The blood oxygen level-dependent functional MR imaging signal can be used to identify brain tumors and distinguish them from normal tissue.

BACKGROUND AND PURPOSE: In neuro-oncology, a major problem is clear identification of tumor from the surrounding normal tissue. We hypothesized that we could use the blood oxygen level-dependent functional MR imaging (BOLD fMRI) signals from tumors and normal brain to identify the tumors and distinguish them from the surrounding brain. MATERIALS AND METHODS: Fourteen patients with meningiomas, gliomas, and metastatic tumors were scanned before surgery. All subjects performed a motor task; 2 subjects were also scanned while in a resting state. The BOLD signals were taken from selected points within the tumor and from the surrounding normal brain and were analyzed by using correlation analysis to determine how closely they were related. RESULTS: The BOLD signals from all of the tumors were significantly different from those in the surrounding normal tissue. In meningiomas and gliomas, selection of a voxel in the tumor for signal-intensity analysis highlighted the entire tumor mass while excluding the normal tissue. The BOLD signal intensity was the same whether the subjects were motionless or finger tapping. CONCLUSIONS: Analysis of the BOLD signal intensity provides a relatively simple and straightforward method for identifying brain tumors and distinguishing them from normal tissue. This approach may be of use in neurosurgery.

Cranial surgery and navigation with a compact intraoperative MRI system.

Experience with a compact unit for intraoperative magnetic resonance imaging (iMRI) and integrated surgical navigation is presented. The system, commercially known as the PoleStar N-10 (Odin Medical Technologies, Yokne'am, Israel) includes a 0.12 Tesla permanent magnet that docks under a regular OR table. A passive infrared-based optical navigation system is included and the device can be controlled by the operating neurosurgeon and staff. We have operated on 93 patients using the PoleStar N-10. Diagnoses included glioma in 27, pituitary adenoma in 19, meningioma in 15, and others in 40. Lesions were removed from the skull base in 35 patients of whom 8 had posterior fossa masses. Surgery was affected by imaging in 51% of operations. Additional lesion, not otherwise apparent, was removed in 21; in 14 other patients unnecessary dissection was avoided when the new image confirmed that the surgical goals had been achieved. Additional time incurred with use of the PoleStar diminished with increasing experience. Testing of the navigation tool confirmed its accuracy to be comparable to other "frameless stereotactic" devices, on the order of 2 mm; likewise accuracy was increased by using T1 weighted imaging with thin slices. The introduction of new, faster imaging sequences and targeting tools has helped to make the PoleStar N-10 a routine tool for intracranial surgical navigation, with the added benefit of updated imaging during the procedure.

Cranial surgery navigation aided by a compact intraoperative magnetic resonance imager.

OBJECT: In this article the authors report on a novel, compact device for magnetic resonance (MR) imaging that has been developed for use in a standard neurosurgical operating room. METHODS: The device includes a permanent magnet with a field strength of 0.12 tesla. The poles of the magnet are vertically aligned, with a gap of 25 cm. When not in use the magnet is stored in a shielded cage in a corner of the operating room; it is easily moved into position and attaches to a regular operating table. The magnet is raised for imaging when needed and may be lowered to allow surgery to proceed unencumbered. Surgical navigation with optical and/or magnetic probes is incorporated into the system. Twenty-five patients have undergone removal of intracranial lesions with the aid of this device. Operations included craniotomy for tumor or other lesion in 18 patients and transsphenoidal resection of tumor in seven. The number of scans ranged from two to five per surgery (average 3.4); image quality was excellent in 45%, adequate in 43%, and poor in 12%. In four patients MR imaging revealed additional tumor that was then resected; in five others visual examination of the operative field was inconclusive but complete tumor removal was confirmed on MR imaging. In 21 patients early postoperative diagnostic MR studies corroborated the findings on the final intraoperative MR image. Using a water-covered phantom, the accuracy of the navigational tools was assessed; 120 data points were measured. The accuracy of the magnetic probe averaged 1.3 mm and 2.1 mm in the coronal and axial planes, respectively; the optical probe accuracy was 2.1 mm and 1.8 mm in those planes. CONCLUSIONS: This device provides high-quality intraoperative imaging and accurate surgical navigation with minimal disruption in a standard neurosurgical operating room.

Therapeutic radiation and the neurosurgeon.

For nearly a century, neurosurgeons have been involved in the use of therapeutic radiation. Long before there was a separate discipline of radiology or radiation therapy, pioneers such as Cushing and Frasier explored the effects of X-rays and radium on patients with brain tumors and arteriovenous malformations. This interest was never completely abandoned and was again pursued with vigor with the emergence of image-guided sterotaxy for use in intracranial brachytherapy and radiosurgery. Neurosurgeons have been and will remain at the forefront of these and other emerging techniques.

