The glymphatic system and subarachnoid hemorrhage: disruption and recovery

Pathogenesis and management of low-pressure hydrocephalus: A narrative review

Patients diagnosed with low-pressure hydrocephalus typically present with enlarged ventricles and unusually low intracranial pressure, often measuring below 5 cmH2O or even below atmospheric pressure. This atypical presentation often leads to low recognition and diagnostic rates. The development of low-pressure hydrocephalus is believed to be associated with a decrease in the viscoelasticity of brain tissue or separation between the ventricular and subarachnoid spaces. Risk factors for low-pressure hydrocephalus include subarachnoid hemorrhage, aqueduct stenosis, prior cranial radiotherapy， ventricular shunting, and cerebrospinal fluid leaks. For potential low-pressure hydrocephalus, diagnostic criteria include neurological symptoms related to hydrocephalus, an Evans index >0.3 on imaging, ICP ≤ 5 cm H2O, symptom improvement with negative pressure drainage, and exclusion of ventriculomegaly caused by neurodegenerative diseases. The pathogenesis and pathophysiological features of low-pressure hydrocephalus differ significantly from other types of hydrocephalus, making it challenging to restore normal ventricular morphology through conventional drainage methods. The primary treatment options for low-pressure hydrocephalus involve negative pressure drainage and third ventriculostomy. With appropriate treatment, most patients can regain their previous neurological function. However, in most cases, permanent shunt surgery is still necessary. Low-pressure hydrocephalus is a rare condition with a high rate of underdiagnosis and mortality. Early identification and appropriate intervention are crucial in reducing complications and improving prognosis.

Research progress of neuroinflammation-related cells in traumatic brain injury: A review

Neuroinflammation after traumatic brain injury (TBI) is related to chronic neurodegenerative diseases and is one of the causes of acute secondary injury after TBI. Therefore, it is particularly important to clarify the role of cellular mechanisms in the neuroinflammatory response after TBI. The objective of this article is to understand the involvement of cells during the TBI inflammatory response (for instance, astrocytes, microglia, and oligodendrocytes) and shed light on the recent progress in the stimulation and interaction of granulocytes and lymphocytes, to provide a novel approach for clinical research. We searched articles in PubMed published between 1950 and 2023, using the following keywords: TBI, neuroinflammation, inflammatory cells, neuroprotection, clinical. Articles for inclusion in this paper were finalized based on their novelty, representativeness, and relevance to the main arguments of this review. We found that the neuroinflammatory response after TBI includes the activation of glial cells, the release of inflammatory mediators in the brain, and the recruitment of peripheral immune cells. These inflammatory responses not only induce secondary brain damage, but also have a role in repairing the nervous system to some extent. However, not all of the mechanisms of cell-to-cell interactions have been well studied. After TBI, clinical treatment cannot simply suppress the inflammatory response, and the inflammatory phenotype of patients' needs to be defined according to their specific conditions after injury. Clinical trials of personalized inflammation regulation therapy for specific patients should be carried out in order to improve the prognosis of patients.

Additive prognostic impact of the cerebrospinal fluid arginine/ornithine ratio to established clinical scores in aneurysmal subarachnoid hemorrhage

Cerebrospinal fluid (CSF) metabolites are increasingly recognized as prognostic factors in aneurysmal subarachnoid hemorrhage (SAH). The CSF arginine/ornithine ratio (Arg/Orn) was shown to predict cerebral vasospasms and clinical outcome in SAH. The additive prognostic value of Arg/Orn over established prognostic scores has not been investigated. CSF Arg/Orn and the established prognostic scores SAH, FRESH, SAH-PDS, HAIR, Rosen-McDonald, Hunt and Hess, WFNS and modified Fisher scale were determined in a prospective cohort of patients with aneurysmal SAH. Logistic regression models to predict a favorable outcome, defined as a modified Rankin Scale score of 0-3 at 3  months follow-up, were constructed for each score, both with and without the addition of Arg/Orn. The impact of Arg/Orn was assessed comparing logistic regression models containing the respective score with and without Arg/Orn with the likelihood ratio chi-squared test. CSF Arg/Orn and clinical scores were determined in 38 SAH patients. Arg/Orn was an independent predictor of clinical outcome when added to established prognostic scores (p < 0.05) with the exception of HAIR (p = 0.078). All models were significantly improved if Arg/Orn was added as a covariable (p < 0.05). The results of this study confirm Arg/Orn as an independent prognostic factor and its addition improves established prognostic models in SAH.

