Introduction to tractography-guided navigation: using 3-tesla magnetic resonance tractography in surgery for cerebral arteriovenous malformations

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.

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 ).

Corticospinal tract mapping in children with ruptured arteriovenous malformations using functionally guided diffusion-tensor imaging

Arteriovenous malformations (AVMs) can lead to distortion or reorganization of functional brain anatomy, making localization of eloquent white matter tracts challenging. To improve the accuracy of corticospinal tract (CST) mapping, recent studies have examined the use of functional imaging techniques to help localize cortical motor activations and use these as seed points to reconstruct CSTs using diffusion-tensor imaging (DTI). The authors examined the role of pretreatment functionally guided DTI CST mapping in 3 children with ruptured AVMs. In 2 patients, magnetoencephalography motor activations were adjacent to the nidus and/or hemorrhagic cavity. However, in 1 child, functional MRI motor activations were detected in both hemispheres, suggestive of partial transfer of cortical motor function. In all children, quantitative analysis showed that fractional anisotropy values and fiber density indices were reduced in the CSTs of the hemisphere harboring the AVM compared with the unaffected side. In 2 children, CST caliber was slightly diminished, corresponding to no motor deficit in 1 patient and a temporary motor deficit in the other. In contrast, 1 child demonstrated marked reduction and displacement of the CSTs, correlating with severe motor deficit. Preoperative motor tractography data were loaded onto the intraoperative neuronavigation platform to guide complete resection of the AVM in 2 cases without permanent neurological deficits. These preliminary results confirm the feasibility of CST mapping in children with ruptured AVMs using functionally guided DTI tractography. Prospective studies are needed to assess the full value of this technique in the risk stratification, prognosis, and multimodality management of pediatric AVMs.

Changes in language pathways in patients with temporal lobe epilepsy: diffusion tensor imaging analysis of the uncinate and arcuate fasciculi

OBJECTIVE

The language pathways consist of ventral and dorsal systems connected via the uncinate fasciculus and arcuate fasciculus, respectively. Seizures in medial temporal lobe epilepsy (mTLE) affect both tracts. Previous studies, however, have focused on the arcuate fasciculus to explain the language disturbance in mTLE. In contrast, we compared changes in both the uncinate and arcuate fasciculi using diffusion tensor imaging.

METHODS

Thirteen patients with left mTLE and 12 with right mTLE were studied. The Wada test showed left dominance for language in all these patients. Sixteen healthy right-handed subjects were also studied. The mean fractional anisotropy and mean apparent diffusion coefficient with their lateralization index of two fasciculi were compared between hemispheres and between subjects.

RESULTS

The mean apparent diffusion coefficient of the arcuate and uncinate fasciculi in both left- and right-mTLE patients increased bilaterally compared with that in healthy subjects. In left mTLE, the fractional anisotropy of the uncinate fasciculus was lower ipsilaterally (P = 0.002) and was significantly lateralized contralaterally (P < 0.001) compared with control subjects, whereas the fractional anisotropy of the arcuate fasciculus showed no lateralization (P = 0.577). In right mTLE, such a difference was not prominent.

CONCLUSION

The seizure network affects both arcuate and uncinate fasciculi bilaterally in both left- and right-mTLE patients. The change is most prominent in the left uncinate fasciculus in left mTLE.

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.