Identification of the corticospinal tracts achieved using blood-oxygen-level-dependent and diffusion functional MR imaging in patients with brain tumors.

Diffusion-weighted MR imaging was used to delineate the corticospinal tract (CST) successfully and to depict its relationship to adjacent brain tumors. The CST was defined by a method by which it seems possible to delimit the distance from the CST to the main tumor mass and to show displacement and infiltration of the tract by the neoplasia. This information cannot be gathered from routine anatomic MR imaging.

Intraoperative MRI and adjuvant radiosurgery.

INTRODUCTION: For many patients with brain tumors, the ideal management strategy may be a planned subtotal resection followed by stereotactic radiosurgery (SRS). However, intraoperative visual inspection may be an inadequate measure of the amount of residual lesion. Intraoperative MRI (IMRI) may help to ensure that the goals of surgery have been achieved and that the best possible target for SRS remains. PATIENTS AND METHODS: We have operated on 68 patients using the PoleStar N-10 IMRI system (Odin Medical Technologies, Yokne'am, Israel). Benign extraaxial lesions were present in 34 patients. In 12 patients subtotal resection and adjuvant SRS were planned. Diagnoses included 5 pituitary adenomas, 4 meningiomas, 2 vestibular schwannomas, and 1 trigeminal schwannoma. Tumor resection was performed until critical structures (e.g. superior sagittal sinus) were being approached and IMRI demonstrated that the lesion was as small as possible. RESULTS: In 1 patient a surgical resection was completed, while in 11 others the plan for subtotal resection was carried out. One patient with an extensive meningioma was treated with fractionated 3-dimensional conformal fractionated radiation therapy, as her tumor remained too large for SRS. In the remaining 10 patients an ideally small target remained for SRS; 3 patients have been treated so far. CONCLUSIONS: Adjuvant SRS after subtotal tumor resection is an excellent management strategy for many patients with intracranial tumors. IMRI can ensure that the surgical goals have been reached. Future comparison of target volumes, integral volume doses, and patient outcomes are planned.

The effect of brain tumors on BOLD functional MR imaging activation in the adjacent motor cortex: implications for image-guided neurosurgery.

BACKGROUND AND PURPOSE: Functional MR (fMR) imaging data coregistered to a neurosurgical navigation system have been proposed as guides for the resection of brain tumor in or adjacent to eloquent cortices. The purpose of this study was to compare data obtained from the side of the brain affected by tumor with the contralateral side and to determine if there are physiological limitations of fMR imaging in accurately determining the location of the primary motor cortex. METHODS: Ten patients with tumors in or directly adjacent to the motor cortex were studied with fMR imaging (finger-tapping paradigm). fMR imaging data were analyzed using multiple R values. These data were coregistered to a real-time intraoperative neurosurgical navigation system. RESULTS: Significant variability of motor cortex activation patterns was noted among individual patients. The activation volumes on the side of the tumor were significantly smaller compared with the contralateral side for all tumors not previously resected (0.66+/-0.47). This was most pronounced in glioblastomas (0.27+/-0.21). We propose that these differences were caused by a loss of autoregulation in the tumor vasculature of glioblastomas and venous effects. CONCLUSION: Notwithstanding the differences noted, the motor cortex was identified successfully in all patients. This was confirmed by intraoperative physiological identification of the motor cortex and a lack of postoperative neurologic deficit.

Functional magnetic resonance imaging aided radiation treatment planning.

Functional MRI (magnetic resonance imaging) allows one to noninvasively identify various eloquent cortices in the brain. The integration of cortical activation information into radiosurgical treatment planning may provide an alternative to prevent or minimize radiation damage to eloquent cortex. A novel approach of directly integrating the fMRI (functional magnetic resonance imaging) brain map into treatment planning is proposed. Three brain tumor patients have been studied using this method with motor and/or visual paradigms. Brain activation was demonstrated in eloquent cortex at the precentral gyrus (motor area) and medial occipital lobe (visual area). The activation maps were transferred to a treatment planning workstation, (XKnife), and 3D (three-dimensional) activation maps were generated and co-registered to a 3D CT (computed tomography) anatomical data set, which provided the calibration localizer, for treatment planning. Radiosurgery was designed based on both functional and structural information by the medical team consisting of a radiation oncologist, a neurosurgeon and a physicist. The average maximum dose for the tumor was 2113 cGy. The average maximum dose for tissue surrounding the tumor was 1600 cGy. The average dose with fMRI information to the eloquent cortex was 163.4 cGy over three patients, while without fMRI information it was 240.5 cGy. The average percentage dose reduction over three patients is 32%. The results suggest that using this method can reduce the dose to the eloquent cortex. This approach provides the physician with additional information for treatment planning and may spare the patient unnecessary radiation exposure to adjacent eloquent cortices.

