in 1 (6%). All patients had a complete (98-100%) resection by postoperative MRI, and in 8 (44%) the tumour was removed from eloquent areas. Evaluation at approximately 6 weeks after surgery showed that 3 (16%) were improved, 14 (78%) were the same, and 1 (6%) was worse. On the second postoperative day no patient was better than their preoperative status, 10 (56%) were the same, and 8 (44%) patients were clinically worse. At 3 months the figures were 2 (11%), 11 (61%), and 4 (22%) respectively, and 1 patient had expired. The extent of resection has been shown to be an important prognostic factor in both low and high grade astrocytomas. This system allows accurate volumetric near en bloc resection and this was achieved in 17 (94%) cases. In one case of hippocampal tumour the tumour was removed in a piecemeal fashion. This system is an effective low cost alternative to frame volumetric systems and is associated with minimal morbidity at 6 weeks.

The spinal vacuum phenomenon: Evaluation by gradient echo mr imaging

To evaluate the ability of gradient echo MR to define the vacuum phenomena, 14 cadaveric lumbar spines were imaged by spin echo and gradient echo MR, CT, and plain radiography following injection of varying amounts of air into the intervertebral disks. Gradient echo MR was more sensitive than spin echo MR or plain radiography in detecting the intradiskal gas collections as small as 0.1 cc. Computed tomography was a sensitive as gradient echo MR. Plain radiography was the least sensitive modality. Increasing the echo time of the gradient echo technique increased the conspicuity of the gas collections due to magnetic susceptibility effects.

Stereotactic magnetic resonance angiography.

Visualization of the surgical trajectory with respect to the cerebral vasculature may enhance the safety of some stereotactic neurosurgical procedures. Traditional stereotactic angiography is tedious and, being an invasive procedure, poses some risk to the patient. A technique of projecting a stereotactically defined surgical trajectory onto magnetic resonance angiograms is presented.

Modifications of the Compass Stereotactic Magnetic Resonance Localizer: Technical Note

Head size, shape, or optimal anterior support placement can preclude stereotactic localization using the Compass magnetic resonance imaging (MRI) localizer. The described modifications of MRI localization largely overcome these limitations and should allow for safer, more versatile MRI stereotactic localization with the Compass system in more patients than using standard techniques.