Possible role of the cavernous sinus veins in cerebrospinal fluid absorption

Extracranial transport of brain lymphatics via cranial nerve in human

Extracranial waste transport from the brain interstitial fluid to the deep cervical lymph node (dCLN) is not extensively understood. The present study aims to show the cranial nerves that have a role in the transport of brain lymphatics vessels (LVs), their localization, diameter, and number using podoplanin (PDPN) and CD31 immunohistochemistry (IHC) and Western blotting. Cranial nerve samples from 6 human cases (3 cadavers, and 3 autopsies) were evaluated for IHC and 3 autopsies for Western blotting. The IHC staining showed LVs along the optic, olfactory, oculomotor, trigeminal, facial, glossopharyngeal, accessory, and vagus nerves. However, no LVs present along the trochlear, abducens, vestibulocochlear, and hypoglossal nerves. The LVs were predominantly localized at the endoneurium of the cranial nerve that has motor components, and LVs in the cranial nerves that had sensory components were present in all 3 layers. The number of LVs accompanying the olfactory, optic, and trigeminal nerves was classified as numerous; oculomotor, glossopharyngeal, vagus, and accessory was moderate; and facial nerves was few. The largest diameter of LVs was in the epineurium and the smallest one was in the endoneurium. The majority of Western blotting results correlated with the IHC. The present findings suggest that specific cranial nerves with variable quantities provide a pathway for the transport of wastes from the brain to dCLN. Thus, the knowledge of the transport of brain lymphatics along cranial nerves may help understand the pathophysiology of various neurological diseases.

Microanatomical study of arachnoid granulations and meningeal architecture around Meckel's cave

Although the microanatomy of Meckel's cave (MC) has been well studied, there are still controversies regarding the meningeal architecture of the space. Moreover, there are only general mentions of the arachnoid granulations near MC in just a few sources. This study is aimed at determining the frequency, location, and anatomical variability of the main clusters of arachnoid granulations around MC. The dissection involved 26 isolated specimens of MC fixed in formalin (neutral buffered, 10%). This number included five freshly harvested specimens examined histologically. Additional paraffin block with MC horizontal section was taken from our neuroanatomical collection. Carefully selected anatomical and histological techniques were applied to assess the complex relationships between the arachnoid granulations and adjacent structures. Arachnoid granulations were found around MC in all specimens with different anatomical variations. The main clusters of arachnoid granulations were close to the trigeminal ganglion and its divisions. The dorsolateral wall of MC was a thick layer formed by interweaving bundles of collagen fibers arranged in various directions. The entire MC was surrounded by a dural sleeve (envelope). This sleeve separated MC from the lateral sellar compartment. At its anterior (rostral) end, it formed a cribriform area pierced by individual fascicles of the trigeminal nerve's primary divisions. The connective tissue forming the sleeve was not only continuous with the epineurium but also shifted to the perineuria surrounding individual nerve fascicles. The meningeal architecture around MC has a complex and multilayer arrangement with a collagenous sleeve closely related to the trigeminal ganglion. Arachnoid granulations are typically found around MC.

High-resolution MRI to noninvasively characterize drainage around the carotid artery into the cervical lymph nodes

BACKGROUND AND PURPOSE

Previous studies have proposed multiple parallel channels for waste clearance from the brain, though many gaps remain in our understanding of these systems. In this study, we examined periarterial fluid drainage around intracranial and extracranial segments of the internal carotid arteries (ICAs) from the brain into the cervical lymph nodes using a noninvasive and clinical-based method.

METHODS

Eighty-one subjects (45 females, aged 15-80 years old) with nonlesioned epilepsy underwent high-resolution 3-dimensional T2-weighted fluid-attenuated inversion recovery (FLAIR) MRI. We utilized a noninvasive and clinical-based method with a manual semiautomated approach to characterize the periarterial lymphatic system's maximum thickness and signal intensities along the ICAs using high-resolution 3-dimensional FLAIR imaging. We conducted group comparisons and correlation analyses to investigate sex- and age-based trends. Results were corrected with Bonferroni's test for multiple comparisons, and we performed power analysis for sample size calculations.

RESULTS

Using high-resolution FLAIR images, we show evidence that fluid drainage emerges around the ICA petrous segment and joins lymphatic flow from cranial nerves in the upper neck, with this flow ultimately draining into the cervical lymph nodes bilaterally. Lymphatic signal at the petrous segment level was significantly thinner in females compared to males bilaterally (w = 413, p = .0001 on the right, w = 356, p < .0001 on the left). Lymphatic drainage around the petrous segments of the ICAs bilaterally was thicker with age in males but not in females.

