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Background: Direct cortical stimulation of the mesial frontal premotor cortex, including the supplementary motor area (SMA), is challenging in humans. Limited access to these brain regions impedes understanding of human premotor cortex functional organization and somatotopy., Objective: To test whether seizure onset within the SMA was associated with functional remapping of mesial frontal premotor areas in a cohort of patients with epilepsy who underwent awake brain mapping after implantation of interhemispheric subdural electrodes., Methods: Stimulation trials from 646 interhemispheric subdural electrodes were analyzed and compared between patients who had seizure onset in the SMA (n = 13) vs patients who had seizure onset outside of the SMA (n = 12). 1:1 matching with replacement between SMA and non-SMA data sets was used to ensure similar spatial distribution of electrodes. Centroids and 95% confidence regions were computed for clustered head, trunk, upper extremity, lower extremity, and vision responses. A generalized linear mixed-effects model was used to test for significant differences in the resulting functional maps. Clinical, radiographic, and histopathologic data were reviewed., Results: After analyzing direct cortical stimulation trials from interhemispheric electrodes, we found significant displacement of the head and trunk responses in SMA compared with non-SMA patients ( P < .01 for both). These differences remained significant after accounting for structural lesions, preexisting motor deficits, and seizure outcome., Conclusion: The somatotopy of the mesial frontal premotor regions is significantly altered in patients who have SMA-onset seizures compared with patients who have seizure onset outside of the SMA, suggesting that functional remapping can occur in these brain regions., (Copyright © Congress of Neurological Surgeons 2022. All rights reserved.)

Background: Three patients enrolled in a clinical trial of 5-aminolevulinic-acid (5-ALA)-induced fluorescence-guidance, which has been demonstrated to facilitate intracranial tumor resection, were found on neuropathological examination to have focal cortical dysplasia (FCD)., Objective: To evaluate in this case series visible fluorescence and quantitative levels of protoporphyrin IX (PpIX) during surgery and correlate these findings with preoperative magnetic resonance imaging (MRI) and histopathology., Methods: Patients were administered 5-ALA (20 mg/kg) approximately 3 h prior to surgery and underwent image-guided, microsurgical resection of their MRI- and electrophysiologically identified lesions. Intraoperative visible fluorescence was evaluated using an operating microscope adapted with a commercially available blue light module. Quantitative PpIX levels were assessed using a handheld fiber-optic probe and a wide-field imaging spectrometer. Sites of fluorescence measurements were co-registered with both preoperative MRI and histopathological analysis., Results: Three patients with a pathologically confirmed diagnosis of FCD (Types 1b, 2a, and 2b) underwent surgery. All patients demonstrated some degree of visible fluorescence (faint or moderate), and all patients had quantitatively elevated concentrations of PpIX. No evidence of neoplasia was identified on histopathology, and in 1 patient, the highest concentrations of PpIX were found at a tissue site with marked gliosis but no typical histological features of FCD., Conclusion: FCD has been found to be associated with intraoperative 5-ALA-induced visible fluorescence and quantitatively confirmed elevated concentrations of the fluorophore PpIX in 3 patients. This finding suggests that there may be a role for fluorescence-guidance during surgical intervention for epilepsy-associated FCD., (Copyright © 2018 by the Congress of Neurological Surgeons.)

Background: Subdural electrodes are often implanted for localization of epileptic regions. Postoperative computed tomography (CT) is typically acquired to locate electrode positions for planning any subsequent surgical resection. Electrodes are assumed to remain stationary between CT acquisition and resection surgery., Objective: To quantify subdural electrode shift that occurred between the times of implantation (Crani 1), postoperative CT acquisition, and resection surgery (Crani 2)., Methods: Twenty-three patients in this case series undergoing subdural electrode implantation were evaluated. Preoperative magnetic resonance and postoperative CT were acquired and coregistered, and electrode positions were extracted from CT. Intraoperative positions of electrodes and the cortical surface were digitized with a coregistered stereovision system. Movement of the exposed cortical surface was also tracked, and change in electrode positions was calculated relative to both the skull and the cortical surface., Results: In the 23 cases, average shift of electrode positions was 8.0 ± 3.3 mm between Crani 1 and CT, 9.2 ± 3.7 mm between CT and Crani 2, and 6.2 ± 3.0 mm between Crani 1 and Crani 2. The average cortical shift was 4.7 ± 1.4 mm with 2.9 ± 1.0 mm in the lateral direction. The average shift of electrode positions relative to the cortical surface between Crani 1 and Crani 2 was 5.5 ± 3.7 mm., Conclusion: The results show that electrodes shifted laterally not only relative to the skull, but also relative to the cortical surface, thereby displacing the electrodes from their initial placement on the cortex. This has significant clinical implications for resection based upon seizure activity and functional mapping derived from intracranial electrodes.

