[Simulation in surgical training]

BACKGROUND

Patient safety during operations hinges on the surgeon's skills and abilities. However, surgical training has come under a variety of restrictions. To acquire dexterity with decreasingly "simple" cases, within the legislative time constraints and increasing expectations for surgical results is the future challenge.

OBJECTIVES

Are there alternatives to traditional master-apprentice learning?

MATERIALS AND METHODS

A literature review and analysis of the development, implementation, and evaluation of surgical simulation are presented.

RESULTS

Simulation, using a variety of methods, most important physical and virtual (computer-generated) models, provides a safe environment to practice basic and advanced skills without endangering patients. These environments have specific strengths and weaknesses.

CONCLUSIONS

Simulations can only serve to decrease the slope of learning curves, but cannot be a substitute for the real situation. Thus, they have to be an integral part of a comprehensive training curriculum. Our surgical societies have to take up that challenge to ensure the training of future generations.

[Space-occupying lesion of the nasopharynx and skull base]

We report the case of a 73-year-old female patient who presented with an asymptomatic tumor of the nasal cavity and nasopharynx as well as bilateral hydromyrinx. MRI scan showed a bilaterally symmetric liquor-intense mass of the skull base, which proved to be a transsphenoidal meningocele. Since the finding was incidental and symptoms were absent, high-risk surgical intervention was not recommended.

A new tool for the navigated placement of intracerebral chemotherapy catheters

OBJECTIVE

The aim of this report is to illustrate a method for the precise placement of chemotherapeutic delivery catheters with the aid of computer-assisted navigation systems.

MATERIALS AND METHODS

We have developed a cannula which can be referenced to our navigation system (BrainLab (®)) to advance and position catheters. The cannula has a length of 10 cm. In the case of a ventricular puncture, CSF will drain through holes at the tip and a side port of the cannula to caution the surgeon. The cannula is fixed to the BrainLab (®) adapter ML and navigated with a BrainLab (®) vector vision (®) system. Using the puncture software, the placement is planned and executed. After placing the cannula as planned, the mandrin is removed and the primed catheter moved forward. When resistance is felt the cannula is withdrawn over the catheter. Further catheters can be placed similarly.

RESULTS

Initial phantom tests showed a good target accuracy. Clinically we have used the cannula in 7 cases with good accuracy.

CONCLUSION

This newly designed tool is easy to handle and well integrated into the navigation system. It provides the means to place catheters precisely to the planned position. Potentially it can be combined with every navigation system using adaptable reference systems.

Entry points for catheter placement in convection-enhanced delivery--a retrospective anatomic analysis

INTRODUCTION

Planning the trajectories for catheter positioning in convection-enhanced delivery (CED) is delicate. The bulk flow follows the path of least resistance. Additional factors such as the varying tumor location and the functional relevance of the surrounding brain areas add to complicate the trajectory planning even further. Therefore several criteria have been established, dealing with the correct general entry and target point position. The goal of our study was to analyze the trajectories for CED catheters placed in our department to find preferable entry point positions.

METHODS

We retrospectively looked at 51 trajectories for CED catheters planned with neuronavigation during 2003-2005 for 21 patients with supratentorial malignant gliomas. We evaluated the entry points for their anatomic position, the functional relevance of the area and their parameter to reach the important white matter tracts for CED. This was done using the anatomic literature, macroscopical studies in our laboratory on human autopsy brains and MR imaging.

RESULTS

Most tumors were located in the fronto-temporo-parietal region. For these locations catheters were predominantly placed via the superior parietal lobule and the superior frontal gyrus. Looking at the anatomic literature and our laboratory results we characterized these areas with properties predisposing them for catheter placement as having wide superficial gyri and few deep sulci. In addition, they have far less functional relevance than the surrounding eloquent areas. Most relevant white matter tracts can be reached from these entry points. Accordingly, we have defined 2 areas that appear most suitable as entry points in CED catheter placement: the superior parietal lobule and superior frontal gyrus.