CONCLUSIONS

We describe the in vivo high-resolution imaging characteristics of periarterial fluid drainage along the vessel walls of ICAs. This represents a potentially major channel for brain waste clearance. We also report interesting sex- and age-based trends in these structures within our cohort.

The meningeal lymphatic vessels and the glymphatic system: Potential therapeutic targets in neurological disorders

The recent discovery of the meningeal lymphatic vessels (mLVs) and glymphatic pathways has challenged the long-lasting dogma that the central nervous system (CNS) lacks a lymphatic system and therefore does not interact with peripheral immunity. This discovery has reshaped our understanding of mechanisms underlying CNS drainage. Under normal conditions, a close connection between mLVs and the glymphatic system enables metabolic waste removal, immune cell trafficking, and CNS immune surveillance. Dysfunction of the glymphatic-mLV system can lead to toxic protein accumulation in the brain, and it contributes to the development of a series of neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. The identification of precise cerebral transport routes is based mainly on indirect, invasive imaging of animals, and the results cannot always be applied to humans. Here we review the functions of the glymphatic-mLV system and evidence for its involvement in some CNS diseases. We focus on emerging noninvasive imaging techniques to evaluate the human glymphatic-mLV system and their potential for preclinical diagnosis and prevention of neurodegenerative diseases. Potential strategies that target the glymphatic-mLV system in order to treat and prevent neurological disorders are also discussed.

Fluid transport in the brain

The brain harbors a unique ability to, figuratively speaking, shift its gears. During wakefulness, the brain is geared fully toward processing information and behaving, while homeostatic functions predominate during sleep. The blood-brain barrier establishes a stable environment that is optimal for neuronal function, yet the barrier imposes a physiological problem; transcapillary filtration that forms extracellular fluid in other organs is reduced to a minimum in brain. Consequently, the brain depends on a special fluid [the cerebrospinal fluid (CSF)] that is flushed into brain along the unique perivascular spaces created by astrocytic vascular endfeet. We describe this pathway, coined the term glymphatic system, based on its dependency on astrocytic vascular endfeet and their adluminal expression of aquaporin-4 water channels facing toward CSF-filled perivascular spaces. Glymphatic clearance of potentially harmful metabolic or protein waste products, such as amyloid-β, is primarily active during sleep, when its physiological drivers, the cardiac cycle, respiration, and slow vasomotion, together efficiently propel CSF inflow along periarterial spaces. The brain's extracellular space contains an abundance of proteoglycans and hyaluronan, which provide a low-resistance hydraulic conduit that rapidly can expand and shrink during the sleep-wake cycle. We describe this unique fluid system of the brain, which meets the brain's requisites to maintain homeostasis similar to peripheral organs, considering the blood-brain-barrier and the paths for formation and egress of the CSF.

The glymphatic hypothesis: the theory and the evidence

The glymphatic hypothesis proposes a mechanism for extravascular transport into and out of the brain of hydrophilic solutes unable to cross the blood-brain barrier. It suggests that there is a circulation of fluid carrying solutes inwards via periarterial routes, through the interstitium and outwards via perivenous routes. This review critically analyses the evidence surrounding the mechanisms involved in each of these stages. There is good evidence that both influx and efflux of solutes occur along periarterial routes but no evidence that the principal route of outflow is perivenous. Furthermore, periarterial inflow of fluid is unlikely to be adequate to provide the outflow that would be needed to account for solute efflux. A tenet of the hypothesis is that flow sweeps solutes through the parenchyma. However, the velocity of any possible circulatory flow within the interstitium is too small compared to diffusion to provide effective solute movement. By comparison the earlier classical hypothesis describing extravascular transport proposed fluid entry into the parenchyma across the blood-brain barrier, solute movements within the parenchyma by diffusion, and solute efflux partly by diffusion near brain surfaces and partly carried by flow along "preferred routes" including perivascular spaces, white matter tracts and subependymal spaces. It did not suggest fluid entry via periarterial routes. Evidence is still incomplete concerning the routes and fate of solutes leaving the brain. A large proportion of the solutes eliminated from the parenchyma go to lymph nodes before reaching blood but the proportions delivered directly to lymph or indirectly via CSF which then enters lymph are as yet unclear. In addition, still not understood is why and how the absence of AQP4 which is normally highly expressed on glial endfeet lining periarterial and perivenous routes reduces rates of solute elimination from the parenchyma and of solute delivery to it from remote sites of injection. Neither the glymphatic hypothesis nor the earlier classical hypothesis adequately explain how solutes and fluid move into, through and out of the brain parenchyma. Features of a more complete description are discussed. All aspects of extravascular transport require further study.

