Off-label intrathecal use of gadobutrol: safety study and comparison of administration protocols

Neurosurgery and the glymphatic system

The discovery of the glymphatic system has fundamentally altered our comprehension of cerebrospinal fluid transport and the removal of waste from brain metabolism. In the past decade, since its initial characterization, research on the glymphatic system has surged exponentially. Its potential implications for central nervous system disorders have sparked significant interest in the field of neurosurgery. Nonetheless, ongoing discussions and debates persist regarding the concept of the glymphatic system, and our current understanding largely relies on findings from experimental animal studies. This review aims to address several key inquiries: What methodologies exist for evaluating glymphatic function in humans today? What is the current evidence supporting the existence of a human glymphatic system? Can the glymphatic system be considered distinct from the meningeal-lymphatic system? What is the human evidence for glymphatic-meningeal lymphatic system failure in neurosurgical diseases? Existing literature indicates a paucity of techniques available for assessing glymphatic function in humans. Thus far, intrathecal contrast-enhanced magnetic resonance imaging (MRI) has shown the most promising results and have provided evidence for the presence of a glymphatic system in humans, albeit with limitations. It is, however, essential to recognize the interconnection between the glymphatic and meningeal lymphatic systems, as they operate in tandem. There are some human studies demonstrating deteriorations in glymphatic function associated with neurosurgical disorders, enriching our understanding of their pathophysiology. However, the translation of this knowledge into clinical practice is hindered by the constraints of current glymphatic imaging modalities.

Glymphatic-lymphatic coupling: assessment of the evidence from magnetic resonance imaging of humans

The discoveries that cerebrospinal fluid participates in metabolic perivascular exchange with the brain and further drains solutes to meningeal lymphatic vessels have sparked a tremendous interest in translating these seminal findings from animals to humans. A potential two-way coupling between the brain extra-vascular compartment and the peripheral immune system has implications that exceed those concerning neurodegenerative diseases, but also imply that the central nervous system has pushed its immunological borders toward the periphery, where cross-talk mediated by cerebrospinal fluid may play a role in a range of neoplastic and immunological diseases. Due to its non-invasive approach, magnetic resonance imaging has typically been the preferred methodology in attempts to image the glymphatic system and meningeal lymphatics in humans. Even if flourishing, the research field is still in its cradle, and interpretations of imaging findings that topographically associate with reports from animals have yet seemed to downplay the presence of previously described anatomical constituents, particularly in the dura. In this brief review, we illuminate these challenges and assess the evidence for a glymphatic-lymphatic coupling. Finally, we provide a new perspective on how human brain and meningeal clearance function may possibly be measured in future.

Current Understanding of the Anatomy, Physiology, and Magnetic Resonance Imaging of Neurofluids: Update From the 2022 "ISMRM Imaging Neurofluids Study group" Workshop in Rome

Neurofluids is a term introduced to define all fluids in the brain and spine such as blood, cerebrospinal fluid, and interstitial fluid. Neuroscientists in the past millennium have steadily identified the several different fluid environments in the brain and spine that interact in a synchronized harmonious manner to assure a healthy microenvironment required for optimal neuroglial function. Neuroanatomists and biochemists have provided an incredible wealth of evidence revealing the anatomy of perivascular spaces, meninges and glia and their role in drainage of neuronal waste products. Human studies have been limited due to the restricted availability of noninvasive imaging modalities that can provide a high spatiotemporal depiction of the brain neurofluids. Therefore, animal studies have been key in advancing our knowledge of the temporal and spatial dynamics of fluids, for example, by injecting tracers with different molecular weights. Such studies have sparked interest to identify possible disruptions to neurofluids dynamics in human diseases such as small vessel disease, cerebral amyloid angiopathy, and dementia. However, key differences between rodent and human physiology should be considered when extrapolating these findings to understand the human brain. An increasing armamentarium of noninvasive MRI techniques is being built to identify markers of altered drainage pathways. During the three-day workshop organized by the International Society of Magnetic Resonance in Medicine that was held in Rome in September 2022, several of these concepts were discussed by a distinguished international faculty to lay the basis of what is known and where we still lack evidence. We envision that in the next decade, MRI will allow imaging of the physiology of neurofluid dynamics and drainage pathways in the human brain to identify true pathological processes underlying disease and to discover new avenues for early diagnoses and treatments including drug delivery. Evidence level: 1 Technical Efficacy: Stage 3.

