Diffusion tensor fiber tractography for arteriovenous malformations: quantitative analyses to evaluate the corticospinal tract and optic radiation

Updates on Neuronavigation: Emerging tools for tumor resection

Multiple studies have been conducted to properly elucidate the various tools available to help enhance the resection of tumor tissue, aneurysms, and arteriovenous malformations (AVM). Diffusion tensor imaging (DTI) tractography is useful in providing a map of the tumor borders, allowing the optimal preservation of function and structure of specific regions of the brain. During neurosurgery, especially craniotomies, the possibility of the brain shifting due to swelling or gravity is high. Thus, tools for intraoperative imaging such as high-frequency linear array ultrasound transducers and doppler ultrasonography are utilized for high resolution images and detecting frequency shifts. 4D-digital subtraction angiography (DSA) is another technique used to create spatial resolutions and 3D maps for aneurysms. These similar techniques can also be utilized to assess the integrity of white matter in AVM. By implementing effective evaluation strategies, healthcare professionals can make informed decisions regarding treatment options, preventive measures, and long-term care plans tailored to individual patients.

Application of diffusion tensor-based tractography in treatment of brain arteriovenous malformations: a systematic review

There is no systematic review investigating the utility of Diffusion tensor-based tractography findings for treating brain arteriovenous malformations (bAVMs). This systematic review aims to investigate the outcomes following bAVM treatment when tractography data is incorporated into treatment planning. PubMed/MEDLINE, Scopus, and Cochrane Library, were searched for published studies. Prospective or retrospective studies involving at least one patient with confirmed bAVM and available data on tractography and clinical outcomes were included. A total of 16 studies were eligible for this review, consisting of 298 patients. 48.2% of patients were female. The mean age of the patients was 27.5 years (range: 5-77). Stereotactic radiosurgery (SRS) and microsurgical resection each were the treatment of choice in eight studies, respectively. Two-hundred forty-eight patients underwent SRS as the primary treatment, while microsurgery was used to resect the bAVMs in 50 patients. The corticospinal tract, optic pathway, and arcuate fasciculus were the most widely investigated white matter tracts. Tractography disruption and failure frequencies were 19.1% and 1.8%, respectively. The pooled proportions (95% CI) of obliteration rates were 88.78% (73.51-95.76) for microsurgery and 51.45% (13-17-88.10) following SRS. Treatment-related non-hemorrhagic complications rates occurred in 24.2% and 9.9% of patients who underwent microsurgical resection and SRS, respectively. Tractography findings can contribute to providing a more accurate dosimetry analysis of functional white matter tracts at risk prior to SRS and minimizing the surgical morbidity following microsurgical resection.

Prediction of the Topography of the Corticospinal Tract on T1-Weighted MR Images Using Deep-Learning-Based Segmentation

INTRODUCTION

Tractography is an invaluable tool in the planning of tumor surgery in the vicinity of functionally eloquent areas of the brain as well as in the research of normal development or of various diseases. The aim of our study was to compare the performance of a deep-learning-based image segmentation for the prediction of the topography of white matter tracts on T1-weighted MR images to the performance of a manual segmentation.

METHODS

T1-weighted MR images of 190 healthy subjects from 6 different datasets were utilized in this study. Using deterministic diffusion tensor imaging, we first reconstructed the corticospinal tract on both sides. After training a segmentation model on 90 subjects of the PIOP2 dataset using the nnU-Net in a cloud-based environment with graphical processing unit (Google Colab), we evaluated its performance using 100 subjects from 6 different datasets.

RESULTS

Our algorithm created a segmentation model that predicted the topography of the corticospinal pathway on T1-weighted images in healthy subjects. The average dice score was 0.5479 (0.3513-0.7184) on the validation dataset.

CONCLUSIONS

Deep-learning-based segmentation could be applicable in the future to predict the location of white matter pathways in T1-weighted scans.

Chinese Cerebrovascular Neurosurgery Society and Chinese Interventional & Hybrid Operation Society, of Chinese Stroke Association Clinical Practice Guidelines for Management of Brain Arteriovenous Malformations in Eloquent Areas

Aim: The aim of this guideline is to present current and comprehensive recommendations for the management of brain arteriovenous malformations (bAVMs) located in eloquent areas. Methods: An extended literature search on MEDLINE was performed between Jan 1970 and May 2020. Eloquence-related literature was further screened and interpreted in different subcategories of this guideline. The writing group discussed narrative text and recommendations through group meetings and online video conferences. Recommendations followed the Applying Classification of Recommendations and Level of Evidence proposed by the American Heart Association/American Stroke Association. Prerelease review of the draft guideline was performed by four expert peer reviewers and by the members of Chinese Stroke Association. Results: In total, 809 out of 2,493 publications were identified to be related to eloquent structure or neurological functions of bAVMs. Three-hundred and forty-one publications were comprehensively interpreted and cited by this guideline. Evidence-based guidelines were presented for the clinical evaluation and treatment of bAVMs with eloquence involved. Topics focused on neuroanatomy of activated eloquent structure, functional neuroimaging, neurological assessment, indication, and recommendations of different therapeutic managements. Fifty-nine recommendations were summarized, including 20 in Class I, 30 in Class IIa, 9 in Class IIb, and 2 in Class III. Conclusions: The management of eloquent bAVMs remains challenging. With the evolutionary understanding of eloquent areas, the guideline highlights the assessment of eloquent bAVMs, and a strategy for decision-making in the management of eloquent bAVMs.

Quantitative visual pathway abnormalities predict visual field defects in patients with pituitary adenomas: a diffusion spectrum imaging study

OBJECTIVES

This study was to investigate clinical applicability of diffusion spectrum imaging (DSI) for quantitative detection of visual pathway abnormalities to predict the degree of visual field defects (VFD) in patients with pituitary adenomas.

METHODS

Sixty-five patients with pituitary adenomas and 33 healthy controls underwent conventional MRI and DSI scanning that allowed high-angular-resolution fiber tracking. Optic chiasmal compression and VFD were confirmed in all patients via radiological and neuro-ophthalmological examinations. Quantitative assessments of chiasmal lift, VFD, and DSI parameters from the optic nerve, optic tract, and optic radiation were performed. Group comparisons and correlation analyses were conducted in patients and controls. Using the 5-fold cross-validation method, the support vector machine classifiers were constructed to predict the degree of visual defects.

