Phase offset between arterial pulsations and subarachnoid space pressure fluctuations are unlikely to drive periarterial cerebrospinal fluid flow.

Circulation of fluid through the central nervous system maintains fluid homeostasis and is involved in solute clearance. The glymphatic system is hypothesised to facilitate waste clearance in the brain, with inflow via periarterial spaces, bulk flow through the parenchyma, and outflow via perivenous spaces. The driving force for this mechanism is unknown. Previous modelling in the spinal cord suggests that timing offsets between arterial and subarachnoid space pressure pulses can enable net inflow in perivascular spaces (PVS). This study adapted the spinal pulse offset mechanism to the brain and simulated movement of tracer particles used in experiments. Both bulk flow and diffusive movement of tracer were simulated. Intracranial pressure pulses were applied to one end of a 300-µm-long perivascular space combined with a moving arterial wall simulating arterial pulsations. The simulations indicate the pulse offset mechanism can enable net inflow via PVS; however, it is unknown whether the temporal offset required is physiologically realistic. Increasing the positive component of the ICP (intracranial pressure) pulse increased net flow. Tracer particles driven by bulk flow reached the outlet of the PVS with a net speed of ~ 16 µm/s when the permeability was two orders of magnitude higher than values in the literature. These particles were unable to penetrate into the parenchyma in the absence of diffusion. Dispersion dominated tracer movement in the parenchyma. Further research is required to reconcile discrepancies between these results, and both experimental and computational studies.

Higher Concentration of Taenia Antigens in the CSF is Related to Slight Ventricle Enlargement and Periventricular Neuronal Decrease in Young Rats

Purpose Experimental models might help understand the pathophysiology of neurocysticercosis-associated hydrocephalus. The present study aimed to compare the extent of hydrocephalus and tissue damage in rats with subarachnoid inoculation of different concentrations of Taenia crassiceps cyst proteins. Methods Sixty young rats were divided into two groups: low- and high-concentration groups. The animals in the low concentration group received 0.02ml of 2.4mg/ml T. crassiceps cyst proteins while those in the high concentration group received 0.02 ml of 11.6mg/ml T. crassiceps cyst proteins. The animals underwent magnetic resonance imaging at 1, 3, and 6 months postinoculation to assess the ventricle volume. Morphological assessment was performed at the end of the observation period. Results Repeated measures of ventricle volumes at 1, 3, and 6 months showed progressive enlargement of the ventricles. At 1 and 3 months, we observed no differences in ventricle volumes between the 2 groups. However, at 6 months, the ventricles were larger in the high concentration group (median » 3.86mm3, range: 2.37­12.68) compared with the low concentration group (median » 2.00mm3, range: 0.37­11.57), p » 0.003. The morphological assessment revealed a few inflammatory features in both groups. However, the density of oligodendrocytes and neurons within the periventricular region was lower in the high concentration group (5.18 versus 9.72 for oligodendrocytes and 15.69 versus 21.00 for neurons; p < 0.001 for both). Conclusion Our results suggest that, in rats, a higher concentration of T. crassiceps cyst proteins in the subarachnoid space could induce ventricle enlargement and reduce the number of neurons within the periventricular area.

High-resolution Micro-CT Myelography to Assess Spinal Subarachnoid Space Changes After Spinal Cord Injury in Rats.