CONCLUSION

Inserting CED catheter via the described entry points will presumably save time in planning and reduce side effects.

Effects of positioning and notching of resurfaced femurs on femoral neck strength: a biomechanical test

PURPOSE

To assess the effects of positioning and notching of resurfaced femurs on the mechanical strength of third-generation saw bone (TGSB) femurs using an in vitro analogue bone model.

METHODS

30 TGSB femurs were equally divided into 6 resurfaced femur groups (intact, anatomic, varus, valgus, anatomically notched, and valgus notched) for testing the load to failure, stiffness, and total energy.

RESULTS

Compared to the intact femurs, the load to failure in all resurfaced femurs was significantly decreased by 29 to 57%. Among the resurfaced femurs, valgus and anatomic femurs had the highest load to failure, followed by valgus notched, varus, and anatomically notched femurs. Notching weakened the construct by a further 24 to 30%.

CONCLUSION

To minimise the risk of femoral neck fracture, resurfaced femoral heads should be placed in an anatomic or valgus orientation, and the superior cortex of the femoral neck should remain intact.

Neuronavigation and resection of lesions located in eloquent brain areas under local anesthesia and neuropsychological-neurophysiological monitoring

BACKGROUND

The aim of this study was to determine the safety and maximal extension of tumor resection achievable with a combination of awake craniotomy under local anesthesia, neuronavigation, and continuous neuropsychological and neurophysiological monitoring in patients with lesions within the eloquent brain.

METHODS

We have performed 55 resections of different pathologies with neuronavigation on 52 patients from January 1998 to December 2002. Mean age was 49 years, the male to female ratio was 37 to 15. All patients underwent a continuous examination by a neuropsychologist and repetitive cortical stimulations during the resection, and a 3-month postoperative neurological examination to determine functional outcome. Neurological outcome and results of resection of patients with gliomas were compared to a control group of 27 patients with lesions in the central region who were operated under general anesthesia during the same time period.

RESULTS

Tumor resection was stopped when a macroscopic total cytoreduction was achieved, or at the onset of neurological dysfunction. There was a higher rate of complete tumor resection (77% vs. 33%) and a lower rate of neurological deterioration (33% vs. 12%) in the study group compared to the control group. Overall, a complete resection in the study group was achieved in 40 patients (72%), a partial resection in 28%. Five patients developed a new deficit during surgery which resolved completely after a change of surgical strategy, 14 patients had a new deficit after surgery which improved within 3 months in 6 patients. There was no operative mortality.

CONCLUSION

The combination of neuronavigation with cortical stimulation and repetitive neurological and language examinations allows a more radical resection of tumors in eloquent brain areas, otherwise considered as inoperable.

Radiation dose of the lens in trans-sphenoidal pituitary surgery: pros and cons of a conventional setup using fluoroscopic guidance and CT-based neuronavigation

BACKGROUND AND PURPOSE

We determined the radiation dose in patients' lenses during pituitary surgery with either conventional fluoroscopy or CT-guided neuronavigation.

MATERIALS AND METHODS

Thermoluminescent dosimeters (TLD-100H) were attached to the lenses of an anthropomorphic Alderson-Rando head phantom. Simulation of the conventional setup of continuous fluoroscopy (61 kV peak, 2.01 mAs) with collimation and automatic exposure control was used with 1 TLD being removed every 5 seconds, followed by another experiment with 1 being removed every 30 seconds. For CT-guided neuronavigation, a spiral of 3-mm-thick sections without gap was performed (140 kV, 220 mA). Patients' charts (n = 87) were reviewed in terms of radiation exposure and perioperative complications.

RESULTS

Radiation dose is distance-dependent (P < .002), with an exposure-time-dependent linear increase (R(2) = 99.27, P < .0001) close to the primary beam only. The radiation dose of the CT (mean, 39.39 mGy) was fivefold higher compared with the maximal time of 3 minutes (8 mGy) reached in our patients by using the conventional setup. CT offers more detailed 3D anatomy available at any time intraoperatively. Tolerance doses needed to develop cataracts were not reached, and perioperative complications occurred without significant differences (Mann-Whitney U test, P = .39) using either method. Continuous use of fluoroscopy reached the mean value of CT after 14.33 minutes.

