Intracranial CSF volumes: natural variations and physiological changes measured by MRI

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.

Direct Measurement of Cerebrospinal Fluid Production in Mice

The emerging interest in brain fluid transport has prompted a need for techniques that provide an understanding of what factors regulate cerebrospinal fluid (CSF) production. Here, we describe a methodology for direct quantification of CSF production in awake mice. We measure CSF production by placing a catheter in a lateral ventricle, while physically blocking outflow from the 4^th ventricle. Using this methodology, we show that CSF production increases during isoflurane anesthesia, and to a lesser extent with ketamine/xylazine anesthesia, relative to the awake state. Aged mice have reduced CSF production, which is even lower in aged mice overexpressing amyloid-β. Unexpectedly, CSF production in young female mice is 30% higher than in age-matched males. Altogether, the present observations imply that a reduction in CSF production might contribute to the age-related risk of proteinopathies but that the rate of CSF production and glymphatic fluid transport are not directly linked.

Liu et al. develop a method for direct quantification of cerebrospinal fluid (CSF) production in awake mice. Using this method, the authors evaluate the effect of brain states, ages, sex, anesthetic types, and amyloid-β burden on CSF production.

In Patients Over 50 Years, Increased Age Is Associated With Decreased Odds of Documented Loss of Consciousness After a Concussion

Background: Advanced aged adults have the highest rate of traumatic brain injury (TBI) related hospital admissions, compared to younger age groups. Data were published in 2014 indicating differential injury and neurological responses to a TBI by age categories. In a recent article examining patients with mTBI and isolated subdural hematoma, it was found that older patients had a decreased risk of documented loss of consciousness (LOC). The primary objective was to determine the extent to which the odds of documented LOC changes with increasing age in a population of older adults suffering an isolated concussion and uncomplicated mTBI.

Methods: This was a retrospective study utilizing 6 years (2010–2015) of National Trauma Data Bank data. This study included patients with (1) diagnosis of concussion; (2) positive or negative loss of consciousness; (3) loss of consciousness durations no longer than 59 min or undefined; (4) age ≥50 years; (5) had a “fall” mechanism of injury; and (6) a valid emergency department Glasgow coma scale 13–15. We excluded patients (1) with any intracranial hemorrhage or intracranial injury of other and unspecified nature; (2) skull fracture; (3) an injury severity scale score >17; (4) a concussion with “unspecified” LOC (ICD-9: 850.9).

Results: There were 7,466 patients included in the study; the median (IQR) age was 70 (60–80) years. The risk of documented LOC was 71% (n = 5,319). An 80-year-old had 72% decreased odds of having a documented LOC, compared to a 50-year-old (OR = 0.28, 99.5%CI [0.23–0.34], P < 0.001). This association held when controlling for multiple demographic, comorbid, and clinical variables, and in sensitivity analyses.

Conclusion: These nationwide data suggest that in patients aged ≥50 years, a significant inverse association exists between age and odds of documented LOC after sustaining a fall-related concussion. Additional studies are needed to validate these findings and to investigate the triad of age, documented LOC, and intracranial hemorrhage. Clinical diagnostic criteria relying on LOC might be at risk of being modified by the association between increasing age and decreasing odds of LOC.

Estrogen- and progesterone-mediated structural neuroplasticity in women: evidence from neuroimaging

There is substantial evidence that the ovarian sex hormones, estrogen and progesterone, which vary considerably over the course of the human female lifetime, contribute to changes in brain structure and function. This structured, quantitative literature reviews aims to summarize neuroimaging literature addressing physiological variation in brain macro- and microstructure across an array of hormonal transitions including the menstrual cycle, use of hormonal contraceptives, pregnancy, and menopause. Twenty-five studies reporting structural neuroimaging of women, addressing variation across hormonal states, were identified from a structured search of PUBMED and were systematically reviewed. Although the studies are heterogenous with regard to methodology, overall the results point to overlapping areas of hormone related effects on brain structure particularly affecting the structures of the limbic system. These findings are in keeping with functional data that point to a role for estrogen and progesterone in mediating emotional processing.

