Cerebrospinal fluid dynamics along the optic nerve

Spaceflight Associated Neuro-ocular Syndrome (SANS) and Its Countermeasures

Astronauts can develop a distinct collection of neuro-ophthalmic findings during long duration spaceflight, collectively known as Spaceflight Associated Neuro-ocular Syndrome (SANS). These clinical characteristics include optic disc edema, hyperopic refractive shifts, globe flattening, and chorioretinal folds, which may pose a health risk for future space exploration. Obtaining knowledge of SANS and countermeasures for its prevention is crucial for upcoming crewed space missions and warrant a multidisciplinary approach. This review examines the potential causes and countermeasures of SANS, including space anticipation glasses, lower body negative pressure, venous thigh cuffs, impedance threshold devices, translaminar pressure gradient modulation, centrifugation, artificial gravity, pharmaceuticals, and precision nutritional supplementation. This paper highlights future research directions for understanding the genetic, anthropometric, behavioral, and environmental susceptibilities to SANS as well as how to use terrestrial analogs for testing future mitigation strategies.

Low-Cost Strategies for the Development of Neurocritical Care in Resource-Limited Settings

This review explores low-cost neurocritical care interventions for resource-limited settings, including economical devices, innovative care models, and disease-specific strategies. Devices like inexpensive ventilators, wearable technology, smartphone-based ultrasound, brain4care, transcranial Doppler, and smartphone pupillometry offer effective diagnostic and monitoring capabilities. Initiatives such as intermediate care units, minimally equipped stroke units, and tele-neurocritical care have demonstrated benefits by reducing hospital stays, preventing complications, and improving clinical and economic outcomes. The review emphasizes locally applicable tailored approaches for diagnosing and managing conditions such as traumatic brain injury, neuroinfections, status epilepticus, autoimmune neurological disorders, and acute stroke as viable and affordable solutions.

Hypothesis on the outflow of optic nerve cerebrospinal fluid in spaceflight associated neuro ocular syndrome

Spaceflight-associated neuro-ocular syndrome (SANS) has been well documented in astronauts. However, its pathogenesis is not fully understood. New findings indicate the impaired outflow of the optic nerve cerebrospinal fluid may participate or contribute to some changes in SANS. In this perspective, we generated a hypothesis that the outflow of cerebrospinal fluid through the optic nerve sheath may be impaired under micro-gravity and then may potentially lead to SANS-related alterations.

Loss of aquaporin-4 impairs cerebrospinal fluid solute clearance through cerebrospinal fluid drainage pathways

The aquaporin-4 (AQP4) water channel is essential in neurofluid dynamics. AQP4 loss impairs solute exchange between the cerebrospinal fluid (CSF) and interstitial fluid (ISF). However, whether AQP4 expression affects solute clearance from the CSF space to the extracranial space remains unclear. This study aimed to investigate this using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) following the intrathecal administration of gadolinium-based contrast agents (GBCAs) to AQP4 knockout (KO) rats. AQP4 KO rats showed reduced efflux of intrathecal GBCAs to the extracranial spaces through CSF drainage pathways and increased retention of intrathecal GBCAs in the CSF space compared with the controls. These results suggest that AQP4 loss impairs solute clearance from the CSF space to the extracranial spaces via the CSF drainage pathways. This study revealed a close relationship between AQP4 expression and CSF solute clearance, contributing to a better understanding of the function of AQP4 in neurofluid dynamics.

Blockage of CSF Outflow in Rats after Deep Cervical Lymph Node Ligation Observed Using Gd-based MR Imaging

PURPOSE

To investigate whether deep cervical lymph node (DCLN) ligation alters intracranial cerebrospinal fluid (CSF) tracer dynamics and outflow using a rat model with intrathecal dynamic contrast-enhanced (DCE) MRI.

