J. W. Berkelbach van der Sprenkel

Cerebral lactate detected by regional proton magnetic resonance spectroscopy in a patient with cerebral infarction.

Water-suppressed image-guided localized proton magnetic resonance spectroscopy was performed in a 59-year-old woman with two major brain infarcts. Spectra were measured in the infarcts, in an area between the infarcts, and in the healthy hemisphere. The volumes of interest were selected on the basis of a fast T2-weighted image. A 1331-2662 Hahn spin-echo sequence was used to suppress the water in the 8-cm3 volume that was selected by means of spatially resolved spectroscopy or stimulated echoes. The spectra were obtained in 5 minutes accumulation time. Spectral editing was applied to separate the resonance of lactate from that of other substances. Our results show no increase of lactate concentration within the infarcts after 6 months; however, a resonance was observed at 1.6 ppm, which is assigned to fatty acids. Peak intensities of brain-specific compounds were decreased. Six months after the onset of clinical symptoms (at the time of bypass surgery), a fivefold increase in lactate concentration compared with normal values was observed in the area between the two infarcts. Four months after bypass surgery, the lactate concentration in this area had decreased to only twice normal. We speculate that lactate is a marker of reversible or impending brain damage.

Neuronavigation and surgery of intracerebral tumours

Approximately four decades after the successful clinical introduction of framebased stereotactic neurosurgery by Spiegel and Wycis, frameless stereotaxy emerged to enable more elaborate image guidance in open neurosurgical procedures. Frameless stereotaxy, or neuronavigation, relies on one of several different localizing techniques to determine the position of an operative instrument relative to the surgical field, without the need for a coordinate frame rigidly fixed to the patients’ skull. Currently, most systems are based on the optical triangulation of infrared light sources fixed to the surgical instrument.In its essence, a navigation system is a three-dimensional digitiser that correlates its measurements to a reference data set, i.e. a preoperatively acquired CT or MRI image stack. This correlation is achieved through a patient-to-image registration procedure resulting in a mathematical transformation matrix mapping each position in ‘world space’ onto ‘image space’. Thus, throughout the remainder of the surgical procedure, the position of the surgical instrument can be demonstrated on a computer screen, relative to the CT or MRI images.Though neuronavigation has become a routinely used addition to the neurosurgical armamentarium, its impact on surgical results has not yet been examined sufficiently. Therefore, the surgeon is left to decide on a case-by-case basis whether to perform surgery with or without neuronavigation. Future challenges lie in improvement of the interface between the surgeon and the neuronavigator and in reducing the brainshift error, i.e. inaccuracy introduced by changes in tissue positions after image acquisition.

Temporal evolution of NMDA-induced excitoxicity in the neonatal rat brain measured with 1H nuclear magnetic resonance imaging.

The aim of this study is to characterize the evolution of excitotoxic damage in neonatal rat brain by diffusion-weighted and T2-weighted magnetic resonance imaging. Results are compared with histological findings. Magnetic resonance imaging was performed at various times (15 min, 24 h, 3 days and 5 days) after intrastriatal microinjection of N-methyl-D-aspartate (NMDA) at postnatal day 8. The transverse relaxation time (T2) and apparent diffusion coefficient of water were determined. The results show an acute reduction of the apparent diffusion coefficient, reflected by an ipsilateral hyperintensity in the diffusion-weighted images, within 15 min after intrastriatal NMDA injection. At this time no changes in the T2-weighted images were apparent. The volume of the hyperintensity was relatively large with a radius of approximately 2 mm and coincided with histological signs of pronounced karyo-dendritic swelling. Subcutaneous administration of MK-801 25 min after the intracerebral NMDA injection readily reversed the hyperintensity and resulted in complete protection as verified by histology. Areas with increased T2 values were observed 1 day after NMDA microinjection and corresponded to regions with obvious cell necrosis. Five days after NMDA injection the lesion was evident using both diffusion- and T2-weighted images and coincided with an overt lesion comprising areas of cell loss and dilatation of the ipsilateral ventricle. In conclusion, this study illustrates the possibility of using diffusion-weighted imaging as a tool to monitor efficacy of treatment strategies at an early stage of excitotoxic injury.

