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André Olivier, Isabelle M. Germano, Arthur Cukiert and Terry Peters

✓ Frameless stereotactic techniques used in conjunction with three-dimensional images allow accurate planning and performance of a variety of neurosurgical procedures. The authors have used the frameless stereotactic Allegro Viewing Wand system to provide real-time correlation of the operating field and computerized images in 42 neurosurgical operations, including 31 epilepsy procedures. The system consists of an image-processing computer that creates three-dimensional and triplanar images; a mobile computer to display reformatted magnetic resonance images; and a hand-guided, articulated, position-sensing arm with a probe. At the start of the operation, the probe identifies the patient's facial and scalp features and correlates these with the computerized images. The position-sensing arm can then guide the operation and locate anatomical structures and lesions of interest. This system can be used to advantage in performing smaller craniotomies and intraoperatively locating anatomical structures and lesions to be removed. Postoperative magnetic resonance images demonstrate that this technique was accurate to within 3 mm in measuring the anteroposterior resection of fixed structures, such as hippocampus and corpus callosum. Disadvantages include longer preoperative preparation for data analysis and lack of both real-time computer analysis of tissue removal and angiographic data display. Preliminary experience suggests that the viewing wand system's advantages outweigh the disadvantages, and it is most helpful as an adjunctive navigational device in the microsurgical treatment of epilepsy.

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Kris A. Smith and Robert F. Spetzler

✓ The use of the supratentorial—infraoccipital approach is reported in seven patients with posteromedial temporal lobe lesions. No patient had permanent morbidity. Gross total resection of three low-grade gliomas and two gangliogliomas was achieved in five patients; one patient had subtotal resection of a low-grade glioma with adjacent gliosis, and one was initially thought to have a glioma but proved to have encephalomalacia on final pathological analysis. The patients ranged in age from 5 to 34 years. All seven patients presented with seizures, and four had uncontrolled seizures preoperatively. Six have been seizure-free since surgery (mean follow-up period 15 months), and one is well controlled on anticonvulsant medication. An anatomical study was performed to delineate the microsurgical anatomy relevant to operating on the medial temporal lobe through this posterior approach. A viewing wand intraoperative navigational system was utilized with this approach and proved helpful in gaining access as far anterior as the uncus through this occipital craniotomy. This approach is favorable in selected patients with posterior, medial, temporal lobe tumors because resection of otherwise difficult lesions may be accomplished without sacrificing lateral temporal lobe cortex or transecting the optic radiations.

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Iain H. Kalfas, Donald W. Kormos, Michael A. Murphy, Rick L. McKenzie, Gene H. Barnett, Gordon R. Bell, Charles P. Steiner, Mary Beth Trimble and Joseph P. Weisenberger

: Frameless stereotaxis for the insertion of lumbar pedicle screws. J Clin Neurosci 1 : 257 – 260 , 1994 Murphy MA, McKenzie RL, Kormos DW, et al: Frameless stereotaxis for the insertion of lumbar pedicle screws. J Clin Neurosci 1: 257–260, 1994 10. Reinhardt HF , Horstmann GA , Gratzl O : Sonic stereometry in microsurgical procedures for deep-seated brain tumors and vascular malformations. Neurosurgery 32 : 51 – 57 , 1993 Reinhardt HF, Horstmann GA, Gratzl O: Sonic stereometry in microsurgical procedures for

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Itzhak Fried, Valeriy I. Nenov, Steven G. Ojemann and Roger P. Woods

( Fig. 3a ). Intraoperatively, the use of frameless stereotaxis with a viewing wand (ISG, Toronto, Canada) enabled translation of the location on the brain to a corresponding location on the three-dimensional reconstruction of the preoperative MR image ( Fig. 3b ). The results of intraoperative electrical stimulation mapping were superimposed on the reconstructed brain surface. Shoulder movements were elicited with stimulation behind the lesion, whereas hand movements were elicited with stimulation immediately anterior and lateral to the lesion ( Fig. 3b ). These

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Martin J. Ryan, Robert K. Erickson, David N. Levin, Charles A. Pelizzari, R. Loch Macdonald and George J. Dohrmann

✓ The accuracy of a novel frameless stereotactic system was determined during 10 surgeries performed to resect brain tumors. An array of three charge-coupled device cameras tracked the locations of infrared light-emitting diodes on a hand-held stylus and on a reference frame attached to the patient's skull with a single bone screw. Patient—image registration was achieved retrospectively by digitizing randomly chosen scalp points with the system and fitting them to a scalp surface model derived from magnetic resonance (MR) images. The reference frame enabled continual correction for patient head movements so that registration was maintained even when the patient's head was not immobilized in a surgical clamp. The location of the stylus was displayed in real-time on cross-sectional and three-dimensional MR images of the head; this information was used to predict the locations of small intracranial lesions. The average distance (and standard deviation) between the actual position of the mass and its stereotactically predicted location was 4.8 ± 3.5 mm. The authors conclude that frameless stereotaxy can be used for accurate localization of intracranial masses without resorting to using fiducial markers during presurgical imaging and without immobilizing the patient's head during surgery.