BACKGROUND AND PURPOSE: The spinal subarachnoid space (SSAS) is vital for neurologic function. Although SSAS alterations are known to occur after spinal cord injury (SCI), there is a lack of high-resolution imaging studies of the SSAS after SCI in rodents. Therefore, the aim here was to assess changes in the SSAS of rats subjected to graded SCI, using high-resolution micro-CT myelography. METHODS: Long-Evans adult rats were subjected to mild or severe spinal cord contusion at T9. Imaging studies of SSAS features were carried out in injured rats at acute (day 1) and subacute (day 15) stages postinjury, as well as in control rats, using high-resolution micro-CT myelography with a contrast-enhanced digital subtraction protocol. We studied a total of 33 rats randomly allocated into five experimental groups. Micro-CT myelograms were assessed by expert observers using both qualitative and quantitative criteria. RESULTS: Qualitative and quantitative analyses showed that SCI induces changes in the SSAS that vary as a function of both injury severity and time elapsed after injury. SSAS blockage was the main alteration detected. Moreover, the method used here allowed fine details to be observed in small animals, such as variations in the preferential pathways for contrast medium flow, neuroimaging nerve root enhancement, and leakage of contrast medium due to tearing of the dural sac. CONCLUSION: Micro-CT myelography provides high-resolution images of changes in the SSAS after SCI in rats and is a useful tool for further experimental studies involving rat SCI in vivo.

Repeated subarachnoid administrations of allogeneic human umbilical cord mesenchymal stem cells for spinal cord injury: a phase 1/2 pilot study.

BACKGROUND AIMS: Stem cell transplantation is a potential treatment for intractable spinal cord injury (SCI), and allogeneic human umbilical cord mesenchymal stem cells (hUC-MSCs) are a promising candidate because of the advantages of immune privilege, paracrine effect, immunomodulatory function, convenient collection procedure and little ethical concern, and there is an urgent need to develop a safe and effective protocol regarding their clinical application. METHODS: A prospective, single-center, single-arm study in which subjects received four subarachnoid transplantations of hUC-MSCs (1 × 106 cells/kg) monthly and were seen in follow-up four times (1, 3, 6 and 12 months after final administration) was conducted. At each scheduled time point, safety and efficacy indicators were collected and analyzed accordingly. Adverse events (AEs) were used as a safety indicator. American Spinal Injury Association (ASIA) and SCI Functional Rating Scale of the International Association of Neurorestoratology (IANR-SCIFRS) total scores at the fourth follow-up were determined as primary efficacy outcomes, whereas these two indicators at the remaining time points as well as scores of pinprick, light touch, motor and sphincter, muscle spasticity and spasm, autonomic system, bladder and bowel functions, residual urine volume (RUV) and magnetic resonance imaging (MRI) were secondary efficacy outcomes. Subgroup analysis of primary efficacy indicators was also performed. RESULTS: Safety and efficacy assessments were performed on 102 and 41 subjects, respectively. Mild AEs involving fever (14.1%), headache (4.2%), transient increase in muscle tension (1.6%) and dizziness (1.3%) were observed following hUC-MSC transplantation and resolved thoroughly after conservative treatments. There was no serious AE. ASIA and IANR-SCIFRS total scores revealed statistical increases when compared with the baselines at different time points during the study, mainly reflected in the improvement of pinprick, light touch, motor and sphincter scores. Moreover, subjects showed a continuous and remarkable decrease in muscle spasticity. Regarding muscle spasm, autonomic system, bladder and bowel functions, RUV and MRI, data/imaging at final follow-up showed significant improvements compared with those at first collection. Subgroup analysis found that hUC-MSC transplantation improved neurological functions regardless of injury characteristics, including level, severity and chronicity. CONCLUSIONS: The authors' present protocol demonstrates that intrathecal administration of' allogeneic hUC-MSCs at a dose of 106 cells/kg once a month for 4 months is safe and effective and leads to significant improvement in neurological dysfunction and recovery of quality of life.

Is stagnant cerebrospinal fluid involved in the pathophysiology of normal tension glaucoma.

Current concepts of the pathophysiology of normal tension glaucoma (NTG) include intraocular pressure, vascular dysregulation and the concept of a translaminar pressure gradient. Studies on NTG performed with cisternography demonstrated an impaired cerebrospinal fluid (CSF) dynamics in the subarachnoid space of the optic nerve sheath, most pronounced behind the lamina cribrosa. Stagnant CSF might be another risk factor for NTG.

Subarachnoid extension of lobar hemorrhage on acute/subacute MRI is associated with cerebral amyloid angiopathy criteria.

