Magnetic resonance elastography with guided pressure waves.

Magnetic resonance elastography aims to non-invasively and remotely characterize the mechanical properties of living tissues. To quantitatively and regionally map the shear viscoelastic moduli in vivo, the technique must achieve proper mechanical excitation throughout the targeted tissues. Although it is straightforward, ante manibus, in close organs such as the liver or the breast, which practitioners clinically palpate already, it is somewhat fortunately highly challenging to trick the natural protective barriers of remote organs such as the brain. So far, mechanical waves have been induced in the latter by shaking the surrounding cranial bones. Here, the skull was circumvented by guiding pressure waves inside the subject's buccal cavity so mechanical waves could propagate from within through the brainstem up to the brain. Repeatable, reproducible and robust displacement fields were recorded in phantoms and in vivo by magnetic resonance elastography with guided pressure waves such that quantitative mechanical outcomes were extracted in the human brain.

Functional and structural microanatomy of the fetal sciatic nerve.

INTRODUCTION: The ultrastructure of a nerve has implications for surgical nerve repair. The aim of our study was to characterize the fascicular versus fibrillar anatomy and the autonomic versus somatic nature of the fetal sciatic nerve (SN). METHODS: Immunohistochemistry for vesicular acetylcholine transporter, tyrosine hydroxylase, and peripheral myelin protein 22 was performed to identify cholinergic, adrenergic, and somatic axons, respectively, in the human fetal SN. Two-dimensional (2D) analysis and 3D reconstructions were performed. RESULTS: The fetal SN is composed of one-third stromal tissue and two-thirds neural tissue. Autonomic fibers are predominant over somatic fibers within the neural tissue. The distribution of somatic fibers is initially random, but then become topographically organized after intra- and interfascicular rearrangements have occurred within the nerve. CONCLUSIONS: The fetal model presents limitations but enables illustration of the nature of the nerve fibers and the 3D fascicular anatomy of the SN. Muscle Nerve 56: 787-796, 2017.

Early life adversity is associated with a smaller hippocampus in male but not female depressed in-patients: a case-control study.

BACKGROUND: Three studies assessed the association of early life adversity (ELA) and hippocampal volumes in depressed patients, of which one was negative and the two others did not control for several potential confounding variables. Since the association of ELA and hippocampal volumes differ in male and female healthy volunteers, we investigated the association of ELA and hippocampal volumes in depressed patients, while focusing specifically on sex and controlling for several relevant socio-demographic and clinical variables. METHODS: Sixty-three depressed in-patients treated in a psychiatric setting, with a current Major Depressive Episode (MDE) and a Major Depressive Disorder (MDD) were included and assessed for ELA. Hippocampal volumes were measured with brain magnetic resonance imaging (MRI) and automatic segmentation. They were compared between patients with (n = 28) or without (n = 35) ELA. After bivariate analyses, multivariate regression analyses tested the interaction of sex and ELA on hippocampal volume and were adjusted for several potential confounding variables. The subgroups of men (n = 26) and women (n = 37) were assessed separately. RESULTS: Patients with ELA had a smaller hippocampus than those without ELA (4.65 (±1.11) cm3 versus 5.25 (±1.01) cm3), bivariate: p = 0.03, multivariate: HR = 0.40, 95%CI [0.23;0.71], p = 0.002), independently from other factors. This association was found in men (4.43 (±1.22) versus 5.67 (±0.77) cm3), bivariate: p = 0.006, multivariate HR = 0.23, 95%CI [0.06;0.82], p = 0.03) but not in women. CONCLUSION: ELA is associated with a smaller hippocampus in male but not female depressed in-patients. The reasons for this association should be investigated in further studies.

Extracranial vertebral artery dissection in children: natural history and management.

