Neurosurgery Blog

Neurosurgery 70:283–294, 2012 DOI: 10.1227/NEU.0b013e31823020e6

Diffusion tensor (DT) imaging-based fiber tracking is a noninvasive magnetic resonance technique that can delineate the course of white matter fibers.

OBJECTIVE: To evaluate the accuracy and usefulness of this DT imaging-based fiber tracking for surgery in patients with gliomas near the pyramidal tract (PT).

METHODS: Subjects comprised 32 patients with gliomas near the PT. DT imagingbased fiber tracks of the PT were generated before and within 3 days after surgery in all patients. A tractography-integrated navigation system was used during the operation. Cortical and subcortical motor-evoked potentials (MEPs) were also monitored during resection to maximize the preservation of motor function. The threshold intensity for subcortical MEPs was examined by searching the stimulus points and changing the stimulus intensity. Minimum distance between the resection border and the illustrated PT was measured on postoperative tractography.

RESULTS: In all subjects, DT imaging-based tractography of the PT was successfully performed, preoperatively demonstrating the relationship between tumors and the PT. With the use of the tractography-integrated navigation system and intraoperative MEPs, motor function was preserved postoperatively in all patients. A significant correlation was seen between threshold intensity for subcortical MEPs and the distance between the resection border and PT on postoperative DT imaging.

CONCLUSION: DT imaging-based fiber tracking is a reliable and accurate method for mapping the course of subcortical PTs. Fiber tracking and intraoperative MEPs were useful for preserving motor function in patients with gliomas near the PT.

Spine 2012 ; 37 : 48 – 56

Study Design. A prospective study evaluating a cohort of patients with spondylotic cervical spine compression.

Objective. To analyze the potential of diffusion tensor imaging (DTI) of the cervical spinal cord in the detection of changes associated with spondylotic myelopathy, with particular reference to clinical and electrophysiological fi ndings.

Summary of Background Data. Conventional magnetic resonance imaging (MRI) may provide confusing fi ndings because of a frequent disproportion between the degree of the spinal cord compression and clinical symptoms . The DTI is known to be more sensitive to subtle pathological changes of the spinal cord compared with conventional MRI. Methods. The DTI of the cervical spinal cord was performed within a group of 52 patients with spondylotic spinal cord compression and 13 healthy volunteers on a 1.5-T MRI scanner. All patients underwent clinical examination that differentiated between asymptomatic and symptomatic myelopathy subgroups, and 45 patients underwent electrophysiological examination. We measured the apparent diffusion coeffi cient and fractional anisotropy of the spinal cord at C2/C3 level without compression and at the maximal compression level (MCL). Sagittal spinal canal diameter, cross-sectional spinal cord area, and presence of T2 hyperintensity at the MCL were also recorded. Nonparametric statistical testing was used for comparison of controls with subgroups of patients.

Results. Significant differences in both the DTI parameters measured at the MCL, between patients with compression and control group, were found, while no difference was observed at the noncompression level. Moreover, fractional anisotropy values were lower and apparent diffusion coeffi cient values were higher at the MCL in the symptomatic patients than in the asymptomatic patients. The DTI showed higher potential to discriminate between clinical subgroups in comparison with standard MRI parameters and electrophysiological fi ndings.

Conclusion. The DTI appears to be a promising imaging modality in patients with spondylotic spinal cord compression. It refl ects the presence of symptomatic myelopathy and shows considerable potential for discriminating between symptomatic and asymptomatic patients.

J Neurosurg 115:1087–1093, 2011. DOI: 10.3171/2011.7.JNS11495

The reliable preoperative visualization of facial nerve location in relation to vestibular schwannoma (VS) would allow surgeons to plan tumor removal accordingly and may increase the safety of surgery. In this prospective study, the authors attempted to validate the reliability of facial nerve diffusion tensor (DT) imaging–based fiber tracking in a series of patients with large VSs. Furthermore, the authors evaluated the potential of this visualization technique to predict the morphological shape of the facial nerve (tumor compression–related flattening of the nerve).

