Category: MRI

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Detecting the Offending Vessel in Hemifacial Spasm

Value of 3-Dimensional High-Resolution Magnetic Resonance Imaging in Detecting the Offending Vessel in Hemifacial Spasm

Neurosurgery 73:58–67, 2013

High-resolution 3-dimensional (3-D) magnetic resonance imaging (MRI) is widely used to predict the neurovascular anatomy within the cerebellopontine angle.

OBJECTIVE: To assess the value of 3-D steady-state free precession imaging (SSFP) and time-of-flight magnetic resonance angiography (TOF MRA) in detecting the offending vessels in hemifacial spasm in comparison to intraoperative endoscopic visualization.

METHODS: 42 patients underwent endoscope-assisted microvascular decompression (MVD). All available preoperative 3-D SSFP and TOF MRA images were checked. Intraoperative videos were captured by a high-definition endoscopic camera attached to endoscopes while exploring the area of facial nerve root exit zone (REZ). Evaluation of the 3-D images was performed by 2 independent groups of observers and compared with the operative findings.

RESULTS: Three-D MRI had an average positive predictive value (PPV) of 89.1% in differentiating between simple and complex compression. Mean accuracy of the images in detection of the offending vessels was 83.3% and 77% according to the first and second groups of observers, respectively. Averaged inter-observer agreement between the 2 groups of observers was substantial, with an averaged Kappa coefficient (K) of 0.56. In the simple compression group, mean accuracy was 97% and 89.4% according to the first and second groups of observers, respectively. Averaged K for agreement was substantial (K = 0.65).

CONCLUSION: According to endoscopic visualization, 3-D SSFP and TOF MRA images are accurate in detecting the offending vessels in simple compression of the facial nerve, and in predicting presence of a complex compression with variable sensitivity in identifying all offending vessels.

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White matter fiber tractography: why we need to move beyond DTI

DTI

J Neurosurg 118:1367–1377, 2013

Diffusion-based MRI tractography is an imaging tool increasingly used in neurosurgical procedures to generate 3D maps of white matter pathways as an aid to identifying safe margins of resection. The majority of white matter fiber tractography software packages currently available to clinicians rely on a fundamentally flawed framework to generate fiber orientations from diffusion-weighted data, namely diffusion tensor imaging (DTI). This work provides the first extensive and systematic exploration of the practical limitations of DTI-based tractography and investigates whether the higher-order tractography model constrained spherical deconvolution provides a reasonable solution to these problems within a clinically feasible timeframe.

Methods. Comparison of tractography methodologies in visualizing the corticospinal tracts was made using the diffusion-weighted data sets from 45 healthy controls and 10 patients undergoing presurgical imaging assessment. Tensor-based and constrained spherical deconvolution–based tractography methodologies were applied to both patients and controls.

Results. Diffusion tensor imaging–based tractography methods (using both deterministic and probabilistic tractography algorithms) substantially underestimated the extent of tracks connecting to the sensorimotor cortex in all participants in the control group. In contrast, the constrained spherical deconvolution tractography method consistently produced the biologically expected fan-shaped configuration of tracks. In the clinical cases, in which tractography was performed to visualize the corticospinal pathways in patients with concomitant risk of neurological deficit following neurosurgical resection, the constrained spherical deconvolution–based and tensor-based tractography methodologies indicated very different apparent safe margins of resection; the constrained spherical deconvolution– based method identified corticospinal tracts extending to the entire sensorimotor cortex, while the tensor-based method only identified a narrow subset of tracts extending medially to the vertex.

Conclusions. This comprehensive study shows that the most widely used clinical tractography method (diffusion tensor imaging–based tractography) results in systematically unreliable and clinically misleading information. The higher-order tractography model, using the same diffusion-weighted data, clearly demonstrates fiber tracts more accurately, providing improved estimates of safety margins that may be useful in neurosurgical procedures. We therefore need to move beyond the diffusion tensor framework if we are to begin to provide neurosurgeons with biologically reliable tractography information.

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Optimizing Contrast-Enhanced Magnetic Resonance Imaging Characterization of Brain Metastases: Relevance to Stereotactic Radiosurgery

Optimizing_Contrast_Enhanced_Magnetic_Resonance

Neurosurgery 72:691–701, 2013

Intracranial metastases are the most common form of intra-axial brain tumor. Management approaches to brain metastases include surgical resection, whole-brain radiotherapy, and stereotactic radiosurgery (SRS). The management approach that is selected is based typically on algorithms that incorporate the number, size, and location of lesions.