Background: Current methods of spine registration for image guidance have a variety of limitations related to accuracy, efficiency, and cost., Objective: To define the accuracy of stereovision-mediated co-registration of a spinal surgical field., Methods: A total of 10 explanted porcine spines were used. Dorsal soft tissue was removed to a variable degree. Bone screw fiducials were placed in each spine and high-resolution computed tomography (CT) scanning performed. Stereoscopic images were then obtained using a tracked, calibrated stereoscopic camera system; images were processed, reconstructed, and segmented in a semi-automated manner. A multistart registration of the reconstructed spinal surface with preoperative CT was performed. Target registration error (TRE) in the region of the laminae and facets was then determined, using bone screw fiducials not included in the original registration process. Each spine also underwent multilevel laminectomy, and TRE was then recalculated for varying amounts of bone removal., Results: The mean TRE of stereovision registration was 2.19 ± 0.69 mm when all soft tissue was removed and 2.49 ± 0.74 mm when limited soft tissue removal was performed. Accuracy of the registration process was not adversely affected by laminectomy., Conclusion: Stereovision offers a promising means of registering an open, dorsal spinal surgical field. In this study, overall mean accuracy of the registration was 2.21 mm, even when bony anatomy was partially obscured by soft tissue or when partial midline laminectomy had been performed.

Background: In open-cranial neurosurgery, preoperative magnetic resonance (pMR) images are typically coregistered for intraoperative guidance. Their accuracy can be significantly degraded by intraoperative brain deformation, especially when resection is involved., Objective: To produce model updated MR (uMR) images to compensate for brain shift that occurred during resection, and evaluate the performance of the image-updating process in terms of accuracy and computational efficiency., Methods: In 14 resection cases, intraoperative stereovision image pairs were acquired after dural opening and during resection to generate displacement maps of the surgical field. These data were assimilated by a biomechanical model to create uMR volumes of the evolving surgical field. A tracked stylus provided independent measurements of feature locations to quantify target registration errors (TREs) in the original coregistered pMR and uMR as surgery progressed., Results: Updated MR TREs were 1.66 ± 0.27 and 1.92 ± 0.49 mm in the 14 cases after dural opening and after partial resection, respectively, compared to 8.48 ± 3.74 and 8.77 ± 4.61 mm for pMR, respectively. The overall computational time for generating uMRs after partial resection was less than 10 min., Conclusion: We have developed an image-updating system to compensate for brain deformation during resection using a computational model with data assimilation of displacements measured with intraoperative stereovision imaging that maintains TREs less than 2 mm on average.

Background: The use of image guidance during spinal surgery has been limited by several anatomic factors such as intervertebral segment motion and ineffective spine immobilization. In its current form, the surgical field is coregistered with a preoperative computed tomography (CT), often obtained in a different spinal confirmation, or with intraoperative cross-sectional imaging. Stereovision offers an alternative method of registration., Objective: To demonstrate the feasibility of stereovision-mediated coregistration of a human spinal surgical field using a proof-of-principle study, and to provide preliminary assessments of the technique's accuracy., Methods: A total of 9 subjects undergoing image-guided pedicle screw placement also underwent stereovision-mediated coregistration with preoperative CT imaging. Stereoscopic images were acquired using a tracked, calibrated stereoscopic camera system mounted on an operating microscope. Images were processed, reconstructed, and segmented in a semi-automated manner. A multistart registration of the reconstructed spinal surface with preoperative CT was performed. Registration accuracy, measured as surface-to-surface distance error, was compared between stereovision registration and a standard registration., Results: The mean surface reconstruction error of the stereovision-acquired surface was 2.20 ± 0.89 mm. Intraoperative coregistration with stereovision was performed with a mean error of 1.48 ± 0.35 mm compared to 2.03 ± 0.28 mm using a standard point-based registration method. The average computational time for registration with stereovision was 95 ± 46 s (range 33-184 s) vs 10to 20 min for standard point-based registration., Conclusion: Semi-automated registration of a spinal surgical field using stereovision is possible with accuracy that is at least comparable to current landmark-based techniques., (Copyright © 2017 by the Congress of Neurological Surgeons)