RESULTS

The mean values of quantitative anisotropy and generalized fractional anisotropy in optic nerve and optic tract showed significant differences between patients and controls (p < 0.05). These parameters were also significantly correlated with the chiasmal lift distance and degree of visual defects (p < 0.05). All patients were divided into mild (n = 42) and severe (n = 23) VFD groups, using the mean deviation value of -8 dB as the threshold. The classifiers achieved an accuracy of 0.83, sensitivity of 0.78, and specificity of 0.86 to discriminate patients with mild and severe visual defects.

CONCLUSIONS

Using high-angular-resolution fiber tracking, DSI may provide quantitative information to detect visual pathway abnormalities and be a potential diagnostic tool for determining the degree of visual field defects in pituitary adenomas.

KEY POINTS

• Abnormal QA and GFA values of optic nerve and optic tract in adenoma patients • Close relationship between DSI parameters and VFD degree in adenoma patients • The classifiers achieved an accuracy of 0.83, sensitivity of 0.78, and specificity of 0.86 to discriminate patients with mild and severe VFD.

Classification of brain arteriovenous malformations located in motor-related areas based on location and anterior choroidal artery feeding

Objective

Surgical management of arteriovenous malformations (AVMs) involving motor cortex or fibre tracts (M-AVMs) is challenging. This study aimed to construct a classification system based on nidus locations and anterior choroidal artery (AChA) feeding to pre-surgically evaluate motor-related and seizure-related outcomes in patients undergoing resection of M-AVMs.

Methods and materials

A total of 125 patients who underwent microsurgical resection of M-AVMs were retrospectively reviewed. Four subtypes were identified based on nidus location: (I) nidus involving the premotor area and/or supplementary motor areas; (II) nidus involving the precentral gyrus; (III) nidus involving the corticospinal tract (CST) and superior to the posterior limb of the internal capsule; (IV) nidus involving the CST at or inferior to the level of posterior limb of the internal capsule. In addition, we divided type IV into type IVa and type IVb according to the AChA feeding. Surgical-related motor deficit (MD) evaluations were performed 1 week (short-term) and 6 months (long-term) after surgery.

Results

The type I patients exhibited the highest incidence (62.0%) of pre-surgical epilepsy among the four subtypes. Multivariate analysis showed that motor-related area subtypes (p=0.004) and diffuse nidus (p=0.014) were significantly associated with long-term MDs. Long-term MDs were significantly less frequent in type I than in the other types. Type IV patients acquired the highest proportion (four patients, 25.0%) of long-term poor outcomes (mRS >2). Type IVb patients showed a significantly higher incidence of post-surgical MDs than type IVa patients (p=0.041). The MDs of type III or IV patients required more recovery time. Of the 62 patients who had pre-surgical seizures, 90.3% (56/62) controlled their seizures well and reached Engel class I after surgery.

Conclusions

Combining the consideration of location and AChA feeding, the classification for M-AVMs is a useful approach for predicting post-surgical motor function and decision-making.

Individual variations of the human corticospinal tract and its hand-related motor fibers using diffusion MRI tractography

The corticospinal tract (CST) is one of the most well studied tracts in human neuroanatomy. Its clinical significance can be demonstrated in many notable traumatic conditions and diseases such as stroke, spinal cord injury (SCI) or amyotrophic lateral sclerosis (ALS). With the advent of diffusion MRI and tractography the computational representation of the human CST in a 3D model became available. However, the representation of the entire CST and, specifically, the hand motor area has remained elusive. In this paper we propose a novel method, using manually drawn ROIs based on robustly identifiable neuroanatomic structures to delineate the entire CST and isolate its hand motor representation as well as to estimate their variability and generate a database of their volume, length and biophysical parameters. Using 37 healthy human subjects we performed a qualitative and quantitative analysis of the CST and the hand-related motor fiber tracts (HMFTs). Finally, we have created variability heat maps from 37 subjects for both the aforementioned tracts, which could be utilized as a reference for future studies with clinical focus to explore neuropathology in both trauma and disease states.

A Tractography-Based Grading Scale of Brain Arteriovenous Malformations Close to the Corticospinal Tract to Predict Motor Outcome After Surgery

Background: Surgical decision-making for brain arteriovenous malformations (AVMs) close to the corticospinal tract (CST) is always challenging. The purpose of this study was to develop a tractography-based grading scale to improve preoperative risk prediction and patient selection.

Methods: We analyzed a consecutive, surgically treated series of 90 patients with AVMs within a 10-mm range from the CST demonstrated by preoperative diffusion tensor tractography. Poor motor outcome was defined as persistent postoperative limb weakness. We examined the predictive ability of nidus-to-CST distance (NCD), the closest CST level (CCL), deep perforating artery supply, as well as variables of the supplemented Spetzler-Martin grading system. Three logistic models were derived from different multivariable logistic regression analyses, of which the most predictive model was selected to construct a prediction grading scale. Receiver operating characteristic analysis was conducted to test the predictive accuracy of the grading scale.

Results: Twenty-one (23.3%) patients experienced persistent postoperative limb weakness after a mean 2.7-year follow-up. The most predictive logistic model showed NCD (P = 0.001), CCL (P = 0.017), patient age (P = 0.004), and AVM diffuseness (P = 0.021) were independent predictors for poor motor outcome. We constructed the CLAD grading scale incorporating these predictors. The predictive accuracy of the CLAD grade was better compared with the supplemented Spetzler-Martin grade (area under curve = 0.84 vs. 0.68, P = 0.023).

Conclusions: Both NCD and CCL predict motor outcome after resection of AVMs close to the CST. We propose the CLAD grading scale as an effective risk-prediction tool in surgical decision-making.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT01758211 and NCT02868008

One-Stage Surgical Resection of Giant Intracranial Arteriovenous Malformations in Selected Patients: A Novel Diffusion Tenser Imaging Score

OBJECTIVE

The effective treatment of giant cerebral arteriovenous malformations (gAVMs) is challenging. The aim of this study was to determine the risk factors for 1-stage resection of gAVM and develop a reliable indicator for patient selection.

