Serial intraoperative magnetic resonance imaging of brain shift.

OBJECTIVE: A major shortcoming of image-guided navigational systems is the use of preoperatively acquired image data, which does not account for intraoperative changes in brain morphology. The occurrence of these surgically induced volumetric deformations ("brain shift") has been well established. Maximal measurements for surface and midline shifts have been reported. There has been no detailed analysis, however, of the changes that occur during surgery. The use of intraoperative magnetic resonance imaging provides a unique opportunity to obtain serial image data and characterize the time course of brain deformations during surgery. METHODS: The vertically open intraoperative magnetic resonance imaging system (SignaSP, 0.5 T; GE Medical Systems, Milwaukee, WI) permits access to the surgical field and allows multiple intraoperative image updates without the need to move the patient. We developed volumetric display software (the 3D Slicer) that allows quantitative analysis of the degree and direction of brain shift. For 25 patients, four or more intraoperative volumetric image acquisitions were extensively evaluated. RESULTS: Serial acquisitions allow comprehensive sequential descriptions of the direction and magnitude of intraoperative deformations. Brain shift occurs at various surgical stages and in different regions. Surface shift occurs throughout surgery and is mainly attributable to gravity. Subsurface shift occurs during resection and involves collapse of the resection cavity and intraparenchymal changes that are difficult to model. CONCLUSION: Brain shift is a continuous dynamic process that evolves differently in distinct brain regions. Therefore, only serial imaging or continuous data acquisition can provide consistently accurate image guidance. Furthermore, only serial intraoperative magnetic resonance imaging provides an accurate basis for the computational analysis of brain deformations, which might lead to an understanding and eventual simulation of brain shift for intraoperative guidance.

Rheolytic thrombectomy of the occluded internal carotid artery in the setting of acute ischemic stroke.

BACKGROUND AND PURPOSE: Acute thromboembolic stroke complicated by ipsilateral carotid occlusion may present both mechanical and inflow-related barriers to effective intracranial thrombolysis. We sought to review our experience with a novel method of mechanical thrombectomy, in such cases, using the Possis AngioJet system, a rheolytic thrombectomy device. METHODS: A review of our interventional neuroradiology database revealed three patients in whom an occluded cervical internal carotid artery was encountered during endovascular treatment for acute stroke and in whom thrombectomy was attempted, using the 5F Possis AngioJet thrombectomy catheter. The medical records and radiographic studies of these patients were reviewed. RESULTS: Three patients were identified (ages, 52--84 years). Two patients had isolated occlusion of the internal carotid artery; in one patient, thrombus extended down into the common carotid artery. Treatment was initiated within 190 to 360 minutes of stroke onset. Thrombectomy of the carotid artery was deemed necessary because of poor collateral flow to the affected hemisphere (chronic contralateral internal carotid artery occlusion [one patient] and thrombus extending to the carotid "T" [one patient]) or inability to pass a microcatheter through the occluded vessel (one patient). Adjunctive therapy included pharmacologic thrombolysis with tissue plasminogen activator (all patients), carotid angioplasty and stenting (two patients), and middle cerebral artery angioplasty (one patient). Patency of the carotid artery was reestablished in two patients, with some residual thrombus burden. In the third patient, the device was able to create a channel through the column of thrombus, allowing intracranial access. CONCLUSION: Rheolytic thrombectomy shows potential for rapid, large-burden thrombus removal in cases of internal carotid artery thrombosis, allowing expedient access to the intracranial circulation for additional thrombolytic therapy.

Silent thromboembolic events associated with the treatment of unruptured cerebral aneurysms by use of Guglielmi detachable coils: prospective study applying diffusion-weighted imaging.

BACKGROUND AND PURPOSE: Aneurysm embolization using Guglielmi detachable coils (GDC) is gaining increasing acceptance as a viable alternative to surgery in the treatment of cerebral aneurysms. Although recent reports describe a significant rate of symptomatic thromboembolic complications with GDC use, many of the neurologic deficits are transient. We sought to determine the incidence of silent thromboembolic events with the use of diffusion-weighted imaging and to correlate radiologic findings with the results of neurologic examinations. METHODS: Diffusion-weighted MR imaging was performed within 48 hours in 14 consecutive elective GDC aneurysm treatments. Embolizations were performed under systemic heparinization; all flush solutions were heparinized, and both guiding catheters and microcatheters were placed for continuous heparinized infusions. Neurologic examination, including the National Institutes of Health Stroke Scale determination, was performed by a stroke neurologist before the coiling procedures were performed, immediately after the procedures were performed, and before discharge. MR imaging examinations were reviewed by a stroke neurologist and an interventional neuroradiologist, with determination and characterization of diffusion-weighted imaging abnormalities. RESULTS: Small areas of restricted diffusion, presumed to represent procedure-related embolic infarctions, were noted on the images of eight of 14 patients. All except one of the areas were located ipsilateral to the side of the catheterization. Six patients had evidence of multiple infarcts. Most lesions were small (<2 mm); one patient with coil stretch and herniation into the parent vessel had numerous infarcts with a dominant posterior frontal infarct. Pre- and posttreatment National Institutes of Health Stroke Scale scores were unchanged for 13 of 14 patients. Overall, the rate of asymptomatic emboli was 61% (eight of 13 treatments) in uncomplicated treatments. Strokes occurred independently of the number of coils used; the mean number of coils used for patients with strokes was 7.6 (range, two to 13) and for patients without evidence of infarcts was 10.2 (range, one to 30). This was not a significant difference (P > .5). CONCLUSION: Silent thromboembolic events related to the use of the GDC system are a common occurrence, despite meticulous technique and systemic anticoagulation. Although clinical sequelae are rare, the high rate of occurrence suggests that alterations in the technique, such as the addition of antiplatelet agents, should be considered.

