Computer-assisted Image Guidance Research Articles

Robotic-assisted percutaneous iliac screw fixation for destructive lumbosacral metastatic lesions: an early single-institution experience.

Robotic-assisted surgery is becoming more widely applied in surgical subspecialties due to its intraoperative and postoperative advantages such as minimally invasive approach, reduced blood loss, shorter hospital stay, and decreased incidence of postoperative complications. However, robotic devices were only recently introduced in the field of spinal surgery. Specifically, percutaneous approaches involving computer-assisted image guidance are relatively new in iliac screw fixation. Previous methods focused on the use of S2-alar-iliac (S2AI) screw fixation which allows for pelvic fixation without a need for side connectors. However, for patients with destructive lesions of the sacrum, placement of these S2AI screws may not be feasible. The purpose of this technical note is to illustrate the implementation of robotic-assisted percutaneous iliac screw fixation in two cases which allows for minimally invasive attachment to the proximal lumbar screws without a side connector and eliminates a potential source of instrumentation failure. Robotic-assisted percutaneous iliac screw fixation was performed on two patients. The robotics system was used to merge the fluoroscopic images with intraoperative computed tomography (CT) images to plan the trajectories for placement of bilateral pedicle and iliac screws. Intraoperative CT scan was again performed to confirm proper placement of all screws. Rods were then engaged bilaterally with the pedicle and iliac screws without the use of side connectors. The patients did not experience immediate postoperative complications and had stable hardware at one-month follow-up. Our cases demonstrate the surgical efficiency of robotic-assisted lumbo-iliac instrumentation which obviates the need to use a side connector, which is commonly used in iliac fixation. This eliminates a step, which can reduce the possibility of instrumentation failure. Robotic-assisted percutaneous iliac screw fixation is a safe and feasible technique to improve operative and clinical outcomes in complex spinal instrumentation surgeries.

The First Experience of Computer-Assisted Image Guidance in Laparoscopic Surgery: The Targeting Animation Guidance (TAG) System

The First Experience of Computer-Assisted Image Guidance in Laparoscopic Surgery: The Targeting Animation Guidance (TAG) System

The surgical learning curve and accuracy of minimally invasive lumbar pedicle screw placement using CT based computer-assisted navigation plus continuous electromyography monitoring - a retrospective review of 627 screws in 150 patients.

ObjectiveThis study retrospectively assessed the accuracy of placement of lumbar pedicle screws placed by a single surgeon using a minimally-invasive, intra-operative CT-based computer navigated technique in combination with continuous electromyography (EMG) monitoring. The rates of incorrectly positioned screws were reviewed in the context of the surgeon's experience and learning curve.MethodsData was retrospectively reviewed from all consecutive minimally invasive lumbar fusions performed by the primary author over a period of over 4 years from April 2008 until October 2012. All cases that had utilized computer-assisted intra-operative CT-based image guidance and continuous EMG monitoring to guide percutaneous pedicle screw placement were analysed for the rates of malposition of the pedicle screws. Pedicle screw malposition was defined as having occurred if the screw trajectory was adjusted intraoperatively due to positive EMG responses, or due to breach of the pedicle cortex by more than 2mm on intraoperative CT imaging performed at the end of the instrumentation procedure. Further analysis of the data was undertaken to determine if the rates of malposition changed with the surgeon's experience with the technique.ResultsSix hundred and twenty-seven pedicle screws were placed in one hundred and fifty patients. The overall rate of intraoperative malposition and subsequent adjustment of pedicle screw placement was 3.8% (24 of 627 screws). Screw malposition was detected by intraoperative CT imaging. Warning of potential screw misplacement was provided by use of the EMG monitoring. With increased experience with the technique, rates of intraoperative pedicle screw malposition were found to decrease from 5.1% of screws in the first fifty patients, to 2.0% in the last 50 patients. Only one screw was suboptimally placed at the end of surgery, which did not result in a neurological deficit.ConclusionThe use of CT-based computer-assisted navigation in combination with continuous EMG monitoring during percutaneous transpedicular screw placement results in very low rates of malposition and neural injury that compare favourably with previously reported rates. Pedicle screw placement accuracy continues to improve as the surgeon becomes more experienced with the technique.