Methods. Diffusion tensor imaging and anatomical images (constructive interference in steady state) were acquired in a series of 22 consecutive patients with large VSs and postprocessed with navigational software to obtain facial nerve fiber tracking. The location of the cerebellopontine angle (CPA) part of the nerve in relation to the tumor was recorded during surgery by the surgeon, who was blinded to the results of the fiber tracking. A correlative analysis was performed of the imaging-based location of the nerve compared with its in situ position in relation to the VS.

Results. Fibers corresponding to the anatomical location and course of the facial nerve from the brainstem to the internal auditory meatus were identified with the DT imaging–based fiber tracking technique in all 22 cases. The location of the CPA segment of the facial nerve in relation to the VS determined during surgery corresponded to the location of the fibers, predicted by the DT imaging–based fiber tracking, in 20 (90.9%) of the 22 patients. No DT imaging–based fiber tracking correlates were found with the 2 morphological types of the nerve (compact or flat).

Conclusions. The current study of patients with large VSs has shown that the position of the facial nerve in relation to the tumor can be predicted reliably (in 91%) using DT imaging–based fiber tracking. These are preliminary results that need further verification in a larger series.

Neurosurgery 69:1124–1130, 2011 DOI: 10.1227/NEU.0b013e3182296a42

The ventralis intermedius (VIM) nucleus of the thalamus is the primary surgical target for treatment of tremor. Most centers rely on indirect targeting based on atlas-defined coordinates rather than patient-specific anatomy, making intraoperative physiological mapping critical. Detailed identification of this target based on patientspecific anatomic features can help optimize the surgical treatment of tremor.

OBJECTIVE: To study colored fractional anisotropic images and diffusion tensor imaging (DTI) tractography to identify characteristic magnetic resonance appearances of the VIM nucleus.

METHODS: Four patients undergoing stereotactic surgery for essential tremor (ET) were retrospectively studied with analysis of magnetic resonance imaging-based colored fractional anisotropy (FA) images and fiber tractography. All were scanned with a 1.5-T magnetic resonance imaging unit, and all sequences were obtained before frame placement. Because the goal of this study was to identify the DTI characteristics of physiologically defined VIM nucleus, we selected and studied patients who had undergone DTI and had efficacious tremor control with intraoperative microlesioning effect and tremor reduction with less than 2.0-V stimulation.

RESULTS: Analysis of color FA maps, which graphically illustrate fiber directionality, revealed consistent anatomic patterns. The region of the VIM nucleus can be seen as an intermediate region where there is a characteristic transition of color. Presumptive VIM nucleus interconnectivity with sensorimotor cortex and cerebellum was identified via the internal capsule and the superior cerebellar peduncle, respectively. FA maps could also be used to distinguish segments of gray matter, white matter, and gray-white matter boundaries.

CONCLUSION: Analysis of DTI and FA maps on widely available 1.5-T magnetic resonance imaging yields clear identification of various structures key to neurosurgical targeting. Prospective evaluation of integrating DTI into neurosurgical planning may be warranted.

Neuroradiology (2011) 53:787–791.DOI 10.1007/s00234-011-0878-7
The dentatorubrothalamic tract (DRTT) originates from the dentate nucleus in the cerebellum and terminates in the contralateral ventrolateral nucleus (VL) of the thalamus after decussating to the contralateral red nucleus. Identification of the DRTT is difficult due to the fact that it is a long, multisynaptic, neural tract crossing to the opposite hemisphere. In the current study, we attempted to identify the DRTT in the human brain using a probabilistic tractography technique of diffusion tensor imaging.
Methods Diffusion tensor imaging was performed at 1.5-T using a synergy-L sensitivity encoding head coil. DRTTs were obtained by selection of fibers passing through three regions of interest (the dentate nucleus, the superior cerebellar peduncle, and the contralateral red nucleus) from 41 healthy volunteers. Probabilistic mapping was obtained from the highest probabilistic location at 2.3 mm above the anterior commissure–posterior commissure level.
Results DRTTs of all subjects, which originated from the dentate nucleus, ascended through the junction of the superior cerebellar peduncle and the contralateral red nucleus and then terminated at the VL nucleus of the thalamus. The highest probabilistic location for the DRTT at the thalamus was compatible with the location of the VL nucleus.
Conclusions We identified the DRTT in the human brain using probabilistic tractography. Our results could be useful in research on movement control.

