Preoperative single-slab 3D time-of-flight magnetic resonance angiography predicts development of new cerebral ischemic events after carotid endarterectomy. Clinical article.

OBJECT: Preoperative impairment of cerebral hemodynamics predicts the development of new cerebral ischemic events after carotid endarterectomy (CEA), including neurological deficits and cerebral ischemic lesions on diffusion weighted MR imaging. Furthermore, the signal intensity of the middle cerebral artery (MCA) on single-slab 3D time-of-flight MR angiography (MRA) can assess hemodynamic impairment in the cerebral hemisphere. The purpose of the present study was to determine whether, on preoperative MR angiography, the signal intensity of the MCA can be used to identify patients at risk for development of cerebral ischemic events after CEA. METHODS: The signal intensity of the MCA ipsilateral to CEA on preoperative MR angiography was graded according to the ability to visualize the MCA in 106 patients with unilateral internal carotid artery stenosis (>or=70%). Diffusion weighted MR imaging was performed within 3 days of and 24 hours after surgery. The presence or absence of new postoperative neurological deficits was also evaluated. RESULTS: Cerebral ischemic events after CEA were observed in 16 patients. Reduced signal intensity of the MCA on preoperative MR angiography was the only significant independent predictor of postoperative cerebral ischemic events. When the reduced MCA signal intensity on preoperative MR angiography was defined as an impairment in cerebral hemodynamics, MR angiography grading resulted in an 88% sensitivity and 63% specificity, with a 30% positive- and a 97% negative-predictive value for the development of postoperative cerebral ischemic events. CONCLUSIONS: Signal intensity of the MCA on preoperative single-slab 3D time-of-flight MR angiography is useful for identifying patients at risk for cerebral ischemic events after CEA.

High-resolution diffusion tensor imaging for the detection of diffusion abnormalities in the trigeminal nerves of patients with trigeminal neuralgia caused by neurovascular compression.

PURPOSE: To detect diffusion abnormalities in the trigeminal nerves of patients with trigeminal neuralgia (TN) caused by neurovascular compression (NVC) by using a high-resolution diffusion tensor imaging (HR-DTI) technique. METHODS: Thirteen patients with TN and 14 healthy controls underwent HR-DTI scanning. After extracting the trigeminal nerve using a tractography technique, we measured the fractional anisotropy (FA) and apparent diffusion coefficient (ADC), and compared the contralateral ratios (CR) of these parameters between the patients and controls, and correlated these ratios with the cross-sectional areas of the nerves. RESULTS: The CRs of the FA values for the trigeminal nerves of the patients (1.00±0.15) had significantly higher variance than those of healthy controls (1.00±0.05) (P<.05) and showed a positive correlation with the cross-sectional area of the nerves (r=0.81). In contrast, the CRs of the ADC values were not significantly different between the two groups (1.02±0.10 and 1.01±0.08, respectively) and had no significant correlation with cross-sectional area. CONCLUSION: HR-DTI can detect an alteration in the relative FA values of affected trigeminal nerves and a correlation with atrophic changes in patients with NVC-induced TN.

Choice of posterior subtemporal transtentorial approach for tumor resection in deep anteromedial superior cerebellum.

The anteromedial superior cerebellar tumor can be accessed by various routes. For tumor presenting at the cerebellar surface in this region, the optimal approach remains contentious. Furthermore, which of the various routes offers the optimal approach to a tumor that is not present at the cerebellar surface but lies deep anteromedial superior cerebellum is a matter of debate. We report herein the case of a 44-year-old woman with hemangioblastoma deep within the subcortex of the anteromedial superior cerebellum. Preoperative magnetic resonance (MR) imaging and three-dimensional anisotropy contrast MR axonography using diffusion-weighted MR imaging demonstrated that the posterior subtemporal transtentorial (PSTT) approach would provide a shorter surgical corridor, minimal cerebellar split, and better preservation of nerve fibers, compared to the other approaches. Surgical tumor removal was successfully achieved using the PSTT approach. During surgery, the PSTT approach provided an operative field that enabled visualization of the proximal side of the superior cerebellar artery as the tumor feeding vessel. Although the vein of Labbé inserted just into the transverse-sigmoid junction, injury to this vein was avoided using optimal head position, cerebrospinal fluid drainage, and various devices. For patients with tumor located within the subcortex of the anteromedial superior cerebellum, the PSTT approach is recommended as an optimal surgical route. Scrupulous evaluation using preoperative neuroimaging is crucial when deciding on the surgical approach.

Prediction of cerebral hyperperfusion after carotid endarterectomy using middle cerebral artery signal intensity in preoperative single-slab 3-dimensional time-of-flight magnetic resonance angiography.