Fijación lumbar posterior empleando el sistema de imagen quirúrgica O-arm: experiencia inicial

The use of transpedicular screw fixation has been widely accepted for the treatment of degenerative and traumatic pathology of the lumbar spine. Complications of spinal instrumentation can be serious. Screw misplacement can result in unintended durotomy, nerve root and/or cauda equina injury. In comparison to fluoroscopy-assisted screw placement, computer-assisted image guidance has been shown to achieve overall higher rates of accuracy. The O-arm is able to obtain computed tomography (CT)-type images with multiplanar reconstruction. In this study we evaluated a cohort of patients who underwent posterior lumbar fusion with pedicle screws utilizing the O-arm imaging system. A retrospective review of 40 consecutive patients who underwent posterior lumbar fusion surgery with O-arm utilization, was performed. The study population included 14 males and 26 females. Age range was 39-85 years with an average of 63.8 years. Twenty one patients had degenerative lumbar stenosis (52.5%) and 19 had spondylolisthesis (47.5%). Intraoperative CT-images were obtained. The mean time for surgery and screw placement was assessed. A total of 252 pedicle screws were sited using O-arm navigation system, with a mean of 6.3 screws per patient (range 4-10). On the basis of intraoperative CT, 3 screws were redirected, representing a 98.81% accuracy rate. The mean duration of surgery was 157.2 (90-240) minutes and the mean time for screw placement was 7.13 (3.08-15) minutes per screw. Three patients (7.5%) developed superficial wound infections which were treated conservatively. No patients required a return to the operating room because of screw malposition. The use of intraoperative O-arm imaging system with computer-assisted navigation significantly increases the surgical accuracy and safety of pedicle screw placement in lumbar fusion surgery.

Placement of thoracolumbar pedicle screws using O-arm-based navigation: technical note on controlling the operational accuracy of the navigation system

Suboptimal placements of pedicle screws may lead to neurological and vascular complications. Computer-assisted image guidance has been shown to improve accuracy in spinal instrumentation. Checking the accuracy of the navigation system during pedicle screw placement is fundamental. We describe a novel technique of using continuous accuracy check of the navigation system during O-arm-based neuronavigation to instrument the thoracolumbar region. Forty thoracic and 42 lumbar screws were inserted in 12 patients. The Mirza evaluation system was used to evaluate the accuracy of the inserted screws. There was no neurological injury and no need to reposition any screw. The accuracy of the screws placement was excellent. Our technique of continuous at will operational accuracy check of the neuronavigation system is associated with extreme accuracy of screw placement, no need to bring a patient back to the operating room to reposition a pedicle screw, and with excellent outcome.

Assessment of Pedicle Screw Placement Accuracy, Procedure Time, and Radiation Exposure Using a Miniature Robotic Guidance System

Controlled, cadaveric implantation trial. To evaluate the effect of a robotic guidance system on screw placement accuracy, amount of radiation exposure, and length of procedure time during percutaneous pedicle screw implantation. Pedicle screws are associated with low complication rates, and several computer-assisted image guidance systems exist that facilitate accurate screw placement. However, these systems may represent substantial radiation exposure risk to patients and surgeons. We implanted 234 pedicle screws in 12 cadavers (study group: 15 surgeons, 197 screws, and 10 specimens; control group: 2 surgeons, 37 screws, and 2 specimens). We measured procedure time, fluoroscopy time, and radiation exposure and evaluated screw placement accuracy with computed tomography scans. To evaluate the learning curve, we compared measurements with those of an experienced robotic guidance user through the 2-sample (heteroscedastic), 1-tail t test (P< 0.05). Relative to control, the study group had fewer screw placement deviations (average, 2.6±0.7 mm vs. 1.1±0.4 mm; P<0.0001), fewer pedicle wall breaches of 4 mm or greater (average, 5.4% vs. 1.5%), lower surgeon radiation exposure (average, 136 mrem vs. 4.2 mrem), lower fluoroscopy time per screw (average, 33.0 s vs. 0.9 s), and shorter procedure time (average, 1.98 h vs. 1.23 h). Use of robotic guidance increased the accuracy of percutaneous pedicle screw placement by 58%, thereby reducing the risk of neurologic injury (as measured by breaches >4 mm), new-user radiation exposure (by 98.2%), and procedure time (by 36%). The advantages associated with a robotic guidance system may make the surgeon more at ease about offering minimally invasive or percutaneous surgical options to patients and more comfortable about implementing pedicle-based fixation in general. This advanced technology may also allow inclusion of patients with complicated anatomic deformities, who are often excluded from pedicle screw-based surgery options.

