Akihiro Hirayama

Research into the Physiology of Cerebrospinal Fluid Reaches a New Horizon: Intimate Exchange between Cerebrospinal Fluid and Interstitial Fluid May Contribute to Maintenance of Homeostasis in the Central Nervous System

Cerebrospinal fluid (CSF) plays an essential role in maintaining the homeostasis of the central nervous system. The functions of CSF include: (1) buoyancy of the brain, spinal cord, and nerves; (2) volume adjustment in the cranial cavity; (3) nutrient transport; (4) protein or peptide transport; (5) brain volume regulation through osmoregulation; (6) buffering effect against external forces; (7) signal transduction; (8) drug transport; (9) immune system control; (10) elimination of metabolites and unnecessary substances; and finally (11) cooling of heat generated by neural activity. For CSF to fully mediate these functions, fluid-like movement in the ventricles and subarachnoid space is necessary. Furthermore, the relationship between the behaviors of CSF and interstitial fluid in the brain and spinal cord is important. In this review, we will present classical studies on CSF circulation from its discovery over 2,000 years ago, and will subsequently introduce functions that were recently discovered such as CSF production and absorption, water molecule movement in the interstitial space, exchange between interstitial fluid and CSF, and drainage of CSF and interstitial fluid into both the venous and the lymphatic systems. Finally, we will summarize future challenges in research. This review includes articles published up to February 2016.

Cerebrospinal fluid image segmentation using spatial fuzzy clustering method with improved evolutionary Expectation Maximization

Visualization of cerebrospinal fluid (CSF), that flow in the brain and spinal cord, plays an important role to detect neurodegenerative diseases such as Alzheimers disease. This is performed by measuring the substantial changes in the CSF flow dynamics, volume and/or pressure gradient. Magnetic resonance imaging (MRI) technique has become a prominent tool to quantitatively measure these changes and image segmentation method has been widely used to distinguish the CSF flows from the brain tissues. However, this is often hampered by the presence of partial volume effect in the images. In this paper, a new hybrid evolutionary spatial fuzzy clustering method is introduced to overcome the partial volume effect in the MRI images. The proposed method incorporates Expectation Maximization (EM) method, which is improved by the evolutionary operations of the Genetic Algorithm (GA) to differentiate the CSF from the brain tissues. The proposed improvement is incorporated into a spatial-based fuzzy clustering (SFCM) method to improve segmentation of the boundary curve of the CSF and the brain tissues. The proposed method was validated using MRI images of Alzheimers disease patient. The results presented that the proposed method is capable to filter the CSF regions from the brain tissues more effectively compared to the standard EM, FCM, and SFCM methods.

Quantitative Analysis of Cerebrospinal Fluid Pressure Gradients in Healthy Volunteers and Patients with Normal Pressure Hydrocephalus

Magnetic resonance imaging (MRI) can depict not only anatomical information, but also physiological factors such as velocity and pressure gradient. Measurement of these physiological factors is necessary to understand the cerebrospinal fluid (CSF) environment. In this study we quantified CSF motion in various parts of the CSF space, determined changes in the CSF environment with aging, and compared CSF pressure gradient between patients with idiopathic normal pressure hydrocephalus (iNPH) and healthy elderly volunteers. Fifty-seven healthy volunteers and six iNPH patients underwent four-dimensional (4D) phase-contrast (PC) MRI. CSF motion was observed and the pressure gradient of CSF was quantified in the CSF space. In healthy volunteers, inhomogeneous CSF motion was observed whereby the pressure gradient markedly increased in the center of the skull and gradually decreased in the periphery of the skull. For example, the pressure gradient at the ventral surface of the brainstem was 6.6 times greater than that at the convexity of the cerebrum. The pressure gradient was statistically unchanged with aging. The pressure gradient of patients with iNPH was 3.2 times greater than that of healthy volunteers. The quantitative analysis of 4D-PC MRI data revealed that the pressure gradient of CSF can be used to understand the CSF environment, which is not sufficiently given by subjective impression of the anatomical image.

Neuroradiologic Diagnosis of Minor Leak prior to Major SAH: Diagnosis by T1-FLAIR Mismatch

BACKGROUND AND PURPOSE: In major SAH, the only method to diagnose a preceding minor leak is to ascertain the presence of a warning headache by interview; however, poor clinical condition and recall bias can cause inaccuracy. We devised a neuroradiologic method to diagnose previous minor leak in patients with SAH and attempted to determine whether warning (sentinel) headaches were associated with minor leaks before major SAH. MATERIALS AND METHODS: We retrospectively evaluated 127 patients who were admitted with SAH within 48 hours of ictus. Previous minor leak before major SAH was defined as T1WI-detected clearly bright hyperintense subarachnoid blood accompanied by SAH blood on FLAIR images that was distributed over a larger area than bright hyperintense subarachnoid blood on T1WI (T1-FLAIR mismatch). RESULTS: The incidence of warning headache before SAH was 11.0% (14 of 127 patients, determined by interview). The incidence of T1-FLAIR mismatch (neuroradiologic diagnosis of minor leak before major SAH) was 33.9% (43 of 127 patients). Of the 14 patients with warning headache, 13 had a minor leak diagnosed by T1-FLAIR mismatch at the time of admission. Variables identified by multivariate analysis as significantly associated with minor leak diagnosed by T1-FLAIR mismatch included 80 years of age or older, rebleeding after admission, intracerebral hemorrhage on CT, and mRS scores of 3–6. CONCLUSIONS: We conclude that warning headaches diagnosed by interview are not a product of recall bias but are the result of actual leaks from aneurysms.