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Eric M. Gabriel and Blaine S. Nashold Jr

, Lang E, Heilen R, et al: Stereotactic percutaneous lumbar discectomy. Neurosurgery 32: 582–586, 1993.) With the advent of frameless stereotaxis, the clinical utility of stereotactic technology for operations on the spine has expanded even further. Cadaveric and clinical data are being accumulated on the use of frameless stereotaxis in the accurate placement of pedicle screws for spinal fusions. For example, Nolte, et al. , 25 reported a method for safe and accurate placement of pedicle screw fixation in cadaveric lumbar vertebrae. Using a space pointer

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Kathryn Ko

✓ Computerized tomography scanning—derived narrow band reflection holograms of patients undergoing craniofacial procedures were created to evaluate the applicability of superimposing these three-dimensional images (3-D) on the operative field during neurological surgery. These sterilized radiological holograms were positioned over the surgical site by using bone sutures as registration points between the skull and the 3-D image to serve as a visual template between the patient and surgeon. Surgeries were then performed with the surgeon looking through the radiological hologram at the patient. Holograms were accurate to within 2 mm (plus or minus) of the actual calvarial anatomy. The use of the holographic image as a visual guide during surgery eliminated intraoperative guesswork or free-handed contouring. To the author's knowledge, this is the first report of the superimposed holographic image used in situ during surgery.

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Neil L. Dorward, Olaf Alberti, James D. Palmer, Neil D. Kitchen and David G. T. Thomas

✓ The authors present the results of accuracy measurements, obtained in both laboratory phantom studies and an in vivo assessment, for a technique of frameless stereotaxy. An instrument holder was developed to facilitate stereotactic guidance and enable introduction of frameless methods to traditional frame-based procedures. The accuracy of frameless stereotaxy was assessed for images acquired using 0.5-tesla or 1.5-tesla magnetic resonance (MR) imaging or 2-mm axial, 3-mm axial, or 3-mm helical computerized tomography (CT) scanning. A clinical series is reported in which biopsy samples were obtained using a frameless stereotactic procedure, and the accuracy of these procedures was assessed using postoperative MR images and image fusion.

The overall mean error of phantom frameless stereotaxy was found to be 1.3 mm (standard deviation [SD] 0.6 mm). The mean error for CT-directed frameless stereotaxy was 1.1 mm (SD 0.5 mm) and that for MR image—directed procedures was 1.4 mm (SD 0.7 mm). The CT-guided frameless stereotaxy was significantly more accurate than MR image—directed stereotaxy (p = 0.0001). In addition, 2-mm axial CT-guided stereotaxy was significantly more accurate than 3-mm axial CT-guided stereotaxy (p = 0.025). In the clinical series of 21 frameless stereotactically obtained biopsies, all specimens yielded the appropriate diagnosis and no complications ensued. Early postoperative MR images were obtained in 16 of these cases and displacement of the biopsy site from the intraoperative target was determined by fusion of pre- and postoperative image data sets. The mean in vivo linear error of frameless stereotactic biopsy sampling was 2.3 mm (SD 1.9 mm). The mean in vivo Euclidean error was 4.8 mm (SD 2 mm). The implications of these accuracy measurements and of error in stereotaxy are discussed.

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Kuniyoshi Abumi, Kiyoshi Kaneda, Yasuhiro Shono and Masanori Fujiya

, Moore MR, Marshall LF: A modified technique for cervical facet fusions. Clin Orthop Rel Res 230: 149–153, 1988 15. Glossop ND , Hu RW , Randle JA : Computer-aided pedicle screw placement using frameless stereotaxis. Spine 21 : 2026 – 2034 , 1996 Glossop ND, Hu RW, Randle JA: Computer-aided pedicle screw placement using frameless stereotaxis. Spine 21: 2026–2034, 1996 16. Graham AW , Swank ML , Kinard RE , et al : Posterior cervical arthrodesis and stabilization with a lateral mass

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Gene H. Barnett, David W. Miller and Joseph Weisenberger

Object. The goal of this study was to develop and assess the use and limitations of performing brain biopsy procedures by using image-guided surgical navigation systems (SNSs; that is, frameless stereotactic systems) with scalp-applied fiducial markers.

Methods. Two hundred eighteen percutaneous brain biopsies were performed in 213 patients by using a frameless stereotactic SNS that operated with either sonic or optical digitizer technology and scalp-applied fiducial markers for the purpose of registering image space with operating room space. Common neurosurgical and stereotactic instrumentation was adapted for use with a localizing wand, and recently developed target and trajectory guidance software was used.

Eight (3.7%) of the 218 biopsy specimens were nondiagnostic; five of these (2.4%) were obtained during procedures in 208 supratentorial lesions and three were obtained during procedures in 10 infratentorial lesions (30%; p < 0.001). Complications related to the biopsy procedure occurred in eight patients (seven of whom had supratentorial lesions and one of whom had an infratentorial lesion, p > 0.25). Five complications were intracerebral hemorrhages (two of which required craniotomy), two were infections, and one was wound breakdown after instillation of intratumoral carmustine following biopsy. There were only three cases of sustained morbidity, and there were two deaths and one delayed deterioration due to disease progression.

Two surgeons performed the majority of the procedures (193 cases). The three surgeons who performed more than 10 biopsies had complication rates lower than 5%, whereas two of the remaining four surgeons had complication rates greater than 10% (p = 0.15).

Twenty-three additional procedures were performed in conjunction with the biopsies: nine brachytherapies; five computer-assisted endoscopies; four cyst aspirations; two instillations of carmustine; two placements of Ommaya reservoirs; and one craniotomy.

Conclusions. Brain biopsy procedures in which guidance is provided by a frameless stereotactic SNS with scalp-applied fiducial markers represents a safe and effective alternative to frame-based stereotactic procedures for supratentorial lesions. There were comparable low rates of morbidity and a high degree of diagnostic success. Strategies for performing posterior fossa biopsies are suggested.