Non-invasive MR imaging of human brain lymphatic networks with connections to cervical lymph nodes

Meningeal lymphatic vessels have been described in animal studies, but limited comparable data is available in human studies. Here we show dural lymphatic structures along the dural venous sinuses in dorsal regions and along cranial nerves in the ventral regions in the human brain. 3D T2-Fluid Attenuated Inversion Recovery magnetic resonance imaging relies on internal signals of protein rich lymphatic fluid rather than contrast media and is used in the present study to visualize the major human dural lymphatic structures. Moreover we detect direct connections between lymphatic fluid channels along the cranial nerves and vascular structures and the cervical lymph nodes. We also identify age-related cervical lymph node atrophy and thickening of lymphatics channels in both dorsal and ventral regions, findings which reflect the reduced lymphatic output of the aged brain.

Comparison of the Morphologic and Mechanical Features of Human Cranial Dura and Other Graft Materials Used for Duraplasty

OBJECTIVE

This study aimed to compare the thickness and mechanical properties of the frontal; parietal; temporal; occipital human dura; autogenous grafts (facia lata, temporal fascia, galea aponeurotica); and artificial dura.

METHODS

Sagittal and transverse dura samples were obtained from standard regions of the cranial dura from 30 autopsies for histologic and mechanical property measurements. Identical measurements were made for the autogenous grafts artificial dura, and the results were statistically analyzed.

RESULTS

The thickness of the temporal (0.35 ± 0.11 mm), parietal (0.44 ± 0.13 mm), frontal (0.38 ± 0.12 mm), and occipital (0.46 ± 0.18 mm) dura showed regional variations. The parietal and occipital dura were significantly thicker than the temporal dura. The occipital dura was considerably thicker than the frontal dura. The frontal and temporal dura of males were significantly thicker than females. The sagittal maximum tensile force measurements were significantly greater than transverse, for the frontal, temporal, and occipital dura. The stiffness measurements in sagittal direction were greater than the measurements in transverse direction for the frontal dura. The mechanical properties and thickness of the autogenous and artificial dura were not similar to the human dura.

CONCLUSIONS

The thickness and mechanical properties of the regional cranial dura should be taken into consideration for a better cure and fewer complications. The mechanical properties of sagittal and transverse dura should be kept in mind for the preference of dura material. The present study's data can pave the way to produce artificial regional dura by mimicking the thickness and mechanical properties of the human dura.

Hydrocephalus in Children: A Neuroradiological Perspective

Concepts about the production, absorption, dynamics, and physiological roles of cerebrospinal fluid (CSF) have dramatically changed over the recent decades. This article will review these new concepts and detail how they must be used for a better assessment and a better understanding of the various aspects of hydrocephalus by using neuroradiological tools.

An immunohistochemical study of lymphatic elements in the human brain

Almost 150 papers about brain lymphatics have been published in the last 150 years. Recently, the information in these papers has been synthesized into a picture of central nervous system (CNS) "glymphatics," but the fine structure of lymphatic elements in the human brain based on imaging specific markers of lymphatic endothelium has not been described. We used LYVE1 and PDPN antibodies to visualize lymphatic marker-positive cells (LMPCs) in postmortem human brain samples, meninges, cavernous sinus (cavum trigeminale), and cranial nerves and bolstered our findings with a VEGFR3 antibody. LMPCs were present in the perivascular space, the walls of small and large arteries and veins, the media of large vessels along smooth muscle cell membranes, and the vascular adventitia. Lymphatic marker staining was detected in the pia mater, in the arachnoid, in venous sinuses, and among the layers of the dura mater. There were many LMPCs in the perineurium and endoneurium of cranial nerves. Soluble waste may move from the brain parenchyma via perivascular and paravascular routes to the closest subarachnoid space and then travel along the dura mater and/or cranial nerves. Particulate waste products travel along the laminae of the dura mater toward the jugular fossa, lamina cribrosa, and perineurium of the cranial nerves to enter the cervical lymphatics. CD3-positive T cells appear to be in close proximity to LMPCs in perivascular/perineural spaces throughout the brain. Both immunostaining and qPCR confirmed the presence of adhesion molecules in the CNS known to be involved in T cell migration.

How does the brain remove its waste metabolites from within?