Subarachnoid hemorrhage extension (SAHE) in the acute phase of cerebral amyloid angiopathy (CAA)-related lobar hemorrhage (LH) assessed by CT is very frequent. Recently, SAHE, together with finger-like projections on CT and ApoE4, has been used in a prediction model for histopathologically proven CAA showing excellent discrimination. Our aim was to analyze SAHE on MRI in the acute and subacute phase of LH in patients with and without associated hemorrhagic features supportive of CAA (i.e. chronic LH, cortical superficial siderosis [CSS], and strictly lobar cerebral microbleeds [CMB]). We retrospectively studied SAHE on MRI performed in the acute and subacute phase (within 21 days) in a cohort of consecutive patients with acute LH recruited between January 2012 and April 2018. Sixty-eight acute LH patients (35 men and 33 women, mean age 74 [range 50-89]) were analyzed. Mean delay between symptom onset and MRI was 3.8 days, and 32 patients underwent MRI within 24 h. Based on MRI, 51 patients were classified as probable CAA and 17 patients without probable CAA. Both groups were comparable regarding age, sex, time of MRI performance, MRI field strength, and acute LH volume. Overall, SAHE was observed in 46 (68%) patients, including 39 (76%) patients with probable CAA and 7 (41%) patients without probable CAA (p = 0.015). SAHE presence was also associated with larger LH volumes. During the work-up in the acute/subacute phase of patients with acute LH, in addition to T2*-weighted imaging in search for other hemorrhagic features (chronic LH, CSS, or lobar CMB) evoking probable underlying CAA etiology, search for SAHE on adapted MRI sequences (FLAIR and T2*-weighted imaging) seems to be interesting because of the association with the presence of probable CAA criteria.

Longitudinal morphological changes during recovery from brain deformation due to idiopathic normal pressure hydrocephalus after ventriculoperitoneal shunt surgery.

The present study aimed to examine time-dependent change in cerebrospinal fluid distribution and various radiological indices for evaluating shunt effectiveness in patients with idiopathic normal pressure hydrocephalus (iNPH). This study included 54 patients with iNPH who underwent MRI before and after ventriculoperitoneal shunt surgery. The volume of the total ventricles and subarachnoid spaces decreased within 1 month after shunting. However, more than 1 year after shunting, the volume of the total ventricles decreased, whereas that of the total subarachnoid spaces increased. Although cerebrospinal fluid distribution changed considerably throughout the follow-up period, the brain parenchyma expanded only 2% from the baseline brain volume within 1 month after shunting and remained unchanged thereafter. The volume of the convexity subarachnoid space markedly increased. The changing rate of convexity subarachnoid space per ventricle ratio (CVR) was greater than that of any two-dimensional index. The brain per ventricle ratio (BVR), callosal angle and z-Evans index continued gradually changing, whereas Evans index did not change throughout the follow-up period. Both decreased ventricular volume and increased convexity subarachnoid space volume were important for evaluating shunt effectiveness. Therefore, we recommend CVR and BVR as useful indices for the diagnosis and evaluation of treatment response in patients with iNPH.

Identifying the Critical Factors Governing Translaminar Pressure Differential Through a Compartmental Model.

Purpose: The effective management of glaucoma is hindered by an incomplete understanding of its pathologic mechanism. While important, intraocular pressure (IOP) alone is inadequate in explaining glaucoma. Non-IOP-mediated risk factors such as cerebrospinal fluid (CSF) pressure have been reported to contribute to glaucomatous optic neuropathy. Due to the difficulty associated with experimental measurement of the salient variables, such as the retrobulbar CSF pressure, porosity of the subarachnoid space (SAS), and especially those concerned with the perioptic SAS, there remains a limited understanding of the CSF behavior contributing to the translaminar pressure gradient (TLPG), hypothesized to be a critical factor in the development of glaucoma. Method: An integrated compartmental model describing the intracranial and orbital CSF dynamics, coupled with intraocular dynamics, is developed based on first principles of fluid mechanics. A sensitivity analysis is performed to identify anatomic characteristics that significantly affect the retrobulbar subarachnoid space (RSAS) pressure and, consequently, the TLPG. Results: Of the 28 parameters considered, the RSAS pressure is most sensitive to CSF flow resistance in the optic nerve SAS and the potential lymphatic outflow from the optic nerve SAS into the orbital space. A parametric study demonstrates that a combination of resistance in the range of 1.600 × 1012 - 1.930 × 1012 Pa s/m3 (200.0 - 241.3 mm Hg min/mL) with 5% to 10% lymphatic CSF outflow yields RSAS pressures that are consistent with the limited number of studies in the literature. Conclusions: The results suggest that a small percentage of lymphatic CSF outflow through the optic nerve SAS is likely. In addition, flow resistance in the orbital CSF space, hypothesized to be a function of patient-specific optic nerve SAS architecture and optic canal geometry, is a critical parameter in regulating the RSAS pressure and TLPG.