SRS is the treatment of choice when metastases detected on imaging are few (maximum, 3-5) and/or of small size (#30 mm) and offers the advantages of noninvasiveness and the ability to treat inaccessible lesions compared with surgical resection.

Contrast-enhanced magnetic resonance imaging (MRI) is the standard imaging technique for determining the number, size, and location of metastatic lesions. In SRS, the capability of MRI to delineate lesion borders precisely in 3 dimensions helps reduce recurrence rates and minimize radiation necrosis in surrounding tissue.

Optimization of the MRI protocol, including selection of the appropriate gadolinium-based contrast agent (GBCA), is paramount for accurate lesion imaging. GBCAs differ in their safety, tolerability, and efficacy because of their diverse physicochemical properties. Gadobutrol and gadobenate dimeglumine are high-relaxivity GBCAs that demonstrate superior efficacy for imaging metastatic lesions compared with other GBCAs, whereas gadobutrol additionally provides macrocyclic stability.

This article reviews recent comparative trials of GBCAs and discusses their relevance for optimizing MRI protocols in the management of brain metastases, with particular relevance to SRS.

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Postoperative ischemic changes following resection of newly diagnosed and recurrent gliomas and their clinical relevance

Postoperative ischemic changes following resection of newly diagnosed and recurrent gliomas and their clinical relevance

J Neurosurg 118:801–808, 2013

The aim of surgical treatment of glioma is the complete resection of tumor tissue with preservation of neurological function. Inclusion of diffusion-weighted imaging (DWI) in the postoperative MRI protocol could improve the delineation of ischemia-associated postoperative neurological deficits. The present study aims to assess the incidence of infarctions following resection of newly diagnosed gliomas in comparison with recurrent gliomas and the influence on neurological function.

Methods. Patients who underwent glioma resection for newly diagnosed or recurrent gliomas had early postoperative MRI, including DWI and apparent diffusion coefficient (ADC) maps. Postoperative areas of restricted diffusion were classified as arterial territorial infarctions, terminal branch infarctions, or venous infarctions. Tumor entity, location, and neurological function were recorded.

Results. New postoperative ischemic lesions were identified in 26 (31%) of 84 patients with newly diagnosed gliomas and 20 (80%) of 25 patients with recurrent gliomas (p < 0.01). New permanent and transient neurological deficits were more frequent in patients with recurrent gliomas than in patients with newly diagnosed tumors. Patients with neurological deficits had a significantly higher rate of ischemic lesions.

Conclusions. Postoperative infarctions occur frequently in patients with newly diagnosed and recurrent gliomas and do have an impact on postoperative neurological function. In this patient cohort there was a higher risk for ischemic lesions and for deterioration of neurological function after resection of recurrent tumors. Radiogenic and postoperative tissue changes could contribute to the higher risk of an ischemic infarction in patients with recurrent tumors.

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Noninvasive Language Mapping in Patients With Epilepsy or Brain Tumors

Noninvasive_Language_Mapping_in_Patients_With

Neurosurgery 72:555–565, 2013

Functional magnetic resonance imaging (fMRI) has become part of routine brain mapping in patients with epilepsy or tumor undergoing resective surgery. However, robust localization of crucial functional areas is required.

OBJECTIVE: To establish a simple, short fMRI task that reliably localizes crucial language areas in individual patients who undergo respective surgery.

METHODS: fMRI was measured during an 8-minute auditory semantic decision task in 28 healthy controls and 35 consecutive patients who had focal epilepsy or a brain tumor. Nineteen underwent resective surgery. Group and individual analyses were performed. Results in patients were compared with postsurgical language outcome and electrocortical stimulation when available.

RESULTS: fMRI activations concordant with the anterior and posterior language areas were found in 96% and 89% of the controls, respectively. The anterior and posterior language areas were both activated in 93% of the patients. These results were concordant with electrocortical stimulation results in 5 patients. Transient postsurgical language deficits were found in 2 patients in whom surgery was performed in the vicinity of the fMRI activations or who had postsurgical complications implicating areas of fMRI activations.

CONCLUSION: The proposed fast fMRI language protocol reliably localized the most relevant language areas in individual subjects. It appears to be a valuable complementary tool for surgical planning of epileptogenic foci and of brain tumors.

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Use of diffusion tensor imaging in glioma resection

DTI.glioma

Neurosurg Focus 34 (4):E1, 2013 

Diffusion tensor imaging (DTI) is increasingly used in the resection of both high- and low-grade gliomas. Whereas conventional MRI techniques provide only anatomical information, DTI offers data on CNS connectivity by enabling visualization of important white matter tracts in the brain

Importantly, DTI allows neurosurgeons to better guide their surgical approach and resection. Here, the authors review basic scientific principles of DTI, include a primer on the technology and image acquisition, and outline the modality’s evolution as a frequently used tool for glioma resection.