Imaging of brain barrier inflammation and brain fluid drainage in human neurological diseases

The intricate relationship between the central nervous system (CNS) and the immune system plays a crucial role in the pathogenesis of various neurological diseases. Understanding the interactions among the immunopathological processes at the brain borders is essential for advancing our knowledge of disease mechanisms and developing novel diagnostic and therapeutic approaches. In this review, we explore the emerging role of neuroimaging in providing valuable insights into brain barrier inflammation and brain fluid drainage in human neurological diseases. Neuroimaging techniques have enabled us not only to visualize and assess brain structures, but also to study the dynamics of the CNS in health and disease in vivo. By analyzing imaging findings, we can gain a deeper understanding of the immunopathology observed at the brain-immune interface barriers, which serve as critical gatekeepers that regulate immune cell trafficking, cytokine release, and clearance of waste products from the brain. This review explores the integration of neuroimaging data with immunopathological findings, providing valuable insights into brain barrier integrity and immune responses in neurological diseases. Such integration may lead to the development of novel diagnostic markers and targeted therapeutic approaches that can benefit patients with neurological disorders.

Mechanisms behind changes of neurodegeneration biomarkers in plasma induced by sleep deprivation

Acute sleep deprivation has been shown to affect cerebrospinal fluid and plasma concentrations of biomarkers associated with neurodegeneration, though the mechanistic underpinnings remain unknown. This study compared individuals who, for one night, were either subject to total sleep deprivation or free sleep, (i) examining plasma concentrations of neurodegeneration biomarkers the morning after sleep deprivation or free sleep and (ii) determining how overnight changes in biomarkers plasma concentrations correlate with indices of meningeal lymphatic and glymphatic clearance functions. Plasma concentrations of amyloid-β 40 and 42, phosphorylated tau peptide 181, glial fibrillary acid protein and neurofilament light were measured longitudinally in subjects who from Day 1 to Day 2 either underwent total sleep deprivation (n = 7) or were allowed free sleep (n = 21). The magnetic resonance imaging contrast agent gadobutrol was injected intrathecally, serving as a cerebrospinal fluid tracer. Population pharmacokinetic model parameters of gadobutrol cerebrospinal fluid-to-blood clearance were utilized as a proxy of meningeal lymphatic clearance capacity and intrathecal contrast-enhanced magnetic resonance imaging as a proxy of glymphatic function. After one night of acute sleep deprivation, the plasma concentrations of amyloid-β 40 and 42 were reduced, but not the ratio, and concentrations of the other biomarkers were unchanged. The overnight change in amyloid-β 40 and 42 plasma concentrations in the sleep group correlated significantly with indices of meningeal lymphatic clearance capacity, while this was not seen for the other neurodegeneration biomarkers. However, overnight change in plasma concentrations of amyloid-β 40 and 42 did not correlate with the glymphatic marker. On the other hand, the overnight change in plasma concentration of phosphorylated tau peptide 181 correlated significantly with the marker of glymphatic function in the sleep deprivation group but not in the sleep group. The present data add to the evidence of the role of sleep and sleep deprivation on plasma neurodegeneration concentrations; however, the various neurodegeneration biomarkers respond differently with different mechanisms behind sleep-induced alterations in amyloid-β and tau plasma concentrations. Clearance capacity of meningeal lymphatics seems more important for sleep-induced changes in amyloid-β 40 and 42 plasma concentrations, while glymphatic function seems most important for change in plasma concentration of phosphorylated tau peptide 181 during sleep deprivation. Altogether, the present data highlight diverse mechanisms behind sleep-induced effects on concentrations of plasma neurodegeneration biomarkers.