Detection and Management of Skull Base Cerebrospinal Fluid Leaks Using HRCT-MRI Fusion Imaging

Background: Endoscopic repair of cerebrospinal fluid (CSF) leaks has been well described in the literature as an effective method for the treatment of sinonasal skull base defects. However, despite the ongoing evolution of the endoscopic techniques for repair, site localization is a diagnostic challenge. The limitations and morbidity associated with diagnostic imaging studies such as high-resolution computer tomography (HRCT), magnetic resonance imaging (MRI), and computed tomography (CT) cisternography in detecting CSF leaks has created a need for more accurate and less invasive radiographic imaging modalities. In our study, we evaluate a novel technique of fusing HRCT and MRI imaging for the detection of CSF leaks, as well as its ability to aid in intraoperative localization of skull base defects through computer-assisted image guidance.

Improving accuracy and reducing radiation exposure in minimally invasive lumbar interbody fusion

The authors assessed the accuracy of placement of lumbar transpedicular screws by using a computer-assisted, imaged-guided, minimally invasive technique with continuous electromyography (EMG) monitoring. This was a consecutive case series with prospective assessment of procedural accuracy. Forty-seven consecutive patients underwent minimally invasive lumbar interbody fusion and placement of pedicle screws (PSs). A computer-assisted image guidance system involving CT-based images was used to guide screw placement, while EMG continuously monitored the lumbar nerve roots at the operated levels with a 5-mA stimulus applied through the pedicle access needle. All patients underwent CT scanning to determine accuracy of PS placement. All episodes of adjusted screw trajectory based on positive EMG responses were recorded. Pedicle screw misplacement was defined as breach of the pedicle cortex by the screw of more than 2 mm. Two hundred twelve PSs were inserted in 47 patients. The screw misplacement rate was 4.7%. One patient experienced new postoperative radiculopathy resulting from a sacral screw that was too long, with lumbosacral trunk impingement. The trajectory of the pedicle access needle was altered intraoperatively on 20 occasions (9.4% of the PSs) based on positive EMG responses, suggesting that nerve root impingement may have resulted from these screws had the EMG monitoring not been used. The combination of computer-assisted navigation combined with continuous EMG monitoring during pedicle cannulation results in a low rate of PS misplacement, with avoidance of screw positions that might cause neural injury. Furthermore, this technique allows reduction of the radiation exposure for the surgical team without compromising the accuracy of screw placement.

Minimally invasive pedicle screw fixation utilizing O-arm fluoroscopy with computer-assisted navigation: Feasibility, technique, and preliminary results

Background:Pedicle screw misplacement is relatively common, with reported rates ranging up to 42%. Although computer-assisted image guidance (CaIG) has been shown to improve accuracy in open spinal surgery, its use in minimally invasive procedures has not been as well evaluated. We present our technique and review the results from a cohort of patients who underwent minimally invasive lumbar pedicle screw placement utilizing the O-arm imaging unit in conjunction with the StealthStation Treon System.Methods:A retrospective review of patients who underwent minimally invasive pedicle screw fixation with CaIG was performed. Eleven consecutive patients were identified and all were included. Nine patients underwent a single-level transforaminal lumbar interbody fusion. Two patients underwent multi-level fusion. Inaccurate pedicle screw placement was determined by postoperative computed tomography (CT) and graded as 0–2, 2–4, 4–6, or 6–8 mm.ResultsA total of 52 screws were placed. Forty screws were inserted in eight patients who had postoperative CT, and a misplacement rate of 7.5% was noted including one lateral and two medial breaches. All breaches were graded as 0–2 mm and were asymptomatic. In the remaining three patients, post-instrumentation O-arm imaging did not demonstrate pedicle screw misplacement.ConclusionAlthough this initial study evaluates a relatively small number of patients, minimally invasive pedicle screw fixation utilizing the O-arm and StealthStation for CaIG appears to be safe and accurate.

Minimally Invasive Image-Guided Removal of Retrobulbar Intraconal Foreign Body

Surgical approaches are becoming increasingly minimally invasive, without compromising either safety or ease. Penetrating ocular foreign bodies has traditionally been approached either by intraocular or supraorbital access. We successfully attempted a minimally invasive approach to remove a retrobulbar foreign body under computer-assisted image guidance in a 19-year-old man involved in an industrial mishap.