Effect of extradural constriction on CSF flow in rat spinal cord.

BACKGROUND: Fluid homeostasis in the central nervous system (CNS) is essential for normal neurological function. Cerebrospinal fluid (CSF) in the subarachnoid space and interstitial fluid circulation in the CNS parenchyma clears metabolites and neurotransmitters and removes pathogens and excess proteins. A thorough understanding of the normal physiology is required in order to understand CNS fluid disorders, including post-traumatic syringomyelia. The aim of this project was to compare fluid transport, using quantitative imaging of tracers, in the spinal cord from animals with normal and obstructed spinal subarachnoid spaces. METHODS: A modified extradural constriction model was used to obstruct CSF flow in the subarachnoid space at the cervicothoracic junction (C7-T1) in Sprague-Dawley rats. Alexa-Fluor 647 Ovalbumin conjugate was injected into the cisterna magna at either 1 or 6 weeks post-surgery. Macroscopic and microscopic fluorescent imaging were performed in animals sacrificed at 10 or 20 min post-injection. Tracer fluorescence intensity was compared at cervical and thoracic spinal cord levels between control and constriction animals at each post-surgery and post-injection time point. The distribution of tracer around arterioles, venules and capillaries was also compared. RESULTS: Macroscopically, the fluorescence intensity of CSF tracer was significantly greater in spinal cords from animals with a constricted subarachnoid space compared to controls, except at 1 week post-surgery and 10 min post-injection. CSF tracer fluorescence intensity from microscopic images was significantly higher in the white matter of constriction animals 1 week post surgery and 10 min post-injection. At 6 weeks post-constriction surgery, fluorescence intensity in both gray and white matter was significantly increased in animals sacrificed 10 min post-injection. At 20 min post-injection this difference was significant only in the white matter and was less prominent. CSF tracer was found predominantly in the perivascular spaces of arterioles and venules, as well as the basement membrane of capillaries, highlighting the importance of perivascular pathways in the transport of fluid and solutes in the spinal cord. CONCLUSIONS: The presence of a subarachnoid space obstruction may lead to an increase in fluid flow within the spinal cord tissue, presenting as increased flow in the perivascular spaces of arterioles and venules, and the basement membranes of capillaries. Increased fluid retention in the spinal cord in the presence of an obstructed subarachnoid space may be a critical step in the development of post-traumatic syringomyelia.

Changing the Currently Held Concept of Cerebrospinal Fluid Dynamics Based on Shared Findings of Cerebrospinal Fluid Motion in the Cranial Cavity Using Various Types of Magnetic Resonance Imaging Techniques.