Magnesium therapy after aneurysmal subarachnoid haemorrhage a dose-finding study for long term treatment

Summary.u2003Background: Magnesium is a neuroprotective agent which might prevent or reverse delayed cerebral ischemia (DCI) after aneurysmal subarachnoid haemorrhage (SAH). Although the dosage for short-term magnesium therapy is well established, there is lack of knowledge on the dosage for extended use of magnesium. Our aim was to find a dosage schedule of magnesium sulphate to maintain a serum magnesium level of 1.0–2.0 mmol/L for 14 days to cover the period of DCI.u2003Methods: We prospectively studied 14 patients admitted within 48 hours after aneurysmal subarachnoid haemorrhage (SAH) to our hospital. Magnesium sulphate was administrated intravenously for 14 days, using 3 different dosage schedules. Group A (n=3) received a bolus injection of 16 mmol magnesium sulphate followed by a continuous infusion of 16 mmol/dayly; group B (n=6) a continuous infusion of 30 mmol/dayly; and group C (n=5) a continuous infusion of 64 mmol/dayly. Serum magnesium was measured at least every two days and all patients were under continuous observation during magnesium treatment. Renal magnesium excretion was measured only in group C.u2003Findings: In treatment group A the mean serum magnesium level during treatment was 1.03±0.14 (range 0.82–1.34) mmol/L, in group B 1.10±0.15 (range 0.87–1.43) mmol/L, and in group C 1.38±0.18 (range 1.11–1.98) mmol/L. The renal magnesium excretion in group C was equal to the administrated doses within 48 hours after treatment had started. All patients in group A reported a flushing sensation during the bolus injection; no other side effects were noted.u2003Interpretation: With a continuous intravenous dosage of 64 mmol/L per day, serum magnesium levels maintained within the range of 1.0–2.0 mmol/L for 14 days.

Temporal evolution of focal cerebral ischemia in the rat assessed by T2-weighted and diffusion-weighted magnetic resonance imaging

SummaryThe present study was undertaken to characterize the formation of ischemic brain edema using diffusion-weighted and T2-weighted magnetic resonance imaging in a rat model of focal ischemia. The extent of edema formation was measured from multislice diffusion-weighted and T2-weighted spin-echo images acquired at various times after ischemia. The spin-spin relaxation time (T2) and the apparent diffusion coefficient in normal and ischemic tissue were also determined. The results show that on the diffusion-weighted images the lesion was clearly visible at 30 minutes after ischemia, while on the T2-weighted images it became increasingly evident after 2–3 hours. On both types of images the hyperintense area increased in size over the first 48 hours. After 1 week the hyperintensity on the diffusion-weighted images rapidly disappeared and evolved as a hypointense lesion in the chronic phase. These results confirm the high sensitivity of diffusion-weighted MRI for the detection of early ischemia. The temporal course of the edema observed on T2W-images is in agreement with the reported increase of total water content occurring in this model. The increase of the lesion observed on the diffusion-weighted images during the first 2 days points to an aggravation of cytotoxic edema that parallels the changes in free water shown by the T2-weighted images. It is shown that the highly elevated T2s of the infarcted area several days after ischemia can substantially contaminate the diffusion-weighted images.

Frameless stereotactic subcaudate tractotomy for intractable obsessive–compulsive disorder

SummaryObsessive–compulsive disorder (OCD) is a chronic, disabling disorder. Psychosurgery may be indicated for a subset of patients for whom no conventional treatment is satisfactory. This paper focuses on the stereotactic subcaudate tractotomy (SST). Thus far, these procedures have been carried out using frame-based stereotactic techniques. However, modern – highly accurate – frameless stereotactic procedures have successfully been introduced in neurosurgical practice. We developed a novel frameless stereotactic subcaudate tractotomy procedure with promising initial results in a patient suffering from intractable OCD. This is the first report on frameless SST. Future studies should examine whether other ablative stereotactic psychosurgery procedures can be done using frameless stereotactic methods.