Impairments in sleep and brain molecular clearance in people with cognitive deterioration and biological evidence of AD: a report of four cases

BACKGROUND

Recent evidence suggests that the failure of the glymphatic system - the brain's waste clearance system, which is active during sleep - plays a key role in the pathophysiology of Alzheimer's Disease (AD). Glymphatic function can be investigated using serial MRIs after intrathecal gadobutrol injection. This technique can reveal the health of the glymphatic system, but has not yet been used in participants with cognitive impairment due to AD.

CASE REPORT

This report describes the sleep and gadobutrol tracer clearance patterns of four participants diagnosed with mild to moderate cognitive impairment with evidence of AD pathology (pathological levels of Ab and p-tau in cerebrospinal fluid). We performed polysomnography and MRI studies before tracer injection and MRI scans at 1.5-2 h, 5-6 h, and 48 h after injection. Despite participants reporting no sleep problems, polysomnography revealed that all participants had moderate to severe sleep disturbances, including reduced sleep efficiency during the study and obstructive sleep apnea. Severe side-effects related to tracer administration were observed, impeding the completion of the protocol in two participants. Participants who finished the protocol displayed delayed and persistent tracer enrichment in the cortex and white matter, even 48 h after injection. These outcomes have not been observed in previous studies in participants without AD.

CONCLUSION

The findings suggest that brains with sleep impairment and AD pathology have poor glymphatic function, and therefore cannot clear the contrast tracer efficiently. This is likely to have caused the severe side effects in our participants, that have not been reported in healthy individuals. Our results may therefore represent the only available data acquired with this technique in participants with AD pathology.

Prospective T1 mapping to assess gadolinium retention in brain after intrathecal gadobutrol

PURPOSE

A possible pathway behind gadolinium retention in brain is leakage of contrast agents from blood to cerebrospinal fluid and entry into brain along perivascular (glymphatic) pathways. The object of this study was to assess for signs of gadolinium retention in brain 4 weeks after intrathecal contrast enhanced MRI.

METHODS

We prospectively applied standardized T1 mapping of the brain before and 4 weeks after intrathecal administration of 0.5 mmol gadobutrol in patients under work-up of cerebrospinal fluid circulation disorders. Due to methodological limitations, a safety margin for percentage change in T1 time was set to 3%. Region-wise differences were assessed by pairwise comparison using t-tests and forest plots, and statistical significance was accepted at .05 level (two-tailed).

RESULTS

In a cohort of 76 participants (mean age 47.2 years ± 17.9 [standard deviation], 47 women), T1 relaxation times remained unchanged in cerebral cortex and basal ganglia 4 weeks after intrathecal gadobutrol. T1 was reduced from 1082 ± 46.7 ms to 1070.6 ± 36.5 ms (0.98 ±2.9%) (mean [standard deviation]) (p=0.001) in white matter, thus within the pre-defined 3% safety margin. The brain stem and cerebellum could not be assessed due to poor alignment of posterior fossa structures at scans from different time points.

CONCLUSION

Gadolinium retention was not detected in the cerebral hemispheres 4 weeks after an intrathecal dose of 0.5 mmol gadobutrol, implying that presence of contrast agents in cerebrospinal fluid is of minor importance for gadolinium retention in brain.

Prospective Safety Study of Intrathecal Gadobutrol in Different Doses

BACKGROUND AND PURPOSE

In our clinical practice, we increasingly use intrathecal contrast-enhanced glymphatic MR imaging to assess CSF disturbances. However, because intrathecal MR imaging contrast agents such as gadobutrol (Gadovist; 1.0 mmol/mL) are used off-label, a thorough understanding of the safety profile is required.

MATERIALS AND METHODS

We performed a prospective safety study from August 2020 to June 2022 of intrathecal gadobutrol, including consecutive patients who received either 0.50, 0.25, or 0.10 mmol. Serious and nonserious adverse events were recorded systematically at 1-3 days, 4 weeks, and >6 months after the intrathecal administration.

