Early Idiopathic Normal Pressure Hydrocephalus Patients With Neuropsychological Impairment Are Associated With Increased Fractional Anisotropy in the Anterior Thalamic Nucleus

Connectivity alteration in thalamic nuclei and default mode network-related area in memory processes in mesial temporal lobe epilepsy using magnetoencephalography

This work aimed to investigate the involvement of the thalamic nuclei in mesial temporal lobe epilepsy (MTLE) and identify the influence of interictal epileptic discharges on the neural basis of memory processing by evaluating the functional connectivity (FC) between the thalamic nuclei and default mode network-related area (DMNRA) using magnetoencephalography. Preoperative datasets of nine patients with MTLE with seizure-free status after surgery and those of nine healthy controls were analyzed. The FC between the thalamic nuclei (anterior nucleus [ANT], mediodorsal nucleus [MD], intralaminar nuclei [IL]), hippocampus, and DMNRA was examined for each of the resting, pre-spike, spike, and post-spike periods in the delta to ripple bands using magnetoencephalography. The FC between the ANT, MD, hippocampus, and medial prefrontal cortex increased in the gamma to ripple bands, whereas the FC between the ANT, IL, and DMNRA decreased in the delta to beta bands, compared with that of the healthy controls at rest. Compared with the rest period, the pre-spike period had significantly decreased FC between the ANT, MD, and DMNRA in the ripple band. Different FC changes between the thalamic nuclei, hippocampus, and DMNRA of specific connections in a particular band may reflect impairment or compensation in the memory processes.

Cognitive Impairment in Idiopathic Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a significant cause of the severe cognitive decline in the elderly population. There is no cure for iNPH, but cognitive symptoms can be partially alleviated through cerebrospinal fluid (CSF) diversion. In the early stages of iNPH, cognitive deficits occur primarily in the executive functions and working memory supported by frontostriatal circuits. As the disease progresses, cognition declines continuously and globally, leading to poor quality of life and daily functioning. In this review, we present recent advances in understanding the neurobiological mechanisms of cognitive impairment in iNPH, focusing on (1) abnormal CSF dynamics, (2) dysfunction of frontostriatal and entorhinal-hippocampal circuits and the default mode network, (3) abnormal neuromodulation, and (4) the presence of amyloid-β and tau pathologies.

The role of diffusion tensor imaging in idiopathic normal pressure hydrocephalus: A literature review

Idiopathic normal pressure hydrocephalus (iNPH) is a syndrome that comprises a triad of gait disturbance, dementia and urinary incontinence, associated with ventriculomegaly in the absence of elevated intraventricular cerebrospinal fluid (CSF) pressure. It is important to identify patients with iNPH because some of its clinical features may be reversed by the insertion of a CSF shunt. The diagnosis is based on clinical history, physical examination and brain imaging, especially magnetic resonance imaging (MRI). Recently, some papers have investigated the role of diffusion tensor imaging (DTI) in evaluating white matter alterations in patients with iNPH. DTI analysis in specific anatomical regions seems to be a promising MR biomarker of iNPH and could also be used in the differential diagnosis from other dementias. However, there is a substantial lack of structured reviews on this topic. Thus, we performed a literature search and analyzed the most recent and pivotal articles that investigated the role of DTI in iNPH in order to provide an up-to-date overview of the application of DTI in this setting. We reviewed studies published between January 2000 and June 2020. Thirty-eight studies and four reviews were included. Despite heterogeneity in analysis approaches, the majority of studies reported significant correlations between DTI and clinical symptoms in iNPH patients, as well as different DTI patterns in patients with iNPH compared to those with Alzheimer or Parkinson diseases. It remains to be determined whether DTI could predict the success after CSF shunting.

Prediction of Memory Impairment in Epilepsy Surgery by White Matter Diffusion

OBJECTIVE

To analyze the relationship between cognitive performance and white matter integrity in patients with temporal lobe epilepsy (TLE) to establish radiologic criteria to help with patient selection for surgery.

METHODS

The study included 19 adults with temporal lobe epilepsy. A tractography analysis of fractional anisotropy and mean diffusivity (MD) of the following fascicles was performed: arcuate fascicle, cingulum, fornix, inferior fronto-occipital fascicle, inferior longitudinal fascicle, parahippocampal fibers of the cingulum, and uncinate fascicle. The Wechsler Memory Scale-Third Edition neuropsychological test was performed to evaluate short- and long-term verbal (Logical Memory I and II subtests) and nonverbal (Visual Reproduction I and II subtests) memory. Relationships between memory scores and diffusion were calculated.

RESULTS

Lower Logical Memory I subtest scores were correlated with lower MD of the right inferior fronto-occipital fascicle, while lower Logical Memory II subtest scores were related to higher values of fractional anisotropy in bilateral cingulum, right uncinate, and right parahippocampal fibers of the cingulum and lower MD in left cingulum fascicle. Finally, lower values in Visual Reproduction I subtest scores were associated with lower values in MD in right cingulum and inferior fronto-occipital fascicles.

CONCLUSIONS

Structural changes of some white matter tracts were associated with deterioration of both short- and long-term memory. These alterations were more associated with verbal memory than with nonverbal memory. These changes mainly consist of an increase in fractional anisotropy and a decrease in MD, which could be interpreted as reorganization phenomena. Diffusion tensor imaging could be a useful tool for cognitive assessment in surgical candidates with temporal lobe epilepsy who are not suitable for neuropsychological testing or in whom their results do not lead to definitive conclusions.