CONCLUSION

Neuronavigation provides better anatomic information and avoids repetitive exposure and accumulation to the staff, with the disadvantage of an increased radiation exposure to the patient causing at least no acute harm. Long-term effects are hard to prove but cannot be neglected either.

MR spectroscopy in patients with intracranial meningiomas

With magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), we tried to get more pre-operative information in patients with suspicious meningioma concerning the histologic diagnosis especially regarding WHO Grades I and II meningiomas. Apart from the known spectra and metabolites such as choline, creatine and N-acetyl-aspartate (NAA), recent publications have shown that lactate is often found in necrotic tumor tissue. Within a 2 year period, 39 patients with an intracranial meningioma were studied with MRS. In 62.5% of histologic atypical meningiomas (WHO Grade II), a lactate peak could be demonstrated in the pre-operative MRS. Interestingly, also patients with multiple meningiomas show different spectra of their tumors.

Activation of the supplementary motor area (SMA) during voluntary pelvic floor muscle contractions—An fMRI study

To identify cortical and subcortical regions involved in voluntary pelvic floor muscle control, functional magnetic resonance imaging (fMRI) was performed at 1.5 T in thirty healthy subjects (15 women, 15 men). The participants performed rhythmical (1 Hz) pelvic floor muscle contractions, which imitated the repetitive interruption of voiding. Since previous reports concerning the representation of pelvic floor muscles in the cortex of the medial wall are inconsistent, a conservative statistical threshold (FWE-corrected P<0.05) was used to detect the most robust foci of activation, and cytoarchitectonic probability maps were used to correlate the results with structural anatomical information. We found a strong and consistent recruitment of the supplementary motor area (SMA), with foci of peak activity located in the posterior portion of the SMA, suggesting that this region is specifically involved in voluntary pelvic floor muscle control. Further significant activations were identified bilaterally in the frontal opercula, the right insular cortex and the right supramarginal gyrus. They may reflect the attentive processing and evaluation of visceral sensations. Weaker signals were detected in the primary motor cortex (M1) and the dorsal pontine tegmentum. There was no significant correlation between bladder volumes and brain activation induced by pelvic floor muscle contractions. We found no significant gender-related differences.

[MRI of carotid stents: influence of stent properties and sequence parameters on visualization of the carotid artery lumen]

PURPOSE

To evaluate MR artifacts of carotid artery stents and to optimize stent properties and sequence parameters.

MATERIAL AND METHODS

Four carotid artery stents - Wallstent (mediloy), Precise (nitinol), ACCULINK (nitinol) and a stent prototype (nitinol) - were investigated in a flow model of the cervical vessels. The model was made of silicon tubing and a flow pump that produces realistic flow curves of the carotid artery. To investigate the effects of magnetic susceptibility and radiofrequency induced shielding artifacts, turbo spin echo and gradient echo sequences as well as CE-MRAs were measured. To improve the visualization of the stent lumen in a CE-MRA, flip angle as well as geometry and covering of the stent prototype were altered.

RESULTS

Susceptibility artifacts in stents of the carotid artery only influence the lumen visualization at the proximal and distal end of the braided mediloy stent. A change of stent coverings has no significant influence on radiofrequency artifacts, whereas a reduction in linking elements between stent segments and a change in diameter of stent struts improves visualization of the stent lumen. By increasing the flip angle in a CE-MRA, visualization of the stent lumen is possible in both mediloy and nitinol stents.

CONCLUSION

The choice of stent material and changes in stent geometry as well as the optimization of the flip angle of the CE-MRA may reduce susceptibility and radiofrequency artifacts, rendering feasible the CE-MRA of a stented carotid artery.