The brain is the command center of the body that regulates the vital functions of circulation, respiration, motor function, metabolic activities, or autonomic nervous system outcomes. The brain coordinates these continuous activities at the expense of huge energy utilization. This energy demand is achieved by active transport of nutrients across the endothelial blood-brain barrier (BBB). This review discusses the barrier interfaces in the CNS that include the BBB, blood-spinal cord barrier, the epithelial choroid plexus, and the epithelial arachnoid. While transporting of nutrients across the BBB is a normal physiological function, the trafficking of xenobiotics and inflammatory cells/agents across these interfaces is harmful to brain cells. This leads to production of waste metabolites in the brain. Clearance of these waste metabolites maintains the normal brain homeostasis, while aggregation is detrimental to neurological complications. Since the CNS lacks lymphatic system, the CSF serves as the clearance path for water-soluble peptides/solutes, but not large size waste metabolites like Aβ protein. In particular, this review will focus on the mechanisms of waste metabolites clearance paths in the CNS. This will include the recently discovered waste metabolites movement from interstitial space (IS) directly into perivascular clearance (PVC), or via IS-CSF-PVC, and its exchange from PVC to circulation. Concluding remarks will discuss the therapeutic approach to improve the clearance mechanisms for ameliorating neurological diseases.

The involvement of perivascular spaces or tissues in the facial intradermal brain-targeted delivery

Our previous work indicates the lymphatic network and perivascular spaces or tissues might be involved in the facial intradermal brain-targeted delivery of Evans blue (EB). In this article, we presented the detailed involvement of both, and the linkage between lymphatic network and perivascular spaces or tissues. The in-vivo imaging, the trigeminal transection and immunohistochemistry were used. In-vivo imaging indicated intradermal injection in the mystacial pad (i.d.) delivered EB into the brain at 2-, 6- and 24 h, while intranasal injection (i.n.) delivered EB into the rostral head and intravenous injection (i.v.) diffused EB weakly into the brain. Trigeminal perineurial and epineurial EB occurred along the perivascular spaces or tissues and along brain vessels. EB diffused into the lymphatic vessels and submandibular lymph nodes. Moreover, perineurial and epineurial EB co-located or overlaid with Lyve1 immuno-reactivity and VEGF antibody, and lymphatic network connected with perivascular spaces or tissues, suggesting lymphatic system-perivascular spaces might involve in the EB delivery with i.d. The trigeminal transection reduced the trigeminal epineurial and perineurial EB and brain EB along vessels. EB diffused in the fasciculus and the perineurium, blood and lymphatic vessels in the mystacial pad, mystacial EB overlaid VEGF or Lyve1 antibody. In summary, the dermal-trigeminal-brain perivascular spaces or tissues and the linkage to the lymphatic network mediated the intradermal brain-targeted delivery.

Extracranial outflow of particles solved in cerebrospinal fluid: Fluorescein injection study

Cerebrospinal fluid is thought to be mainly absorbed into arachnoid granules in the subarachnoid space and drained into the sagittal sinus. However, some observations such as late outbreak of arachnoid granules in fetus brain and recent cerebrospinal fluid movements study by magnetic resonance images, conflict with this hypothesis. In this study, we investigated the movement of cerebrospinal fluid in fetuses. Several kinds of fluorescent probes with different molecular weights were injected into the lateral ventricle or subarachnoid space in mouse fetuses at a gestational age of 13 days. The movements of the probes were monitored by live imaging under fluorescent microscope. Following intraventricular injection, the probes dispersed into the 3rd ventricle and aqueduct immediately, but did not move into the 4th ventricle and spinal canal. After injection of low and high molecular weight conjugated probes, both probes dispersed into the brain but only the low molecular weight probe dispersed into the whole body. Following intra-subarachnoid injection, both probes diffused into the spinal canal gradually. Neither probe dispersed into the brain and body. The probe injected into the lateral ventricle moved into the spinal central canal by the fetus head compression, and returned into the aqueduct by its release. We conclude this study as follows: (i) The movement of metabolites in cerebrospinal fluid in the ventricles will be restricted by molecular weight; (ii) Cerebrospinal fluid in the ventricle and in the subarachnoid space move differently; and (iii) Cerebrospinal fluid may not appear to circulate. In the event of high intracranial pressure, the fluid may move into the spinal canal.

Visualization of cerebrospinal fluid-filled spaces in the cavernous sinus using magnetic resonance imaging