DTI-based segmentation and quantification of human brain lateral ventricular CSF volumetry and mean diffusivity: validation, age, gender effects and biophysical implications

The human brain lateral ventricular (LV) cerebrospinal fluid (CSF) volume has been used as a neuroimaging marker of brain changes in health and disease. The LV CSF diffusivity may offer a useful quality assurance measure and become a potential noninvasive marker of deep brain temperature. In this work we sought to validate a method for human brain lateral ventricular (LV) cerebrospinal fluid (CSF) using diffusion tensor imaging (DTI) contrast to provide LV volume and corresponding DTI metrics. We compared LV volume obtained using DTI with that obtained using validated segmentations of the LV on T1-weighted data. DTI and T1-weighted data were acquired at 3T on 49 healthy males and 56 age-matched females aged 18-59 years. We showed histogram distributions of LV DTI metrics to establish quality assurance measures. We also analyzed the age and gender effects of LV volume and diffusivity. LV volumes estimated using both T1-weighted and DTI correlated strongly in males and females (ICC=0.99; median Dice index ~80%). The LV-to-intracranial volume percentage increased significantly with age only in males, using the DTI-based approach (r=0.39; p=0.005). LV CSF Mean diffusivity was greater in males than females ((~1.2%; p=0.03). Mean diffusivity of lateral ventricular CSF decreased significantly with age in healthy adults (r=-0.30; p=0.02). Our results highlight the importance of age and gender-based analyses and the potential of LV diffusivity measures as a quantitative marker.

Multicenter study of brain volume abnormalities in children and adolescent-onset psychosis

The goal of the study is to determine the extent of structural brain abnormalities in a multicenter sample of children and adolescents with a recent-onset first episode of psychosis (FEP), compared with a sample of healthy controls. Total brain and lobar volumes and those of gray matter (GM), white matter, and cerebrospinal fluid (CSF) were measured in 92 patients with a FEP and in 94 controls, matched for age, gender, and years of education. Male patients (n = 64) showed several significant differences when compared with controls (n = 61). GM volume in male patients was reduced in the whole brain and in frontal and parietal lobes compared with controls. Total CSF volume and frontal, temporal, and right parietal CSF volumes were also increased in male patients. Within patients, those with a further diagnosis of "schizophrenia" or "other psychosis" showed a pattern similar to the group of all patients relative to controls. However, bipolar patients showed fewer differences relative to controls. In female patients, only the schizophrenia group showed differences relative to controls, in frontal CSF. GM deficit in male patients with a first episode correlated with negative symptoms. Our study suggests that at least part of the GM deficit in children and adolescent-onset schizophrenia and in other psychosis occurs before onset of the first positive symptoms and that, contrary to what has been shown in children-onset schizophrenia, frontal GM deficits are probably present from the first appearance of positive symptoms in children and adolescents.

Clinical trial of intrathecal administration of 5-fluoro-2'-deoxyuridine for treatment of meningeal dissemination of malignant tumors

Intrathecal administration of 5-fluoro-2'-deoxyuridine (FdUrd) was performed in patients with meningeal dissemination of malignant tumors during the period from January 1996 to September 1998, and they were followed up until February 1999. The study population consisted of 23 patients: 12 with lung cancer, 4 with breast cancer, 2 with colon cancer, 1 with malignant lymphoma, 2 with glioblastoma and 2 with metastatic brain tumors of unknown origin. FdUrd was administered intrathecally through an Ommaya reservoir placed in the lateral ventricle initially at a dose of 1 microg twice per week, and the dose was increased to 10 microg and administration schedule was also increased every day. Headache and nuchal pain were relieved in all patients regardless of responsiveness to intrathecal FdUrd therapy as determined from the findings in the cerebrospinal fluid (CSF). Patients showed no side effects during the course of intrathecal chemotherapy except for slight nausea in two patients and dull headache in one. Sixteen of the 23 patients showed decreased cell number in the cerebrospinal fluid (CSF). Positive cytological findings in CSF became negative in 6 of the 23 patients, and the levels of CSF tumor markers were decreased in 14. Responsiveness to intrathecal administration of FdUrd was defined as 'response' when both the cell number and tumor markers were decreased in both ventricular and spinal CSF or when the cell number was decreased in cases in which the tumor markers were not detected. Overall, 16 of the 23 patients (70%) showed complete or partial responses to intrathecal FdUrd therapy as determined from CSF findings. These results demonstrated the efficacy of intrathecal FdUrd chemotherapy without apparent neurotoxicity for treatment of meningeal dissemination of malignant tumors.