INTRODUCTION: The objective of this study is to describe clinical and imaging presentation and outcome in extracranial vertebral artery dissection. METHODS: Single-centre retrospective study over a 14-year period included 20 consecutive patients under the age of 16 years with extracranial vertebral artery dissection. The diagnosis was based on vascular imaging performed at the acute phase and clinical symptoms. RESULTS: A male predominance was observed (sex ratio 9/1). The first symptoms consisted of headache (45%), neck pain (15%), nausea (30%) and vertigo (30%). Clinical signs leading to admission to hospital were hemiparesis (60%), visual disorders with oculomotor disorders (20%) or visual field defects (20%) and cerebellar syndrome (35%). Eight patients (40%) reported repeated transient episodes of neurological deficits, prior to the diagnosis. The segment most commonly affected was V2-V3 (50%), followed by V3 (15%) and V2 (15%), V3-V4 (10%) and proximal V4 (10%). All patients but one presented cerebral infarction. Eleven patients received first-line treatment with low molecular weight heparin (LMWH), and nine patients received aspirin. Three patients experienced a recurrence of symptoms, one under vitamin K antagonist (VKA) and 2 under aspirin. All three were switched to LMWH with success. Fifty-eight percent of the dissected arteries were occluded at long-term follow-up, although 73% of them were patent at the acute phase. CONCLUSION: Initial imaging must include posterior fossa vessels and the craniocervical region with V2-V3 segments. Conventional angiography may be indicated in the absence of a definitive diagnosis on noninvasive imaging. Healing of the dissected vertebral artery predominantly resulted in occlusion, which does not constitute a pejorative factor but indicates good quality healing.

Statistical analysis of multi-b factor diffusion weighted images can help distinguish between vasogenic and tumor-infiltrated edema.

PURPOSE: The diffusion model can be transformed into a multicompartment model by means of multi-b factor diffusion-weighted sequences. We adapted a method of statistical analysis of these images and evaluated its performance to distinguish tumor-infiltrated edema from vasogenic edema. MATERIALS AND METHODS: Forty-nine patients with infiltrating tumors (38 patients: low to high-grade gliomas) or vasogenic edema (11 patients: metastases, abscess, extra-axial lesions) were studied by multi-b factor diffusion-weighted imaging. Comparison of histological results and morphological and perfusion MRI defined 69 characteristic volumes of interest in the peritumoral edema of 69 distinct infiltrating lesions (40) or lesions inducing vasogenic edema (29). RESULTS: The factorial analysis had a sensitivity of 92.9% and a specificity of 90.6% between tumor-infiltrated and vasogenic edema. Simplified interpretation confined to values of the high and mean diffusivity compartments had a sensitivity of 87.5% and a specificity of 89.2% between strictly tumor-infiltrated edema and vasogenic edema with the advantage of simplified interpretation based on two-color parametric mapping. CONCLUSION: Discrimination between tumor-infiltrated edema and vasogenic edema can be achieved by means of a 90-s multi-b factor diffusion-weighted sequence and factorial analysis. Simplified visual and quantitative interpretation of the results should also allow integration of multi-b factor analysis into routine neuroradiology practice.

Cortical border-zone infarcts: clinical features, causes and outcome.

OBJECTIVE: To report the clinical features, causes and outcome of cerebral cortical border-zone infarcts BZI (C-BZI). METHODS: The authors prospectively included patients with MRI-confirmed C-BZI among individuals consecutively admitted in Stroke Unit. RESULTS: Forty-five patients presented C-BZI out of 589 with MRI-confirmed cerebral infarcts (7.6%). Particular clinical characteristics existed in C-BZI in comparison with other cerebral infarctions as a whole, including: (1) frequent transient symptoms at onset (27% vs 9%; p<0.001) and low severity score (NIHSS=3.1±3.0 vs 5.2±6.1; p=0.02); (2) early seizures in first 2 weeks (7/45 (15.6%) vs 12/544 (2.2%); p<0.001), even when focusing only on other infarctions involving the cerebral cortex (15.6% vs 4.3%; p<0.01); (3) heterogeneous clinical presentation but specific transcortical aphasia allowing a clinical suspicion of BZI before MRI; and (4) frequently associated internal carotid disease (69%), with subsequent early surgery in 75% of the cases. Following adapted care in stroke unit, C-BZIs' prognosis appeared good (Rankin score ≤2 at D90) for 82% of the patients. CONCLUSION: Some clinical features are overrepresented in such infarctions, including initial transient symptoms preceding the onset of a completed deficit, transcortical aphasia and early seizures. Despite lower initial severity, C-BZIs justify early management in stroke unit, often followed by carotid surgery, leading to an overall good prognosis.