The cavernous sinus (CS) has been extensively studied and is commonly acknowledged as a dural venous sinus. There have been no reports documenting cerebrospinal fluid (CSF)-filled spaces in the CS. Here, we explore such structures in the CS using magnetic resonance imaging (MRI). A total of 183 patients underwent T2-weighted or constructive interference steady-state (CISS) sequence MRI. Imaging data from coronal sections were analyzed. Of the 183 patients, 26.8% had CSF-filled spaces in the CS. These spaces appeared to communicate with the suprasellar cistern through dural defects found in the superior wall of the CS, and also appeared to surround the cavernous portion of the internal carotid artery (ICc) and pituitary gland, and further be adjacent to the oculomotor and trigeminal cisterns. Dural defects were identified in 81.6% of patients, with CSF-filled spaces adjacent to the oculomotor and trigeminal cisterns found in 81.6% and 12.2% of patients, respectively. The distribution of these spaces could be classified into four types based on their topographical relationships with the ICc, namely the circumferential, medial, lateral, and superior types. The circumferential and medial types were the most frequently found and comprised >80% on both sides. The CS may involve CSF-filled spaces in physiological conditions that are formed through dural defects in the superior wall and adjacent cranial nerve cisterns. These findings are critical when considering approaches to the CS, modes of lateral extension of pituitary tumors, and CSF dynamics in the CS.

How Do Meningeal Lymphatic Vessels Drain the CNS?

The many interactions between the nervous and the immune systems, which are active in both physiological and pathological states, have recently become more clearly delineated with the discovery of a meningeal lymphatic system capable of carrying fluid, immune cells, and macromolecules from the central nervous system (CNS) to the draining deep cervical lymph nodes. However, the exact localization of the meningeal lymphatic vasculature and the path of drainage from the cerebrospinal fluid (CSF) to the lymphatics remain poorly understood. Here, we discuss the potential differences between peripheral and CNS lymphatic vessels and examine the purported mechanisms of CNS lymphatic drainage, along with how these may fit into established patterns of CSF flow.

Imaging the Perivascular Space as a Potential Biomarker of Neurovascular and Neurodegenerative Diseases

Although the brain lacks conventional lymphatic vessels found in peripheral tissue, evidence suggests that the space surrounding the vasculature serves a similar role in the clearance of fluid and metabolic waste from the brain. With aging, neurodegeneration, and cerebrovascular disease, these microscopic perivascular spaces can become enlarged, allowing for visualization and quantification on structural MRI. The purpose of this review is to: (i) describe some of the recent pre-clinical findings from basic science that shed light on the potential neurophysiological mechanisms driving glymphatic and perivascular waste clearance, (ii) review some of the pathobiological etiologies that may lead to MRI-visible enlarged perivascular spaces (ePVS), (iii) describe the possible clinical implications of ePVS, (iv) evaluate existing qualitative and quantitative techniques used for measuring ePVS burden, and (v) propose future avenues of research that may improve our understanding of this potential clinical neuroimaging biomarker for fluid and metabolic waste clearance dysfunction in neurodegenerative and neurovascular diseases.

MR assessment of pediatric hydrocephalus: a road map

PURPOSE

This study was conducted to design a rational approach to the MR diagnosis of hydrocephalus based on a pathophysiologic reevaluation of its possible mechanisms and to apply it to the different etiological contexts.

METHOD

A review of the literature reports describing new physiologic models of production and absorption and of the hydrodynamics of the CSF was made.

RESULTS

Besides the secretion of CSF by the choroid plexuses, and its passive, pressure-dependent transdural absorption (arachnoid villi, dural clefts, cranial, and spinal nerve sheaths), water transporters, aquaporins, allow water (if not ions and organic molecules) to exchange freely between the brain parenchyma and the CSF spaces across the ependymal and the pial interfaces (including the Virchow-Robin spaces). Consequently, the CSF bulk flow is not necessarily global, and situations of balanced absorption-secretion may occur separately in different CSF compartments such as the ventricular, intracranial, or intraspinal CSF spaces. This means that rather than from a hypothetical pressure gradient from the plexuses to the dural sinuses, the dynamics of the CSF depend on the force provided in those different compartments by the arterial systolic pulsation of the pericerebral (mostly), intracerebral, and intraventricular (choroid plexuses) vascular beds.

CONCLUSION

Using MR imaging, diverse varieties of hydrocephalus may tentatively be explained by applying those concepts to the correspondingly diverse causal diseases. Hopefully, this may have an impact on the choice of the treatment strategies also.

Intranasal administration of oxytocin: behavioral and clinical effects, a review

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The mechanisms behind the effects of IN-applied substances need more attention.

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The mechanisms involved in the brain-distribution of IN-OT are completely unexplored.

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The possibly cascading effects of IN-OT on the intrinsic OT-system require serious investigation.

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IN-OT induces clear and specific changes in neural activation.

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IN-OT is a promising approach to treat certain clinical symptoms.

The intranasal (IN-) administration of substances is attracting attention from scientists as well as pharmaceutical companies. The effects are surprisingly fast and specific. The present review explores our current knowledge about the routes of access to the cranial cavity. ‘Direct-access-pathways’ from the nasal cavity have been described but many additional experiments are needed to answer a variety of open questions regarding anatomy and physiology.