Background: Extent of resection (EOR) correlates with glioblastoma outcomes. Resectability and EOR depend on anatomical, clinical, and surgeon factors. Resectability likely influences outcome in and of itself, but an accurate measurement of resectability remains elusive. An understanding of resectability and the factors that influence it may provide a means to control a confounder in clinical trials and provide reference for decision making., Objective: To provide proof of concept of the use of the collective wisdom of experienced brain tumor surgeons in assessing glioblastoma resectability., Methods: We surveyed 13 academic tumor neurosurgeons nationwide to assess the resectability of newly diagnosed glioblastoma. Participants reviewed 20 cases, including digital imaging and communications in medicine-formatted pre- and postoperative magnetic resonance images and clinical vignettes. The selected cases involved a variety of anatomical locations and a range of EOR. Participants were asked about surgical goal, eg, gross total resection, subtotal resection (STR), or biopsy, and rationale for their decision. We calculated a "resectability index" for each lesion by pooling responses from all 13 surgeons., Results: Neurosurgeons' individual surgical goals varied significantly ( P = .015), but the resectability index calculated from the surgeons' pooled responses was strongly correlated with the percentage of contrast-enhancing residual tumor ( R = 0.817, P < .001). The collective STR goal predicted intraoperative decision of intentional STR documented on operative notes ( P < .01) and nonresectable residual ( P < .01), but not resectable residual., Conclusion: In this pilot study, we demonstrate the feasibility of measuring the resectability of glioblastoma through crowdsourcing. This tool could be used to quantify resectability, a potential confounder in neuro-oncology clinical trials., (Copyright © 2016 by the Congress of Neurological Surgeons)

Background: The use of 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence has shown promise as a surgical adjunct for maximizing the extent of surgical resection in gliomas. To date, the clinical utility of 5-ALA in meningiomas is not fully understood, with most descriptive studies using qualitative approaches to 5-ALA-PpIX., Objective: To assess the diagnostic performance of 5-ALA-PpIX fluorescence during surgical resection of meningioma., Methods: ALA was administered to 15 patients with meningioma undergoing PpIX fluorescence-guided surgery at our institution. At various points during the procedure, the surgeon performed qualitative, visual assessments of fluorescence by using the surgical microscope, followed by a quantitative fluorescence measurement by using an intraoperative probe. Specimens were collected at each point for subsequent neuropathological analysis. Clustered data analysis of variance was used to ascertain a difference between groups, and receiver operating characteristic analyses were performed to assess diagnostic capabilities., Results: Red-pink fluorescence was observed in 80% (12/15) of patients, with visible fluorescence generally demonstrating a strong, homogenous character. Quantitative fluorescence measured diagnostically significant PpIX concentrations (cPpIx) in both visibly and nonvisibly fluorescent tissues, with significantly higher cPpIx in both visibly fluorescent (P < .001) and tumor tissue (P = .002). Receiver operating characteristic analyses also showed diagnostic accuracies up to 90% for differentiating tumor from normal dura., Conclusion: ALA-induced PpIX fluorescence guidance is a potential and promising adjunct in accurately detecting neoplastic tissue during meningioma resective surgery. These results suggest a broader reach for PpIX as a biomarker for meningiomas than was previously noted in the literature.

Background and Importance: Fluorescence-guided resection with 5-aminolevulinic acid (5-ALA), which has shown promising results in the resection of malignant gliomas, has been used for meningioma resection in an attempt to more clearly delineate the tumor margin. However, no article has investigated the fluorescence pattern of meningiomas on a histological level. Understanding the microscopic pattern of fluorescence could help assess the precision and utility of using 5-ALA for these tumors. We present the case of a recurrent atypical meningioma operated on with 5-ALA fluorescence-guided resection for delineation of tumor tissue from surrounding uninvolved dura., Clinical Presentation: A 53-year-old woman presented with recurrent atypical meningioma of the falx. Prior treatment included surgical resection 6 years earlier with subsequent fractionated radiation therapy and radiosurgery for tumor progression. The patient was given 5-ALA 20 mg/kg body weight dissolved in 100 mL water 3 hours before induction of anesthesia. Intraoperative fluorescence was coregistered with preoperative imaging. Neuropathological analysis of the resected falx with confocal microscopy enabled correlation of fluorescence with the extent of tumor on a histological level., Conclusion: Fluorescence guidance allowed clear intraoperative delineation of tumor tissue from adjacent, uninvolved dura. On a microscopic level, there was a very close correlation of fluorescence with tumor, but some tumor cells did not fluoresce., (Copyright © 2011 by the Congress of Neurological Surgeons)