METHODS

A prospectively maintained database of patients with AVM in our hospital was reviewed. The neuroradiological findings and clinical characteristics of the patients and lesions were analyzed with respect to postoperative functional deficits (FD). A novel blood oxygen level-dependent functional magnetic resonance imaging score and a diffusion tensor imaging (DTI) score were created to predict surgical outcomes. Furthermore, the long-term outcomes of gAVMs treated by other methods in the literature were reviewed.

RESULTS

A total of 35 patients with 35 gAVMs were included. The mean diameter of the gAVMs was 64.8 ± 4.9 mm. In the univariate analysis, the functional magnetic resonance imaging score (P = 0.022) and DTI score (P = 0.003) were both significantly associated with long-term FD. The Spetzler-Martin score (P = 0.092) trended toward significance. Multivariate analysis revealed that a high DTI score (odds ratio, 2.19; 95% confidence interval, 1.08-4.46; P = 0.030) was the only independent risk factor that was correlated with long-term FD. The predictive effect of the DTI score (area under the curve = 0.822) is superior to that of the Spetzler-Martin score (area under the curve = 0.640) according to the receiver operating characteristic analysis, and the cutoff point was 2.5 (sensitivity = 0.860 and specificity = 0.867).

CONCLUSIONS

One-stage surgical resection of gAVMs in patients with a low DTI score (0-2) seems to be feasible. The DTI score could be a reliable indicator for patient selection.

Diffusion Tensor Imaging for Ruptured Cerebral Arteriovenous Malformation

Non-ruptured arteriovenous malformations (AVMs) rarely cause tract disruption. Few studies have described how ruptured AVMs influence white matter (WM) tract morphology. We reviewed consecutive AVM cases treated at a tertiary care hospital where diffusion tensor imaging (DTI) tractography was obtained preoperatively. DTI was performed using the Synaptive Plan (Synaptive Medical Inc., Toronto, Canada). Quality control was performed by clinical application specialist. Perinidal fractional anisotropy (FA) value of corticospinal tracts (CST) was obtained. A reference FA value was obtained from the corresponding area on the contralateral side. Images were evaluated by a consultant neuroradiologist. Radiological findings were correlated with clinical findings. White matter morphology was described by a consultant neuroradiologist. All three cases included in the study had a history of haemorrhage in the past. Two patients had disruption of CST and presented with a significant neurological deficit. In one patient FA value of CST around the nidus was comparable to the contralateral side and did not show any neurological deficit. DTI integrated neuronavigation was used to plan the trajectory and complete resection of the AVM with excellent postoperative recovery.

White matter tractography for neurosurgical planning: A topography-based review of the current state of the art

We perform a review of the literature in the field of white matter tractography for neurosurgical planning, focusing on those works where tractography was correlated with clinical information such as patient outcome, clinical functional testing, or electro-cortical stimulation. We organize the review by anatomical location in the brain and by surgical procedure, including both supratentorial and infratentorial pathologies, and excluding spinal cord applications. Where possible, we discuss implications of tractography for clinical care, as well as clinically relevant technical considerations regarding the tractography methods. We find that tractography is a valuable tool in variable situations in modern neurosurgery. Our survey of recent reports demonstrates multiple potentially successful applications of white matter tractography in neurosurgery, with progress towards overcoming clinical challenges of standardization and interpretation.

Risk factors for neurological deficits after surgical treatment of brain arteriovenous malformations supplied by deep perforating arteries

The treatment of brain arteriovenous malformations supplied by deep perforating arteries (PA) (P-BAVM) remains challenging. The aims of this study were to determine the outcomes after surgical treatment in patients with P-BAVMs and to identify the risk factors associated with postoperative neurological deficits. We retrospectively reviewed the medical charts and imaging records of 228 consecutive patients with BAVMs who underwent microsurgical resection of their BAVMs at Beijing Tiantan Hospital between September 2012 and March 2016. Patients were included if the BAVMs were totally or partially supplied by PA. All patients had undergone preoperative diffusion tensor imaging (DTI), MRI, 3D time-of-flight MRA (3D TOF-MRA) and digital subtraction angiography (DSA) followed by resection. Both functional and angioarchitectural factors were analysed with respect to the postoperative neurological deficits, including motor deficits, visual field deficits and aphasia. Statistical analysis was performed using the statistical package SPSS (version 20.0.0, IBM Corp.). Fifty-nine patients with P-BAVMs were enrolled. Radical obliteration was achieved in all P-BAVMs according to postoperative DSA. Forty-five (76.3%) patients obtained neurological deficits 1 week after surgery. At a mean follow-up of 14.7 ± 9.4 (3-30) months after surgery, 34 patients (57.6%) had long-term neurological deficits. Multivariable logistic regression analyses showed that a shorter lesion-to-eloquent fibre tracts distance (LFD) was an independent risk factor for short- (P = 0.014) and long-term (P = 0.013) neurological deficits. The cut-off point of LFD for long-term neurological deficits was 5.20 mm. The predominant supply of the PA (P = 0.008) was an independent risk factor for long-term neurological deficits. This study identified a high risk of surgical morbidity for P-BAVMs. The predominant supply of the PA and a shorter LFD are crucial risk factors for postoperative neurological deficits in patients with P-BAVMs.

Semi-Automatic Segmentation of Optic Radiations and LGN, and Their Relationship to EEG Alpha Waves

At rest, healthy human brain activity is characterized by large electroencephalography (EEG) fluctuations in the 8-13 Hz range, commonly referred to as the alpha band. Although it is well known that EEG alpha activity varies across individuals, few studies have investigated how this may be related to underlying morphological variations in brain structure. Specifically, it is generally believed that the lateral geniculate nucleus (LGN) and its efferent fibres (optic radiation, OR) play a key role in alpha activity, yet it is unclear whether their shape or size variations contribute to its inter-subject variability. Given the widespread use of EEG alpha in basic and clinical research, addressing this is important, though difficult given the problems associated with reliably segmenting the LGN and OR. For this, we employed a multi-modal approach and combined diffusion magnetic resonance imaging (dMRI), functional magnetic resonance imaging (fMRI) and EEG in 20 healthy subjects to measure structure and function, respectively. For the former, we developed a new, semi-automated approach for segmenting the OR and LGN, from which we extracted several structural metrics such as volume, position and diffusivity. Although these measures corresponded well with known morphology based on previous post-mortem studies, we nonetheless found that their inter-subject variability was not significantly correlated to alpha power or peak frequency (p >0.05). Our results therefore suggest that alpha variability may be mediated by an alternative structural source and our proposed methodology may in general help in better understanding the influence of anatomy on function such as measured by EEG or fMRI.