Among the IN-applied substances oxytocin (OT) has an extensive history. Originally applied in women for its physiological effects related to lactation and parturition, over the last decade most studies focused on their behavioral ‘prosocial’ effects: from social relations and ‘trust’ to treatment of ‘autism’.

Only very recently in a microdialysis study in rats and mice, the ‘direct-nose-brain-pathways’ of IN-OT have been investigated directly, implying that we are strongly dependent on results obtained from other IN-applied substances. Especially the possibility that IN-OT activates the ‘intrinsic’ OT-system in the hypothalamus as well needs further clarification.

We conclude that IN-OT administration may be a promising approach to influence human communication but that the existing lack of information about the neural and physiological mechanisms involved is a serious problem for the proper understanding and interpretation of the observed effects.

Treatment of patients with traumatic subdural effusion and concomitant hydrocephalus

Object

Traumatic subdural effusion (TSE) is a common sequela of traumatic brain injury. Surgical intervention is suggested only when TSE exerts mass effect. The authors have found that many patients with TSE exerting mass effect have concomitant hydrocephalus. Patient experiencing this occurrence were studied, and the pathogenesis of this phenomenon was discussed in the context of recent advances in the understanding of CSF circulation.

Methods

During a 2-year period, the authors' institution treated 14 patients with TSE who developed hydrocephalus, after 1 of the patients suffered subdural drainage and other 13 received subdural peritoneal shunt (SPSs). Thirteen of those who had SPSs received programmable ventriculoperitoneal shunts (VPSs) for the hydrocephalus. The clinical characteristics as well as the imaging and operative findings of these patients were reviewed.

Results

All patients with symptomatic TSE exerting mass effect received SPSs. All of these patients had a modified Frontal Horn Index of more than 0.33 at presentation, and high opening pressure on durotomy. Following a brief period (4–7 days) of clinical improvement, the condition of all patients deteriorated due to hydrocephalus. Programmable VPSs were inserted with the initial pressure set at approximately 8–10 cm H2O according to opening pressure at ventriculostomy. Shunt valve pressure was gradually decreased to 5–7 cm H2O, according to clinical and radiological follow-up.

Conclusions

Elevated modified Frontal Horn Index in patients with TSE is suggestive of concomitant hydrocephalus. The authors propose that tearing of the dura-arachnoid plane following trauma contributes to TSE and may also impede CSF circulation, causing hydrocephalus. Shunt pressure was adjusted to relative low pressure, indicating the old age of the patients and poor reexpansion of brain parenchyma after the mass effect. Subdural peritoneal shunts and VPSs are indicated in those patients with TSE exerting mass effect with concomitant hydrocephalus.

Direct venous spinal reabsorption of cerebrospinal fluid: a new concept with serial magnetic resonance cisternography in rabbits

OBJECT

For nearly 100 years it has been believed that the main reabsorption of CSF occurs in arachnoid projections into the superior sagittal sinus, but a significant number of experiments and cases conflict with this hypothesis. According to recently published studies, CSF is permanently produced and absorbed in the whole CSF system. Clusters of arachnoidal villi, which are speculated to have a role in the reabsorption of CSF, have recently been revealed in the dorsal root of the spinal nerves. Huge absorptive surface areas of microvessels have been suggested to serve a putative role in reabsorption. The authors' aim was to observe direct venous connections between the subarachnoid space and the perispinal veins.

METHODS

Eleven adult (6 months old) New Zealand white male rabbits weighing approximately 3.0 kg each were used in this experiment. After obtaining precontrast MR cisternography images, subarachnoid access was gained percutaneously via a cisternal approach by using a 20-gauge intravenous indwelling cannula. One rabbit died as a result of brainstem trauma during percutaneous cannulation before contrast administration, but contrast agent was still injected to see the possible MR imaging results of spinal CSF reabsorption after death. Magnetic resonance imaging was performed at 15, 60, 120, and 180 minutes after the administration of contrast agent. After intramuscular injections of anesthetic, 2 rabbits died 120 and 150 minutes after contrast injection, but the MR imaging study at 180 minutes after contrast injection was still performed.

RESULTS

Direct connections between the subarachnoid space and the perispinal veins were observed in all rabbits during serial MR cisternography. The enhancement power was not affected by the amount of injected contrast agent or by cervical or lumbar penetration but was increased at higher contrast concentrations or upon seizure (physical activity).

CONCLUSIONS

Extracranial reabsorption of CSF has been finally proved with direct radiological confirmation of spinal venous reabsorption of CSF using serial MR cisternography. The authors believe that this study can help to develop a more accurate model of CSF dynamics, which will allow understanding of many CSF-related diseases, as well as the development of new strategies for treatment.