Beware of the ventriculogallbladder shunt.

We report a case of distal end malfunction in a child with ventriculoabdominal shunt. The distal placement was in the gallbladder rather than the peritoneal cavity, as is usually the case with a ventriculoperitoneal shunt. Surgeons should be alerted to the possibility of distal terminus of a shunt to be other than the peritoneal cavity, as revision surgery in patients with ventriculogallbladder shunt requires exposure of the metal connector on the gallbladder wall to prevent biliary leakage.

Falcotentorial plasmacytoma. Case report.

Intracranial solitary plasmacytomas are extremely rare tumors and are often misdiagnosed preoperatively. The authors report the successful treatment of a patient who harbored such a tumor involving both the falx and tentorium; this is the second case reported. A 59-year-old woman suffered from a seizure disorder due to a falcotentorial lesion, which had been identified 3 years earlier and was thought at the time to be an en plaque meningioma. Most recently, the patient presented with symptoms of increased intracranial pressure and hemiparesis. Computerized tomography and magnetic resonance imaging of her head revealed progressive growth of the tumor. The patient underwent partial resection of the tumor and chemo- and radiation therapies. Intracranial plasmacytomas must always be included in a differential diagnosis because potential complete cure can be achieved using fairly conservative treatment modalities.

Microsurgical removal of a vestibular schwannoma after stereotactic radiosurgery: surgical and pathologic findings.

OBJECTIVE: The objective of this study was to provide objective evidence of the enhanced difficulty of preserving the facial nerve in patients who need microsurgery after failed stereotactic radiosurgery (SRS) of vestibular schwannoma. STUDY DESIGN: This study was a retrospective case review. SETTING: A tertiary care referral center was the setting for the study. PATIENTS: The authors present a case of a young woman with a vestibular schwannoma that enlarged 2 years after treatment with SRS. INTERVENTION: Microsurgery via the translabyrinthine approach was used. RESULTS: At surgery, extensive scarring between the facial nerve and tumor capsule was seen, and the nerve could not be identified at all beyond several millimeters proximal to the porus acusticus. Adhesions of the tumor to the ninth and tenth cranial nerves, the brain stem, and the anterior inferior cerebellar artery were also markedly increased. Histologic examination confirmed fibrotic adhesions surrounding the facial nerve. CONCLUSIONS: The unusual degree of fibrosis, scarring, and adhesions of the tumor to the surrounding structures after SRS made microsurgical removal of the tumor difficult and preservation of the facial nerve impossible.

Decreased BOLD functional MR activation of the motor and sensory cortices adjacent to a glioblastoma multiforme: implications for image-guided neurosurgery.

A patient with a glioblastoma multiforme and mild sensorimotor deficits had significantly less activation of the motor and sensory cortices on the side with the tumor than on the contralateral side on blood oxygen level-dependent (BOLD) functional MR images. This difference, which may be due to pressure effects or loss of vascular autoregulation, should be considered in preoperative planning in which BOLD functional MR imaging is used to identify eloquent cortices to be avoided during brain tumor surgery.

Cervical myelopathy due to migration of Torkildsen's shunt: case report.

BACKGROUND: Ventriculocisternal (Torkildsen's) shunts were used often in the past for the treatment of patients with obstructive hydrocephalus. Cisternal shunts may still be indicated in the management of syringomyelia. CASE DESCRIPTION: Presented is a case of a patient developing cervical myelopathy due to migration of a Torkildsen's shunt placed 30 years before. Initially thought to have a malfunctioning shunt, he then underwent removal of the catheter, which was demonstrated on magnetic resonance imaging (MRI) to be compressing the cervicomedullary junction. The patient improved slightly after removal of the catheter. CONCLUSIONS: Patients with cisternal shunts in whom a cervical myelopathy develops should be evaluated with MRI to rule out upper spinal cord compression caused by a migrated catheter.

The relationship of imaging techniques to the accuracy of frameless stereotaxy.