Visualization of pulsatile CSF motion around membrane-like structures with both 4D velocity mapping and time-SLIP technique

PURPOSE We compared the depiction of pulsatile CSF motion obtained by 4-dimensional phase-contrast velocity mapping (4D-VM) with that by time-spatial labeling inversion pulse (time-SLIP) technique in the presence of membrane structures. MATERIALS AND METHODS We compared the 2 techniques using a flow phantom comprising tubes with and without a thin rubber membrane and applied the techniques to 6 healthy volunteers and 2 patients to analyze CSF dynamics surrounding thin membrane structures, such as the Liliequist membrane (LM), or the wall of an arachnoid cyst. RESULTS Phantom images exhibited propagation of the flow and pressure gradient beyond the membrane in the tube. In contrast, fluid labeled by the time-SLIP technique showed little displacement from the blockage of spin travelling by the membrane. A similar phenomenon was observed around the LM in healthy volunteers and the arachnoid cyst wall in a patient. CONCLUSION Four-dimensional phase-contrast velocity mapping permitted visualization of the propagation of CSF pulsation through the intracranial membranous structures. This suggests that 4D-VM and the time-SLIP technique provide different information on flow and that both techniques are useful for classifying the pathophysiological status of CSF and elucidating the propagation pathway of CSF pulsation in the cranium.

Magnetic Resonance Imaging Technique for Visualization of Irregular Cerebrospinal Fluid Motion in the Ventricular System and Subarachnoid Space

BACKGROUND Many studies have shown that cerebrospinal fluid (CSF) behaves irregularly, rather than with laminar flow, in the various CSF spaces. We adapted a modified previously known magnetic resonance imaging technique to visualize irregular CSF motion. Subsequently, we assessed the usefulness and clinical significance of the present method. MATERIALS AND METHODS Normal CSF motion in 10 healthy volunteers was visualized with the dynamic improved, motion-sensitized, driven-equilibrium steady-state free precession technique. Subsequently, CSF motion visualization with a modified sequence was applied to 3 patients. RESULTS In healthy volunteers, we achieved visualization of the irregularity of CSF flow in the ventricles and spinal canal, whereas CSF motion was diminished in the peripheral part of the intracranial subarachnoid space. In one case, we confirmed the patency of the patients third ventriculostomy fenestration site. In the other, we verified the usefulness of the proposed sequence for determining the communication between the ventricle or subarachnoid space and the cyst. CONCLUSIONS Using the present sequence, we obtained images that accentuated CSF motion, which is largely composed of irregular motion. This method does not require pulse triggering or complex post-processing of images and allows visualization of CSF motion in a short period of time in selected whole imaging planes. It can therefore be applied clinically to diagnose various diseases that cause abnormalities in the CSF space.

Visualization of pulsatile CSF motion separated by membrane-like structure based on four-dimensional phase-contrast (4D-PC) velocity mapping

This work was performed to indicate the usefulness of magnetic resonance (MR) 4-dimentional phase contrast (4D-PC) technique in assessing CerebroSpinal Fluid (CSF) motion in comparison with the time-Spatial Labeling Inversion Pulse (Time-SLIP) technique. 4D-velocity vector, their curl, and, pressure gradient were evaluated in both flow phantom, and normal volunteers and a patient with hydrocepharus. The velocity and pressure gradient fields obtained by the 4D-PC technique were useful to visualize the CSF dynamics under the presence of a membrane-like structure, unlike the Time-SLIP in which the spin travel was visualized. Quantitative property was another advantage of the 4D-PC. The curl and the pressure gradient fields obtained with actual units should help clinicians to classify the conditions of the patients with CSF disorders.