Surgical navigation in the open MRI

The introduction of MRI into neurosurgery has opened multiple avenues, but also introduced new challenges. The open-configuration intraoperative MRI installed at the Brigham and Women's Hospital in 1996 has been used for more than 500 open craniotomies and beyond 100 biopsies. Furthermore the versatile applicability, employing the same principles, is evident by its frequent use in other areas of the body. However, while intraoperative scanning in the SignaSP yielded unprecedented imaging during neurosurgical procedures their usage for navigation proved bulky and unhandy. To be fully integrated into the procedure, acquisition and display of intraoperative data have to be dynamic and primarily driven by the surgeon performing the procedure. To use the benefits of computer-assisted navigation systems together with immediate availability of intraoperative imaging we developed a software package. This "3D Slicer" has been used routinely for biopsies and open craniotomies. The system is stable and reliable. Pre- and intraoperative data can be visualized to plan and perform surgery, as well as to accommodate for intraoperative deformations, "brain shift", by providing online data acquisition.

Processing and visualization for diffusion tensor MRI

This paper presents processing and visualization techniques for Diffusion Tensor Magnetic Resonance Imaging (DT-MRI). In DT-MRI, each voxel is assigned a tensor that describes local water diffusion. The geometric nature of diffusion tensors enables us to quantitatively characterize the local structure in tissues such as bone, muscle, and white matter of the brain. This makes DT-MRI an interesting modality for image analysis. In this paper we present a novel analytical solution to the Stejskal-Tanner diffusion equation system whereby a dual tensor basis, derived from the diffusion sensitizing gradient configuration, eliminates the need to solve this equation for each voxel. We further describe decomposition of the diffusion tensor based on its symmetrical properties, which in turn describe the geometry of the diffusion ellipsoid. A simple anisotropy measure follows naturally from this analysis. We describe how the geometry or shape of the tensor can be visualized using a coloring scheme based on the derived shape measures. In addition, we demonstrate that human brain tensor data when filtered can effectively describe macrostructural diffusion, which is important in the assessment of fiber-tract organization. We also describe how white matter pathways can be monitored with the methods introduced in this paper. DT-MRI tractography is useful for demonstrating neural connectivity (in vivo) in healthy and diseased brain tissue.

Interventional and intraoperative magnetic resonance imaging

The goal of the Image Guided Therapy Program, as the name implies, is to develop the use of imaging to guide minimally invasive therapy. The program combines interventional and intraoperative magnetic resonance imaging (MRI) with high-performance computing and novel therapeutic devices. In clinical practice the multidisciplinary program provides for the investigation of a wide range of interventional and surgical procedures. The Signa SP 0.5 T superconducting MRI system (GE Medical Systems, Milwaukee, WI) has a 56-cm-wide vertical gap, allowing access to the patient and permitting the execution of interactive MRI-guided procedures. This system is integrated with an optical tracking system and utilizes flexible surface coils and MRI-compatible displays to facilitate procedures. Images are obtained with routine pulse sequences. Nearly real-time imaging, with fast gradient-recalled echo sequences, may be acquired at a rate of one image every 1.5 s with interactive image plane selection. Since 1994, more than 800 of these procedures, including various percutaneous procedures and open surgeries, have been successfully performed at Brigham and Women's Hospital (Boston, MA).

Registration of 3-D intraoperative MR images of the brain using a finite-element biomechanical model

We present a new algorithm for the nonrigid registration of three-dimensional magnetic resonance (MR) intraoperative image sequences showing brain shift. The algorithm tracks key surfaces of objects (cortical surface and the lateral ventricles) in the image sequence using a deformable surface matching algorithm. The volumetric deformation field of the objects is then inferred from the displacements at the boundary surfaces using a linear elastic biomechanical finite-element model. Two experiments on synthetic image sequences are presented, as well as an initial experiment on intraoperative MR images showing brain shift. The results of the registration algorithm show a good correlation of the internal brain structures after deformation, and a good capability of measuring surface as well as subsurface shift. We measured distances between landmarks in the deformed initial image and the corresponding landmarks in the target scan. Cortical surface shifts of up to 10 mm and subsurface shifts of up to 6 mm were recovered with an accuracy of 1 mm or less and 3 mm or less respectively.