OBJECTIVE: We analyzed the accuracy of a frameless stereotactic system using computed tomographic (CT) and magnetic resonance imaging (MRI) scans of different slice thickness and T(1) versus T(2) weighting of MRI. METHODS: An open skull with graphite pegs fixed to its base was used for all scans. CT scans were done with slice thicknesses of 1, 2 and 3 mm. MRI-visible markers were placed on top of pegs for T(1)-weighted and T(2)-weighted MRI scans, which were acquired at thicknesses of 1.5, 3 and 5 mm. For each scan, 3 separate registrations of a probe were performed; the distance between the actual probe location and that displayed on the registered image was noted. Each measurements was repeated 3 times for each registration. RESULTS: Greatest accuracy was achieved with 3-mm-slice CT scans; this was not improved by using thinner slices. T(1)-weighted 1.5-mm MRI scans were 23% less accurate and T(2)-weighted 3-mm scans 37% less accurate. CONCLUSIONS: Frameless stereotaxy should be done using CT scans when the greatest possible accuracy is desired. There appears to be no advantage to using slice thicknesses less than 3 mm. For most craniotomy applications, T(1)-weighted MRI using 3-mm slices provides sufficient accuracy. Lesions imaged only on T(2)-weighted MRI also can be approached with adequate precision using 3-mm scans.

Thalamic stimulation in patients with multiple sclerosis.

OBJECTIVE: To assess tremor control and side effects in patients with multiple sclerosis (MS) treated with chronic thalamic stimulation for relief of upper extremity tremor. METHODS: Five patients were studied before and after thalamic placement of a deep brain stimulation (DBS) system. Preoperative and postoperative evaluation included magnetic resonance imaging, Extended Disability Status Scale (EDSS), the Bain-Finchley visual analog scale for tremor, video recording and neuropsychological testing. Stereotactic targeting of the Vim nucleus was done using computed tomography; intraoperative testing was done under local anesthesia before permanent implantation. RESULTS: Functionally useful tremor suppression was obtained in 3/5 patients. Neuropsychological deficits of higher cortical function, memory and visuospatial coordination were observed in all patients before surgery; in 1 patient with improved postoperative visuospatial coordination, worsened memory was found. New brainstem plaque formation was seen several weeks after surgery in 1 patient who had an acute worsening of MS which improved after high-dose intravenous steroids. CONCLUSIONS: Chronic thalamic stimulation may help selected patients with MS-induced tremor. Given the complexity of their underlying illness, patients must be selected carefully, and long-term follow-up is vital to evaluate the true utility of DBS.

Functional magnetic resonance image-guided surgery of tumors in or near the primary visual cortex.

OBJECTIVE: To assess the accuracy of functional magnetic resonance imaging (fMRI) of the primary visual cortex in patients undergoing surgery for tumors in the occipital lobe. METHODS: Two patients with nondominant occipital lobe tumors were studied, one with a solitary lung metastasis and another with radiation necrosis after radiosurgery for a low-grade astrocytoma. At surgery, visual evoked potentials (VEPs) were stimulated using Light-emitting-diode goggles and recorded using cortical grids placed immediately after brain exposure. The location of the peak VEP was compared to that predicted by the registered functional scan. RESULTS: In each case, the epicenter of visual activation as represented on the registered fMRI corresponded to the site of peak VEP recording. Prediction error for the visual cortex, measured in patient 1, was 1.0 mm. Visual confirmation showed the registration in the second patient to be accurate as well. CONCLUSION: As previously demonstrated for sensorimotor fMRI, visual fMRI accurately predicts the location of the primary visual cortex. Additional confirmation is expected with more clinical experience.

Functional magnetic resonance imaging and radiosurgical dose planning.

OBJECTIVE: To assess the effect of functional magnetic resonance imaging (fMRI) on stereotactic radiosurgical (SRS) dose planning. METHODS: Patients included those undergoing SRS whose lesions were in or near areas that could be identified with fMRI. After processing, an fMR scan was registered to the anatomic scan, and this dataset was registered to a stereotactic CT scan. The imaged functional areas were contoured along with standard anatomical targets. Dose planning was done at first with the functional volumes rendered invisible; the plans were then adjusted as needed using the functional targets. Doses were measured using a dose-volume histogram tool. RESULTS: SRS was performed in 12 patients, 1 of whom also underwent SRT. Functional volumes studied included motor cortex in 8 patients, visual in 6 and language in 3; a total of 33 functional targets were imaged. Prescription doses ranged from 12 to 22.5 Gy (mean 19.5 Gy), and the maximum dose to functional volumes from 8 cGy to 18.5 Gy (mean 2.9 Gy). In 6 patients, arc adjustment using functional targets yielded a >50% reduction in dose to at least one functional volume; in all patients, the dose reduction to 50 and 75% of functional volumes averaged 4% (12 cGy) and 13% (30 cGy), respectively, while the reduction of maximal dose averaged 24% (50 cGy). CONCLUSIONS: fMRI can be used in SRS to reduce irradiation of eloquent brain using standard prescription doses. Appropriate arc adjustment may allow for escalation of the dose to the targeted lesion.