RESULTS

The study included 196 patients who received intrathecal gadobutrol, including patients assessed for idiopathic normal pressure hydrocephalus (iNPH, n = 144) or patients examined for other CSF disorders (non-iNPH cohort; n = 52). The intrathecal gadobutrol doses were either 0.50 mmol (n = 56), 0.25 mmol (n = 111), or 0.10 mmol (n = 29). No serious adverse events were observed. Nonserious adverse events on days 1-3 after intrathecal gadobutrol were, to some degree, dose-dependent but mild-to-moderate, including severe headache, nausea, and/or dizziness in 6/196 (6.3%) patients, and they were more common in the non-iNPH than in the iNPH cohort. At 4 weeks, none reported severe nonserious adverse events, and 9/179 (5.0%) patients had mild-to-moderate symptoms. After >6 months, 2 patients reported mild headache.

CONCLUSIONS

The present study adds to the accumulating evidence that intrathecal gadobutrol in doses up to 0.50 is safe.

Quantification approaches for magnetic resonance imaging following intravenous gadolinium injection: A window into brain-wide glymphatic function

The glymphatic system is a brain-wide network of perivascular pathways along which cerebrospinal fluid and interstitial fluid rapidly exchange, facilitating solute and waste clearance from the brain parenchyma. The characterization of this exchange process in humans has relied primarily upon serial magnetic resonance imaging following intrathecal gadolinium-based contrast agent injection. However, less invasive approaches are needed. Here, we administered a gadolinium-based contrast agent intravenously in eight healthy participants and acquired magnetic resonance imaging scans prior to and 30, 90, 180, and 360 min post contrast injection. Using a region-of-interest approach, we observed that peripheral tissues and blood vessels exhibited high enhancement at 30 min after contrast administration, likely reflecting vascular and peripheral interstitial distribution of the gadolinium-based contrast agent. Ventricular, grey matter and white matter enhancement peaked at 90 min, declining thereafter. Using k-means clustering, we identify distinct distribution volumes reflecting the leptomeningeal perivascular network, superficial grey matter and deep grey/white matter that exhibit a sequential enhancement pattern consistent with parenchymal contrast enhancement via the subarachnoid cerebrospinal fluid compartment. We also outline the importance of correcting for (otherwise automatic) autoscaling of signal intensities, which could potentially lead to misinterpretation of gadolinium-based contrast agent distribution kinetics. In summary, we visualize and quantify delayed tissue enhancement following intravenous administration of gadolinium-based contrast agent in healthy human participants.

Assessment of Meningeal Lymphatics in the Parasagittal Dural Space: A Prospective Feasibility Study Using Dynamic Contrast-Enhanced Magnetic Resonance Imaging

OBJECTIVE

Meningeal lymphatic vessels are predominantly located in the parasagittal dural space (PSD); these vessels drain interstitial fluids out of the brain and contribute to the glymphatic system. We aimed to investigate the ability of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in assessing the dynamic changes in the meningeal lymphatic vessels in PSD.

MATERIALS AND METHODS

Eighteen participants (26-71 years; male:female, 10:8), without neurological or psychiatric diseases, were prospectively enrolled and underwent DCE-MRI. Three regions of interests (ROIs) were placed on the PSD, superior sagittal sinus (SSS), and cortical vein. Early and delayed enhancement patterns and six kinetic curve-derived parameters were obtained and compared between the three ROIs. Moreover, the participants were grouped into the young (< 65 years; n = 9) or older (≥ 65 years; n = 9) groups. Enhancement patterns and kinetic curve-derived parameters in the PSD were compared between the two groups.

RESULTS

The PSD showed different enhancement patterns than the SSS and cortical veins (P < 0.001 and P < 0.001, respectively) in the early and delayed phases. The PSD showed slow early enhancement and a delayed wash-out pattern. The six kinetic curve-derived parameters of PSD was significantly different than that of the SSS and cortical vein. The PSD wash-out rate of older participants was significantly lower (median, 0.09; interquartile range [IQR], 0.01-0.15) than that of younger participants (median, 0.32; IQR, 0.07-0.45) (P = 0.040).

CONCLUSION

This study shows that the dynamic changes of meningeal lymphatic vessels in PSD can be assessed with DCE-MRI, and the results are different from those of the venous structures. Our finding that delayed wash-out was more pronounced in the PSD of older participants suggests that aging may disturb the meningeal lymphatic drainage.