Diffusion tensor imaging tractography parameters of limbic system bundles in temporal lobe epilepsy patients.

PURPOSE: To investigate changes in diffusion tensor imaging (DTI) measures in limbic system white matter of patients with temporal lobe epilepsy (TLE) using diffusion tensor tractography. MATERIALS AND METHODS: DTI metrics including fractional anisotropy (FA), λ1, λ2, λ3, and trace (Tr) coefficients were obtained from tractography for bilateral fornix, superior and inferior cingulum fibers in 18 patients and 10 healthy controls. Hippocampal signal-to-noise ratio (SNR) quantitative analysis was performed in order to confirm the magnetic resonance imaging (MRI) hippocampal lesion presence or absence in TLE patients. RESULTS: Nine patients presented unilateral hippocampal sclerosis (TLE+HS) and nine patients had no signal abnormalities on conventional MRI (TLE-HS). On the ipsilateral seizure side, all three investigated tracts showed significant DTI indices abnormalities in both patient groups when compared with controls, most marked on the inferior cingulum. Contralateral to the seizure side, the three tracts presented significant DTI parameters in only the TLE+HS group when compared with controls. CONCLUSION: The DTI abnormalities found in the TLE-HS group may suggest that in the inferior cingulum the structural integrity is more affected than in the fornix or superior cingulum white matter bundles. The eigenvalues taken separately add complementary information to the FA and Tr metrics and may be useful indices in better understanding the architectural reorganization of limbic system tracts in TLE patients without HS.

Diffusion tensor imaging and white matter lesions at the subacute stage in mild traumatic brain injury with persistent neurobehavioral impairment.

Mild traumatic brain injury (mTBI) can induce long-term behavioral and cognitive disorders. Although the exact origin of these mTBI-related disorders is not known, they may be the consequence of diffuse axonal injury (DAI). Here, we investigated whether MRI at the subacute stage can detect lesions that are associated with poor functional outcome in mTBI by using anatomical images (T(1) ) and diffusion tensor imaging (DTI). Twenty-three patients with mTBI were investigated and compared with 23 healthy volunteers. All patients underwent an MRI investigation and clinical tests between 7 and 28 days (D15) and between 3 and 4 months (M3) after injury. Patients were divided in two groups of poor outcome (PO) and good outcome (GO), based on their complaints at M3. Groupwise differences in gray matter partial volume between PO patients, GO patients and controls were analyzed using Voxel-Based Morphometry (VBM) from T(1) data at D15. Differences in microstructural architecture were investigated using Tract-Based Spatial Statistics (TBSS) and the diffusion images obtained from DTI data at D15. Permutation-based non-parametric testing was used to assess cluster significance at p < 0.05, corrected for multiple comparisons. Twelve GO patients and 11 PO patients were identified on the basis of their complaints. In PO patients, gray matter partial volume was significantly lower in several cortical and subcortical regions compared with controls, but did not differ from that of GO patients. No difference in diffusion variables was found between GO and controls. PO patients showed significantly higher mean diffusivity values than both controls and GO patients in the corpus callosum, the right anterior thalamic radiations and the superior longitudinal fasciculus, the inferior longitudinal fasciculus and the fronto-occipital fasciculus bilaterally. In conclusion, PO patients differed from GO patients by the presence of diffusion changes in long association white matter fiber tracts but not by gray matter partial volume. These results suggest that DTI at the subacute stage may be a predictive marker of poor outcome in mTBI.

Clinical, functional and structural determinants of central pain in syringomyelia.