The "cerebrospinal fluid (CSF) circulation theory" of CSF flowing unidirectionally and circulating through the ventricles and subarachnoid space in a downward or upward fashion has been widely recognized. In this review, observations of CSF motion using different magnetic resonance imaging (MRI) techniques are described, findings that are shared among these techniques are extracted, and CSF motion, as we currently understand it based on the results from the quantitative analysis of CSF motion, is discussed, along with a discussion of slower water molecule motion in the perivascular, paravascular, and brain parenchyma. Today, a shared consensus regarding CSF motion is being formed, as follows: CSF motion is not a circulatory flow, but a combination of various directions of flow in the ventricles and subarachnoid space, and the acceleration of CSF motion differs depending on the CSF space. It is now necessary to revise the currently held concept that CSF flows unidirectionally. Currently, water molecule motion in the order of centimeters per second can be detected with various MRI techniques. Thus, we need new MRI techniques with high-velocity sensitivity, such as in the order of 10 µm/s, to determine water molecule movement in the vessel wall, paravascular space, and brain parenchyma. In this paper, the authors review the previous and current concepts of CSF motion in the central nervous system using various MRI techniques.

Automated detection of imaging features of disproportionately enlarged subarachnoid space hydrocephalus using machine learning methods.

OBJECTIVE: Create an automated classifier for imaging characteristics of disproportionately enlarged subarachnoid space hydrocephalus (DESH), a neuroimaging phenotype of idiopathic normal pressure hydrocephalus (iNPH). METHODS: 1597 patients from the Mayo Clinic Study of Aging (MCSA) were reviewed for imaging characteristics of DESH. One core feature of DESH, the presence of tightened sulci in the high-convexities (THC), was used as a surrogate for the presence of DESH as the expert clinician-defined criterion on which the classifier was trained. Anatomical MRI scans were automatically segmented for cerebrospinal fluid (CSF) and overlaid with an atlas of 123 named sulcal regions. The volume of CSF in each sulcal region was summed and normalized to total intracranial volume. Area under the receiver operating characteristic curve (AUROC) values were computed for each region individually, and these values determined feature selection for the machine learning model. Due to class imbalance in the data (72 selected scans out of 1597 total scans) adaptive synthetic sampling (a technique which generates synthetic examples based on the original data points) was used to balance the data. A support vector machine model was then trained on the regions selected. RESULTS: Using the automated classification model, we were able to classify scans for tightened sulci in the high convexities, as defined by the expert clinician, with an AUROC of about 0.99 (false negative ≈ 2%, false positive ≈ 5%). Ventricular volumes were among the classifier's most discriminative features but are not specific for DESH. The inclusion of regions outside the ventricles allowed specificity from atrophic neurodegenerative diseases that are also accompanied by ventricular enlargement. CONCLUSION: Automated detection of tight high convexity, a key imaging feature of DESH, is possible by using support vector machine models with selected sulcal CSF volumes as features.

Measurement and Associations of the Optic Nerve Subarachnoid Space in Normal Tension and Primary Open-Angle Glaucoma.

PURPOSE: To measure the area of the optic nerve subarachnoid space (ONSASA) in patients with normal tension glaucoma (NTG), primary open-angle glaucoma (POAG), and controls and examine its association with relevant ocular and systemic parameters. DESIGN: Cross-sectional study. METHODS: The study included 40 patients with NTG, 42 with POAG, and 45 healthy controls. B-scan ultrasound was performed binocularly, using a 12.5-MHz linear array probe. The measurement of the optic nerve subarachnoid space (ONSAS) and calculation of the ONSASA using ImageJ 1.51e analysis software was done by 2 experienced observers in a masked manner. RESULTS: The ONSASA between 3 and 7 mm behind the globe in NTG (5.15 ± 0.81 mm2) was significantly smaller than that in the POAG (6.24 ± 1.62 mm2, P = .0008) or control (6.40 ± 2.20 mm2; P = .0007) groups. ONSASA in the POAG and control groups were not significantly different (P = .13). ONSASA was significantly associated with mean IOP (P = .0004) and highest IOP (P = .0007). The optic nerve sheath diameter in NTG compared to POAG was significantly different at 3 mm (4.46 ± 0.43 mm vs 4.79 ± 0.40 mm, P = .0007), 5 mm (4.40 ± 0.39 mm vs 4.65 ± 0.47 mm, P = .003), and 7 mm (4.36 ± 0.35 mm vs 4.61 ± 0.30 mm, P = .004) behind the globe. CONCLUSIONS: The ONSASA is smaller in NTG as compared to normal control. This is compatible with a lower cerebrospinal fluid pressure in the optic nerve in NTG, implying that trans-lamina cribrosa pressure difference might be abnormally higher in the NTG group than in normal controls.