Effect of functional MRI-guided navigation on surgical outcomes: a prospective controlled trial in patients with arteriovenous malformations

OBJECTIVE The impact of functional MRI (fMRI)-guided navigation on the surgical outcome of patients with arteriovenous malformations (AVMs) is undetermined. This large, randomized controlled trial (RCT) was designed to determine the safety and efficacy of fMRI-guided microsurgery of AVMs. This paper reports the preliminary results of the interim analysis. METHODS Between September 2012 and June 2015, eligible patients were randomized to the standard microsurgery group (control group) or the fMRI-guided surgery group (experimental group) in a 1:1 ratio. Patients in the control group underwent conventional digital subtraction angiography and MRI before surgery. The surgery was performed according to the standard procedure. However, patients in the experimental group underwent blood oxygen level-dependent (BOLD) fMRI and diffusion tensor imaging within 1 week before surgery. Moreover, preoperative eloquent brain tissue mapping and intraoperative fMRI navigation were performed in addition to the standard procedure. The preliminary end points were the total removal rate of AVMs and postoperative surgical complications. The primary end points were modified Rankin Scale (mRS) score (favorable: mRS Score 0-2; poor: mRS Score 3-6) and surgery-related permanent functional deficits (S-PFD) at the last clinic visit (≥ 6 months). Statistical analysis was performed using the statistical package from SPSS. RESULTS The interim analysis included 184 participants (93 in the experimental group and 91 in the control group). Patients were equally distributed between the 2 groups. Neither the preliminary nor the primary end points, including postoperative complications (p = 0.781), residual AVM (p = 1.000), last mRS score (p = 0.654), and S-PFD (p = 0.944) showed any significant difference between the control and experimental group. According to the results of the univariate analysis, eloquent adjacent brain tissue (OR 0.14; 95% CI 0.06-0.32; p < 0.001), large size of the nidus (OR 1.05; 95% CI 1.02-1.08; p = 0.002), or diffuse nidus (OR 3.05; 95% CI 1.42-6.58; p = 0.004) were all significantly associated with S-PFD. Additionally, a high Spetzler-Martin score (OR 3.54; 95% CI 2.08-6.02; p < 0.001), no previous hemorrhage (OR 2.35; 95% CI 1.00-5.54; p = 0.05), or a low preoperative mRS score (OR 0.42; 95% CI 0.17-1.00; p = 0.049) were also significantly associated with S-PFD. Multivariate analysis revealed that independent factors correlated with S-PFD were eloquent adjacent brain tissue (OR 0.17; 95% CI 0.04-0.70; p = 0.014) and low preoperative mRS score (OR 0.22; 95% CI 0.07-0.69; p = 0.009). CONCLUSIONS This preplanned interim analysis revealed no significant differences in the primary end points between the experimental and control group, prompting an early termination of this RCT. The preliminary data indicated that the additional intervention of fMRI navigation is not associated with a more favorable surgical outcome in patients with AVMs. The results indicated that eloquent adjacent brain tissue and a low preoperative mRS score are independent risk factors for S-PFD. Clinical trial registration no.: NCT01758211 ( clinicaltrials.gov ).

Risk factors for worsened muscle strength after the surgical treatment of arteriovenous malformations of the eloquent motor area

OBJECT Case selection for the surgical treatment of arteriovenous malformations (AVMs) of the eloquent motor area remains challenging. The aim of this study was to determine the risk factors for worsened muscle strength after surgery in patients with this disorder. METHODS At their hospital the authors retrospectively studied 48 consecutive patients with AVMs involving motor cortex and/or the descending pathway. All patients had undergone preoperative functional MRI (fMRI) and diffusion tensor imaging (DTI), followed by resection. Both functional and angioarchitectural factors were analyzed with respect to the change in muscle strength. Functional factors included lesion-to-corticospinal tract distance (LCD) on DTI and lesion-to-activation area distance (LAD) and cortical reorganization on fMRI. Based on preoperative muscle strength, the changes in muscle strength at 1 week and 6 months after surgery were defined as short-term and long-term surgical outcomes, respectively. Statistical analysis was performed using the statistical package SPSS (version 20.0.0, IBM Corp.). RESULTS Twenty-one patients (43.8%) had worsened muscle strength 1 week after surgery. However, only 10 patients (20.8%) suffered from muscle strength worsening 6 months after surgery. The LCD was significantly correlated with short-term (p < 0.001) and long-term (p < 0.001) surgical outcomes. For long-term outcomes, patients in the 5 mm ≥ LCD > 0 mm (p = 0.009) and LCD > 5 mm (p < 0.001) categories were significantly associated with a lower risk of permanent motor worsening in comparison with patients in the LCD = 0 mm group. No significant difference was found between patients in the 5 mm ≥ LCD > 0 mm group and LCD > 5 mm group (p = 0.116). Nidus size was the other significant predictor of short-term (p = 0.021) and long-term (p = 0.016) outcomes. For long-term outcomes, the area under the ROC curve (AUC) was 0.728, and the cutoff point was 3.6 cm. Spetzler-Martin grade was not associated with short-term surgical outcomes (0.143), although it was correlated with long-term outcomes (0.038). CONCLUSIONS An AVM with a nidus in contact with tracked eloquent fibers (LCD = 0) and having a large size is more likely to be associated with worsened muscle strength after surgery in patients with eloquent motor area AVMs. Surgical treatment in these patients should be carefully considered. In patients with an LCD > 5 mm, radical resection may be considered to eliminate the risk of hemorrhage.