Centripetal Propagation of Vasoconstriction at the Time of Headache Resolution in Patients with Reversible Cerebral Vasoconstriction Syndrome

In this retrospective cohort study, the authors evaluated 16 patients diagnosed with reversible cerebral vasoconstriction syndrome who underwent MR imaging, including MRA, within 72 hours of RCVS onset (initial MRA) and within 48 hours of thunderclap headache remission. In 14 of the 16 patients (87.5%), centripetal propagation of vasoconstriction occurred from the initial MRA to remission of thunderclap headache, with typical segmental vasoconstriction of major vessels (M1, P1, A1). The authors conclude that there is evidence of centripetal propagation of vasoconstriction on MRA performed at the time of remission of the thunderclap headache, and this time point may represent a useful opportunity to diagnose RCVS with greater confidence. BACKGROUND AND PURPOSE: Reversible cerebral vasoconstriction syndrome is characterized by thunderclap headache and diffuse segmental vasoconstriction that resolves spontaneously within 3 months. Previous reports have proposed that vasoconstriction first involves small distal arteries and then progresses toward major vessels at the time of thunderclap headache remission. The purpose of this study was to confirm centripetal propagation of vasoconstriction on MRA at the time of thunderclap headache remission compared with MRA at the time of reversible cerebral vasoconstriction syndrome onset. MATERIALS AND METHODS: Of the 39 patients diagnosed with reversible cerebral vasoconstriction syndrome at our hospital during the study period, participants comprised the 16 patients who underwent MR imaging, including MRA, within 72 hours of reversible cerebral vasoconstriction syndrome onset (initial MRA) and within 48 hours of thunderclap headache remission. RESULTS: In 14 of the 16 patients (87.5%), centripetal propagation of vasoconstriction occurred from the initial MRA to remission of thunderclap headache, with typical segmental vasoconstriction of major vessels. These mainly involved the M1 portion of the MCA (10 cases), P1 portion of the posterior cerebral artery (10 cases), and A1 portion of the anterior cerebral artery (5 cases). CONCLUSIONS: This study found evidence of centripetal propagation of vasoconstriction on MRA obtained at the time of thunderclap headache remission, compared with MRA obtained at the time of reversible cerebral vasoconstriction syndrome onset. If clinicians remain unsure of the diagnosis during early-stage reversible cerebral vasoconstriction syndrome, this time point represents the best opportunity to diagnose reversible cerebral vasoconstriction syndrome with confidence.

Endoscopic Microvascular Decompression with Transposition for Trigeminal Neuralgia and Hemifacial Spasm: Technical Note.

Background Endoscopic microvascular decompression (MVD) offers reliable identification of neurovascular conflicts under superb illumination, and it provides minimally invasive surgery for trigeminal neuralgia and hemifacial spasm. Transposition techniques have been reported as a decompression method to prevent adhesion and granuloma formation around decompression sites, providing better surgical outcomes. The feasibility and effects of transposition under endoscopic MVD were evaluated. Material and Methods Fully endoscopic MVD was performed using 4‐mm 0‐ and 30‐degree endoscopes. The endoscope was fixed with a pneumatic holding system, and a bimanual technique using single‐shaft instruments was performed. Transposition was performed with Teflon felt string and fibrin glue. Surgical results were evaluated using the scoring system proposed by Kondo et al. Results The endoscope was introduced via a retrosigmoid keyhole. The 0‐degree endoscope was advanced through the lateral aspect of the cerebellar tentorial surface to the trigeminal nerve in cases of trigeminal neuralgia and through the petrosal surface of the cerebellum to the facial nerve in cases of hemifacial spasm. Neurovascular conflicts and perforators from the offending artery were clearly demonstrated under the 30‐degree endoscopic view, and transposition of the offending artery was safely performed with preservation of perforators. Clinical symptoms improved without permanent complications. Conclusion Endoscopic MVD with the transposition technique is feasible. Superb endoscopic views demonstrate perforators arising from the offending artery behind the corner, allowing damage to perforators to be avoided during the transposition technique. Endoscopic MVD using the transposition technique is expected to offer excellent surgical results.

Density of the cerebral cortex in computed tomography angiography source images and clinical outcomes in Grade V subarachnoid hemorrhage

Abstract Objective: Among patients diagnosed with Grade V subarachnoid hemorrhage (SAH) according to the World Federation of Neurosurgical Societies (WFNS), the identification of those with the possibility of recovery is not feasible, although approximately one-fifth of these patients have favorable outcomes according to a recently published series of surgical papers. We hypothesized that computed tomography angiography (CTA) source images (SIs), which have applied to the detection of acute ischemia, might be useful for selecting Grade V patients with possibilities for favorable outcomes. Methods: We retrospectively assessed 170 SAH patients who underwent surgery between January 2009 and February 2012 and quantitatively measured their mean cerebral cortical densities from the initial CTA-SIs. Results: The cortical densities of 123 patients of Grades I–IV were strongly affected by the following two CTA-SI findings that were revealed by multivariate analysis: the density of the internal carotid artery (ICA) just proximal to the petrous portion and the ratio of the subarachnoid (SA) space to intracranial volume (P < 0·05). Favorable outcomes were obtained in 9 of the 47 Grade V patients (19·1%), and the predictors of the favorable outcomes according to multivariate analysis were increased cortical densities on the CTA-SIs and female patients (P < 0·05). Conclusion: The outcomes of Grade V patients could be partly predicted based on the estimates of cortical density from the CTA-SIs, and this measure might be useful for the selection of Grade V patients for surgery, provided that both ICA density and SA space ratio are confirmed before the evaluation of cortical density.