Flow dynamics of cerebrospinal fluid between the intracranial cavity and the subarachnoid space of the optic nerve measured with a diffusion magnetic resonance imaging sequence in patients with normal tension glaucoma.

IMPORTANCE: This study offers a new approach for the quantification of CSF dynamics. BACKGROUND: Non-invasive method to quantify the CSF dynamics in the subarachnoid space of the optic nerve is highly desirable. The aim of the study was to measure slow-flow CSF velocities in healthy controls and normal tension glaucoma patients between the intracranial cavity and the subarachnoid space of the optic nerve. DESIGN: Prospective observational study. PARTICIPANTS: Eleven age-matched healthy volunteers and 15 normal tension glaucoma patients. METHODS: Using phase contrast images, the phase shift in MRI diffusion images can be used to determine the flow velocity. Flow-range ratio between the intracranial cavity and the subarachnoid space of the optic nerve was calculated. MAIN OUTCOME MEASURE: Flow-range ratio between the intracranial cavity and the subarachnoid space of the optic nerve was calculated. RESULTS: First, phantom measurements were provided to validate the slow-flow velocity calculations. Second, flow-range ratio was validated for the healthy controls (0.63 ± 0.05), with the range being similar for the right and left optic nerve (P = 0.1). Statistically significant results were obtained (P < 0.05) when comparing the flow-range ratio in the optic nerve of healthy controls (n = 22 eyes, 0.63 ± 0.05) with the flow-range ratio in pathological optic nerves (n = 23, 0.55 ± 0.08) of normal tension glaucoma patients. MANOVA revealed no dependency between flow-range ratio and patient dependent variables. CONCLUSION AND RELEVANCE: Diffusion-weighted imaging provides a method to evaluate CSF flow within the subarachnoid space of the optic nerve in a non-invasive manner. Compared to healthy controls, patients with normal tension glaucoma measure a significantly lower flow-range ratio. This finding suggests a possible role of impaired CSF dynamics in the pathophysiology in normal tension glaucoma.

Parenchymal Pressure Inconsistency in Different Brain Areas After Kaolin Injection into the Subarachnoid Space of Neonatal Rats.

AIM: To describe the relationship between the parenchymal pressure changes and the development of hydrocephalus in kaolininjected neonatal rats according to cerebral regions and time intervals of developing hydrocephalus. MATERIAL AND METHODS: Neonatal rats aged 2 to 3 days were examined in 5 groups as kaolin frontal "K-F", kaolin parietal "KP", saline frontal "SF-F", saline parietal "SF-P" and control "C", based on the injected material and injection sites. All injections were performed into the cortical subarachnoid space of the right frontal and right parietal regions. The fifth group was injection free. On the 3 < sup > rd < /sup > , 7 < sup > th < /sup > , 15 < sup > th < /sup > , 30 < sup > th < /sup > and 60 < sup > th < /sup > days after injection, parenchymal pressures (PP) of 5-7 rats from each group were measured from different regions. RESULTS: We compared the control group with saline-injected and kaolin-injected groups and found statistically significant parenchymal pressure differences based on regional measurements. In the kaolin groups, the mean PP values were obviously higher than the saline-injected group. Within each kaolin-injected group, the pressure values were variable and inconsistent regarding the parenchymal regions. CONCLUSION: Hydrocephalus cannot be totally explained with existent "bulk-flow" or "hydrodynamic" theories. Although our experimental design was planned to develop hydrocephalus according to the bulk flow theory, our results were more compatible with the hydrodynamic theory. The present comments on the occurrence and pathogenesis of hydrocephalus are still open to debate and may require further comprehensive studies.

Potential role of the Virchow Robin space in the pathogenesis of bacterial meningitis.