Analysis of dural sac thickness in human spine-cadaver study with confocal infrared laser microscope

BACKGROUND CONTEXT

The thickness of the human spine dural sac can show differences between individuals and levels, and these differences can alter clinical outcomes.

PURPOSE

To analyze spinal cord dural sac thicknesses.

STUDY DESIGN

Anatomical study of human cadavers.

METHODS

The subjects of this study were 19 human cadavers with no prior history of spinal surgery or deformity. Seventeen specimens from T1/T2 to L5/S1 were obtained from each of 19 cadavers, a total of 323 specimens. Multiple sections were prepared from these specimens. Microscopic measurements were taken with an infrared laser-based confocal microscope to determine the mean dural sac thickness at each level. In addition, a magnetic resonance image of the lumbar spine was obtained from each subject. Relations between dural sac thicknesses at different levels were analyzed with respect to gender, age, and stenosis level.

RESULTS

Overall mean dural sac thickness was 0.307±0.122 mm in this human cadaver series. Dura thicknesses differed significantly at different levels (p=.046). Overall, dural thickness was highest at T9/T10 and lowest at L2/L3 (p=.0007) as well as highest at the lower thoracic level followed by the upper thoracic and lumbar levels (p=.003). In addition, dural sac thickness was found to increase slightly but significantly with age (p=.019). However, dural thickness was similar between men and women (p=.123). And, no significant dural thickness differences were found for stenotic and nonstenotic lesions (p=.885).

CONCLUSION

Dural sac thickness was found to be significantly dependent on spinal level and age in human cadavers. An appreciation of dural sac thickness differences can be useful in the clinical field, and it is hoped that this encourages further study of dural physiology.

The "Shaken Baby" syndrome: pathology and mechanisms

The "Shaken Baby" syndrome (SBS) is the subject of intense controversy; the diagnosis has in the past depended on the triad of subdural haemorrhage (SDH), retinal haemorrhage and encephalopathy. While there is no doubt that infants do suffer abusive injury at the hands of their carers and that impact can cause catastrophic intracranial damage, research has repeatedly undermined the hypothesis that shaking per se can cause this triad. The term non-accidental head injury has therefore been widely adopted. This review will focus on the pathology and mechanisms of the three physiologically associated findings which constitute the "triad" and are seen in infants suffering from a wide range of non-traumatic as well as traumatic conditions. "Sub" dural bleeding in fact originates within the deep layers of the dura. The potential sources of SDH include: the bridging veins, small vessels within the dura itself, a granulating haemorrhagic membrane and ruptured intracranial aneurysm. Most neuropathologists do not routinely examine eyes, but the significance of this second arm of the triad in the diagnosis of Shaken Baby syndrome is such that it merits consideration in the context of this review. While retinal haemorrhage can be seen clinically, dural and subarachnoid optic nerve sheath haemorrhage is usually seen exclusively by the pathologist and only rarely described by the neuroradiologist. The term encephalopathy is used loosely in the context of SBS. It may encompass anything from vomiting, irritability, feeding difficulties or floppiness to seizures, apnoea and fulminant brain swelling. The spectrum of brain pathology associated with retinal and subdural bleeding from a variety of causes is described. The most important cerebral pathology is swelling and hypoxic-ischaemic injury. Mechanical shearing injury is rare and contusions, the hallmark of adult traumatic brain damage, are vanishingly rare in infants under 1 year of age. Clefts and haemorrhages in the immediate subcortical white matter have been assumed to be due to trauma but factors specific to this age group offer other explanations. Finally, examples of the most common causes of the triad encountered in clinical diagnostic and forensic practice are briefly annotated.

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

The cerebrospinal fluid (CSF) system provides nutrients to and removes waste products from the brain. Recent findings suggest, however, that in addition, the CSF contains message molecules in the form of actively released neuroactive substances. The concentrations of these vary between locations, suggesting they are important for the changes in brain activity that underlie different brain states, and induce different sensory input and behavioral output relationships.The cranial CSF displays a rapid caudally-directed ventricular flow followed by a slower rostrally-directed subarachnoid flow (mainly towards the cribriform plate and from there into the nasal lymphatics). Thus, many brain areas are exposed to and can be influenced by substances contained in the CSF. In this review we discuss the production and flow of the CSF, including the mechanisms involved in the regulation of its composition. In addition, the available evidence for the release of neuropeptides and other neuroactive substances into the CSF is reviewed, with particular attention to the selective effects of these on distant downstream receptive brain areas. As a conclusion we suggest that (1) the flowing CSF is involved in more than just nutrient and waste control, but is also used as a broadcasting system consisting of coordinated messages to a variety of nearby and distant brain areas; (2) this special form of volume transmission underlies changes in behavioral states.