Clinical evaluation of stereotactic brain biopsies with an MKM-mounted instrument holder.

Summary¶Object. The aim of this study was to assess the clinical usefulness and accuracy of robot-assisted frameless stereotactic brain biopsies with a recently introduced MKM-mounted instrument holder.n Methods. Twenty-three patients with intracranial lesions participated in this study. Depending on the size of the intracranial lesion, fiducials for image-to-patient co-ordinate transformation consisted either of bone screws or adhesive markers. Shortly after surgery, postoperative MRI-imaging was performed to demonstrate the location of the biopsy site. These images were compared with the preoperative images to assess the biopsy localisation error.n Results. Postoperative biopsy sites could be demonstrated in six patients with bone screws and in 14 with adhesive markers. These two subgroups yielded average biopsy localisation errors of 3.3u2009mm (SD 1.7u2009mm) and 4.5u2009mm (SD 2.0u2009mm) respectively. This difference was not statistically significant. One biopsy was located in a liquefied haematoma. All others yielded pathological tissue. There were two postoperative haemorrhages, of which only one was temporarily symptomatic. There was no mortality in the first 30 days after surgery.n Conclusions. Robot-assisted frameless point-stereotactic techniques represent an alternative to frame-based techniques for the performance of stereotactic biopsies.

Frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles: a simple modification to free-hand procedures

The aim of this report is to introduce a simple modification to the free-hand frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles. In this technical note, we describe our experience with ventricular catheter placement in two children suffering from shunt dependent idiopathic intracranial hypertension using an image-guided instrument holder with a catheter guide. In both patients, the surgical procedure proved to be easy and accurate, with good initial clinical results. The use of an image-guided instrument holder is a modification to the free-hand frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles.

The impact of auditory feedback on neuronavigation

Summary.Object. We aimed to develop an auditory feedback system to be used in addition to regular neuronavigation, in an attempt to improve the usefulness of the information offered by neuronavigation systems.Instrumentation. Using a serial connection, instrument co-ordinates determined by a commercially available neuronavigation system were transferred to a laptop computer. Based on preoperative segmentation of the images, the software on the laptop computer produced an audible signal whenever the instrument moved into an area the surgeon wanted to avoid.Methods. To evaluate the impact of our setup on volumetric resections, phantom experiments were conducted. CT scans were acquired from eight blocks of floral foam. In each of these scans, a target-volume was segmented. This target-volume was subsequently resected using either regular neuronavigation or neuronavigation extended with auditory feedback. A ‘postoperative’ CT scan was used to compare the resection cavity to the preoperatively planned target-volume.Findings. The resemblance between the resection cavity and the target-volume was greater each time auditory feedback had been used. This corresponded with more complete removal of the target-volume. However, it also corresponded with the removal of more non-target ‘tissue’ in two out of four cases.Conclusions. The usefulness of auditory feedback was made plausible and the use of a new type of navigation phantom was illustrated. Based on these results, we recommend incorporation of auditory feedback in commercially available neuronavigation systems, especially since this is relatively inexpensive.

The postorbital approach to the middle cerebral artery in cats.

The study of the relation between behavior, cerebral blood flow, and metabolism in animal models of cerebral ischemia has gained interest in the last 10 years. The most suitable models are those with the fewest side effects. One-sided blindness caused by decompression of the eye and coagulation of the optic nerve has been an inevitable side effect of transorbital occlusion of the middle cerebral artery. The postorbital technique is a new surgical approach to the middle cerebral artery that leaves the intraorbital structures intact. After resection of the postorbital processes and gentle retraction of the eye, the optic foramen is approached with the help of an operating microscope. This approach is possible because cats have no lateral bony orbital wall. A subperiostal approach to the optic foramen is made, after which the optic foramen is enlarged. Opening of the dura gives access to the middle cerebral artery in the same way as the transorbital approach. In this way, occlusion of the middle cerebral artery is possible with minimal impairment of vision.