METHODS

Six bilateral DCLN-ligated and six sham-operated rats were subjected to DCE MRI with Gd-BTDO3A, and dynamic T1-weighted images were acquired. ROIs were collected from the CSF at the C1 level (CSF_C1), CSF between the olfactory bulbs (CSF_OB), CSF at the pituitary recess (CSF_PitR), and CSF at the pineal recess (CSF_PinR), upper nasal turbinate (UNT), olfactory bulbs, cerebrum, and the jugular region. Time-intensity curves were evaluated, and the maximum slope, peak timing, peak signal ratio, and elimination half-life for the four CSF ROIs and UNT were calculated and compared.

RESULTS

Delayed tracer arrival in the rostral CSF space and the nasal cavity with tracer retention in the ventral CSF space were observed in the ligation group. The maximum slopes were smaller in the ligation group at UNT (sham: 0.075 ± 0.0061, ligation: 0.044 ± 0.0086/min, P = 0.011). A significant difference was not detected in peak timings. The peak signal ratio values were lower in the ligation group at UNT (sham: 2.12 ± 0.19, ligation: 1.72 ± 0.11, P = 0.011). The elimination half-life was delayed in the ligation group at CSF_C1 (sham: 30.5 ± 2.70, ligation: 44.4 ± 12.6 min, P = 0.043), CSF_OB (sham: 30.2 ± 2.67, ligation: 44.8 ± 7.47 min, P = 0.021), and CSF_PitR (sham: 30.2 ± 2.49, ligation: 41.3 ± 7.57 min, P = 0.021).

CONCLUSION

The DCLN ligation in rats blocked CSF outflow into the nasal cavity and caused CSF retention.

Rapid Amplification of Cerebrospinal Fluid Pressure as a Possible Mechanism for Optic Nerve Sheath Bleeding in Infants With Nonaccidental Head Injury

Purpose

Subdural hemorrhage along the optic nerve (ON) is a histopathological indicator of abusive head trauma (AHT) in infants. We sought to determine if this bleeding could be caused by an abrupt increase in intracranial pressure transmitted to cerebrospinal fluid (CSF) at the optic foramen (OF).

Methods

A theoretical model is developed to simulate the effect of a pressure perturbation of maximal amplitude P applied at the optic foramen for a short duration T on the CSF-filled ON subarachnoid space (ONSAS). The ONSAS is modelled as a fluid-filled channel with an elastic wall representing the flexible ONSAS-arachnoid/dura interface. A constitutive law describing the relationship between CSF pressure and ONSAS deformation is inferred from published measurements. CSF pressure profiles along the ONSAS are examined systematically over a broad range of P and T.

Results

The pressure perturbation initiated at the OF produces a pressure wave that stretches the ONSAS. This wave propagates rapidly along the ONSAS toward the scleral end of the ON, where it is reflected back toward the brain. For sufficiently small T a shock wave with amplification up to six times larger than P over a timescale of tens of milliseconds is observed at the scleral end of the ON. Comparatively smaller amplifications are observed for slower perturbations.

Conclusions

A sudden increase in CSF pressure in the cranial cavity can cause a rapid expansion of the ONSAS, which may lead to rupture of the bridging blood vessels. Our study predicts a plausible mechanism for subdural hemorrhage that occurs in abusive head trauma in infants.

Investigating Optic Nerve Sheath Diameter in Prone Position Spinal Surgery Patients: A Pilot Study

Purpose

This study aimed to evaluate the effect of intraoperative positioning and ocular immobility on the amount of cerebrospinal fluid around the optic nerve in patients undergoing prone spinal surgery by measuring the optic nerve sheath diameter (ONSD) using ultrasound.

Methods

Consecutive participants (n = 15 patients, 30 eyes) were scanned preoperatively, intraoperatively approximately 20 minutes before the end of the surgery, and postoperatively in the post-anesthesia care unit at least 10 min after the completion of the surgery at one academic hospital.

Results

On average, patients who underwent prone spinal surgery had a 21% increase in ONSD intraoperatively, with a positive time-dependent relationship with the overall length of surgery (P < 0.001). ONSDs postoperatively returned to baseline and were not significantly different from preoperative measurements.