Population pharmacokinetic modeling of CSF to blood clearance: prospective tracer study of 161 patients under work-up for CSF disorders

Background

Quantitative measurements of cerebrospinal fluid to blood clearance has previously not been established for neurological diseases. Possibly, variability in cerebrospinal fluid clearance may affect the underlying disease process and may possibly be a source of under- or over-dosage of intrathecally administered drugs. The aim of this study was to characterize the cerebrospinal fluid to blood clearance of the intrathecally administered magnetic resonance imaging contrast agent gadobutrol (Gadovist, Bayer Pharma AG, GE). For this, we established a population pharmacokinetic model, hypothesizing that cerebrospinal fluid to blood clearance differs between cerebrospinal fluid diseases.

Methods

Gadobutrol served as a surrogate tracer for extra-vascular pathways taken by several brain metabolites and drugs in cerebrospinal fluid. We estimated cerebrospinal fluid to blood clearance in patients with different cerebrospinal fluid disorders, i.e. symptomatic pineal and arachnoid cysts, as well as tentative spontaneous intracranial hypotension due to cerebrospinal fluid leakage, idiopathic intracranial hypertension, or different types of hydrocephalus (idiopathic normal pressure hydrocephalus, communicating- and non-communicating hydrocephalus). Individuals with no verified cerebrospinal fluid disturbance at clinical work-up were denoted references.

Results

Population pharmacokinetic modelling based on 1,140 blood samples from 161 individuals revealed marked inter-individual variability in pharmacokinetic profiles, including differences in absorption half-life (time to 50% of tracer absorbed from cerebrospinal fluid to blood), time to maximum concentration in blood and the maximum concentration in blood as well as the area under the plasma concentration time curve from zero to infinity. In addition, the different disease categories of cerebrospinal fluid diseases demonstrated different profiles.

Conclusions

The present observations of considerable variation in cerebrospinal fluid to blood clearance between individuals in general and across neurological diseases, may suggest that defining cerebrospinal fluid to blood clearance can become a useful diagnostic adjunct for work-up of cerebrospinal fluid disorders. We also suggest that it may become useful for assessing clearance capacity of endogenous brain metabolites from cerebrospinal fluid, as well as measuring individual cerebrospinal fluid to blood clearance of intrathecal drugs.

Investigation of Human Intrathecal Solute Transport Dynamics Using a Novel in vitro Cerebrospinal Fluid System Analog

BACKGROUND

Understanding the relationship between cerebrospinal fluid (CSF) dynamics and intrathecal drug delivery (ITDD) injection parameters is essential to improve treatment of central nervous system (CNS) disorders.

METHODS

An anatomically detailed in vitro model of the complete CSF system was constructed. Patient-specific cardiac- and respiratory-induced CSF oscillations were input to the model in the subarachnoid space and within the ventricles. CSF production was input at the lateral ventricles and CSF absorption at the superior sagittal sinus. A model small molecule simulated drug product containing fluorescein was imaged within the system over a period of 3-h post-lumbar ITDD injections and used to quantify the impact of (a) bolus injection volume and rate, (b) post-injection flush volume, rate, and timing, (c) injection location, and (d) type of injection device. For each experiment, neuraxial distribution of fluorescein in terms of spatial temporal concentration, area-under-the-curve (AUC), and percent of injected dose (%ID) to the brain was quantified at a time point 3-h post-injection.

RESULTS

For all experiments conducted with ITDD administration in the lumbar spine, %ID to the brain did not exceed 11.6% at a time point 3-h post-injection. Addition of a 12 mL flush slightly increased solute transport to the brain up to +3.9%ID compared to without a flush (p < 0.01). Implantation of a lumbar catheter with the tip at an equivalent location to the lumbar placed needle, but with rostral tip orientation, resulted in a small improvement of 1.5%ID to the brain (p < 0.05). An increase of bolus volume from 5 to 20 mL improved solute transport to the brain from 5.0 to 6.3%ID, but this improvement was not statistically significant. Increasing bolus injection rate from 5 to 13.3 mL/min lacked improvement of solute transport to the brain, with a value of 6.3 compared to 5.7%ID.