Thoracic Pedicle Screws

Experimental design using cadaveric computerized tomography (CT) scans and a computer-assisted image guidance system to compare various thoracic pedicle screw start points and trajectories. To compare described thoracic pedicle screw start points and trajectories to determine which allows strictly intrapedicular screw placement with the most margin of error. Thoracic pedicle screws are being used in a variety of spinal conditions to include fracture, tumor, and deformity. Optimal thoracic pedicle screw start points have received increasing attention in the literature. Optimal thoracic pedicle trajectory is still undetermined. Using fine cut CT scans of 3 cadaveric male specimens (aged 65-70 years) loaded onto a computer-assisted image guidance system, 966 pedicle screws, were virtually inserted. The effective pedicle diameter (EPD) and maximum insertional arc (MIA) was assessed using 3 different trajectories and start points: (1) straight ahead, (2) straight forward, and (3) anatomic. EPD was measured by placing a maximum-sized virtual screw, using a specific trajectory, without cortical violation of the pedicle and/or the vertebral body. The MIA was assessed by measurement of the angle formed by the most superiorly and inferiorly directed 0.1-mm virtual screw through a given start point without violation of the pedicle cortex and obtaining at least 50% vertebral body purchase. Mean EPD in the sagittal plane was 7.6 +/- 0.3 (SEM) mm for the straight forward trajectory and 9.1 +/- 0.3 (SEM) mm for the anatomic trajectory, a 20% increase (P < 0.0005). Mean EPD in the axial plane was 4.1 +/- 0.2 (SEM) mm for the straight ahead trajectory and 5.0 +/- 0.2 (SEM) mm for the anatomic trajectory, a 22% increase (P < 0.0005). EPD was found to be statistically different based on the trajectory used for placement in both the axial and sagittal planes in the upper (T1-T4), middle (T5-T8), and lower (T9-T12) thoracic spine. Mean MIA in the sagittal plane was 18.7 +/- 1.1 (SEM) for straight ahead start points, 25.8 degrees +/- 0.8 degrees (SEM) for straight forward start points, and 30.2 degrees +/- 0.8 degrees (SEM) for anatomic start points, a 38% increase (P < 0.0005) in MIA compared with straight ahead and a 17% increase (P < 0.0005) in MIA compared with straight forward. Mean MIA in the axial plane was 17.8 degrees +/- 0.6 degrees (SEM) for straight ahead and anatomic start points, and 18.6 degrees +/- 0.6 degrees (SEM) for straight forward start points. This difference was not statistically significant (P = 0.086). MIA was found to be statistically different based on start points used in the sagittal, but not the axial plane, in the upper, middle, and lower thoracic spine. EPD and MIA are trajectory (EPD) and start point (MIA) dependent. In the axial plane, anatomic EPD was greater than straight ahead EPD. In the sagittal plane, anatomic EPD was greater than straight forward EPD. Using anatomic start points in the sagittal plane, a greater MIA is achievable. These data suggest that in the diminutive thoracic pedicle or when a larger screw is needed, an anatomic trajectory using anatomic start points may allow a larger bone channel for intrapedicular placement of instrumentation.

Comparison of two novel fluoroscopy-based stereotactic methods for cervical pedicle screw placement and review of the literature