Conclusion

Our findings suggest pooling and inadequate clearance of perioptic cerebrospinal fluid during prone spinal surgery that improves following termination of the procedure and return of the patient to an upright position.

Heart-on-a-chip systems with tissue-specific functionalities for physiological, pathological, and pharmacological studies

Recent advances in heart-on-a-chip systems hold great promise to facilitate cardiac physiological, pathological, and pharmacological studies. This review focuses on the development of heart-on-a-chip systems with tissue-specific functionalities. For one thing, the strategies for developing cardiac microtissues on heart-on-a-chip systems that closely mimic the structures and behaviors of the native heart are analyzed, including the imitation of cardiac structural and functional characteristics. For another, the development of techniques for real-time monitoring of biophysical and biochemical signals from cardiac microtissues on heart-on-a-chip systems is introduced, incorporating cardiac electrophysiological signals, contractile activity, and biomarkers. Furthermore, the applications of heart-on-a-chip systems in intelligent cardiac studies are discussed regarding physiological/pathological research and pharmacological assessment. Finally, the future development of heart-on-a-chip toward a higher level of systematization, integration, and maturation is proposed.

Automatic segmentation and quantification of the optic nerve on MRI using a 3D U-Net

Purpose

Pathological conditions associated with the optic nerve (ON) can cause structural changes in the nerve. Quantifying these changes could provide further understanding of disease mechanisms. We aim to develop a framework that automatically segments the ON separately from its surrounding cerebrospinal fluid (CSF) on magnetic resonance imaging (MRI) and quantifies the diameter and cross-sectional area along the entire length of the nerve.

Approach

Multicenter data were obtained from retinoblastoma referral centers, providing a heterogeneous dataset of 40 high-resolution 3D T2-weighted MRI scans with manual ground truth delineations of both ONs. A 3D U-Net was used for ON segmentation, and performance was assessed in a tenfold cross-validation (n = 32 ) and on a separate test-set (n = 8 ) by measuring spatial, volumetric, and distance agreement with manual ground truths. Segmentations were used to quantify diameter and cross-sectional area along the length of the ON, using centerline extraction of tubular 3D surface models. Absolute agreement between automated and manual measurements was assessed by the intraclass correlation coefficient (ICC).

Results

The segmentation network achieved high performance, with a mean Dice similarity coefficient score of 0.84, median Hausdorff distance of 0.64 mm, and ICC of 0.95 on the test-set. The quantification method obtained acceptable correspondence to manual reference measurements with mean ICC values of 0.76 for the diameter and 0.71 for the cross-sectional area. Compared with other methods, our method precisely identifies the ON from surrounding CSF and accurately estimates its diameter along the nerve's centerline.

Conclusions

Our automated framework provides an objective method for ON assessment in vivo.

Perioptic cerebro-spinal fluid transudation: case report of an unusual finding of optic hydrops in idiopathic intracranial hypertension

Background

Idiopathic intracranial hypertension (IIH) has well-described imaging findings, typically reversible with the adequate treatment. We hereby report a case of IIH with a peculiar imaging finding, that to our knowledge and by the research conducted, has never been described before—cerebro-spinal fluid (CSF) transudation across the optic nerve sheath.

Case presentation

A 15-year-old girl with a 2-week history of occipital headache, nausea and vomiting, diplopia, blurred vision and tinnitus in her right ear, was admitted in the neuropediatric department and after extensive diagnostic work-up was diagnosed with IIH. The MRI showed typical signs of idiopathic intracranial hypertension, including enlargement of the perioptic CSF spaces associated with a peculiar finding described as a blurred hyperintensity T2/FLAIR of the perioptic fat, which was likely related to transudation of CSF. The adequate medical therapy (including corticosteroids and acetazolamide) for 2 weeks didn’t revert the signs and symptoms and so a lumboperitoneal shunt was placed with complete resolution of the clinical picture and the imaging findings described.

Conclusions

The documentation of CSF transudation around the optic nerve in the setting of hydrops has never been reported before and should be recognized by the neuroradiologist. It seems to be reversible, like the other findings of IIH and its physiopathology is not clear.