Background: Several neurological disorders are treated with deep brain stimulation; however, the mechanism underlying its ability to abolish oscillatory phenomena associated with diseases as diverse as Parkinson's disease and epilepsy remain largely unknown., Objective: To investigate the role of specific neurotransmitters in deep brain stimulation and determine the role of non-neuronal cells in its mechanism of action., Methods: We used the ferret thalamic slice preparation in vitro, which exhibits spontaneous spindle oscillations, to determine the effect of high-frequency stimulation on neurotransmitter release. We then performed experiments using an in vitro astrocyte culture to investigate the role of glial transmitter release in high-frequency stimulation-mediated abolishment of spindle oscillations., Results: In this series of experiments, we demonstrated that glutamate and adenosine release in ferret slices was able to abolish spontaneous spindle oscillations. The glutamate release was still evoked in the presence of the Na channel blocker tetrodotoxin, but was eliminated with the vesicular H-ATPase inhibitor bafilomycin and the calcium chelator 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester. Furthermore, electrical stimulation of purified primary astrocytic cultures was able to evoke intracellular calcium transients and glutamate release, and bath application of 2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester inhibited glutamate release in this setting., Conclusion: Vesicular astrocytic neurotransmitter release may be an important mechanism by which deep brain stimulation is able to achieve clinical benefits.

Objective: This work presents qualitative and quantitative side-by-side comparisons of oblique coregistered magnetic resonance imaging (MRI) scans and ultrasound images obtained during 35 neurosurgical procedures., Methods: Spatially registered series of ultrasound images were recorded for subsequent off-line evaluation and comparison with corresponding preoperative MRI studies. The degree of misalignment was reduced by reregistering the target volume directly with segmented features., Results: The initial apparent spatial misalignment of the target volume after craniotomy ranged from 0.11 to 8.73 mm (mean, 4.01 mm). After reregistration, the mutual information in overlapping segmented features was increased, presumably evidence of a better alignment locally. Additionally, the degree of feature congruence, which was assessed quantitatively through a convex hull approximation, demonstrated that the ultrasound volume was consistently smaller than its MRI counterpart., Conclusion: Although intraoperative ultrasound tends to be difficult to interpret by itself, when accurately coregistered with preoperative MRI scans, its potential utility as a navigational guide is enhanced.

Objective: To measure and compensate for soft tissue deformation during image-guided neurosurgery, we have developed a novel approach to estimate the three-dimensional (3-D) topology of the cortical surface and track its motion over time., Methods: We use stereopsis to estimate the 3-D cortical topology during neurosurgical procedures. To facilitate this process, two charge-coupled device cameras have been attached to the binocular optics of a stereoscopic operating microscope. Before surgery, this stereo imaging system is calibrated to obtain the extrinsic and intrinsic camera parameters. During surgery, the 3-D shape of the cortical surface is automatically estimated from a stereo pair of images and registered to the preoperative image volume to provide navigational guidance. This estimation requires robust matching of features between the images, which, when combined with the camera calibration, yields the desired 3-D coordinates. After the 3-D cortical surface has been estimated from stereo pairs, its motion is tracked by comparing the current surface with its previous locations., Results: We are able to estimate the 3-D topology of the cortical surface with an average error of less than 1.2 mm. Executing on a 1.1-GHz Pentium machine, the 3-D estimation from a stereo pair of 1024 x 768 resolution images requires approximately 60 seconds of computation. By applying stereopsis over time, we are able to track the motion of the cortical surface, including the pulsatile movement of the cortical surface, gravitational sag, tissue bulge as a result of increased intracranial pressure, and the parenchymal shape changes associated with tissue resection. The results from 10 surgical patients are reported., Conclusion: We have demonstrated that a stereo vision system coupled to the operating microscope can be used to efficiently estimate the dynamic topology of the cortical surface during surgery. The 3-D surface can be coregistered to the preoperative image volume. This unique intraoperative imaging technique expands the capability of the current navigational system in the operating room and increases the accuracy of anatomic correspondence with preoperative images through compensation for brain deformation.