This experimental study was designed to compare two different fluoroscopy-based stereotactic surgical techniques for transcutaneous cervical pedicle screw (CPS) placement in the subaxial human cervical spine: (1) a custom-made aiming frame (AF) in combination with conventional fluoroscopy versus (2) a targeting device in combination with a computer-assisted image guidance system [i.e. virtual fluoroscopy (VF)]. Surgery was carried out on six preserved human total body specimens in a laboratory setting. Sixty pedicles (levels C3-C7) were measured in a multislice computed tomography (CT) image data set prior to surgery. Two groups consisting of three specimens and 30 pedicles each were defined according to the surgical technique. The AF consisted of radiolucent components with a fully adjustable arm for carrying the instruments necessary for placing the screws. The arm was angled according to the cervical pedicle axis, as determined by the preoperative CT scans and intraoperative lateral fluoroscopy. For VF, a targeting device was combined with a computer-assisted image-guided surgery unit. For both stereotactic techniques, 3.5 mm screws made of carbon fibre polyetheretherketone (ECF-PEEK) were inserted transcutaneously through stab incisions. Screw placement was assessed using a four-point grading system ranging from ideal (I) to unacceptable (III) where I = screw centred in pedicle, IIa = perforation of pedicle wall is less than one-fourth of the screw diameter, IIb = perforation of the pedicle wall is more than one-fourth of the screw diameter without contact to neurovascular structures, and III = CPS in contact with neurovascular structures. Fifty-eight pedicle screws could be evaluated without interfering metal artefacts according to the same CT protocol that was used preoperatively. The AF technique achieved a significantly smaller number of screws in contact with neurovascular structures compared with the VF technique (P = 0.021; Fisher's exact test) (Grade I n = 15; 64.3% AF vs. n = 13; 43.3% VF and Grade III n = 2; 7.1% AF vs. n = 10; 33.3% VF). Although neither of the two techniques was capable of completely preventing CPS perforations, transcutaneous CPS placement with a conventional fluoroscopy-based stereotactic AF can be considered a less expensive alternative to VF. This AF technique is able to reduce the number and severity of lateral pedicle wall violations compared to screw placement via the wide standard posterior open midline approach to the subaxial cervical spine. The results of this study are discussed in context with those obtained from different published modifications, since the first technical description of this surgical technique in 1994 by Abumi and co-workers.

Comparison of Radiation Exposure in Lumbar Pedicle Screw Placement With Fluoroscopy Vs Computer-Assisted Image Guidance With Intraoperative Three-Dimensional Imaging

Background/objective: Little is known about the long-term effects of chronic exposure to ionizingradiation. Studies have shown that spine surgeons may be exposed to significantly more radiation than thatobserved in surgery on the appendicular skeleton. Computer-assisted image guidance systems have beenshown in preliminary studies to enable accurate instrumentation of the spine. Computer-assisted image guidance systems may havesignificant application to the surgical management of spinal trauma and deformity. The objective of this study was to compare C-arm fluoroscopy and computer-assisted imageguidance in terms of radiation exposure to the operative surgeon when placing pedicle screw-rod constructsin cadaver specimens.Methods: Twelve single-level (2 contiguous vertebral bodies) lumbar pedicle screw-rod constructs (48screws) in 4 fresh cadavers were placed using standard C-arm fluoroscopy and computer-assisted imageguidance (Stealth Station with lso-C3D ).Pedicle screw-rod constructs were placed at L1-L2, L3-L4, and L5-S1 in 4 fresh cadaver specimens. Imaging was alternated between C-arm fluoroscopy and computer-assistedimage guidance with Stealth Station lso-C3D. Radiation exposure was measured using ringand badge dosimeters to monitor the thyroid, torso, and index finger. Postprocedure CT scans were obtained to judge accuracy of screw placement.Results: Mean radiation exposure to the torso was 4.33 ± 2.66 mRemfor procedures performed with standard fluoroscopy and 0.33 ± 0.82 mRem for procedures performed with computer-assisted image guidance. This difference was statistically significant (P = 0.012). Radiation exposure to the index finger and thyroid was negligible for all procedures. The accuracy of screw placement was similar for both techniques.Conclusions: Computer-assisted image guidance systems allow for the safe and accurate placement ofpedicle screw-rod constructs with a significant reduction in exposure to ionizing radiation to the torso of theoperating surgeon.

Image-Guided Transnasal Endoscopic Resection of an Orbital Solitary Fibrous Tumor

Solitary fibrous tumors are rare mesenchymal tumors that may involve the orbit. Orbital solitary fibrous tumors are generally removed via an external orbitotomy. A 64-year-old woman with a history of breast cancer was examined for a 6-month history of gradual painless loss of vision in the right eye and evidence of a retrobulbar optic neuropathy. Imaging revealed a posterior medial orbital mass. Initial endoscopic biopsy demonstrated histopathologic changes consistent with a solitary fibrous tumor. The patient subsequently underwent an image-guided, transnasal, endoscopic resection of the tumor using the LandmarX system (Medtronics, Minneapolis, MN, U.S.A.). Three weeks after surgery, her visual acuity and visual field had returned to normal, and they remained normal for 2 years with no neuroimaging evidence of recurrent tumor. The transnasal endoscopic technique is useful in both biopsy and removal of posterior medial orbital lesions, particularly when a computer-assisted image guidance system is used. This approach should be added to the armamentarium of surgical approaches to orbital lesions.