Surgical Treatment of Cavernous Malformations Involving the Posterior Limb of the Internal Capsule: Utility and Predictive Value of Preoperative Diffusion Tensor Imaging

OBJECTIVE

The surgical treatment of cavernous malformations involving the posterior limb of the internal capsule (PLIC-CMs) is challenging. The aim of this study was to determine the utility and predictive value of preoperative diffusion tensor imaging (DTI) in the surgical treatment of PLIC-CMs.

METHODS

Patients with PLIC-CMs who were surgically treated between September 2012 and June 2015 were reviewed. All patients underwent preoperative DTI. Three major fiber tracts were selected for evaluation: 1) corticospinal tract (CST); 2) arcuate fasciculus (AF); and 3) optic radiation (OR). The utility of preoperative DTI for surgical approach selection and intraoperative navigation was documented. An involvement grading system of the major fibers was applied to determine the predictive value of preoperative DTI. A last modified Rankin Scale (mRS) score of 0-2 was considered a good outcome, and a last mRS >2 was considered a poor outcome.

RESULTS

Thirteen patients with 13 PLIC-CMs were reviewed in this study. All the lesions were radically resected via the corridor formed by CST, AF, and OR. None of the patents suffered from mRS >3, and 7 patients (53.8%) got good outcomes at the last clinic visit. The difference between the preoperative mRS scores and last mRS scores was not significant (P = 0.673). The involvement grade of the fiber tracts was significantly associated with the surgical outcome (P = 0.011).

CONCLUSIONS

Preoperative DTI may be a promising tool to determine the surgical approach and predict the surgical outcomes in patients with PLIC-CMs.

Preservation of the optic radiations based on comparative analysis of diffusion tensor imaging tractography and anatomical dissection

Background: Visualization of the precise course of the visual pathways is relevant to prevent damage that may inflict visual field deficits during neurosurgical resections. In particular the optic radiations (OR) are susceptible to such damage during neurosurgery. Cortical pathways can be mapped in vivo, by using Diffusion Tensor Imaging (DTI). Visualization of these pathways would be potentially helpful to prevent neurosurgical visual morbidity. In this study an anatomical dissection of the visual pathways was compared to DTI fiber tractography (DTI-FT) data of four human brains. The feasibility of a definition of a Safety Zone is investigated.

Methods: Four adult brains were dissected using Klingler's fiber dissection method, which allowed preparation of the OR. Measurements before and after dissection were used to establish distances from the cortex to the OR. DTI-scans were also obtained from these brains to determine the same distances.

Results: Measurements from specific landmark points on the cortex to the lateral border of the OR were performed in four brains. Analysis through DTI tractography corresponded with the dissection results. Based on the combined results of both dissection and DTI-FT, we defined a quantitative surgical Safety Zone with respect to various anatomical landmarks (in particular the ventricle system).

Conclusion: We conclude that there is a good correlation between the visualizations of the optic pathways based on dissection and DTI. Furthermore, we conclude that defining a neurosurgical Safety Zone which could preserve the integrity of the OR during surgery, based on the combination of DTI-FT images and dissection is feasible.

Advances and innovations in brain arteriovenous malformation surgery

Arteriovenous malformations (AVMs) of the brain are very complex and intriguing pathologies. Since their initial description by Luschka and Virchow in the middle of the 19th century, multiple advances and innovations have revolutionized their management and surgical treatment. Here, we review the historical landmarks in the surgical treatment of AVMs and then illustrate the most recent and futuristic technologies aiming to improve outcomes in AVM surgeries. In particular, we examine potential advances in patient selection, imaging, surgical technique, neuroanesthesia, and postoperative neuro-rehabilitation and quantitative assessments. Finally, we illustrate how concurrent advances in radiosurgery and endovascular techniques might present new opportunities to treat AVMs more safely from a surgical perspective.

DTI of the visual pathway - white matter tracts and cerebral lesions

DTI is a technique that identifies white matter tracts (WMT) non-invasively in healthy and non-healthy patients using diffusion measurements. Similar to visual pathways (VP), WMT are not visible with classical MRI or intra-operatively with microscope. DIT will help neurosurgeons to prevent destruction of the VP while removing lesions adjacent to this WMT. We have performed DTI on fifty patients before and after surgery between March 2012 to January 2014. To navigate we used a 3DT1-weighted sequence. Additionally, we performed a T2-weighted and DTI-sequences. The parameters used were, FOV: 200 x 200 mm, slice thickness: 2 mm, and acquisition matrix: 96 x 96 yielding nearly isotropic voxels of 2 x 2 x 2 mm. Axial MRI was carried out using a 32 gradient direction and one b0-image. We used Echo-Planar-Imaging (EPI) and ASSET parallel imaging with an acceleration factor of 2 and b-value of 800 s/mm². The scanning time was less than 9 min. The DTI-data obtained were processed using a FDA approved surgical navigation system program which uses a straightforward fiber-tracking approach known as fiber assignment by continuous tracking (FACT). This is based on the propagation of lines between regions of interest (ROI) which is defined by a physician. A maximum angle of 50, FA start value of 0.10 and ADC stop value of 0.20 mm²/s were the parameters used for tractography. There are some limitations to this technique. The limited acquisition time frame enforces trade-offs in the image quality. Another important point not to be neglected is the brain shift during surgery. As for the latter intra-operative MRI might be helpful. Furthermore the risk of false positive or false negative tracts needs to be taken into account which might compromise the final results.

Evaluating contextual processing in diffusion MRI: application to optic radiation reconstruction for epilepsy surgery

Diffusion MRI and tractography allow for investigation of the architectural configuration of white matter in vivo, offering new avenues for applications like presurgical planning. Despite the promising outlook, there are many pitfalls that complicate its use for (clinical) application. Amongst these are inaccuracies in the geometry of the diffusion profiles on which tractography is based, and poor alignment with neighboring profiles. Recently developed contextual processing techniques, including enhancement and well-posed geometric sharpening, have shown to result in sharper and better aligned diffusion profiles. However, the research that has been conducted up to now is mainly of theoretical nature, and so far these techniques have only been evaluated by visual inspection of the diffusion profiles. In this work, the method is evaluated in a clinically relevant application: the reconstruction of the optic radiation for epilepsy surgery. For this evaluation we have developed a framework in which we incorporate a novel scoring procedure for individual pathways. We demonstrate that, using enhancement and sharpening, the extraction of an anatomically plausible reconstruction of the optic radiation from a large amount of probabilistic pathways is greatly improved in three healthy controls, where currently used methods fail to do so. Furthermore, challenging reconstructions of the optic radiation in three epilepsy surgery candidates with extensive brain lesions demonstrate that it is beneficial to integrate these methods in surgical planning.