Cine phase-contrast MR images failed to predict clinical outcome following ETV

BACKGROUND

To predict success of endoscopic third ventriculostomy (ETV) in patients with obstructive hydrocephalus, we evaluated pre- and post- operative phase-contrast cine magnetic resonance images (PC MRI) on cerebrospinal fluid (CSF), cine flow in basal cisterns around the brain stem, and cervical medullar junction (CMJ) retrospectively.

METHODS

The study involved 102 patients with mean age of 36.74+/-23.25, and F/M = 1.55. All patients had PC MRI taken both pre- and post-operatively. A dynamic MRI video of PC MRI was reviewed at sagittal, axial, and coronal sections to determine cistern flows around the brain stem and CMJ. For quantitative analysis, quadrants were divided around midbrain axially to evaluate interpeduncular, quadrageminal, and ambient cisterns of both sides using scores of 0 to 60. Pre- and post- pontine and CMJ flows were shown in sagittal view and scored 0 to 20, and lateral cerebellopontine cisterns of both sides were measured on coronal image and scored 0 to 20.

RESULTS

No significant difference in CSF flow was seen from three individual views and total cine score, or between ETV success and failure groups by multivariate analysis of variance. Kaplan-Meier Analysis and Spearman's Correlation Test produced no relationship between MRI cine flow scores and interval period after surgery to ETV failure.

CONCLUSION

PC MRI cine flow failed to demonstrate significant differences between successful and failed ETV groups. This indicates in addition to achieving an adequate fenestration, CSF pathways beyond the basal cisterns around the brain stem and CMJ may play an essential role in achieving ETV success.

Demonstration of fluid channels in human dura and their relationship to age and intradural bleeding

PURPOSE

This paper aims to make a systematic study of human dura to establish the presence of fluid transport channels and their relationship to age.

METHODS

Samples of parasagittal dura from autopsy cases from mid-gestation to the ninth decade were examined by light microscopy.

RESULTS

We have demonstrated the presence of unlined rounded spaces, uncommon in the fetus and neonate but increasingly evident after 30 weeks of postnatal life. We have shown that intradural bleeding is inversely correlated with the presence of these channels and with age.

CONCLUSIONS

We suggest that dural maturation, involving the development of arachnoid granulations, may be related to dilatation of intradural fluid channels, allowing them to be identified histologically. The risk of reflux of blood into the dura appears to reduce with age.

Anatomy and development of the meninges: implications for subdural collections and CSF circulation

The dura is traditionally viewed as a supportive fibrous covering of the brain containing the dural venous sinuses but otherwise devoid of vessels and lacking any specific function. However, review of the embryology and anatomy reveals the dura to be a complex, vascularized and innervated structure, not a simple fibrous covering. The dura contains an inner vascular plexus that is larger in the infant than in the adult, and this plexus likely plays a role in CSF absorption. This role could be particularly important in the infant whose arachnoid granulations are not completely developed. Although subdural hemorrhage is frequently traumatic, there are nontraumatic conditions associated with subdural hemorrhage, and the inner dural plexus is a likely source of bleeding in these nontraumatic circumstances. This review outlines the development and age-specific vascularity of the dura and offers an alternative perspective on the role of the dura in homeostasis of the central nervous system.

Topographic study on nerve-associated lymphatic vessels in the murine craniofacial region by immunohistochemistry and electron microscopy

The distribution and fine structure of lymphatic vessels associated with nerves was studied by immunohistochemistry in the murine craniofacial region. The tissue sections and blocks were immunostained for LYVE-1, protein gene product 9.5, CD34 and aquaporin-1 to demonstrate the lymphatic vessels, nerves, blood vessels and water channel protein, respectively. Transmission electron microscopic examination was also performed to investigate the relationship between the lymphatics and nerves. In the nasal area, the lymphatics were found in dura mater on the cribriform plate and beneath the nasal mucosa, this supposedly supplying the cerebrospinal fluid drainage route along the olfactory nerves. The proximal portions of the cranial nerves were equipped with the lymphatics in the epineurium. In the distal portions of the nerves, the lymphatics were distributed in close proximity of the perineural sheath, and thus might contribute to maintenance of microenvironment suitable for the nerves by an absorptive activity of the lymphatic endothelial cells. The present findings suggest that the lymphatic system associated with the cranial nerves provides the pathway for transport of cerebrospinal fluid, tissue fluid, and free cells involved in immune response and tumor metastasis in the craniofacial region.