Nasopharyngeal extension of a craniopharyngioma in a 4 year old girl

Nasopharyngeal extension of a craniopharyngioma is very rare and usually presents with headache, nasal obstruction and visual disturbances. We present a case of a 4 year old girl, who became symptomatic with visual deterioration. MRI showed a huge supra - and infrasellar cystic craniopharyngioma with extension into the sphenoid sinus. Primary treatment was a transnasal puncture of the cyst followed by a subfrontal approach with removal of the tumour preserving the chiasm and optic nerves. The visual acuity postoperatively improved while she needed hormone replacement due to panhypopituitarism. Follow-up 12 months after the operation showed no recurrence. This is the youngest patient of about 27 patients reported so far in the literature.

CURVES: curve evolution for vessel segmentation

The vasculature is of utmost importance in neurosurgery. Direct visualization of images acquired with current imaging modalities, however, cannot provide a spatial representation of small vessels. These vessels, and their branches which show considerable variations, are most important in planning and performing neurosurgical procedures. In planning they provide information on where the lesion draws its blood supply and where it drains. During surgery the vessels serve as landmarks and guidelines to the lesion. The more minute the information is, the more precise the navigation and localization of computer guided procedures. Beyond neurosurgery and neurological study, vascular information is also crucial in cardiovascular surgery, diagnosis, and research. This paper addresses the problem of automatic segmentation of complicated curvilinear structures in three-dimensional imagery, with the primary application of segmenting vasculature in magnetic resonance angiography (MRA) images. The method presented is based on recent curve and surface evolution work in the computer vision community which models the object boundary as a manifold that evolves iteratively to minimize an energy criterion. This energy criterion is based both on intensity values in the image and on local smoothness properties of the object boundary, which is the vessel wall in this application. In particular, the method handles curves evolving in 3D, in contrast with previous work that has dealt with curves in 2D and surfaces in 3D. Results are presented on cerebral and aortic MRA data as well as lung computed tomography (CT) data.

MR imaging-guided prostate biopsy with surgical navigation software: device validation and feasibility

Magnetic resonance (MR) imaging--guided prostate biopsy in a 0.5-T open imager is described, validated in phantom studies, and performed in two patients. The needles are guided by using fast gradient-recalled echo and T2-weighted fast spin-echo images. Surgical navigation software provided T2-weighted images critical to targeting the peripheral zone and the tumor. MR imaging can be used to guide prostate biopsy.

An integrated visualization system for surgical planning and guidance using image fusion and an open MR

A surgical guidance and visualization system is presented, which uniquely integrates capabilities for data analysis and on-line interventional guidance into the setting of interventional MRI. Various pre-operative scans (T1- and T2-weighted MRI, MR angiography, and functional MRI (fMRI)) are fused and automatically aligned with the operating field of the interventional MR system. Both pre-surgical and intra-operative data may be segmented to generate three-dimensional surface models of key anatomical and functional structures. Models are combined in a three-dimensional scene along with reformatted slices that are driven by a tracked surgical device. Thus, pre-operative data augments interventional imaging to expedite tissue characterization and precise localization and targeting. As the surgery progresses, and anatomical changes subsequently reduce the relevance of pre-operative data, interventional data is refreshed for software navigation in true real time. The system has been applied in 45 neurosurgical cases and found to have beneficial utility for planning and guidance. J. Magn. Reson. Imaging 2001;13:967-975.

An integrated visualization system for surgical planning and guidance using image fusion and an open MR

A surgical guidance and visualization system is presented, which uniquely integrates capabilities for data analysis and on-line interventional guidance into the setting of interventional MRI. Various pre-operative scans (T1- and T2-weighted MRI, MR angiography, and functional MRI (fMRI)) are fused and automatically aligned with the operating field of the interventional MR system. Both pre-surgical and intra-operative data may be segmented to generate three-dimensional surface models of key anatomical and functional structures. Models are combined in a three-dimensional scene along with reformatted slices that are driven by a tracked surgical device. Thus, pre-operative data augments interventional imaging to expedite tissue characterization and precise localization and targeting. As the surgery progresses, and anatomical changes subsequently reduce the relevance of pre-operative data, interventional data is refreshed for software navigation in true real time. The system has been applied in 45 neurosurgical cases and found to have beneficial utility for planning and guidance. J. Magn. Reson. Imaging 2001;13:967-975.