Neuroradiology(2011)53:787–791.DOI 10.1007/s00234-011-0878-7
The dentatorubrothalamic tract (DRTT) originates  from the dentate nucleus in the cerebellum and terminates in the contralateral ventrolateral nucleus (VL) of the thalamus after decussating to the contralateral red nucleus. Identification of the DRTT is difficult due to the fact that it is a long, multisynaptic, neural tract crossing to the opposite hemisphere.
In the current study, we attempted to identify the DRTT in the human brain using a probabilistic tractography technique of diffusion tensor imaging.
Methods Diffusion tensor imaging was performed at 1.5-T using a synergy-L sensitivity encoding head coil. DRTTs were obtained by selection of fibers passing through three regions of interest (the dentate nucleus, the superior cerebellar peduncle, and the contralateral red nucleus) from 41 healthy volunteers. Probabilistic mapping was obtained from the highest probabilistic location at 2.3 mm above the anterior commissure–posterior commissure level.
Results DRTTs of all subjects, which originated from the dentate nucleus, ascended through the junction of the superior cerebellar peduncle and the contralateral red nucleus and then terminated at the VL nucleus of the thalamus. The highest probabilistic location for the DRTT at the thalamus was compatible with the location of the VL nucleus.
Conclusions We identified the DRTT in the human brain using probabilistic tractography. Our results could be useful in research on movement control.

Neurosurgery 68:1069–1076, 2011 DOI: 10.1227/NEU.0b013e31820a1a20

Deep brain stimulation (DBS) has been proven to alleviate tremor of various origins. Distinct regions have been targeted. One explanation for good clinical tremor control might be the involvement of the dentatorubrothalamic tract (DRT) as has been suggested in superficial (thalamic) and inferior (posterior subthalamic) target regions. Beyond a correlation with atlas data and the postmortem evaluation of patients treated with lesion surgery, proof for the involvement of DRT in tremor reduction in the living, the scope of this work, is elusive.

OBJECTIVE: To report a case of unilateral refractory tremor in tremor-dominant Parkinson disease treated with thalamic DBS.

METHODS: Preoperative diffusion tensor imaging (DTI) was performed. Correlation with individual DBS electrode contact locations was obtained through postoperative fusion of helical computed tomography (CT) data with DTI fiber tracking.

RESULTS: Tremor was alleviated effectively. An evaluation of the active electrode contact position revealed clear involvement of the DRT in tremor control. A closer evaluation of clinical effects and side effects revealed a highly detailed individual fiber map of the subthalamic region with DTI fiber tracking.

CONCLUSION: This is the first time the involvement of the DRT in tremor reduction through DBS has been shown in the living. The combination of DTI with postoperative CT and the evaluation of the electrophysiological environment of distinct electrode contacts led to an individual detailed fiber map and might be extrapolated to refined DTI-based targeting strategies in the future. Data acquisition for a larger study group is the topic of our ongoing research.

J Neurosurg Spine 13:371–380, 2010. DOI: 10.3171/2010.3.SPINE09399

The aim of this retrospective study was to evaluate the predictive value of diffusion tensor (DT) imaging with respect to resectability of intramedullary spinal cord tumors and to determine the concordance of this method with intraoperative surgical findings.

Methods. Diffusion tensor imaging was performed in 14 patients with intramedullary lesions of the spinal cord at different levels using a 3-T magnet. Routine MR imaging scans were also obtained, including unenhanced and enhanced T1-weighted images and T2-weighted images. Patients were classified according to the fiber course with respect to the lesion and their lesions were rated as resectable or nonresectable. These results were compared with the surgical findings (existence vs absence of cleavage plane). The interrater reliability was calculated using the κ coefficient of Cohen.

Results. Of the 14 patients (7 male, 7 female; mean age 49.2 ± 15.5 years), 13 had tumors (8 ependymomas, 2 lymphomas, and 3 astrocytoma). One lesion was proven to be a multiple sclerosis plaque during further diagnostic workup. The lesions could be classified into 3 types according to the fiber course. In Type 1 (5 cases) fibers did not pass through the solid lesion. In Type 2 (3 cases) some fibers crossed the lesion, but most of the lesion volume did not contain fibers. In Type 3 (6 cases) the fibers were completely encased by tumor. Based on these results, 6 tumors were considered resectable, 7 were not. During surgery, 7 tumors showed a good cleavage plane, 6 did not. The interrater reliability (Cohen κ) was calculated as 0.83 (p < 0.003), which is considered to represent substantial agreement. The mean duration of follow-up was 12.0 ± 2.9. The median McCormick grade at the end of follow-up was II.