CONCLUSION

The in vitro modeling approach allowed precisely controlled and repeatable parametric investigation of ITDD injection protocols and devices. In combination, the results predict that parametric changes in lumbar spine ITDD-injection related parameters and devices can alter %ID to the brain and be tuned to optimize therapeutic benefit to CNS targets.

Intrathecal Contrast-Enhanced Magnetic Resonance Imaging of Cerebrospinal Fluid Dynamics and Glymphatic Enhancement in Idiopathic Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease, characterized by cerebrospinal fluid (CSF) flow disturbance. Today, the only available treatment is CSF diversion surgery (shunt surgery). While traditional imaging biomarkers typically assess CSF space anatomy, recently introduced imaging biomarkers of CSF dynamics and glymphatic enhancement, provide imaging of CSF dynamics and thereby more specifically reveal elements of the underlying pathophysiology. The biomarkers address CSF ventricular reflux grade as well as glymphatic enhancement and derive from intrathecal contrast-enhanced MRI. However, the contrast agent serving as CSF tracer is administered off-label. In medicine, the introduction of new diagnostic or therapeutic methods must consider the balance between risk and benefit. To this end, we performed a prospective observational study of 95 patients with iNPH, comparing different intrathecal doses of the MRI contrast agent gadobutrol (0.10, 0.25, and 0.50 mmol, respectively), aiming at the lowest reasonable dose needed to retrieve diagnostic information about the novel MRI biomarkers. The present observations disclosed a dose-dependent enrichment of subarachnoid CSF spaces (cisterna magna, vertex, and velum interpositum) with dose-dependent ventricular reflux of tracer in iNPH, as well as dose-dependent glymphatic tracer enrichment. The association between tracer enrichment in CSF and parenchymal compartments were as well dose-related. Intrathecal gadobutrol in a dose of 0.25 mmol, but not 0.10 mmol, was at 1.5T MRI considered sufficient for imaging altered CSF dynamics and glymphatic enhancement in iNPH, even though 3T MRI provided better sensitivity. Tracer enrichment in CSF at the vertex and within the cerebral cortex and subcortical white matter was deemed too low for maintaining diagnostic information from a dose of 0.10 mmol. We conclude that reducing the intrathecal dose of gadobutrol from 0.50 to 0.25 mmol gadobutrol improves the safety margin while maintaining the necessary diagnostic information about disturbed CSF homeostasis and glymphatic failure in iNPH.

Application of a three-dimensional printed model to localize a cranial cerebrospinal fluid leak: a case report

Localization of defect sites is a major challenge for surgical repair of cerebrospinal fluid (CSF) leaks. Here, we report a case in which we applied a 3-dimensional (3D) printed model to accurately identify the defect sites and facilitate the successful repair of a cranial CSF leak. A 37-year-old female patient diagnosed with recurrent nasopharyngeal carcinoma suffered CSF rhinorrhea and severe bacterial meningitis. Lumbar drainage and antibiotic administration failed to control the condition. In addition to high resolution computed tomography and magnetic resonance imaging, we applied a 3D printed model of the skull to improve the understanding of the osseous destruction at the skull base and aid in accurately localizing the defect sites of the right middle fossa. Accordingly, a right temporalis pedicled flap combined with an autogenous fascia lata flap was applied to cover the defect sites. The leak stopped postoperatively, and meningitis was relieved by enhanced antibacterial treatment. As a complement to high resolution computed tomography and magnetic resonance imaging, a 3D printed model may improve localization of complex defect sites and surgical planning by allowing preoperative visualization of the skull condition.

Molecular trans-dural efflux to skull bone marrow in humans with cerebrospinal fluid disorders

Dural sinuses were recently identified as a hub for peripheral immune surveillance of brain-derived antigens cleared through CSF. However, animal studies have also indicated that substances and cells may enter the intracranial compartment directly from bone marrow.