Serial intraoperative magnetic resonance imaging of brain shift

OBJECTIVE

A major shortcoming of image-guided navigational systems is the use of preoperatively acquired image data, which does not account for intraoperative changes in brain morphology. The occurrence of these surgically induced volumetric deformations ("brain shift") has been well established. Maximal measurements for surface and midline shifts have been reported. There has been no detailed analysis, however, of the changes that occur during surgery. The use of intraoperative magnetic resonance imaging provides a unique opportunity to obtain serial image data and characterize the time course of brain deformations during surgery.

METHODS

The vertically open intraoperative magnetic resonance imaging system (SignaSP, 0.5 T; GE Medical Systems, Milwaukee, WI) permits access to the surgical field and allows multiple intraoperative image updates without the need to move the patient. We developed volumetric display software (the 3D Slicer) that allows quantitative analysis of the degree and direction of brain shift. For 25 patients, four or more intraoperative volumetric image acquisitions were extensively evaluated.

RESULTS

Serial acquisitions allow comprehensive sequential descriptions of the direction and magnitude of intraoperative deformations. Brain shift occurs at various surgical stages and in different regions. Surface shift occurs throughout surgery and is mainly attributable to gravity. Subsurface shift occurs during resection and involves collapse of the resection cavity and intraparenchymal changes that are difficult to model.

CONCLUSION

Brain shift is a continuous dynamic process that evolves differently in distinct brain regions. Therefore, only serial imaging or continuous data acquisition can provide consistently accurate image guidance. Furthermore, only serial intraoperative magnetic resonance imaging provides an accurate basis for the computational analysis of brain deformations, which might lead to an understanding and eventual simulation of brain shift for intraoperative guidance.

Automated segmentation of MR images of brain tumors

An automated brain tumor segmentation method was developed and validated against manual segmentation with three-dimensional magnetic resonance images in 20 patients with meningiomas and low-grade gliomas. The automated method (operator time, 5-10 minutes) allowed rapid identification of brain and tumor tissue with an accuracy and reproducibility comparable to those of manual segmentation (operator time, 3-5 hours), making automated segmentation practical for low-grade gliomas and meningiomas.

Intra-operative MR guidance during trans-sphenoidal pituitary resection: preliminary results

The use of intra-operative MR image guidance has the potential to improve the precision, extent, and safety of trans-sphenoidal pituitary resections. The trans-sphenoidal approach to pituitary surgery has been performed for some time (1--3). Until now these surgeries have relied on direct visualization without the aid of image guidance. An open-bore configuration 0.5T SIGNA SP MR system (GE Medical Systems, Milwaukee, Wisconsin) has been used to provide image guidance for seventeen trans-sphenoidal pituitary adenoma resections (4). The intra-operative MRI system allowed the radiologist to successfully direct the surgeon toward the sella turcica while avoiding the cavernous sinus, optic chiasm and other critical structures. Imaging performed during the surgery monitored the extent of resection and allowed for removal of tumor beyond the surgeon's view in seven cases. Dynamic MR imaging was used to distinguish residual tumor from normal gland and postoperative changes, permitting more precise tumor localization. A heme-sensitive long TE gradient echo sequence was used to find the presence of hemorrhagic debris. All patients tolerated the procedure well without significant complications. J. Magn. Reson. Imaging 2001;13:136-141.