The present study aimed to investigate the relationship between neuropathic symptoms (i.e. pain and paraesthesia/dysaesthesia) and structural damage and functional alterations of spinal sensory tracts in patients with syringomyelia. Three-dimensional fibre tracking of the cervical spinal cord (at level C3-C4), electrophysiological assessments of nociceptive (laser-evoked potentials) and non-nociceptive (somatosensory-evoked potentials) pathways and quantitative sensory testing were carried out in 37 patients with syringomyelia, 27 with neuropathic pain and 21 controls. Four regions of the body (both hands and shoulders) were systematically examined with laser-evoked potentials and quantitative sensory testing, and somatosensory-evoked potentials were induced from both hands. The diffusion tensor imaging variables investigated included the mean fractional anisotropy, the mean apparent diffusion coefficient and the number of reconstructed nerve fibres of the tracts located within three volumes of interest (full spinal section, anterior cord and posterior cord). Consistent with the results of previous studies, patients with or without neuropathic pain were indistinguishable on the basis of quantitative sensory testing, laser-evoked and somatosensory-evoked potentials and three-dimensional fibre tracking analyses. However, in patients with neuropathic pain, higher average daily pain intensity was correlated with greater structural damage to the spinal cord, as assessed by fractional anisotropy (Spearman's ρ = -0.64, P = 0.020) and the number of reconstructed nerve fibres (r = -0.75; P = 0.020) of the full spinal cord. The number of reconstructed nerve fibres was negatively correlated with two neuropathic dimensions, i.e. 'deep spontaneous pain' (r = -0.59, P = 0.040) and 'paraesthesia/dysaesthesia' (i.e. pins and needles/tingling) (r = -0.67, P = 0.020), suggesting that various pain descriptors have distinct underlying mechanisms. Patients with both spontaneous and evoked pain clearly differed from patients with spontaneous pain only. Patients with spontaneous pain only had more severe spinal cord damage, and the correlation between average daily pain intensity and fractional anisotropy of the full spinal cord was particularly strong in this subgroup of patients (Spearman's ρ = -0.93, P = 0.008). By contrast, patients with both spontaneous and evoked pain had not only less structural spinal cord damage, but also better preserved spinothalamic and lemniscal tracts on quantitative sensory testing and electrophysiological testing. These data showed, for the first time, a direct relationship between central neuropathic pain and objective markers of spinal cord damage, and confirmed the clinical relevance of 3D fibre tracking for the sensory assessment of patients with a spinal cord lesion.

PWI-MRI and contrast extravasation in brain AVM help to estimate angiogenic activity.

INTRODUCTION: The aim of this study is to investigate perfusion characteristics of brain arteriovenous malformation (AVM) by means of MRI perfusion-weighted imaging (PWI). METHODS: Forty-three patients with brain AVM were prospectively included and investigated by PWI-MRI. Diagnosis of type of disease was made by angiogram. According to angiographic features, the study group was classified in three groups: two groups of patients with classical AVM (group 1 with few or no angiogenic feature (13 patients) and group 2 with many angiogenic features (18 patients)) and one group (group 3) which included patients with cerebral proliferative angiopathy (CPA; 12 patients). Twenty-one patients had never been treated endovascularly for their AVM and 22 patients received partial treatment by endovascular embolisation. Through PWI, corrected cerebral blood volume (CBVc), mean transit time (MTT), and percentage of microvascular leakage (MVL) as an indirect measure of permeability were assessed. RESULTS: The three patient groups did not differ significantly in baseline and clinical parameters. CBVc, MTT, and MVL differed significantly between the three groups (p = 0.003, p = 0.04, p = 0.01, respectively), with the lowest mean values found in group 1 and the highest in group 3. Mean MVL was 11.4 in group 1, 18.6 in group 2, and 21.9 in group 3. CONCLUSION: MRI can demonstrate differences in PWI parameters among patients with classical AVM and CPA, which are related to angiographic features of these AVMs. Through PWI, the level of angiogenic activity in AVMs may be monitored.

Prospective Follow-up of Intramedullary Slitlike Cavities: A Consecutive Series of 48 Patients.