Intraoperative diffusion imaging on a 0.5 Tesla interventional scanner.

Intraoperative line scan diffusion imaging (LSDI) on a 0.5 Tesla interventional MRI was performed during neurosurgery in three patients. Diffusion trace images were obtained in acute ischemic cases. Scan time per slice was 46 seconds and 94 seconds, respectively, for diffusion tensor images. Diagnosis of acutely developed vascular occlusion was confirmed with follow-up scans. White matter tracts were displayed with the principal eigenvectors and provided guidance for the tumor surgery. In all cases, the diagnostic utility of LSDI was established. J. Magn. Reson. Imaging 2001;13:115-119.

Intra-operative MR guidance during trans-sphenoidal pituitary resection: preliminary results.

The use of intra-operative MR image guidance has the potential to improve the precision, extent, and safety of trans-sphenoidal pituitary resections. The trans-sphenoidal approach to pituitary surgery has been performed for some time (1--3). Until now these surgeries have relied on direct visualization without the aid of image guidance. An open-bore configuration 0.5T SIGNA SP MR system (GE Medical Systems, Milwaukee, Wisconsin) has been used to provide image guidance for seventeen trans-sphenoidal pituitary adenoma resections (4). The intra-operative MRI system allowed the radiologist to successfully direct the surgeon toward the sella turcica while avoiding the cavernous sinus, optic chiasm and other critical structures. Imaging performed during the surgery monitored the extent of resection and allowed for removal of tumor beyond the surgeon's view in seven cases. Dynamic MR imaging was used to distinguish residual tumor from normal gland and postoperative changes, permitting more precise tumor localization. A heme-sensitive long TE gradient echo sequence was used to find the presence of hemorrhagic debris. All patients tolerated the procedure well without significant complications. J. Magn. Reson. Imaging 2001;13:136-141.

Intraoperative MR systems. Midfield approaches.

Intraoperative MR imaging provides an unrestricted view of intracranial structures and lesions that has revolutionized the way that neurosurgery is performed in the authors' institution. Intraoperative imaging allows the practitioner to update and adjust the approach to intracranial lesions continuously. With this system, important anatomic and vascular structures can be successfully avoided; boundaries of low-grade tumors can be accurately defined, and foci of possible higher grade within these lesions can be identified; foci of high-grade astrocytomas can be differentiated from radiated brain; hyperacute hemorrhage or infarction during and after procedures can be determined; and the possible communication of cystic collections with CSF can be ascertained. These advantages provide a level of comfort to the surgeon and a presumptive margin of safety to the patient that is unattainable during conventional surgical approaches, and given the choice, the authors' neurosurgeons would prefer to operate in the interventional magnet. Preliminary reports concerning the efficacy and usefulness of MR-guided navigational tools for the performance of neurosurgery are encouraging, as noted earlier, Wirtz et al have shown that the more extensive removal of glioblastomas afforded by intraoperative MR leads to significantly prolonged patient survival compared with conventional surgery. Further outcomes analysis must be performed, however, to determine whether these new techniques significantly decrease overall long-term morbidity or increase survival in those patients who have low-grade astrocytomas.

Image-guided therapy and intraoperative MRI in neurosurgery.

Computer-assisted 3D planning, navigation and the possibilities offered by intra-operative imaging updates have made a large impact on neurological surgery. Three-dimensional rendering of complex medical image information, as well as co-registration of multimodal sources has reached a highly sophisticated level. When introduced into surgical navigation however, this pre-operative data is unable to account for intra-operative changes, ('brain-shift'). To update structural information during surgery, an open-configured, intra-operative MRI (Signa SP, 0.5 T) was realised at our institution in 1995. The design, advantages, limitations and current applications of this system are discussed, with emphasis on the integration of imaging into procedures. We also introduce our integrated platform for intra-operative visualisation and navigation, the 3D Slicer.