The Use of Computerized Image Guidance in Lumbar Disk Arthroplasty

Surgical navigation systems have been increasingly studied and applied in the application of spinal instrumentation. Successful disk arthroplasty requires accurate midline and rotational positioning for optimal function and longevity. A surgical simulation study in human cadaver specimens was done to evaluate and compare the accuracy of standard fluoroscopy, computer-assisted fluoroscopic image guidance, and Iso-C3D image guidance in the placement of lumbar intervertebral disk replacements. Lumbar intervertebral disk prostheses were placed using three different image guidance techniques in three human cadaver spine specimens at multiple levels. Postinstrumentation accuracy was assessed with thin-cut computed tomography scans. Intervertebral disk replacements placed using the StealthStation with Iso-C3D were more accurately centered than those placed using the StealthStation with FluoroNav and standard fluoroscopy. Intervertebral disk replacements placed with Iso-C3D and FluoroNav had improved rotational divergence compared with standard fluoroscopy. Iso-C3D and FluoroNav had a smaller interprocedure variance than standard fluoroscopy. These results did not approach statistical significance. Relative to both virtual and standard fluoroscopy, use of the StealthStation with Iso-C3D resulted in improved accuracy in centering the lumbar disk prosthesis in the coronal midline. The StealthStation with FluoroNav appears to be at least equivalent to standard fluoroscopy and may offer improved accuracy with rotational alignment while minimizing radiation exposure to the surgeon. Surgical guidance systems may offer improved accuracy and less interprocedure variation in the placement of intervertebral disk replacements than standard fluoroscopy. Further study regarding surgical navigation systems for intervertebral disk replacement is warranted.

An Evaluation of Image-Guided Technologies in the Placement of Percutaneous Iliosacral Screws

A surgical simulation study in human cadaver spine specimens was conducted to evaluate the accuracy of 3 different surgical navigation systems compared to standard fluoroscopy in the percutaneous placement of iliosacral screws. To compare the accuracy of percutaneous iliosacral screw placement using standard fluoroscopy, computer-assisted fluoroscopic image guidance, Iso-C3D image guidance (Medtronic Surgical Navigation Technologies, Louisville, CO), and electromagnetic fluoroscopic image guidance. Conventional percutaneous sacroiliac screw placement has a malposition rate as high as 15%, as reported in the English-speaking literature (Hinsche et al [Clin Orthop Relat Res 2002;395:135-44] and Templeman et al [Clin Orthop Relat Res 1996;329:194-8]). Iso-C3D and computer-assisted image guidance technologies have been proposed to increase this accuracy rate. Two iliosacral screws were placed bilaterally (4 screws) in each of 4 cadavers using standard fluoroscopy, computer-assisted fluoroscopic image guidance, Iso-C3D image guidance, and electromagnetic fluoroscopic image guidance. Screw positions were analyzed by computerized tomography after instrumentation and assigned a score based on deviation from ideal screw position. The StealthStation with FluoroNav (Medtronic Surgical Navigation Technologies) appeared to provide the highest accuracy of all guidance techniques. This result was more accurate than standard fluoroscopy. Computer-assisted fluoroscopy based image navigation appears to be more accurate than standard fluoroscopy in placing these screws. However, errors may occur with all techniques. Further refinement in registration procedures may highly improve the accuracy of percutaneous screw placement in a variety of spinopelvic procedures.

Benefits and limitations of image guidance in the surgical treatment of intracranial dural arteriovenous fistulas