Meningitis is an infectious disease commonly arising from a bacterial etiology. The rapid progression of morbidity and mortality due to bacterial meningitis requires critical and imminent time-dependent clinical intervention. Although it is unambiguously clear that bacteria must infiltrate the cerebrospinal fluid, the sequence of events in the pathogenesis of bacterial meningitis has not been fully elucidated. Most reviews of the pathogenesis of bacterial meningitis do not specify the anatomical location of bacteria following BBB traversal. We propose an additional hypothesis focusing on the Virchow-Robin space (VRS). The VRS consists of a small, but identifiable perivascular space formed by a sheath of cells derived from the pia mater. The VRS has been described as an immunological space and possibly having a role in several neuropathological diseases. Solute exchange between cerebrospinal fluid and extracellular fluid occurs at the VRS, with subsequent drainage into the subarachnoid space. Because the VRS is continuous with the subpial space, a more direct route to the meninges is facilitated. The involvement of the VRS may have profound implications on the pathogenesis and therapeutic strategies: (1) nasopharyngeal colonization; (2) penetration into the blood stream after crossing the mucosal and epithelial membranes; (3) proliferation in the bloodstream; (4) extravasations through the endothelium of the post-capillary venules to the perivascular VRS; (5) migration from VRS to subpial space; (6) traversal through pia mater, entering the CSF in the subarachnoid space; (7) invasion of the meninges. The implication of the VRS in the pathogenesis of bacterial meningitis would be twofold. First, the VRS could provide an additional route of entry of bacteria into the brain. Second, the VRS could provide an area for bacterial proliferation, and thereby serve as a bacterial reservoir in relatively close proximity to the meninges. The clinical consequences of this hypothesis are: 1) clinical interpretation of laboratory findings, and 2) effective antibiotic delivery into the VRS. If the role of the VRS is established as part of bacterial meningitis pathogenesis, antibiotic pharmacokinetics and pharmacodynamics in the VRS need to be determined. This may result in developing novel antibiotic delivery and clinical strategies to improve morbidity and mortality.

DIAGNOSIS OF ENDOCRINE DISEASE: Primary empty sella: a comprehensive review.

Primary empty sella (PES) is characterized by the herniation of the subarachnoid space within the sella, which is often associated with variable degrees of flattening of the pituitary gland in patients without previous pituitary pathologies. PES pathogenetic mechanisms are not well known but seem to be due to a sellar diaphragm incompetence, associated to the occurrence of upper sellar or pituitary factors, as intracranial hypertension and change of pituitary volume. As PES represents in a majority of cases, a neuroradiological findings without any clinical implication, the occurrence of endocrine, neurological and opthalmological symptoms, due to the above describes anatomical alteration, which delineates from the so called PES syndrome. Headache, irregular menses, overweight/obesity and visual disturbances compose the typical picture of PES syndrome and can be the manifestation of an intracranial hypertension, often associated with PES. Although hyperprolactinemia and growth hormone deficit represent the most common endocrine abnormalities, PES syndrome is characterized by heterogeneity both in clinical manifestation and hormonal alterations and can sometime reach severe extremes, as occurrence of papilledema, cerebrospinal fluid rhinorrhea and worsening of visual acuity. Consequently, a multidisciplinary approach, with the integration of endocrine, neurologic and ophthalmologic expertise, is strongly advocated and recommended for a properly diagnosis, management, treatment and follow-up of PES syndrome and all of the related abnormalities.

A Poroelastic Fluid/Structure-Interaction Model of Cerebrospinal Fluid Dynamics in the Cord With Syringomyelia and Adjacent Subarachnoid-Space Stenosis.