Quantitative volumetric analysis of the optic radiation in the normal human brain using diffusion tensor magnetic resonance imaging-based tractography

To attain the volumetric information of the optic radiation in normal human brains, we performed diffusion tensor imaging examination in 13 healthy volunteers. Simultaneously, we used a brain normalization method to reduce individual brain variation and increase the accuracy of volumetric information analysis. In addition, tractography-based group mapping method was also used to investigate the probability and distribution of the optic radiation pathways. Our results showed that the measured optic radiation fiber tract volume was a range of about 0.16% and that the fractional anisotropy value was about 0.53. Moreover, the optic radiation probability fiber pathway that was determined with diffusion tensor tractography-based group mapping was able to detect the location relatively accurately. We believe that our methods and results are helpful in the study of optic radiation fiber tract information.

Surgical treatment of Spetzler-Martin grade III to V cerebral arteriovenous malformations: 10 years experience in Kyoto University

Cerebral arteriovenous malformations (AVMs) are abnormal connections between arteries and veins leading to arteriovenous shunting with nidus formation. This study reviewed the clinical outcomes of surgical treatment for AVMs of Spetzler-Martin grades III to V in our institute. In addition, we summarized the technical aspects of surgical treatment for cerebral AVMs. Our development of the surgical modality for high-grade AVMs included intraoperative digital subtraction cerebral angiography, non-stick bipolar forceps, magnetic resonance tractography, and indocyanine green videoangiography. Excellent outcomes were obtained, but about 40% of all patients with AVMs could not receive surgical treatment. Multimodality approach including Onyx embolization may extend the surgical indications.

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

Object

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.

Visual pathway study using in vivo diffusion tensor imaging tractography to complement classic anatomy

BACKGROUND

Knowledge of the individual course of the optic radiations (ORs) is important to avoid postoperative visual deficits. Cadaveric studies of the visual pathways are limited because it has not been possible to separate the OR from neighboring tracts accurately and results may not apply to individual patients. Diffusion tensor imaging studies may be able to demonstrate the relationships between the OR and neighboring fibers in vivo in individual subjects.

OBJECTIVE

To use diffusion tensor imaging tractography to study the OR and the Meyer loop (ML) anatomy in vivo.

METHODS

Ten healthy subjects underwent magnetic resonance imaging with diffusion imaging at 3 T. With the use of a fiducial-based diffusion tensor imaging tractography tool (Slicer 3.3), seeds were placed near the lateral geniculate nucleus to reconstruct individual visual pathways and neighboring tracts. Projections of the ORs onto 3-dimensional brain models were shown individually to quantify relationships to key landmarks.

RESULTS

Two patterns of visual pathways were found. The OR ran more commonly deep in the whole superior and middle temporal gyri and superior temporal sulcus. The OR was closely surrounded in all cases by an inferior longitudinal fascicle and a parieto/occipito/temporo-pontine fascicle. The mean left and right distances between the tip of the OR and temporal pole were 39.8 ± 3.8 and 40.6 ± 5.7 mm, respectively.

CONCLUSION

Diffusion tensor imaging tractography provides a practical complementary method to study the OR and the Meyer loop anatomy in vivo with reference to individual 3-dimensional brain anatomy.

Intraoperative high-field magnetic resonance imaging combined with fiber tract neuronavigation-guided resection of cerebral lesions involving optic radiation

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) combined with optic radiation neuronavigation may be safer for resection of cerebral lesions involving the optic radiation.

OBJECTIVE

To investigate whether iMRI combined with optic radiation neuronavigation can help maximize tumor resection while protecting the patient's visual field.

METHODS

Forty-four patients with cerebral tumors adjacent to the optic radiation were enrolled in the study. The reconstructed optic radiations were observed so that a reasonable surgical plan could be developed. During the surgery, microscope-based fiber tract neuronavigation was routinely implemented. The lesion location (lateral or not to the optic radiation) and course of the optic radiation (stretched or not) were categorized, and their relationships to the visual field defect were determined.

RESULTS

Analysis of the visible relationship between the optic radiation and the lesion led to a change in surgical approach in 6 patients (14%). The mean tumor residual rate for glioma patients was 5.3% (n = 36) and 0% for patients with nonglioma lesions (n = 8). Intraoperative MRI and fiber tract neuronavigation increased the average size of resection (first and last iMRI scanning, 88.3% vs 95.7%; P < .01). Visual fields after surgery improved in 5 cases (11.4%), exhibited no change in 36 cases (81.8%), and were aggravated in 3 cases (6.8%).

CONCLUSION

Diffusion tensor imaging information was helpful in surgical planning. When iMRI was combined with fiber tract neuronavigation, the resection rate of brain lesions involving the optic radiation was increased in most patients without harming the patients' visual fields.

Imaging of cerebral arteriovenous malformations and dural arteriovenous fistulas

Imaging plays a major role in the identification, grading, and treatment of cerebral arteriovenous malformations and cerebral dural arteriovenous fistulas. Digital subtraction angiography is the gold standard in the diagnosis and characterization of these vascular malformations, but advances in both magnetic resonance imaging and computed tomography, including advanced imaging techniques, have provided new tools for further characterizing these lesions as well as the surrounding brain structures that may be affected. This article discusses the role of conventional as well as advanced imaging modalities that are providing novel ways to characterize these vascular malformations.

Diffusion MR imaging: basic principles

From their origin as simple techniques primarily used for detecting acute cerebral ischemia, diffusion MR imaging techniques have rapidly evolved into a versatile set of tools that provide the only noninvasive means of characterizing brain microstructure and connectivity, becoming a mainstay of both clinical and investigational brain MR imaging. In this article, the basic principles required for understanding diffusion MR imaging techniques are reviewed with clinical neuroradiologists in mind.