Despite major advances in endovascular embolization techniques, microsurgical resection remains a reliable and effective treatment modality for dural arteriovenous fistulas (DAVF). However, intraoperative detection of these lesions and identification of feeding arteries and draining veins can be challenging. In a series of 6 patients who were not candidates for definitive treatment by endovascular embolization we evaluated the benefits and limitations of computer-assisted image guidance for surgical ablation of DAVF. Of the 6 patients, 5 presented with haemorrhage and one with seizures. Diagnosis of DAVF was made by conventional angiography and dynamic contrast enhanced MR angiography (CE-MRA). All patients were surgically treated with the assistance of a 3D high resolution T1-weighted MR data set and time-of-flight MR angiography (MRA) obtained for neuronavigation. Registration was based on cranial fiducials and image-guided surgery was performed with the navigation system. Four of the 6 patients suffered from DAVF draining into the superior sagittal sinus, one fistula drained into paracavernous veins adjacent to the superior petrosal sinus and one patient had a pial fistula draining in the straight sinus. DAVF diagnosed with conventional angiography could be located on CE-MRA and MRA prior to surgery. MRI and MRA images were combined on the neuronavigation workstation and DAVF were located intraoperatively by using a tracking device. In 4 out of 6 cases neuronavigation was used for direct intraoperative identification of DAVF. Brain shift prevented direct tracking of pathological vessels in the other 2 cases, where navigation could only be used to assist craniotomy. Microsurgical dissection and coagulation of the fistulas led to complete cure in all patients as confirmed by angiography. Neuronavigation may be used as an additional tool for microsurgical treatment of DAVF. However, in this small series of 6 cases, surgical procedures have not been substantially altered by the use of the neuronavigation system. Image guidance has been beneficial for the location of small, superficially located DAVF, whereas a navigated approach to deep-seated lesions was less accurate due to the familiar problem of brain shift and brain retraction during surgery.

Cavernous malformations--navigational supported surgery.

Navigational supported surgery of intracranial lesions is expected to be associated with a lower rate of brain traumatization as well as an avoidance of additional neurological deficits and surgical morbidity. In our study we used the computer-assisted image guidance for resection of cerebral cavernous malformations. In all patients the planning procedure for the following image-guided surgery was realized using preoperative MRl data sets and a neuronavigation system (STP 4.0, SNN). In cases in which the cavernoma was situated near functional eloquent regions, functional MR images were fused preoperatively. During the last 24 months, 21 patients were surgically treated for cerebral cavernoma. No patient was operated twice. The mean size of cavernoma was 18.3 mm, ranging from 5 to 60 mm, the mean distance between cortical surface and cavernoma was 26 mm, ranging from 5 to 50 mm. The surgical procedure lasted in the median 180 min. All patients showed an identical or better neurological outcome. Neuronavigation allows an accurate definition of the intraoperative target, a correct approach and a safe surgery. With the help of neuronavigation the surgical approach and the extirpation of cavernous malformations were realized in a comfortable and safe way and allowed a minimization of tissue manipulation.

Computer-assisted anterior spinal surgery for a case of recurrent giant cell tumor

A computer-assisted image guidance system has recently been used for posterior spinal surgery. We applied this system to anterior revision surgery of the cervicothoracic junction for a patient with recurrent thoracic spinal giant cell tumor. Anterior computer-assisted spinal surgery was achieved by attaching reference markers to threaded pins inserted into a vertebral body. The locations of anatomic structures in the surgical field of this patient were difficult to identify because of previous surgery. Both accurate resection of the tumor and anterior fusion with iliac bone autograft between C6 and T3 were successfully performed using a computer-assisted image guidance system. This system is useful for anterior spinal surgery because it enables a surgeon to perform safe and accurate surgery.

Accuracy of computer-guided screw fixation of the sacroiliac joint.

Computer-assisted image guidance allows precise preoperative planning and intraoperative localization of surgical instruments. The technique recently was validated for the insertion of pedicle screws. In the laboratory, the precision of a surface-matching algorithm was evaluated for registration and accuracy and safety of screw placement into the vertebral bodies of S1 and S2 for fixation of the sacroiliac joint. Using six plastic pelves, 24 screw holes were made through the sacroiliac joint into the vertebral body of S1, and 12 holes were made through the sacroiliac joint into S2. The accuracy of the hole position was evaluated using a postoperative computed tomography examination. The safety factor was assessed by analysis of the remaining bone stock around the holes calculating a theoretical cylindrical volume being outside bone with increasing bore hole diameters. The registration was accurate with a mean error less than 1.4 mm in the posterior parts of the pelvis. The drilling followed precisely the preoperatively planned trajectories; perforation of the cortex of the sacrum was not observed. The safety factor of the S1 vertebral body is higher than that of S2 allowing larger diameter screw insertion into S1. This technique provides a safe and precise guide for transcutaneous or open insertion of iliosacral screws in cases of iliosacral dislocation or sacral fracture.