Is endoscopic third ventriculostomy safe and efficient in the treatment of obstructive chronic hydrocephalus in adults? A prospective clinical and MRI study.

BACKGROUND: In case of suspected normal pressure hydrocephalus, MRI is performed systematically and can sometimes highlight an obstruction of the flow pathways of the CSF (aqueductal stenosis or other downstream obstruction). It seems legitimate for these patients to ask the question of a treatment with endoscopic third ventriculostomy (ETV), even if the late decompensation of an obstruction may suggest an association with a CSF resorption disorder. The aim of this study was to evaluate clinical and radiological evolution after ETV in a group of elderly patients with an obstructive chronic hydrocephalus (OCH). METHODS: ETV was performed in 15 patients with OCH between 2012 and 2017. Morphometric (callosal angle, ventricular surface, third ventricular width, and Evans' index) and velocimetric parameters (stroke volume of the aqueductal (SVa) CSF) parameters were measured prior and after surgery with brain MRI. The clinical score (mini-mental status examination (MMSE) and the modified Larsson's score, evaluating walking, autonomy, and incontinence) were performed pre- and postoperatively. RESULTS: SVa was less than 15 µL/R-R in 12 out of the 15 patients; in the other three cases, the obstruction was located at a distance from the middle part of the aqueduct. Fourteen out of 15 patients were significantly improved: mean Larsson's score decreased from 3.8 to 0.6 (P ≤ 0.01) and mean MMSE increased from 25.7 to 28 (P = 0.084). Evans' index and ventricular area decreased postoperatively and the callosal angle increased (P ≤ 0.01). The mean follow-up lasted 17.9 months. No postoperative complications were observed. CONCLUSION: ETV seems to be a safe and efficient alternative to shunt for chronic hydrocephalus with obstruction; the clinical improvement is usual and ventricular size decreases slightly.

Diffusion tensor imaging in musculoskeletal disorders.

Diffusion tensor (DT) imaging is an emerging magnetic resonance (MR) imaging technique for evaluating the microstructure of well-organized biologic tissues such as muscles and nerves. DT imaging provides information about tissue microstructure by producing three-dimensional maps of water molecule movements. The two main parameters of measurement at DT imaging, fractional anisotropy and the apparent diffusion coefficient, allow quantitation of architectural changes occurring in tissue. These parameters are modified in the presence of cervical spondylotic myelopathy, cervical spine trauma, carpal tunnel syndrome, lumbar nerve compression, peripheral nerve tumors, and muscle ischemia. Their alteration may be observed at DT imaging even when no abnormality is seen at conventional MR imaging, a fact that suggests that DT imaging allows the detection of abnormalities at an earlier stage of injury. Experimental studies in animals have shown that DT imaging consistently allows identification of pathophysiologic alterations in tissue that correlate with histologic findings. Tractographic images accurately depict both normal and abnormal diffusion in anatomic structures such as the thigh and pelvic muscles, cervical spine, and lumbar nerves. Patients with chronic diseases also may benefit from follow-up evaluation with DT imaging, although DT imaging sequences must be further adapted to improve the evaluation of specific anatomic regions by reducing artifacts, optimizing spatial resolution, and minimizing acquisition time. Given its proven potential for use in identifying abnormalities that are otherwise identifiable only with electrophysiologic and histopathologic studies, and with future technical improvements, DT imaging could soon become a standard method for early diagnosis, management, and follow-up of disease in the spine, muscles, and peripheral nerves.

Diffusion tensor imaging and fibre tracking in cervical spondylotic myelopathy.

OBJECTIVES: To (1) obtain microstructural parameters (Fractional Anisotropy: FA, Mean Diffusivity: MD) of the cervical spinal cord in patients suffering from cervical spondylotic myelopathy (CSM) using tractography, (2) to compare DTI parameters with the clinical assessment of these patients (3) and with information issued from conventional sequences. METHODS: DTI was performed on 20 symptomatic patients with cervical spondylotic myelopathy, matched with 15 volunteers. FA and MD were calculated from tractography images at the C2-C3 level and compressed level in patients and at the C2-C3 and C4-C7 in controls. Patients were clinically evaluated using a self-administered questionnaire. RESULTS: The FA values of patients were significantly lower at the compressed level than the FA of volunteers at the C4-C7 level. A significant positive correlation between FA at the compressed level and clinical assessment was demonstrated. Increased signal intensity on T2-weighted images did not correlate either with FA or MD values, or with any of the clinical scores. CONCLUSION: FA values were significantly correlated with some of the patients' clinical scores. High signal intensity of the spinal cord on T2 was not correlated either with the DTI parameters or with the clinical assessment, suggesting that FA is more sensitive than T2 imaging.