OBJECTIVE: Cerebral hyperperfusion after carotid endarterectomy (CEA) occurs in patients with preoperative impairments in cerebral hemodynamics. Signal intensity of the middle cerebral artery (MCA) on single-slab 3-dimensional time-of-flight magnetic resonance angiography (MRA) can assess hemodynamic impairment in the cerebral hemisphere. The purpose of the present study was to determine whether the signal intensity of the MCA on preoperative MRA could identify patients at risk for cerebral hyperperfusion after CEA. METHODS: The signal intensity of the MCA ipsilateral to CEA on preoperative MRA was graded according to the ability to visualize the MCA in 81 patients with ipsilateral internal carotid artery stenosis (>or=70%). Cerebral blood flow was also quantified using single-photon emission computed tomography before and immediately after CEA and on the third postoperative day. RESULTS: Cerebral hyperperfusion immediately after CEA (cerebral blood flow increase >or=100% compared with preoperative values) was observed in 10 patients. Multivariate analysis revealed that only reduced signal intensity of the MCA was significantly associated with the development of postoperative cerebral hyperperfusion (95% confidence interval, 1.015-1.401; P = 0.0319). When the reduced signal intensity of the MCA on MRA was defined as an impairment in cerebral hemodynamics, MRA grading resulted in 100% sensitivity and 63% specificity, with a 28% positive predictive value and a 100% negative predictive value for the development of post-CEA hyperperfusion. Hyperperfusion syndrome developed on the fourth and sixth postoperative days in 2 of the 10 patients who exhibited hyperperfusion immediately after CEA. CONCLUSION: Signal intensity of the MCA, as assessed by this simple MRA method, may identify patients at risk for post-CEA cerebral hyperperfusion.

Computer-assisted identification of the central sulcus in patients with brain tumors using MRI.

PURPOSE: To develop computer-assisted image processing to identify the central sulcus from the MRI data sets in patients with brain tumors. MATERIALS AND METHODS: All MR images were acquired with a 3.0 Tesla scanner by three-dimensional (3D) spoiled gradient recalled acquisition using the steady state (SPGR) gradient-echo sequence and short inversion time inversion-recovery fast spin-echo sequence. The sulci were extracted automatically from reconstructed two-dimensional images of the cortical surface of 30 patients with brain tumors, and the extracted sulci were scored according to matching of the accepted anatomical features of the central sulcus. The candidates with the three highest scores were then superimposed on the 3D images. The correct position of the central sulcus was agreed by two senior neurosurgeons and one neuroradiologist. RESULTS: One of the three candidates corresponded to the central sulcus identified by the manual segmentation method for all 60 affected and unaffected hemispheres in the 30 patients. The candidate with the highest score coincided with the central sulcus in 26 of the 28 unaffected hemispheres and in 28 of the 32 affected hemispheres. CONCLUSION: The proposed method of computer-assisted image processing can provide accurate guidance to identifying the central sulcus in patients with brain tumors.

Feasibility of 1.6-mm isotropic voxel diffusion tensor tractography in depicting limbic fibers.

INTRODUCTION: We attempted to assess the feasibility of a 1.6-mm isotropic voxel diffusion tensor imaging (DTI) tractography at 3T in visualizing nerve bundles in the limbic system. METHODS: We examined 20 healthy volunteers by conventional DTI with a voxel size of 1.6 x 1.6 x 3.0 mm and by high-resolution DTI with a voxel size of 1.6 x 1.6 x 1.6 mm and generated tractographs of three limbic nerve bundles: the fornix, cingulum, and uncinate fasciculus. We visually assessed whether these bundles reached their targets and compared their diffusion parameters between the two techniques. RESULTS: The entire pathways of the fornix, cingulum, and uncinate fasciculus were more readily visualized by high-resolution DTI than by conventional DTI. Among these, the fimbria of the fornix and the uncinate fasciculus adjacent to the temporal pole were identified more frequently by high-resolution DTI (visualization rate 83 and 100%, respectively) than by conventional DTI (visualization rate 63 and 83%, respectively) at a statistical significance of P < 0.05 and P < 0.01, respectively). Fractional anisotropy values in the fornix, cingulum, and uncinate fasciculus by high-resolution DTI were significantly higher than those by conventional DTI (P < 0.01); in contrast, the apparent diffusion coefficient values of all these fibers except that of the fornix remained unchanged between the two techniques. CONCLUSION: The 1.6-mm istropic voxel DTI at 3T is a feasible visualization tool and can improve the precision of tracking nerve bundles of the limbic system.