Object: Predicting whether intramedullary slitlike cavity (SC) will worsen over time or remain stable is an outstanding clinical challenge. The aim of this study was to identify early features of SC (clinical and magnetic resonance imaging [MRI] findings). Methods: We prospectively included all patients referred to our institution following the discovery of a SC and divided them in two groups: typical SC (defined as a cavity spanning fewer than three vertebrae, not enlarging the spinal cord, and located at the midline between the anterior third and posterior two-thirds of the spinal cord) or atypical SC (all others). Clinical evolution and changes in MRI features were evaluated during follow-up. In some patients, diffusion tensor imaging was performed and cervical cord cross-sectional area was analyzed. Results: A total of 48 consecutive patients were included in the study. The mean follow-up was 58 months. Of the seven patients presenting with deficits at first consultation, two worsened and five remained stable. Of the 41 patients without deficits, seven worsened and 34 remained stable. None of the patients developed severe motor deficits or experienced enlargement of the cavity; 7% of patients who presented with typical SC worsened compared with 35% with atypical SC. The negative predictive value was 0.93 (P = 0.02). Conclusion: Most patients remained stable and a subset of patients developed minor motor deficits. For clinical management, we propose surveillance of patients with a typical SC and close follow-up of those with an atypical SC and/or presenting with deficits.

Smaller hippocampal volumes predict lower antidepressant response/remission rates in depressed patients: A meta-analysis.

OBJECTIVES: Whether hippocampal volume predicts response and/or remission after antidepressant treatment of major depressive episodes (MDE) in major depressive disorder (MDD) remains unclear. We meta-analysed prospective studies comparing baseline hippocampal volume in patients with or without response/remission after antidepressant treatment. METHODS: Pubmed, Embase and Google Scholar were searched for studies of patients with current MDE in MDD, with hippocampal volume assessments at baseline, initiation of antidepressant drug treatment, and prospective assessment of response/remission after treatment. RESULTS: Six studies (374 patients), of which two were positive and four negative, were meta-analysed. Compared to responders/remitters, patients who failed to achieve response/remission had smaller total hippocampus volumes at baseline (mean volume difference = 260 mm3, 95% CI [93; 427], P = 0.002). These results remained significant in patients under 60 years of age (P = 0.02), in those over 60 years old (P = 0.04), and for right (P = 0.006) and left (P = 0.02) hippocampi. The probability of non-response/non-remission was 68.6% for patients with a total hippocampal volume at least 10% lower than the average, and 47.1% for patients with a total hippocampal volume 10% higher than the average. CONCLUSIONS: In depressed patients treated with antidepressant drugs, smaller hippocampal volumes predict lower response/remission rates.

Mechanisms of central neuropathic pain: a combined psychophysical and fMRI study in syringomyelia.

The pathophysiology of central pain syndromes is still poorly understood and their treatment remains a major challenge. It has long been suggested that lesions of the spinothalamic pathways are necessary for developing these pain syndromes. The recently proposed thermosensory disinhibition theory suggests that reduction of the inhibition of thermal sensory afferents that affect nociceptive systems may play a major pathophysiological role. Syringomyelia, which is frequently associated with central neuropathic pain, is characterized by a selective or preferential lesion of the spinothalamic tract resulting in thermosensory deficits of various extents and magnitudes. Thus, syringomyelia represents a unique 'pathological model' particularly suited to investigating the relationship between spinothalamic tract dysfunction, thermosensory deficits and pain. Here, we systematically compared the sensory loss (thermal and mechanical), using quantitative sensory testing, between 46 consecutive syringomyelia patients with or without neuropathic pain. We then further investigated the mechanisms of evoked pains in these patients, using functional MRI (fMRI) in a subgroup of patients with cold or brush-evoked allodynia, compared with patients without pain and healthy volunteers. We found no significant difference in the magnitude or extent of sensory deficits between patients with or without neuropathic pain, suggesting that lesions of the spinothalamic pathways are not sufficient for developing central pain. However, a different pattern of sensory deficits was observed between patients with spontaneous pain only (n = 11) and patients with both spontaneous pain and allodynia (n = 20), suggesting that the mechanisms of central pain are not univocal. In patients with spontaneous pain only, the thermal sensory loss was significantly more asymmetrical and there was a direct relationship between the extent of thermosensory deficits (i.e. deafferentation) and the intensity of burning pain. In contrast, patients with allodynia had reduced thermal deficits, in terms of both magnitude and extent. In addition, the sensory deficits were different between patients with cold or tactile allodynia, suggesting distinct pathophysiological mechanisms related to the sub-modalities of allodynia. Our fMRI study further confirmed this, showing that different sub-types of allodynia were associated with distinct patterns of brain activity, which do not necessarily correspond to the 'pain matrix' involved in acute physiological pain. The prefrontal cortex was the only area consistently activated by pathological evoked pains, suggesting that alteration of high-level pain modulatory mechanisms might play a major role in allodynia due to central lesion.