A supervised framework for the registration and segmentation of white matter fiber tracts

A supervised framework is presented for the automatic registration and segmentation of white matter (WM) tractographies extracted from brain DT-MRI. The framework relies on the direct registration between the fibers, without requiring any intensity-based registration as preprocessing. An affine transform is recovered together with a set of segmented fibers. A recently introduced probabilistic boosting tree classifier is used in a segmentation refinement step to improve the precision of the target tract segmentation. The proposed method compares favorably with a state-of-the-art intensity-based algorithm for affine registration of DTI tractographies. Segmentation results for 12 major WM tracts are demonstrated. Quantitative results are also provided for the segmentation of a particularly difficult case, the optic radiation tract. An average precision of 80% and recall of 55% were obtained for the optimal configuration of the presented method.

Lack of the cerebral peduncle involvement in a series of adult supratentorial AVM: a diffusion tensor imaging study

Congenital as arteriovenous malformation(AVM) is, most patients with AVM would be asymptomatic until adults. During the past 2 years, 23 cases of adult supratentorial AVM patients had DTI after admission. The region of interest was placed in the cerebral peduncle. Their FA value and fiber number was compared with those of cavernous malformation (CM) and tumor (glioma and meningioma). In the AVM group, there was no significant difference in FA of the cerebral peduncle (ipsilateral 0.758±0.055 versus contralateral 0.755±0.049; P>0.05) and fiber number (319.6±82.9 versus 304.7±89.1; P>0.05). In the CM group, FA of the cerebral peduncle on ipsilateral side (0.711±0.092) was significantly lower than that of contralateral side (0.768±0.043) (P<0.01). Similar result was in fiber number of the CM group (251±82.1 versus 307.3±77.0; P<0.05). In tumor group, FA of ipsilateral side (0.713±0.084) was lower than that of contralateral (0.751±0.052) without significant difference. There was no significant difference in fiber number between ipsilateral and contralateral sides in the tumor group (308.9±112.4 versus 287.9±62.4). Unlike non-AVM lesions (CM and tumor), FA value and fiber number of the ipsilateral cerebral peduncle is less influenced in the AVM group. The lack of the cerebral peduncle involvement indicates that there is plasticity of white matter in AVM.

Principles and limitations of computational algorithms in clinical diffusion tensor MR tractography

There have been numerous reports documenting the graphic reconstruction of 3D white matter architecture in the human brain by means of diffusion tensor MR tractography. Different from other reviews addressing the physics and clinical applications of DTI, this article reviews the computational principles of tractography algorithms appearing in the literature. The simplest voxel-based method and 2 widely used subvoxel approaches are illustrated first, together with brief notes on parameter selection and the restrictions arising from the distinct attributes of tract estimations. Subsequently, some advanced techniques attempting to offer improvement in various aspects are briefly introduced, including the increasingly popular research tracking tool using HARDI. The article explains the inherent technical limitations in most of the algorithms reported to date and concludes by providing a reference guideline for formulating routine applications of this important tool to clinical neuroradiology in an objective and reproducible manner.

Arcuate fasciculus tractography integrated into Gamma Knife surgery

Object

To prevent speech disturbances after Gamma Knife surgery (GKS), the authors integrated arcuate fasciculus (AF) tractography based on diffusion tensor (DT) MR imaging into treatment planning for GKS.

Methods

Arcuate fasciculus tractography was retrospectively integrated into planning that had been previously performed by neurosurgeons and radiation oncologists. This technique was retrospectively applied to 12 patients with arteriovenous malformations adjacent to the AF. Diffusion tensor images were acquired before the frame was affixed to the patient's head and DT tractography images of the AF were created using the authors' original software. The data from DT tractography and stereotactic 3D imaging studies obtained after frame fixation were transported to a treatment planning workstation for GKS and coregistered so that the delivered doses and incidence of posttreatment aphasia could be assessed.

Results

The AF could not be depicted in 2 patients who initially presented with motor aphasia caused by hemorrhaging from arteriovenous malformations. During the median follow-up period of 29 months after GKS, aphasia developed in 2 patients: 30 Gy delivered to the frontal portion of the AF caused conduction aphasia in 1 patient, and 9.6 Gy to the temporal portion led to motor aphasia in the other. Speech dysfunction was not observed after a maximum radiation dose of 10.0–16.8 Gy was delivered to the frontal fibers in 4 patients, and 3.6–5.2 Gy to the temporal fibers in 3.

Conclusions

The authors found that administration of a 10-Gy radiation dose during GKS was tolerated in the frontal but not the temporal fibers of the AF. The authors recommend confirmation of the dose by integration of AF tractography with GKS, especially in lesions located near the temporal language fibers.

Semiautomatic tractography: motor pathway segmentation in patients with intracranial vascular malformations

Object

The visualization of white matter tracts using tractography has previously been achieved by displaying streamlines that pass between regions of interest (ROIs). These techniques require a significant amount of user interaction, and their results are entirely dependent on the positioning of the ROIs. Furthermore, in patients with intracerebral hemorrhage secondary to intracranial vascular malformation, there is often significant cerebral edema and susceptibility artifact from the hematoma, which degrade the reliability of tractography. In this paper, the authors' objectives were to visualize the motor pathways of patients with hemorrhagic and nonhemorrhagic vascular malformations by using a novel semiautomated technique that functions without the need for multiple ROIs.

Methods

The authors investigated the tractography appearance of the descending motor pathways in 6 patients with intracranial vascular malformations. Of these patients 4 presented with a spontaneous intracranial hemorrhage, 2 of whom were clinically hemiparetic. Diffusion tensor imaging was performed using a 1.5-T clinical MR imaging system, and whole-brain tractography was performed after reconstruction of the data. A fractional anisotropy threshold of 0.05 was used to terminate the tractography. The semiautomatic motor pathway segmentation technique required definition of a single voxel within the corticospinal tract of the medulla from which the descending motor pathways were automatically defined by grouping together all streamlines within the entire image with a geometry similar to that of the single streamline generated from this initial voxel. The results of this segmentation were then visually assessed and compared with the patient's motor function.