We used MRI and a CSF tracer to investigate in vivo whether intracranial molecules can move via dura to skull bone marrow in patients with suspicion of CSF disorders. Tracer enrichment in CSF, dural regions and within skull bone marrow was assessed up to 48 h after intrathecal administration of gadobutrol (0.5 ml, 1 mmol/ml) in 53 patients. In participants diagnosed with disease, tracer enrichment within diploe of skull bone marrow was demonstrated nearby the parasagittal dura, nearby extensions of parasagittal dura into diploe, and in diploe of skull bone remote from the dura extensions.

This crossing of meningeal and skull barriers suggests that bone marrow may contribute in brain immune surveillance also in humans.

Imaging of Acquired Skull Base Cerebrospinal Fluid Leaks

Acquired skull base cerebrospinal fluid (CSF) leaks can result from trauma, tumors, iatrogenic causes, or may be spontaneous. Spontaneous skull base CSF leaks are likely a manifestation of underlying idiopathic intracranial hypertension. The initial assessment of rhinorrhea or otorrhea which is suspected to be due to an acquired skull base CSF leak requires integration of clinical assessment and biochemical confirmation of CSF. Imaging with high-resolution CT is performed to locate osseous defects, while high-resolution T2w MRI may detect CSF traversing the dura and bony skull base. When leaks are multiple or if samples of fluid cannot be obtained for testing, then recourse to invasive cisternography may be necessary.

Development and application of a liquid chromatography-mass spectrometry method for residual iodixanol quantification in AAV-based gene therapy product development

Adeno-associated viruses (AAVs) are non-enveloped viruses which have become popular gene transfer vectors to deliver DNA to target cells in clinical gene therapy. Iodixanol-based density gradient is one of the widely used purification methods for serotype-independent AAV. However, residual iodixanol in AAV could be a safety concern, and further purification to remove this process-related impurity is typically needed. An analytical assay with high sensitivity is essential for the detection of residual iodixanol to ensure the safety of AAV products. We developed a liquid chromatography-mass spectrometry (LC-MS) method with the limit of quantification (LOQ) of 0.01 μg/mL for residual iodixanol measurement in AAV. The method also demonstrated linearity over four orders of magnitude which allows quantifying a high iodixanol concentration in in-process samples with excellent recovery and accuracy. In addition, we further explored a highly efficient purification method for removal of the residual iodixanol, to minimize the safety concern from iodixanol as a process impurity.

Special MRI Techniques to Suss out Spontaneous Cerebrospinal Fluid Leaks

Anterior skull base cerebrospinal fluid (CSF) fistulas result from skull base osteodural defects, allowing subarachnoid space CSF to escape into pneumatized cavities such as the paranasal sinuses and nasal fossa. Precise localization, characterization, and effective treatment of CSF leaks is essential to prevent meningitis, treatment failure, or recurrence. Advances in magnetic resonance imaging have improved radiologists' ability to localize and characterize anterior skull base CSF fistulas. This article reviews new imaging techniques enabling diagnostic location of CSF fistulas, with an emphasis on magnetic resonance imaging-based techniques.

Clinical application of intrathecal gadobutrol for assessment of cerebrospinal fluid tracer clearance to blood

BACKGROUNDMethodology for estimation of cerebrospinal fluid (CSF) tracer clearance could have wide clinical application in predicting excretion of intrathecal drugs and metabolic solutes from brain metabolism and for diagnostic workup of CSF disturbances.METHODSThe MRI contrast agent gadobutrol (Gadovist) was used as a CSF tracer and injected into the lumbar CSF. Gadobutrol is contained outside blood vessels of the CNS and is eliminated along extravascular pathways, analogous to many CNS metabolites and intrathecal drugs. Tracer enrichment was verified and assessed in CSF by MRI at the level of the cisterna magna in parallel with obtaining blood samples through 48 hours.RESULTSIn a reference patient cohort (n = 29), both enrichment within CSF and blood coincided in time. Blood concentration profiles of gadobutrol through 48 hours varied between patients diagnosed with CSF leakage (n = 4), idiopathic normal pressure hydrocephalus dementia (n = 7), pineal cysts (n = 8), and idiopathic intracranial hypertension (n = 4).CONCLUSIONAssessment of CSF tracer clearance is clinically feasible and may provide a way to predict extravascular clearance of intrathecal drugs and endogenous metabolites from the CNS. The peak concentration in blood (at about 10 hours) was preceded by far peak tracer enhancement at MRI in extracranial lymphatic structures (at about 24 hours), as shown in previous studies, indicating a major role of the spinal canal in CSF clearance capacity.FUNDINGThe work was supported by the Department of Neurosurgery, Oslo University Hospital; the Norwegian Institute for Air Research; and the University of Oslo.