Diffusion tensor magnetic resonance imaging and fiber tracking in spinal cord lesions: current and future indications.

Diffusion-weighted imaging and fractional anisotropy may be more sensitive than other conventional magnetic resonance imaging techniques to detect, characterize, and map the extent of spinal cord lesions. Fiber tracking offers the possibility of visualizing the integrity of white matter tracts surrounding some lesions, and this information may help in formulating a differential diagnosis and in planning biopsies or resection. Fractional anisotropy measurements may also play a role in predicting the outcome of patients who have spinal cord lesions. In this article, we address several conditions in which diffusion-weighted imaging and fiber tracking is known to be useful and speculate on others in which we believe these techniques will be useful in the near future.

[Techniques and progress in the imaging of the ear]. / Les techniques et avancées dans l'imagerie de l'oreille.

Ear and temporal bone imaging is essential for the diagnostic and preoperative management of middle ear lesions. The scanner is the exam of choice to analyze the walls and the contents of the middle ear. MRI is used to characterize the opacities of the middle ear and to evaluate possible neurological complications. Modern imaging techniques allow intraoperative guidance in otological surgery. Hearing implants are not always a contraindication to MRI but require precautions according to the type of implant.

Pilomotor seizures associated with sequential changes in magnetic resonance imaging.

Piloerection is rarely described in seizures. This symptom has been most frequently observed in patients with temporal lobe epilepsy and is rarely the principal clinical feature of seizures. No specific etiology of epilepsy associated with pilomotor seizures has been reported. We present the first case of a patient who experienced sudden and transitory epilepsy with pilomotor seizures occurring several times a day for months, and associated with sequential changes of the left hippocampus demonstrated by magnetic resonance imaging. [Published with video sequences].

Hippocampal volume predicts antidepressant efficacy in depressed patients without incomplete hippocampal inversion.

BACKGROUND: Incomplete hippocampal inversion (IHI), also called malrotation, is a frequent atypical anatomical pattern of the hippocampus. Because of the crucial implication of the hippocampus in Major Depressive Disorder (MDD) and the neurodevelopmental hypothesis of MDD, we aimed to assess the prevalence of IHI in patients with MDD, the link of IHI with hippocampal volume (HV) and the impact of IHI on the predictive value of HV for response and remission after antidepressant treatment. METHODS: IHI (right and left, partial and total and IHI scores) and HV were assessed in 60 patients with a current Major Depressive Episode (MDE) in a context of MDD and 60 matched controls. Patients were prospectively assessed at baseline and after one, three and six months of antidepressant treatment for response and remission. RESULTS: The prevalence of IHI did not significantly differ between MDD patients (right = 23.3%; left = 38.3%) and controls (right = 16.7%; left = 33.3%). IHI was not significantly associated with MDD clinical characteristics. IHI alone did not predict response and remission after antidepressant treatment. However, an interaction between left HV and left IHI predicted six-month response (p = 0.04), HDRS score decrease (p = 0.02) and both three-month (p = 0.04) and six-month (p = 0.03) remission. A case-control design in 30 matched patients with or without left IHI confirmed that interaction. In patients without left IHI, left HV at baseline were smaller in six-month non-remitters as compared to remitters (2.2(± 0.43) cm3 vs 2.97(± 0.5) cm3 p = 0.02), and in six-month non-responders as compared to responders (2.18(± 0.42) cm3 vs 2.86(± 0.54) cm3, p = 0.03). In patients with left IHI, no association was found between left HV at baseline and antidepressant response and remission. CONCLUSION: IHI is not more frequent in MDD patients than in controls, is not associated with HV, but is a confounder that decreases the predictive value of hippocampal volume to predict response or remission after antidepressant treatment. IHI should be systematically assessed in future research studies assessing hippocampal volume in MDD.