An existing axisymmetric fluid/structure-interaction (FSI) model of the spinal cord, pia mater, subarachnoid space, and dura mater in the presence of syringomyelia and subarachnoid-space stenosis was modified to include porous solids. This allowed investigation of a hypothesis for syrinx fluid ingress from cerebrospinal fluid (CSF). Gross model deformation was unchanged by the addition of porosity, but pressure oscillated more in the syrinx and the subarachnoid space below the stenosis. The poroelastic model still exhibited elevated mean pressure in the subarachnoid space below the stenosis and in the syrinx. With realistic cord permeability, there was slight oscillatory shunt flow bypassing the stenosis via the porous tissue over the syrinx. Weak steady streaming flow occurred in a circuit involving craniocaudal flow through the stenosis and back via the syrinx. Mean syrinx volume was scarcely altered when the adjacent stenosis bisected the syrinx, but increased slightly when the syrinx was predominantly located caudal to the stenosis. The fluid content of the tissues over the syrinx oscillated, absorbing most of the radial flow seeping from the subarachnoid space so that it did not reach the syrinx. To a lesser extent, this cyclic swelling in a boundary layer of cord tissue just below the pia occurred all along the cord, representing a mechanism for exchange of interstitial fluid (ISF) and cerebrospinal fluid which could explain recent tracer findings without invoking perivascular conduits. The model demonstrates that syrinx volume increase is possible when there is subarachnoid-space stenosis and the cord and pia are permeable.

Influence of the State of the Subarachnoid Space of the Cranial Base in Hydrocephalus Resolution after Endoscopy.

Objective To compare the resolution rate of hydrocephalus after endoscopy (predominantly endoscopic third ventriculostomy [ETV]) using flexible endoscopes during a 5-year period in patients with a permeable and a nonpermeable subarachnoid space (SAS). Material and Methods We conducted a retrospective cohort study of the videos and records of 150 hydrocephalic patients chosen randomly who underwent ETV (and other endoscopic procedures) with a flexible endoscope. The patients were classified into two groups based on the neuroendoscopic findings. The first group included patients with a permeable SAS, and the second group included patients with a nonpermeable SAS. A normal SAS or one with slight arachnoiditis was considered permeable. Adhesive arachnoiditis and immature or mechanically obliterated SASs were considered nonpermeable. Results We found a success rate of 70% in patients with a permeable SAS versus 33% in patients with a nonpermeable SAS. The baseline characteristics of both groups were homogeneous. We obtained a statistically significant difference (p < 0.0001) with hazard ratio (HR) 3.42 (95% confidence interval [CI], 1.88-6.22). Another important factor involved was age that showed a statistically significant difference (p < 0.0018) with HR 3.28 (95% CI, 1.55-6.93). Conclusion The permeability of the SAS is an important prognostic factor in the resolution rate of hydrocephalus after ETV (and other endoscopic procedures) using flexible neuroendoscopes. Therefore we recommend that the characteristics of the SAS be examined following every endoscopic procedure for hydrocephalus to identify patients at risk of recurrence.

Sustained high-pressure in the spinal subarachnoid space while arterial expansion is low may be linked to syrinx development.

Syringomyelia (a spinal cord cyst) usually develops as a result of conditions that cause cerebrospinal fluid (CSF) obstruction. The mechanism of syrinx formation and enlargement remains unclear, though previous studies suggest that the fluid enters via the perivascular spaces (PVS) of the penetrating arteries of the spinal cord, and that alterations in the CSF pulse timing and pressure could contribute to enhanced PVS inflow. This study uses an idealised computational model of the PVS to investigate the factors that influence peri-arterial fluid flow. First, we used three sample patient-specific models to explore whether changes in subarachnoid space (SAS) pressures in individuals with and without syringomyelia could influence PVS inflow. Second we conducted a parametric study to determine how features of the CSF pulse altered perivascular fluid, including alterations to timing and magnitude of the peak SAS pressure, the timing of reversal from high to low pressure (diastolic phase), and the area under the pressure-time curve. The model for the patient with syringomyelia had higher net CSF inflow to the PVS than the two subjects without syringomyelia. In the parametric study, only increasing the area under the high pressure region of the SAS pulse substantially increased PVS inflow, when coupled with a temporal shift in arterial and SAS pulses. This suggests that a period of sustained high SAS pressure while arterial diameter is low may increase net CSF pumping into the PVS.