Tractography of lumbar nerve roots: initial results.

OBJECTIVES: The aims of this preliminary study were to demonstrate the feasibility of in vivo diffusion tensor imaging (DTI) and fibre tracking (FT) of the lumbar nerve roots, and to assess potential differences in the DTI parameters of the lumbar nerves between healthy volunteers and patients suffering from disc herniation. METHODS: Nineteen patients with unilateral sciatica related to posterolateral or foraminal disc herniation and 19 healthy volunteers were enrolled in this study. DTI with tractography of the L5 or S1 nerves was performed. Mean fractional anisotropy (FA) and mean diffusivity (MD) values were calculated from tractography images. RESULTS: FA and MD values could be obtained from DTI-FT images in all controls and patients. The mean FA value of the compressed lumbar nerve roots was significantly lower than the FA of the contralateral nerve roots (p = 0.0001) and of the nerve roots of volunteers (p = 0.0001). MD was significantly higher in compressed nerve roots than in the contralateral nerve root (p = 0.0002) and in the nerve roots of volunteers (p = 0.04). CONCLUSION: DTI with tractography of the lumbar nerves is possible. Significant changes in diffusion parameters were found in the compressed lumbar nerves.

In vivo diffusion tensor imaging and tractography of human thigh muscles in healthy subjects.

OBJECTIVE: The aims of this study were to assess whether similar measurements of mean apparent diffusion coefficient and fractional anisotropy in muscles can be obtained with regions of interest drawn on cross-sectional diffusion tensor images and tractography and to assess whether water diffusivity in human thigh muscles is influenced by muscular compartment, age, and sex. SUBJECTS AND METHODS: Sixteen healthy volunteers (eight women, eight men) participated in this study. The right thigh of each subject was imaged with diffusion tensor imaging, and the mean apparent diffusion coefficient and fractional anisotropy values were calculated for each muscle of the quadriceps femoris and hamstrings. Fiber tracking was performed with a line propagation technique from the regions of interest drawn on cross-sectional diffusion tensor images. RESULTS: The water diffusivity parameters obtained with tractography did not differ significantly from those obtained with diffusion tensor imaging in the three regions of interest evaluated in each muscle. The mean apparent diffusion coefficient of women (1.80 × 10⁻³ mm²/s) was similar to that of men (1.79 × 10⁻³ mm²/s). Women and men had identical fractional anisotropy values (0.26). The fractional anisotropy value in young volunteers (0.27) was similar to that in older subjects (0.26). The hamstrings had a lower mean apparent diffusion coefficient (1.64 × 10⁻³ mm²/s) than the quadriceps femoris (1.91 × 10⁻³ mm²/s), but the quadriceps femoris had a significantly lower fractional anisotropy value (0.25) than the hamstrings (0.28). CONCLUSION: Our study showed that the water diffusivity values (mean apparent diffusion coefficient and fractional anisotropy) of the thigh muscles did not differ significantly with respect to sex or age of the subject. The quadriceps femoris and the hamstrings did have different mean apparent diffusion coefficient and fractional anisotropy values, which may reflect differences in hydration and muscular architecture.

Ultrasound and magnetic resonance imaging of the peripheral nerves: current techniques, promising directions, and open issues.

High-resolution ultrasound (US) and magnetic resonance (MR) imaging are the two imaging methods of choice for the study of peripheral nerves. The many advances that have been made in recent years, either by US or MR imaging, including diffusion tensor imaging and tractography, offer new perspectives for the assessment of many pathological processes affecting peripheral nerves such as entrapment syndromes, tumors and tumor-like lesions, and traumatic disorders. Most of these improvements have especially increased the spatial resolution of nerve imaging. US and MR imaging are complementary, each having advantages and disadvantages. Tractography is still emerging in the musculoskeletal field, particularly for the analysis of peripheral nerves, but this technique seems promising.

Motor-related circuit dysfunction in MSA-P: Usefulness of combined whole-brain imaging analysis.