Results

The authors' semiautomatic algorithm consistently visualized the location of the descending motor pathways in patients with nonhemorrhagic and hemorrhagic vascular malformations. In 1 patient whose complete right hemiplegia (complete paralysis) was caused by a large left frontal hematoma that bisected the descending motor pathways, the authors were unable to reconstruct the motor pathways due to severe tract degeneration. However, in all cases in which motor function was intact or only mildly impaired, the technique clearly delineated the motor pathways, even in the presence of large anatomical displacement by the vascular abnormality or associated hemorrhage.

Conclusions

Semiautomatic tractography allows consistent and rapid demonstration of the descending motor pathways in patients with hemorrhagic and nonhemorrhagic intracranial vascular malformations. The technique allows the use of a comparatively low fractional anisotropy threshold and does not require the definition of multiple ROIs. These techniques may help to improve the clinical feasibility and potentially the reliability of tractography for the evaluation of patients with intracranial vascular malformations as well as other space-occupying lesions of the brain.

Identifying the human optic radiation using diffusion imaging and fiber tractography

Measuring the properties of the white matter pathways from retina to cortex in the living human brain will have many uses for understanding visual performance and guiding clinical treatment. For example, identifying the Meyer's loop portion of the optic radiation (OR) has clinical significance because of the large number of temporal lobe resections. We use diffusion tensor imaging and fiber tractography (DTI-FT) to identify the most likely pathway between the lateral geniculate nucleus (LGN) and the calcarine sulcus in sixteen hemispheres of eight healthy volunteers. Quantitative population comparisons between DTI-FT estimates and published postmortem dissections match with a spatial precision of about 1 mm. The OR can be divided into three bundles that are segmented based on the direction of the fibers as they leave the LGN: Meyer's loop, central, and direct. The longitudinal and radial diffusivities of the three bundles do not differ within the measurement noise; there is a small difference in the radial diffusivity between the right and left hemispheres. We find that the anterior tip of Meyer's loop is 28 +/- 3 mm posterior to the temporal pole, and the population range is 1 cm. Hence, it is important to identify the location of this bundle in individual subjects or patients.

Surgery of cerebral arteriovenous malformations

Despite remarkable progress, the microsurgical extirpation of cerebral arteriovenous malformations (AVMs) even by experienced neurosurgeons is not always easy or safe. This article focuses on how to render AVM surgery safer, and offers strategies and tactics for avoiding perilous bleeding and preserving postoperative neurological function. Our treatment strategies and surgical techniques are offered from the operating surgeon's perspective. An understanding of pathophysiology of cerebral AVMs is important for their appropriate surgical treatment. Sophisticated neuroimaging techniques and scrupulous neurophysiological examinations alert to possible complications, and improved surgical approaches help to minimize the sequelae of unanticipated complications. At the early stage of cerebral AVM surgery, extensive dissection of the sulci, fissures, and subarachnoid cistern should be performed to expose feeders, nidus, and drainers. Problems with the surgery of large and/or deep-seated lesions are exacerbated when arterial bleeding from the nidus continues even after all major feeders are thought to have been occluded. We routinely place catheters for angiography at the surgery of complex AVMs to find missing feeding arteries or to identify the real-time hemodynamic status of the lesion. Temporary clip application on feeders and less coagulation of the nidus is necessary to control intranidal pressure and to avoid uncontrollable bleeding from the nidus and adjacent brain. Intraoperative navigation images superimposed on tractography images can provide us with valuable information to minimize neurological deficits. Deeper insight into AVM nature and into events that occur during AVM surgery as well as the inclusion of molecular biological approaches will open new horizons for the safe and effective treatment of AVMs.

Evidence of rapid ongoing brain development beyond 2 years of age detected by fiber tracking

BACKGROUND AND PURPOSE

Development of callosal fibers is important for psychomotor and cognitive functions. We hypothesized that brain maturation changes are detectable beyond 2 years of age by using diffusion tensor imaging (DTI) of the corpus callosum (CC).

MATERIALS AND METHODS

T2 and fractional anisotropy (FA) maps of the brain of 55 healthy subjects between 0.2 and 39 years of age were obtained. Quantitative T2 and FA values were measured at the genu and splenium of the CC (gCC and sCC). Fiber tracking, volumetric determination, and the fiber density calculations of the CC were related to age. A paired t test was used for significant differences between the values at the gCC and sCC.

RESULTS

T2 relaxation times at gCC and sCC decrease fast in the first months of life and very little after 2 years of age. The FAgCC increases until 5 years of age and remains nearly constant thereafter; it showed a significant increase from 0 to 2 years versus 2-5 years, whereas there was no difference in the other age groups. FAsCC values showed no significant changes after 2 years of age. The fiber density of the CC shows a tendency of inverse age dependence from childhood to adulthood.

CONCLUSION

Rapid ongoing changes in brain maturation (increase in FAgCC) are detectable until 5 years of age. DTI reveals more information about brain maturation than T2 relaxometry.

Signal intensity of the motor cortex on phase-weighted imaging at 3T

BACKGROUND AND PURPOSE

It is known that the motor cortex shows hypointensity on T2-weighted images in older patients. The goal of this study was to assess the signal intensity of the motor cortices on the phase-weighted imaging performed with a Windows-based software program that we developed ourselves.

MATERIALS AND METHODS

All studies were performed at 3T MR imaging. First, the TE for the phase-weighted image was optimized; the best contrast between the motor and other cortices was obtained with a TE of 40 ms. The study population consisted of 45 healthy subjects (23 females, 22 males; mean age, 32.1 years). The signal intensity of the motor cortices was divided into 3 grades by 2 neuroradiologists in comparison with that of the superior frontal cortex (SFC): In grade I, the motor cortex was isointense to the SFC; in grade II, the motor cortex was slightly hypointense to the SFC; and in grade III, the motor cortex was markedly hypointense to the SFC.

RESULTS

The motor cortex was classified as either grade II or III in all subjects older than 20 years of age on the phase-weighted images. Even at 10-19 years of age, the grade II or III appearance was found in 14 (88%) of 16 motor cortices (8 subjects) on the phase-weighted images.

CONCLUSION

In adolescents, the motor cortex is hypointense to other cerebral cortices on phase-weighted MR imaging, which probably reflects differences in the concentration of nonheme iron and/or in the tissue architecture.