Objective: Intraoperative tissue deformation that occurs during the course of neurosurgical procedures may compromise patient-to-image registration, which is essential for image guidance. A new approach to account for brain shift, using computational methods driven by sparsely available operating room (OR) data, has been augmented with techniques for modeling tissue retraction and resection., Methods: Modeling strategies to arbitrarily place and move an intracranial retractor and to excise designated tissue volumes have been implemented within a computationally tractable framework. To illustrate these developments, a surgical case example, which uses OR data and the preoperative neuroanatomic image volume of the patient to generate a highly resolved, heterogeneous, finite-element model, is presented. Surgical procedures involving the retraction of tissue and the resection of a left frontoparietal tumor were simulated computationally, and the simulations were used to update the preoperative image volume to represent the dynamic OR environment., Results: Retraction and resection techniques are demonstrated to accurately reflect intraoperative events, thus providing an approach for near-real-time image-updating in the OR. Information regarding subsurface deformation and, in particular, changing tumor margins is presented. Some of the current limitations of the model, with respect to specific tissue mechanical responses, are highlighted., Conclusion: The results presented demonstrate that complex surgical events such as tissue retraction and resection can be incorporated intraoperatively into the model-updating process for brain shift compensation in high-resolution preoperative images.

Objective: Image-guided neurosurgery incorporating preoperatively obtained imaging information is subject to spatial error resulting from intraoperative brain displacement and deformation. A strategy to update preoperative imaging using readily available intraoperative information has been developed and implemented., Methods: Preoperative magnetic resonance imaging is used to generate a patient-specific three-dimensional finite element model of the brain by which deformation resulting from multiple surgical processes may be simulated. Sparse imaging data obtained subsequently, such as from digital cameras or ultrasound, are then used to prescribe the displacement of selected points within the model. Based on the model, interpolation to the resolution of preoperative imaging may then be performed., Results: The algorithms for generation of the finite element model and for its subsequent deformation were successfully validated using a pig brain model. In these experiments, the method recovered 84% of the intraoperative shift resulting from surgically induced tissue motion. Preliminary clinical application in the operating room has demonstrated feasibility., Conclusion: A strategy by which intraoperative brain deformation may be accounted for has been developed, validated in an animal model, and demonstrated clinically.

Objective: To determine whether magnetic resonance imaging (MRI), compared with computed tomography (CT), provides consistent and accurate target localization for ventrolateral thalamotomy and posteroventral pallidotomy., Methods: For 93 procedures (78 pallidotomies and 15 thalamotomies) in 83 patients, coordinates for the anterior commissure, posterior commissure, and stereotactic target were calculated from MRI- and CT-derived images and compared., Results: The mean differences for the target were -0.41 mm on the x axis (P < 0.001), 0.06 mm on the y axis (P = 0.412), and -0.34 mm on the z axis (P < 0.01). The mean absolute differences were 0.53 mm on the x axis (median, 0.50 mm; range, 0.00-2.00 mm), 0.46 mm on the y axis (median, 0.50 mm; range, 0.00-2.00 mm), and 0.78 mm on the z axis (median, 0.50 mm; range, 0.00-6.00 mm). The mean three-dimensional distance between MRI- and CT-derived coordinates for the anterior commissure was 1.65 mm, with a distance of more than 4 mm in two cases (2%). The mean three-dimensional distance for the posterior commissure was 1.65 mm, with a distance of more than 4 mm in two cases (2%). The mean three-dimensional distance for the target was 1.25 mm (median, 1.14 mm; range, 0.00-6.27 mm), with a distance of more than 4 mm in one case (1%)., Conclusion: Statistically significant but relatively small differences between MRI- and CT-derived target coordinates were found. In some cases (approximately 2% of this series), the differences between MRI- and CT-derived coordinates may be relatively large (greater than 4 mm and up to 8 mm). However, given the superior anatomic resolution of MRI and the nature of the stereotactic procedures under consideration, we conclude that MRI, when validated within an institution, may be used alone for target localization in pallidotomy and thalamotomy.

A history of Arctic and Antarctic exploration, whether to find a Northwest Passage, North Pole, or South Pole, is a story of triumph and tribulation. The hardship experienced by polar explorers in the last 1000 years permeates the tales of achievement. Physicians and surgeons have played prominent roles in all major polar explorations. No significant Arctic voyage, particularly in the last 300 years, was made without a member of the party trained in the management of medical emergencies and in basic surgery. During times of health, surgeons functioned as the voyage naturalists with expertise in biology, botany, zoology, and the writing of scientific catalogs. Spurred by our interest and fascination with the history of polar exploration, we reviewed the roles of physicians and natural scientists in Arctic and Antarctic adventures.