CSF Dynamics: Implications for Hydrocephalus and Glymphatic Clearance

Beyond its neuroprotective role, CSF functions to rid the brain of toxic waste products through glymphatic clearance. Disturbances in the circulation of CSF and glymphatic exchange are common among those experiencing HCP syndrome, which often results from SAH. Normally, the secretion of CSF follows a two-step process, including filtration of plasma followed by the introduction of ions, bicarbonate, and water. Arachnoid granulations are the main site of CSF absorption, although there are other influencing factors that affect this process. The pathway through which CSF is through to flow is from its site of secretion, at the choroid plexus, to its site of absorption. However, the CSF flow dynamics are influenced by the cardiovascular system and interactions between CSF and CNS anatomy. One, two, and three-dimensional models are currently methods researchers use to predict and describe CSF flow, both under normal and pathological conditions. They are, however, not without their limitations. "Rest-of-body" models, which consider whole-body compartments, may be more effective for understanding the disruption to CSF flow due to hemorrhages and hydrocephalus. Specifically, SAH is thought to prevent CSF flow into the basal cistern and paravascular spaces. It is also more subject to backflow, caused by the presence of coagulation cascade products. In regard to the fluid dynamics of CSF, scar tissue, red blood cells, and protein content resulting from SAH may contribute to increased viscosity, decreased vessel diameter, and increased vessel resistance. Outside of its direct influence on CSF flow, SAH may result in one or both forms of hydrocephalus, including noncommunicating (obstructive) and communicating (nonobstructive) HCP. Imaging modalities such as PC-MRI, Time-SLIP, and CFD model, a mathematical model relying on PC-MRI data, are commonly used to better understand CSF flow. While PC-MRI utilizes phase shift data to ultimately determine CSF speed and flow, Time-SLIP compares signals generated by CSF to background signals to characterizes complex fluid dynamics. Currently, there are gaps in sufficient CSF flow models and imaging modalities. A prospective area of study includes generation of models that consider "rest-of-body" compartments and elements like arterial pulse waves, respiratory waves, posture, and jugular venous posture. Going forward, imaging modalities should work to focus more on patients in nature in order to appropriately assess how CSF flow is disrupted in SAH and HCP.

Exploration of cerebral vasospasm from the perspective of microparticles

Cerebral vasospasm is a frequently encountered clinical problem, especially in patients with traumatic brain injury and subarachnoid hemorrhage. Continued cerebral vasospasm can cause cerebral ischemia, even infarction and delayed ischemic neurologic deficits. It significantly affects the course of the disease and the outcome of the patient. However, the underlying mechanism of cerebral vasospasm is still unclear. Recently, increasing studies focus on the pathogenic mechanism of microparticles. It has been found that microparticles have a non-negligible role in promoting vasospasm. This research aims to summarize the dynamics of microparticles in vivo and identify a causal role of microparticles in the occurrence and development of cerebral vasospasm. We found that these various microparticles showed dynamic characteristics in body fluids and directly or indirectly affect the cerebral vasospasm or prompt it. Due to the different materials carried by microparticles from different cells, there are also differences in the mechanisms that lead to abnormal vasomotor. We suggest that microparticle scavengers might be a promising therapeutic target against microparticles associated complications.

Hypothermia reduces glymphatic transportation in traumatic edematous brain assessed by intrathecal dynamic contrast-enhanced MRI

The glymphatic system has recently been shown to clear brain extracellular solutes and can be extensively impaired after traumatic brain injury (TBI). Despite hypothermia being identified as a protective method for the injured brain via minimizing the formation of edema in the animal study, little is known about how hypothermia affects the glymphatic system following TBI. We use dynamic contrast-enhanced MRI (DCE-MRI) following cisterna magna infusion with a low molecular weight contrast agent to track glymphatic transport in male Sprague-Dawley rats following TBI with hypothermia treatment and use diffusion-weighted imaging (DWI) sequence to identify edema after TBI, and further distinguish between vasogenic and cytotoxic edema. We found that hypothermia could attenuate brain edema, as demonstrated by smaller injured lesions and less vasogenic edema in most brain subregions. However, in contrast to reducing cerebral edema, hypothermia exacerbated the reduction of efficiency of glymphatic transportation after TBI. This deterioration of glymphatic drainage was present brain-wide and showed hemispherical asymmetry and regional heterogeneity across the brain, associated with vasogenic edema. Moreover, our data show that glymphatic transport reduction and vasogenic edema are closely related to reducing perivascular aquaporin-4 (AQP4) expression. The suppression of glymphatic transportation might eliminate the benefits of brain edema reduction induced by hypothermia and provide an alternative pathophysiological factor indicating injury to the brain after TBI. Thus, this study poses a novel emphasis on the potential role of hypothermia in managing severe TBI.

Exploration of treatments for subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) continues to be a leading cause of morbidity and mortality, with cerebral vasospasm as a common etiology of worse clinical progression. The purpose of this study was to evaluate and review the current literature concerning the effective treatment of SAH. The treatment options for SAH are expanding as new therapeutic targets are identified. Nimodipine is the primary medication prescribed due to its neuroprotective properties. In addition, certain drugs can enhance lymphatic flow and influence the recovery process, such as Dexmedetomidine, SSRIs, and DL-3-n-butylphthalide. Vasospastic and ischemic patients commonly undergo transluminal balloon angioplasty. Clinical trials have not yet provided conclusive evidence to support the use of magnesium or statins. Moreover, other agents such as calcium channel blockers, milrinone, hydrogen sulfide, exosomes, erythropoietin, cilostazol, fasudil, albumin, Eicosapentaenoic acid, corticosteroids, minocycline, and stellate ganglion blockade should be investigated further.