Intraoperative diffusion imaging on a 0.5 Tesla interventional scanner

Intraoperative line scan diffusion imaging (LSDI) on a 0.5 Tesla interventional MRI was performed during neurosurgery in three patients. Diffusion trace images were obtained in acute ischemic cases. Scan time per slice was 46 seconds and 94 seconds, respectively, for diffusion tensor images. Diagnosis of acutely developed vascular occlusion was confirmed with follow-up scans. White matter tracts were displayed with the principal eigenvectors and provided guidance for the tumor surgery. In all cases, the diagnostic utility of LSDI was established. J. Magn. Reson. Imaging 2001;13:115-119.

Motion robust imaging for continuous intraoperative MRI

The sensitivity of MR imaging to motion and susceptibility normally requires that the physician using intraoperative MRI cease surgical activity while image data sets are acquired. We demonstrate that line scan imaging allows the physician to continue operating without the delays caused by imaging. Consequently, patient anesthesia, surgery, and operating room time can be reduced. J. Magn. Reson. Imaging 2001;13:158-161.

Integration of interventional MRI with computer-assisted surgery

Interventional MRI (IMRI) has entered into a new stage in which computer-based techniques play an increasing role in planning, monitoring, and controlling the procedures. The use of interactive imaging, navigational image guidance techniques, and image processing methods is demonstrated in various applications. The integration of intraoperative MRI guidance and computer-assisted surgery will greatly accelerate the clinical utility of image-guided therapy in general and interventional MRI in particular. J. Magn. Reson. Imaging 2001;13:69-77.

[Neuronavigation in the region of the skull base]

Neuronavigation (computer-aided surgery planning and performance) has proven to be helpful in performing neurosurgical operations. The experiences of our department gained on more than 500 patients operated upon will be presented, with special focus on more than 100 operations for lesions on the skull base. Navigation is one of several modern surgical tools, its value cannot be defined without observing other improvements e.g. in the area of preoperative diagnostics, intraoperative monitoring, microsurgical instruments and microsurgical approaches.

Three-dimensional optical flow method for measurement of volumetric brain deformation from intraoperative MR images

A three-dimensional optical flow method to measure volumetric brain deformation from sequential intraoperative MR images and preliminary clinical results from five cases are reported. Intraoperative MR images were scanned before and after dura opening, twice during tumor resection, and immediately after dura closure. The maximum cortical surface shift measured was 11 mm and subsurface shift was 4 mm. The computed deformation field was most satisfactory when the skin was segmented and removed from the images before the optical flow computation.

Craniotomy for tumor treatment in an intraoperative magnetic resonance imaging unit

OBJECTIVE

The complex three-dimensional anatomic features of the brain and its vulnerability to surgical intervention make the surgical treatment of intracranial tumors challenging. We evaluated the surgical treatment of supratentorial tumors using intraoperative magnetic resonance imaging (MRI), which provides real-time guidance, allows localization of intracranial tumors and their margins, and facilitates continuous assessment of surgical progress.

METHODS

Sixty patients underwent craniotomies for tumor treatment in the General Electric intraoperative MRI unit at the Brigham and Women's Hospital (Boston, MA) during a 1-year period. The patients selected were those with intracranial tumors that were considered difficult to resect because of their locations or previous incomplete operations. Twenty-nine low-grade and 19 high-grade gliomas, 8 metastatic lesions, 2 meningiomas, 1 pineoblastoma, and 1 astroblastoma were resected.

RESULTS

Tumors were accurately localized and targeted, and the extent of resection, as well as any intraoperative complications, could be immediately assessed during surgery. Marked brain shifting occurred during the procedures, and repeated intraoperative imaging allowed surgical accommodation for this shifting. In more than one-third of the cases, intraoperative imaging showed residual tumor when resection appeared complete on the basis of surgical observation alone.

CONCLUSION

Intraoperative MRI is a revolutionary tool for the surgical treatment of brain tumors, providing observation of the procedure as it is being performed. With intraoperative MRI, tumor resection is safer, the extent of resection can be directly evaluated, and intraoperative complications can be noted if they occur. Outcomes after resection depend on minimizing injury to normal brain tissue and achieving maximal tumor resection. The use of intraoperative MRI directly affects these factors.