Conclusions. These preliminary data suggest that DT imaging in patients with spinal cord tumors is capable of predicting the resectability of the lesion. A further prospective study is needed to confirm these results and any effect on patient outcome.

Acta Neurochir DOI 10.1007/s00701-010-0742-2

The safe and reversible nature of deep brain stimulation (DBS) has allowed movement disorder neurosurgery to become commonplace throughout the world. Fundamental understanding of individual patient’s anatomy is critical for optimizing the effects and side effects of DBS surgery. Three patients undergoing stereotactic surgery for movement disorders, at the institution’s intraoperative magnetic resonance imaging operating suite, were studied with fiber tractography. Stereotactic targets and fiber tractography were determined on preoperative magnetic resonance imagings using the Schaltenbrand–Wahren atlas for definition in the BrainLab iPlan software (BrainLAB Inc., Feldkirchen, Germany). Subthalamic nucleus, globus pallidus interna, and ventral intermediate nucleus targets were studied. Diffusion tensor imaging parameters used ranged from 2 to 8 mm for volume of interest in the x/y/z planes, fiber length was kept constant at 30 mm, and fractional anisotropy threshold varied from 0.20 to 0.45. Diffusion tensor imaging tractography allowed reliable and reproducible visualization and correlation between frontal eye field, premotor, primary motor, and primary sensory cortices via corticospinal tracts and corticopontocerebellar tracts. There is an apparent increase in the number of cortical regions targeted by the fiber tracts as the region of interest is enlarged. This represents a possible mechanism of the increased effects and side effects observed with higher stimulation voltages. Currently available diffusion tensor imaging techniques allow potential methods to characterize the effects and side effects of DBS. This technology has the potential of being a powerful tool to optimize DBS neurosurgery

Neurosurgery 66:917-924, 2010 DOI: 10.1227/01.NEU.0000367801.35654.EC

Diffusion tensor imaging (DTI) parameters were investigated in patients with chronic idiopathic hydrocephalus to evaluate microstructural changes of brain tissue caused by chronic ventricular dilatation.

METHODS: Eleven patients fulfilling the criteria for possible or probable idiopathic normal pressure hydrocephalus and 10 healthy control subjects underwent MRI at 3 Tesla, including DTI with 12 gradient directions. Patients were scanned before lumbar cerebrospinal fluid (CSF) withdrawal tests. Differences in fractional anisotropy (FA) and mean diffusivity (MD) between patients and controls were assessed using 2 different methods: manual definition of regions of interest and a fully automated method, TBSS (Tract-Based Spatial Statistics). DTI parameters were correlated with clinical findings.

RESULTS: Compared with the control group, patients with chronic idiopathic hydrocephalus had significantly higher MD values in both the periventricular corticospinal tract (CST) and the corpus callosum (CC), whereas FA values were significantly higher in the CST but lower in the CC. DTI parameters of the CST correlated with the severity of gait disturbances.

CONCLUSION:Microstructural changes in periventricular functionally relevant white matter structures (CSF, CC) in chronic idiopathic hydrocephalus can be visualized using DTI. Further studies should investigate the change of DTI parameters after CSF shunting and its relation to neurologic outcome.

J Neurosurg 112:832–839, 2010. (DOI: 10.3171/2009.7.JNS09550)

