M. Serdar Alp

Head registration techniques for image-guided surgery

Localization of the pathological structures in relation to the surrounding anatomy and understanding of the surgical anatomy are probably the most important keys to successful neurosurgery. Image-guided surgery is an important tool for understanding an individuals anatomy and for precisely locating the lesion. Head registration is the most important step in image-guided surgery, required by every system in use today, although these systems show great differences. In this study, head registration techniques and user algorithms in 83 image-guided surgery cases were analyzed. Several types of fiducials including skin markers, bone fiducials, and the stereotactic frame were used for registration. Clinical applications, ease of use, and computer-calculated accuracy values for each type were compared. The average accuracy was 1.50 mm. X-spot skin markers are the fiducials most commonly used with CT scan. The stereotactic frame was the most accurate method, with an accuracy of 0.69 mm. Disc-shaped fiducials were used when MRI was the imaging modality; they provided an average accuracy of 2.62 mm. Head registration is an important part of image-guided surgery; the procedure used for registration should be based on the requirements of each individual case. Our results indicated that the stereotactic frame is the most accurate method of registration; however, skin markers provide reasonable accuracy with significant ease of use and patient comfort.

Contemporary management of subarachnoid hemorrhage and vasospasm: the UIC experience

BACKGROUND Cerebral vasospasm is a well-known and serious complication of aneurysmal subarachnoid hemorrhage. The means of monitoring and treatment of vasospasm have been widely studied. Each neurosurgical center develops a protocol based on their experience, availability of equipment and personnel, and cost, so as to keep morbidity and mortality rates as low as possible for their patients with vasospasm. METHODS At the University of Illinois at Chicago, we have developed algorithms for the diagnosis and management of cerebral vasospasm based on the experience of the senior authors over the past 25 years. This paper describes in detail our approach to diagnosis and treatment of aneurysmal subarachnoid hemorrhage and vasospasm. Our discussion is highlighted with data from a retrospective analysis of 324 aneurysm patients. RESULTS Over 3 years, 324 aneurysms were treated; 185 (57%) were clipped, 139 (43%) were coiled. The rate of vasospasm for the 324 patients was 27%. The rate of hydrocephalus was 32% for those patients who underwent clipping, and 29% for those coiled. The immediate outcomes for those who underwent clipping was excellent in 35%, good in 38%, poor in 15.5%, vegetative in 3%, and death in 8% of the patients. For those who underwent coiling the immediate outcome was excellent in 64%, good in 14.5%, vegetative in 2.5%, and death in 14.5% of the patients. These statistics include all Hunt and Hess grades. For those patients who underwent clipping, 51% were intact at 6 months follow-up, 15% had a permanent deficit, 10% had a focal cranial nerve deficit, and 2% had died from complications not directly related to the procedure. For those patients who had undergone coiling, 75% were intact at 6 months follow-up, 12.5% had a permanent deficit, and 12.5% had a cranial nerve deficit, with no deaths. CONCLUSIONS The morbidity and mortality of cerebral vasospasm is significant. A good outcome after aneurysmal subarachnoid hemorrhage is dependent upon careful patient management in the preoperative, perioperative, and postoperative periods. The timely work-up and aggressive treatment of neurological deterioration, whether or not it is because of vasospasm, is paramount.

Transverse sinus dural fistula: Combined surgical and endovascular approach: A case report