Current literature supporting its use is summarized, highlighting important clinical studies on the application of DTI in preoperative planning for glioma resection, preoperative diagnosis, and postoperative outcomes.

The authors conclude with a review of future directions for this technology.

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A systematic review of functional magnetic resonance imaging and diffusion tensor imaging modalities used in presurgical planning of brain tumour resection

fMRI and DTI

Neurosurg Rev (2013) 36:205–214

Historically, brain tumour resection has relied upon standardised anatomical atlases and classical mapping techniques for successful resection. While these have provided adequate results in the past, the emergence of new technologies has heralded a wave of less invasive, patient-specific techniques for the mapping of brain function.

Functional magnetic resonance imaging (fMRI) and, more recently, diffusion tensor imaging (DTI) are two such techniques. While fMRI is able to highlight localisation of function within the cortex, DTI represents the only technique able to elucidate white matter structures in vivo. Used in conjunction, both of these techniques provide important presurgical information for thorough preoperative planning, as well as intraoperatively via integration into frameless stereotactic neuronavigational systems.

Together, these techniques show great promise for improved neurosurgical outcomes. While further research is required for more widespread clinical validity and acceptance, results from the literature provide a clear road map for future research and development to cement these techniques into the clinical setup of neurosurgical departments globally.

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Definition of a Stereotactic 3-Dimensional Magnetic Resonance Imaging Template of the Human Insula

3D MRI template of the insula

Neurosurgery 72[ONS Suppl 1]:ons35–ons46, 2013

This study proposes a 3-dimensional (3-D) template of the insula in the bicommissural reference system with posterior commissure (PC) as the center of coordinates.

OBJECTIVE: Using the bicommissural anterior commissure (AC)–PC reference system, this study aimed to define a template and design a method for the 3-D reconstruction of the human insula that may be used at an individual level during stereotactic surgery.

METHODS: Magnetic resonance imaging (MRI)–based morphometric analysis was performed on 100 cerebral cortices with normal insulae based on a 3-step procedure: Step 1: AC-PC reference system–based reconstruction of the insula from the 1-mm thick 3-D T1-weighted MRI slices. Step 2: Digitalization and superposition of the data obtained in the 3 spatial planes. Step 3: Representation of pixels as colors on a scale corresponding to the probability of localization of each insular anatomic component.

RESULTS: The morphometric analysis of the insula confirmed our previously reported findings of a more complex shape delimited by 4 peri-insular sulci. A very significant correlation between the coordinates of the main insular structures and the length of AC-PC was demonstrated. This close correlation allowed us to develop a method that allows the 3-D reconstruction of the insula from MRI slices and only requires the localization of AC and PC. This process defines an area deemed to contain insula with 100% probability.

CONCLUSION: This 3-D reconstruction of the insula should be useful to improve its localization and other cortical areas and allow the differentiation of insular cortex from opercular cortex. KEY WORDS:

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Vessel Wall Magnetic Resonance Imaging Identifies the Site of Rupture in Patients With Multiple Intracranial Aneurysms

Vessel_Wall_Magnetic_Resonance_Imaging_Identifies

Neurosurgery 72:492–496, 2013

High-resolution magnetic resonance vessel wall imaging (MR-VWI) is increasingly used to study steno-occlusive cerebrovascular disease, but has not yet been applied to patients with aneurysmal subarachnoid hemorrhage (SAH).

OBJECTIVE: To study the ability of high-resolution MR-VWI to determine the site of rupture in patients with aneurysmal SAH.

METHODS: Medical records of patients admitted with aneurysmal SAH between December 2011 and May 2012 were reviewed. MR-VWI was routinely performed for patients treated in the IMRIS Neurovascular Suite immediately before definitive treatment of the ruptured aneurysm.

RESULTS: We report for the first time high-resolution MR-VWI in 5 patients with aneurysmal SAH. Three patients harbored multiple intracranial aneurysms. The ruptured aneurysms demonstrated thick vessel wall enhancement in all cases. None of the associated unruptured aneurysms demonstrated this MR imaging finding.

CONCLUSION: High-resolution MR-VWI identified the site of rupture in patients with aneurysmal SAH, including those patients harboring multiple intracranial aneurysms. It may represent a useful tool in the investigation of aneurysmal SAH.

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