Ventriculomegaly is a common imaging finding in many types of conditions. It is difficult to determine whether it is related to true hydrocephalus or to an atrophic process by using only imaging procedures such as MR imaging after traumatic injury, stroke, or infectious disease. Diffusion tensor (DT) imaging can distinguish the compression characteristics of white matter, indicating that increased diffusion anisotropy may be related to white matter compression. In this preliminary study, the authors compared the DT imaging findings of ventriculomegaly with those of chronic hydrocephalus or atrophy to clarify the potential of diffusion anisotropy in the identification of hydrocephalus. Methods. Ten patients with chronic hydrocephalus, 8 patients with atrophy (defined by conventional devices and surgical outcome), and 14 healthy volunteers underwent DT imaging. Images were acquired before and after shunting or once in cases without shunting. The fractional anisotropy (FA) values at many points around the lateral ventricle were evaluated. Results. The FA patterns around the lateral ventricle in the chronic hydrocephalus and atrophy groups were different. Especially in the caudate nucleus, FA was increased in the chronic hydrocephalus group compared with the atrophy group. Furthermore, the FA values returned to normal levels after shunt placement. Conclusions. Assessment of the FA value of the caudate nucleus may be an important, less invasive method for distinguishing true hydrocephalus from ventriculomegaly. Further research in a large number of patients is needed to verify the diagnostic ability of this method.

Neuroradiology (2009) 51:831–840. DOI 10.1007/s00234-009-0580-1

To date, very scant data is available regarding normal diffusion properties of white matter (WM) fibers. The present study aimed to initiate the establishment of a database of normal diffusion tensor metrics of cerebral WM fibers, including the uncinate fasciculus (UF), posterior cingulum (PC), fornix, and corticospinal tract (CST) for healthy adults using tract-specific analysis by diffusion tensor tractography (DTT).We also attempted to clarify whether age and laterality exerted any effects on this study group.

Methods DTT of WM fibers were generated for 100 healthy subjects, then mean diffusivity (MD) and fractional anisotropy (FA) of the tracts were measured. Pearson correlation analysis was used to evaluate age relationships. Paired t testing was used to compare hemispheric asymmetry. Interobserver correlation tests were also performed.

Results Our results showed FA values for UF (right, 0.42±0.03; left, 0.40±0.03), PC (0.51±0.06, 0.52±0.06), fornix (0.37±0.06, 0.38±0.06), CST (0.70±0.06, 0.69±0.07), and MD values for UF (0.81±0.03, 0.82±0.04), PC (0.72±0.03, 0.72±0.04), fornix (1.86±0.32, 1.94±0.37), and CST (0.72±0.03, 0.74±0.04). We identified a significant positive

correlation between age and MD in the right UF and bilateral fornices, and a negative correlation between age and FA in bilateral fornices. Hemispheric asymmetry was observed in FA of UF (right>left) and MD of CST (left>right).

Conclusions The results constitute a normative dataset for diffusion parameters of four WM tracts that can be used to identify, characterize, and establish the significance of changes in diseases affecting specific tracts.

J Neurosurg 111:785–795, 2009.DOI: 10.3171/2008.9.JNS08414

Object. To validate the corticospinal tract (CST) illustrated by diffusion tensor imaging, the authors used tractography-integrated neuronavigation and direct fiber stimulation with monopolar electric currents.
Methods. Forty patients with brain lesions adjacent to the CST were studied. During the operation, the motor responses (motor evoked potential [MEP]) elicited at the hand by the cortical stimulation to the hand motor area were continuously monitored, maintaining the consistent stimulus intensity (mean 15.1 ± 2.21 mA). During lesion resection, direct fiber stimulation was applied to elicit MEP (referred to as fiber MEP) to identify the CST functionally. The threshold intensity for the fiber MEP was determined by searching for the best stimulus point and changing the stimulus intensity. The minimum distance between the resection border and illustrated CST was measured on postoperative
isotropic images.
Results. Direct fiber stimulation demonstrated that tractography accurately reflected anatomical CST functioning. There were strong correlations between stimulus intensity for the fiber MEP and the distance between the CST and the stimulus points. The results indicate that the minimum stimulus intensity of 20, 15, 10, and 5 mA had stimulus points ~ 16, 13.2, 9.6, and 4.8 mm from the CST, respectively. The convergent calculation formulated 1.8 mA as the electrical threshold of the CST for the fiber MEP, which was much smaller than that of the hand motor area.
Conclusions. The investigators found that diffusion tensor imaging–based tractography is a reliable way to map the white matter connections in the entire brain in clinical and basic neuroscience applications. By combining these techniques, investigating the cortical-subcortical connections in the human CNS could contribute to elucidating the neural networks of the human brain and shed light on higher brain functions.