Intracranial cavernomas: indications for and results of surgery

Between April 1991 and April 1997, 46 patients were treated in our department presenting with intracranial cavernomas. Initial symptoms were focal seizures, bleeding episodes, and/or headaches. Mean age was 41 year (range 9 to 68 years). There were 24 female and 22 male patients. Computed tomography and magnetic resonance imaging were performed in order to establish the diagnosis, angiography was only indicated when the hemorrhaged area was so close to the subarachnoid space in the vicinity of the basal cisterns that an aneurysm had to be ruled out. Aggressive indication for surgery also in brainstem cavernomas was based on the natural history of the lesion, since the majority of patients presenting with intracranial bleeding had suffered several (up to six) episodes of previous hemorrhages. Patients' clinical status upon admission and accessibility of the cavernoma were taken into account for planning the operation. The operative planning and approach were greatly facilitated by using a neuronavigational device and intraoperative electrophysiological monitoring particularly in cavernomas located in the brainstem, thalamus, and medulla oblongata. Surgical removal of the lesions resulted in a new permanent neurological deficit only in two patients (4%). These data show that patients benefit from modern neurosurgical techniques in contrast to conservative approach in this disease of rather prolonged natural course.

[Interhemispheric subdural hematoma]

The interhemispheric subdural hematoma (ISH) is a special subdural hematoma with regard to both location and symptomatology. The most widely described clinical signs and symptoms associated with an ISH are a lucid interval and the falx syndrome. The latter is featured by a contralateral hemiparesis that is accentuated in the lower extremity but spares the face. Minor head trauma or a preexisting coagulation disorder are also often found. Nonsurgical treatment should be chosen in patients with little neurologic dysfunction and a stable clinical course. Patients with progressive neurologic deterioration and focal neurologic deficits should be operated on without delay. This article provides a review of 99 published cases of ISH and adds 3 cases to the existing literature.

[Perimesencephalic subarachnoid hemorrhage--an independent clinical picture of non-aneurysmatic subarachnoid hemorrhage with a benign course]

Two hundred seventy-three Patients with acute SAH were treated within the last 46 months (1.4.1991 to 31.1.1995). Diagnosis was made upon visible SAH on CT-scans or bloody spinal tap regardless of a negative CT-scan. These patients harbored 194 aneurysms, 25 AVM and cavernomas. Within the same time-period we treated 27 Patients without SAH but harboring vascular malformations (17 aneurysms, 10 AVM and cavernomas). In 30 patients (11%) no bleeding source was detectable. Fourteen of these patients (5.1%) had blood concentrated within the perimesencephalic cisterns on the CT-scans. On admission all of these 14 patients (8 men, 6 female, aged 30 to 63 years) were awake and without mentionable neurological deficit, equalling Hunt & Hess grade 1 (11 patients) and 2 (3 patients). Neither the initial nor control angiography revealed a vascular malformation as a bleeding source. MRI-scans performed for 11 patients did not reveal further etiological clues. During a follow-up interval of 3 to 48 months, none of these patients suffered a rebleeding. Vasospasm was not or only slightly present, no ischemia leading to neurological deficit. GOS reached 5 and Karnofsky-scale was 100 for all of these patients. We conclude that the perimesencephalic SAH is a homogeneous entity with a different natural course than the common aneurysmatic SAH. Probably leakage within the capillary or venous circulation causes this form of SAH with a benign clinical course. Further experience is required to determine whether control angiography is mandatory in these patents with a distinct CT appearance.

[Neuronavigation. Computer-assisted surgery in neurosurgery]

Computers in Neurosurgery were limited to diagnostics, planning stereotactic procedures, Radiosurgery and Radiation therapy. The possibility of intra-operative localisation only evolved since the mid 80's with the advent of more powerful computers. The computer adds more precision to microneurosurgical procedures, allowing neuronavigation in interaction with the computer. Diverse neuronavigationsystems are described in the literature [7-9, 11, 13]. We are working with the "ISG Viewing Wand" since april 1994. 113 operations were planed and executed aided by this system. We report on our experiences, the advantages and limitations of this system.