Objective: A quantitative analysis of intraoperative cortical shift and deformation was performed to gain a better understanding of the nature and extent of this problem and the resultant loss of spatial accuracy in surgical procedures coregistered to preoperative imaging studies., Methods: Three-dimensional feature tracking and two-dimensional image analysis of the cortical surface were used to quantify the observed motion. Data acquisition was facilitated by a ceiling-mounted robotic platform, which provided a number of precision tracking capabilities. The patient's head position and the size and orientation of the craniotomy were recorded at the start of surgery. Error analysis demonstrated that the surface displacement measuring methodology was accurate to 1 to 2 mm. Statistical tests were performed to examine correlations between the amount of displacement and the type of surgery, the nature of the cranial opening, the region of the brain involved, the duration of surgery, and the degree of invasiveness., Results: The results showed that a displacement of an average of 1 cm occurred, with the dominant directional component being associated with gravity. The mean displacement was determined to be independent of the size and orientation of the cranial opening., Conclusion: These data suggest that loss of spatial registration with preoperative images is gravity-dominated and of sufficient extent that attention to errors resulting from misregistration during the course of surgery is warranted.

The frameless stereotactic operating microscope has expanded the potential application of modern stereotaxis to procedures outside of the intracranial compartment by removing the constraint of a rigid frame. We studied seven patients all of whom had a history, examination, and imaging studies consistent with lumbosacral spinal pathology for which they subsequently underwent surgery with the operating microscope. The ability of the frameless stereotactic system with preoperative computed tomography data to locate the level of the lesion as well as define the boundary of the spinal pathology intraoperatively was assessed. In parallel with this application of the frameless system, we analyzed the relationship between the lumbar intervertebral disc spaces (L3-L4, L4-L5, L5-S1) and skin surface fiducials using lateral radiographs. In seven patients with extracranial cases (six herniated lumbar discs and one lumbar spondylolysis with Grade I spondylolisthesis) who underwent operations by this system, the accuracy of the digitization component of the system with respect to localization of an independent test fiducial was 3.28 mm (SD, 0.61). The accuracy of the entire system in locating the independent fiducial within the viewing plane was 6.05 mm (SD, 4.04). Disc space localization had a far greater error of 28.81 mm (SD, 7.49). There was no consistent pattern to the magnitude or direction of the displacement of the lumbar intervertebral discs with respect to the fiducial markers in the sagittal plane. Although accuracy at the level of the fiducial plane was similar to that of intracranial applications, paraspinal tissue and vertebral column deformations rendered poorer accuracy with deeper structures.

After toxicity studies in dogs, a preliminary feasibility trial of the continuous intracranial infusion of a muscarinic agonist was begun in four patients with biopsy-documented Alzheimer's disease. During the last 8 months, a totally implantable infusion system has been used to deliver bethanechol chloride into the cerebrospinal fluid of these patients at doses of 0.05 to 0.7 mg/day. Complications have been few and resolved spontaneously or were easily reversible. The subjective response to this treatment has been encouraging, with reports of improved cognitive and social function during drug infusion and a return to base line function with single-blind saline placebo infusions. Obviously, further evaluation will be necessary to demonstrate the efficacy of this treatment, and a double-blind placebo-controlled crossover trial is now being done. However, we think the preliminary results are encouraging and warrant the consideration of this approach as a potential treatment in patients with Alzheimer's disease.

Lhermitte-Duclos disease is a rare disorder characterized by a slowly enlarging mass lesion in the cerebellum. The pathophysiology of the disease is poorly understood, but recent reports have suggested that a clinically significant mass may recur many years after total gross removal of the tumor. Computed tomography and angiography have been relatively insensitive in imaging the tumor either at presentation or during the postoperative period. The authors present three patients with histologically proven Lhermitte-Duclos disease who have undergone magnetic resonance imaging (MRI). In the first case, preoperative T1- and T2-weighted images clearly demonstrated the location and extent of the lesion, which was verified at operation. In the other two cases, only postoperative images were obtained. These demonstrated the extent of residual tumor and indicate a high probability of lesion expansion during periods of 4 and 10 years, respectively. We conclude that MRI is an important tool in both the diagnosis and the treatment of patients with Lhermitte-Duclos disease.