The aim of this study was to evaluate in vivo changes in the brain's macro- and microstructure (notably in the motor system) in the parkinsonian variant of multiple system atrophy (MSA-P) and in Parkinson's disease (PD) and to characterize the cerebral anatomical differences between the two conditions. We used a combination of voxel-based morphometry (VBM) and whole-brain, voxel-based diffusion tensor imaging analysis (VB-DTI). Forty-seven right-handed subjects (14 MSA-P patients, 19 PD patients, and 14 controls) were evaluated using VBM and VB-DTI in an analysis of covariance (ANCOVA) with a significance threshold set to P < 0.005. In MSA-P patients, VBM analysis revealed a lower density of grey matter (GM) in a motor-related circuit (especially in the left primary motor cortex, PMC), relative to PD patients, and in the left supplementary motor area (SMA), relative to controls). Diffusion tensor imaging analysis revealed lower fractional anisotropy (FA) values in the left PMC and the right cerebellum in MSA-P patients, compared with controls. Using a volumetric diffusion technique, our study revealed selective tissue degeneration in motor circuits, regardless of the volume loss detected in VBM and in agreement with pathology reports and clinical motor characteristics. Our findings suggest that MSA-P is characterized by both macro- and microstructural changes in the sensorimotor circuit.

Intracranial arteriovenous malformation: time-resolved contrast-enhanced MR angiography with combination of parallel imaging, keyhole acquisition, and k-space sampling techniques at 1.5 T.

PURPOSE: To prospectively compare the agreement between digital subtraction angiography (DSA) and time-resolved magnetic resonance (MR) angiography with sensitivity encoding (SENSE) in combination with keyhole acquisition and contrast material-enhanced robust-timing angiography (CENTRA) k-space sampling techniques for the characterization of intracranial arteriovenous malformations (AVMs). MATERIALS AND METHODS: The institutional review board approved the study; informed consent was obtained from all patients (or their parents). Twenty-eight patients (15 male, 13 female; mean age, 38.6 years; age range, 16-61 years) with 29 previously diagnosed, untreated intracranial AVMs who were referred for stereotactic gamma knife radiosurgery were evaluated. Preinterventional imaging included intraarterial DSA and time-resolved MR angiography. The time-resolved MR angiography sequence included SENSE with a 1.5-T imager and was optimized by applying keyhole acquisition and CENTRA techniques. Time-resolved MR angiograms were reviewed by two independent raters and compared with DSA images with regard to arterial feeders, nidus size, and venous drainage. kappa Statistics were applied to determine interobserver and intermodality agreement. RESULTS: MR angiography enabled time-resolved (1.7 seconds per volume) visualization of cerebral vessels from axis to vertex at high spatial resolution (true voxel size, 1 x 1 x 2 mm). All 25 nidi detected at intraarterial DSA were visualized at time-resolved MR angiography. Intermodality agreement was excellent for arterial feeders (kappa = 0.91; 95% confidence interval [CI]: 0.786, 1.000) and venous drainage (kappa = 0.94; 95% CI: 0.814, 1.000) and was good for nidus size (kappa = 0.76; 95% CI: 0.562, 0.950). CONCLUSION: The agreement (good to excellent) between time-resolved MR angiographic and DSA findings suggests that time-resolved MR angiography is a reliable tool for the characterization of intracranial AVMs with respect to arterial feeders, nidus size, and venous drainage.

Gamma Knife surgery for arteriovenous malformations in the brain: integration of time-resolved contrast-enhanced magnetic resonance angiography into dosimetry planning. Technical note.

OBJECT: The aim of this study was to develop an algorithm for the integration of time-resolved contrast-enhanced magnetic resonance (MR) angiography into dosimetry planning for Gamma Knife surgery (GKS) of arteriovenous malformations (AVMs) in the brain. METHODS: Twelve patients harboring brain AVMs referred for GKS underwent intraarterial digital subtraction (DS) angiography and time-resolved MR angiography while wearing an externally applied cranial stereotactic frame. Time-resolved MR angiography was performed on a 1.5-tesla MR unit (Achieva, Philips Medical Systems) using contrast-enhanced 3D fast field echo sequencing with stochastic central k-space ordering. Postprocessing with interactive data language (Research Systems, Inc.) produced hybrid data sets containing dynamic angiographic information and the MR markers necessary for stereotactic transformation. Image files were sent to the Leksell GammaPlan system (Elekta) for dosimetry planning. RESULTS: Stereotactic transformation of the hybrid data sets containing the time-resolved MR angiography information with automatic detection of the MR markers was possible in all 12 cases. The stereotactic coordinates of vascular structures predefined from time-resolved MR angiography matched with DS angiography data in all cases. In 10 patients dosimetry planning could be performed based on time-resolved MR angiography data. In two patients, time-resolved MR angiography data alone were considered insufficient. The target volumes showed a notable shift of centers between modalities. CONCLUSIONS: Integration of time-resolved MR angiography data into the Leksell GammaPlan system for patients with brain AVMs is feasible. The proposed algorithm seems concise and sufficiently robust for clinical application. The quality of the time-resolved MR angiography sequencing needs further improvement.