BACKGROUND The treatment of a large dural sinus fistula can be very difficult and complicated. The very extensive and complex nature of these malformations may require a combination therapy in the form of surgery and multistaged embolization. The transverse sinus fistula in our patient was fed by multiple large high-flow feeders and was draining retrograde into the superior sagittal sinus (SSS) and the cortical veins. The SSS did not fill in the late venous phase of the carotid angiogram, suggesting increased venous pressure. METHODS A case of transverse sinus dural fistula is described that was managed by a combination of surgery and embolization. The complex nature of this malformation encouraged us to adopt a combination of multistaged embolization and surgery for the management and clinical control. The patient underwent embolization of multiple feeders from the branches of the external carotid artery. After this procedure, the patient underwent endovascular occlusion of the transverse sinus via the SSS. Throughout the endovascular treatment, the patient had concomitant intracranial pressure monitoring and SSS pressure monitoring, along with transcranial cerebral oximetry (TCCO). Despite this aggressive endovascular intervention, the fistula could not be completely closed. The patient then underwent surgical excision of the transverse sinus along with duraplasty and cranioplasty. RESULTS The patient had a good recovery and posttreatment angiogram revealed normal antegrade flow in the SSS with no evidence of the fistula. The combined surgical and endovascular techniques are described and their use in clinical practice is discussed. CONCLUSIONS The complexity of certain large dural sinus fistulae should not be underestimated. They may require a prolonged multistaged treatment for their total obliteration. Also, despite the large size and complexity of the disease, complete cure can be achieved.

MAGNETIC FIELD GRADIENTS IN THE MRI SUITE AND THEIR EFFECTS ON ANEURYSM CLIPS

We studied magnetic field intensity in the magnetic resonance imaging suite at our hospital and its possible effect on several different types of aneurysm clips, including one Heifetz 17-7 PH, six Heifetz Elgiloy, one Mayfield, six Perneczky, fifteen Sugita, one Sundt-Kees Variangle, four Variangle-McFadden and fifteen Yasargil clips. We carefully observed the clips for any translational or rotational movements along the path from the door towards the magnetic resonance imaging gantry. The magnetic field strength was 0.04 kiloGauss at the entrance of the room, with an acute increase of magnetic strength at 310 cm away from the entrance to the room, 90 cm to the entrance of the gantry. The magnetic strength continued to increase at a rate of 1.0-1.5 kiloGauss for every 20 cm up to the entrance to the gantry. No movement was observed in any of the clips at the entrance to the suite except for the Heifetz 17-7 PH clip, which showed small movement in the longitudinal plane of the clip. At the entrance to the gantry, the Heifetz 17-7 PH, Sundt-Kees Variangle, and Mayfield clips were aligned on the walls of the test container perpendicular to the magnetic bore. The, Heifetz Elgiloy, Perneczky, Sugita, Variangle-McFadden, and Yasargil clips showed no movement throughout the path of the stretcher or near the gantry.

Magnetic characteristics of Yaşargil aneurysm clips

BACKGROUND Metallic bioimplants are subject to great scrutiny in order to ensure that they are totally harmless to patients. Aneurysm clips are no exception to this rule. Considering the number of aneurysm clips used and their potential for injury, they should be evaluated very meticulously. Determining the magnetic characteristics of these clips is an important part of the evaluation process. In this study, a new method for evaluating magnetism is described and the importance of that information is briefly discussed. METHODS Twenty Yaşargil aneurysm clips were analyzed using a vibrating sample magnetometer under 1.5 Tesla. This device is highly sensitive, and is capable of measuring the magnetism of small objects. RESULTS Our measurements showed magnetism of the aneurysm clips ranged from 0.0334-0.1369 electromagnetic units (emu). CONCLUSIONS Magnetometer measurements and real life tests under magnetic resonance imaging (MRI) have shown that these clips have a very low magnetism and are safe to use in 1.5 Tesla MRI scanners. This study also proves that the vibrating sample magnetometer is a useful device for analyzing the magnetism of aneurysm clips, and their emu values can be used as another industry standard in the production line to increase the safety of these clips.

Changes in cerebral oxygen saturation with change in posture: a preliminary report.

BACKGROUND Disease of the major vessels in the neck can disrupt autoregulation and lead to changes in the cerebral blood flow and cerebral autoregulation. These changes can be reflected by means of cerebral oxygen saturation. METHODS We measured cerebral oxygen saturation in 20 patients with atherosclerotic disease of the carotid and vertebral arteries and compared results with 10 normal subjects. Saturation was measured using a noninvasive near-infrared device, the transcranial cerebral oximeter. RESULTS There were marked decreases in cerebral oxygen saturation in patients with carotid-vertebral artery disease when the position of the patient was changed, from supine to erect. CONCLUSION Changes in regional cerebral oxygen saturation inpatients with carotid-vertebral artery disease may reflect disruption of cerebral autoregulation.