Direction and magnitude of cerebrospinal fluid flow vary substantially across central nervous system diseases

Background

Several central nervous system diseases are associated with disturbed cerebrospinal fluid (CSF) flow patterns and have typically been characterized in vivo by phase-contrast magnetic resonance imaging (MRI). This technique is, however, limited by its applicability in space and time. Phase-contrast MRI has yet to be compared directly with CSF tracer enhanced imaging, which can be considered gold standard for assessing long-term CSF flow dynamics within the intracranial compartment.

Methods

Here, we studied patients with various CSF disorders and compared MRI biomarkers of CSF space anatomy and phase-contrast MRI at level of the aqueduct and cranio-cervical junction with dynamic intrathecal contrast-enhanced MRI using the contrast agent gadobutrol as CSF tracer. Tracer enrichment of cerebral ventricles was graded 0–4 by visual assessment. An intracranial pressure (ICP) score was used as surrogate marker of intracranial compliance.

Results

The study included 94 patients and disclosed marked variation of CSF flow measures across disease categories. The grade of supra-aqueductal reflux of tracer varied, with strong reflux (grades 3–4) in half of patients. Ventricular tracer reflux correlated with stroke volume and aqueductal CSF pressure gradient. CSF flow in the cerebral aqueduct was retrograde (from 4th to 3rd ventricle) in one third of patients, with estimated CSF net flow volume about 1.0 L/24 h. In the cranio-cervical junction, net flow was cranially directed in 78% patients, with estimated CSF net flow volume about 4.7 L/24 h.

Conclusions

The present observations provide in vivo quantitative evidence for substantial variation in direction and magnitude of CSF flow, with re-direction of aqueductal flow in communicating hydrocephalus, and significant extra-cranial CSF production. The grading of ventricular reflux of tracer shows promise as a clinical useful method to assess CSF flow pattern disturbances in patients.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00251-6.

In Vivo Evidence for Impaired Glymphatic Function in the Visual Pathway of Patients With Normal Pressure Hydrocephalus

Purpose

Impaired ability to remove toxic metabolites from central nervous system may be an important link between cerebral and ophthalmic degenerative diseases. The aim of the present study was to compare the glymphatic function in the visual pathway in patients with idiopathic normal pressure hydrocephalus (iNPH), a neurodegenerative dementia subtype, with a reference group.

Methods

We compared 31 subjects with Definite iNPH (i.e., shunt-responsive) with 13 references in a prospective and observational study. After intrathecal injection of the magnetic contrast agent gadobutrol (Gadovist, 0.5 mL, 1.0 mmol/mL, Bayer Pharma AG), serving as a tracer, consecutive magnetic resonance imaging (MRI) scans were obtained (next 24-48 hours). The normalized MRI T1 signal recorded in the cerebrospinal fluid (CSF) and along the visual pathway served as a semi-quantitative measure of tracer enrichment. Gadobutrol does not penetrate the blood-brain barrier and is thus confined to the extravascular space. Overnight measurements of pulsatile intracranial pressure were used as a surrogate marker for the intracranial compliance.

Results

The tracer enriched the prechiasmatic cistern similarly in both groups, but clearance was delayed in the iNPH group. Moreover, both delayed enrichment and clearance of the tracer were observed in the visual pathway in the iNPH subjects. The enrichment in the visual pathway and the CSF correlated. Individuals with elevated pulsatile intracranial pressure showed reduced enrichment within the visual pathway.

Conclusions

There was delayed enrichment and clearance of a tracer in the visual pathway of iNPH patients, which suggests impaired glymphatic function in the visual pathway in this disease.