Modified solution for filling MRI coordinate indicators for the ZD stereotactic frame

Increased use of magnetic resonance imaging and magnetic resonance angiography in stereotactic planning highlight some technical problems in imaging. Visualization of markers during imaging are vital in stereotactic planning. In magnetic resonance imaging-guided stereotaxy, specially designed plates are used that contain water-based copper sulfate solutions as a marker. Replacement of copper sulfate solution is usually required after some time due to precipitation and leaking. The refilling procedure is quite cumbersome and can cause technical problems in imaging. In this study, we describe copper sulfate solution mixed with a water-soluble gel as a simple but useful alternative to water-based copper sulfate resolution to ease the refilling procedure and to overcome the air bubbles.

Application of transcranial cerebral oxygen monitoring during the balloon occlusion test

The purpose of this paper is to evaluate the value of transcranial cerebral oximeter in combination with other monitoring techniques during the balloon occlusion test. In this study 22 patients underwent balloon occlusion testing and were monitored by neurological examination, electroencephalography, transcranial Doppler, and transcranial cerebral oximetry. Eighteen patients had an intracranial aneurysm and four patients had skull base meningiomas. Seventeen patients passed the test without any symptoms. One patient underwent extracranial-intracranial by-pass surgery after failing the first test and passed the second test after the treatment. Transcranial cerebral oximeter showed 10% or less decrease in rSO2 in patients who passed the test and 10% or higher decrease in rSO2 for more than one minute in patients who failed. Electroencephalography and cerebral oximetry are found to be the most dependable monitoring methods for predicting neurological deficits after balloon inflation. Transcranial cerebral oximeter has provided non- invasive monitoring with real-time quantitative information and it was very useful during the balloon occlusion test.

Transcranial cerebral oximetry in random normal subjects

Near infrared optical spectroscopy is becoming a useful method for monitoring regional cerebral oxygenation status. The method is simple, reliable and noninvasive and the information which it provides is clinically significant in managing a growing number of neurological ailments. Use of this technique has been described previously by numerous authors. In the present study, regional cerebral oxygen saturation was measured at rest in 94 subjects randomly elected from a diverse population of individuals. This sample consisted of 38 males and 65 females, with the age ranging from 18 - 70. There were 68 light-skinned individuals and 35 with darker skin comprising various ethnic and cultural backgrounds. Mean regional cerebral hemoglobin oxygen saturation was recorded as 67.14 plus or minus 8.84%. The association of the mean regional cerebral hemoglobin oxygen saturation in various group of individuals in relationship of their age, race, sex and skin color is examined.

Evaluation of cerebral oximetry during endovascular treatment of carotid-cavernous fistula

Endovascular treatment of carotid cavernous fistula is done routinely in our institution. We have been monitoring these patients with transcranial cerebral oximetry. The transcranial cerebral oximeter is a reliable, low-cost, non-invasive device that provides real-time evaluation of regional brain oxygen saturation during and after endovascular treatment of cerebrovascular diseases. We used the INVOS 3100A (Somanetics, Troy, MI) in our study. We discuss seven patients with carotid-cavernous fistulas treated by endovascular balloon occlusion, each monitored continuously before, during, and after the procedure with transcranial cerebral oximetry. The cerebral oxygen saturation depicted was directly related to the side of the venous drainage of the fistula, with the brain oxygen saturation 15 - 20% higher on the side of the venous drainage. Following endovascular occlusion of the fistula, oxygen saturation gradually became equal on both sides. In our patients treated for carotid-cavernous fistula, we evaluated the sensitivity and usefulness of cerebral oximetry as an important non-invasive monitoring tool for the endovascular treatment of carotid-cavernous fistula.