Anatomy and Physiology of Cerebrospinal Fluid

European Annals of Otorhinolaryngology, Head and Neck diseases (2011) 128, 309—316 Available online at www.sciencedirect.com REVIEW OF THE LITERATURE Anatomy and physiology of cerebrospinal fluid L. Sakka a,b,∗, G. Coll b, J. Chazal a,b a Laboratoire d’anatomie, faculté de médecine, université d’Auvergne, 28, place Henri-Dunant, 63001 Clermont-Ferrand cedex 1, France b Image-Guided Clinical Neuroscience and Connectomics, université d’Auvergne, UFR Médecine, CHU de Clermont-Ferrand, Hôpital Gabriel Montpied, 58 rue Montalembert, 63003 Clermont-Ferrand, France Available online 18 November 2011 KEYWORDS Summary The cerebrospinal fluid (CSF) is contained in the brain ventricles and the cranial Cerebrospinal fluid; and spinal subarachnoid spaces. The mean CSF volume is 150 ml, with 25 ml in the ventricles CSF; and 125 ml in subarachnoid spaces. CSF secretion; CSF is predominantly, but not exclusively, secreted by the choroid plexuses. Brain interstitial CSF circulation; fluid, ependyma and capillaries may also play a poorly defined role in CSF secretion. CSF space CSF circulation from sites of secretion to sites of absorption largely depends on the arterial comparative anatomy pulse wave. Additional factors such as respiratory waves, the subject’s posture, jugular venous pressure and physical effort also modulate CSF flow dynamics and pressure. Cranial and spinal arachnoid villi have been considered for a long time to be the predominant sites of CSF absorption into the venous outflow system. Experimental data suggest that cranial and spinal nerve sheaths, the cribriform plate and the adventitia of cerebral arteries constitute substantial pathways of CSF drainage into the lymphatic outflow system. CSF is renewed about four times every 24 hours. Reduction of the CSF turnover rate during ageing leads to accumulation of catabolites in the brain and CSF that are also observed in certain neurodegenerative diseases. The CSF space is a dynamic pressure system. CSF pressure determines intracranial pressure with physiological values ranging between 3 and 4 mmHg before the age of one year, and between 10 and 15 mmHg in adults. Apart from its function of hydromechanical protection of the central nervous system, CSF also plays a prominent role in brain development and regulation of brain interstitial fluid homeostasis, which influences neuronal functioning. © 2011 Elsevier Masson SAS. All rights reserved. For a long time, the essential function of cerebrospinal fluid protects the central nervous system. Recent data derived (CSF) was considered to be that of a fluid envelope that from molecular biology show that CSF plays an essential role in homeostasis of the interstitial fluid of the brain parenchyma and regulation of neuronal functioning. Disor- ∗ Corresponding author. Tel.: +33 6 85 53 35 25. ders of CSF hydrodynamics and composition are responsible E-mail address: [email protected] (L. Sakka). for the major alterations of cerebral physiology observed in 1879-7296/$ – see front matter © 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.anorl.2011.03.002 310 L. Sakka et al. hydrocephalus and dementia, reflecting the importance of However, the fourth ventricle is not yet open and CSF cir- exchanges between CSF and the neuronal environment. culation is only effective on the 41st day. Formation of the subarachnoid spaces is therefore not exclusively due to CSF Comparative anatomy pressure. Formation of the subarachnoid spaces remains poorly understood. Capillaries appear to play a decisive role in Comparative anatomy of the meninges helps to elucidate the secretion and absorption of CSF during embryogenesis. the functional anatomy and ontogenesis of the CSF system Arachnoid cysts, dilatations of subarachnoid spaces predom- in man [1]. inantly located around blood vessels, appear to correspond The appearance of cerebrospinal fluid inside the neuraxis to CSF spaces partly communicating with adjacent circulat- precedes circulation of cerebrospinal fluid in subarachnoid ing blood sinuses. spaces during phylogenesis [2] The single primitive meninx with a large venous sinus in the spinal perimeningeal tissue of Selachii suggests the The first choroid plexuses presence of a CSF venous absorption system. Large Teleostei present a pial layer lined by reticular tissue prefiguring the The first choroid plexuses appear on the 41st day in the 4th arachnoid membrane, but with no real CSF spaces. CSF is ventricle [8]. The epithelium of the choroid plexus, contin- therefore contained in ventricular cavities. A peripheral uous with the ependyma, is derived from the neural tube, fibrous layer differentiates and the perimeningeal tissue while the leptomeningeal axis is derived from the paraxial develops into an adipose tissue, which prefigures spinal mesoderm. The time at which the choroid plexuses start to epidural fat. In amphibians, reptiles and birds, the meninges secrete CSF has not been clearly determined. comprise a dura mater and a pia mater. The perimeningeal tissue is considerably reduced, persisting at the spinal level in the form of epidural fat. In mammals, the subarachnoid Arachnoid villi develop from the wall of space is clearly distinct from the pia mater. intracranial venous sinuses Participation of the central nervous system venous drainage in CSF absorption is first observed in Amniotes From the 26th week, cerebral veins dilate at their anas- and is enhanced in the course of phylogenesis. Intracranial tomosis in the superior sagittal sinus. Villi are formed at venous sinuses derived from cerebral epidural veins, and the 35th week: the arachnoid stroma lined by endothe- subarachnoid spaces develop in parallel [2]. Spinal epidural lium protrudes into the lumen of the superior sagittal sinus veins regress with a smaller participation in CSF absorption. via a defect in the dura mater. Real arachnoid granulations appear at the 39th week [9] and continue to develop The development of cerebrospinal fluid spaces until the age of about 18 months [10,11]. Cranial arachnoid granulations are essentially situated in contact with the pos- retraces the steps of phylogenesis terior half of the superior sagittal sinus and adjacent venous lacunae and more rarely in contact with the transverse, Cerebral and spinal meninges are derived from superior petrosal, cavernous and sphenoparietal sinuses. different embryonic tissues These granulations ensure the bulk of CSF absorption at the end of organogenesis. However, comparative anatomy The three meningeal layers differentiate at the third month suggests other sites of CSF absorption in the absence of of intrauterine life. The meninges play a role in ontogene- arachnoid villi or granulations. sis of the underlying brain tissue by inducing proliferation and differentiation of neuroblasts and axonal growth [3]. Volumes Experimental destruction of fetal meninges over the cere- bellum induces cerebellar hypoplasia, neuronal ectopia and The CSF volume, estimated to be about 150 ml in adults, is the formation of glial tissue in subarachnoid spaces [4,5]. distributed between 125 ml in cranial and spinal subarach- Certain multiple malformation syndromes, such as Dandy noid spaces and 25 ml in the ventricles, but with marked Walker syndrome, comprising hypoplasia of the vermis and interindividual variations. abnormalities of the cerebellar parenchyma and CSF spaces, Abnormally narrow ventricles, described as ‘‘slit ventri- could be due to similar mechanisms. cles’’, are observed in complex disorders of CSF circulation associated with cerebral oedema in patients with a CSF The formation of subarachnoid spaces is not shunt. Inversely, hydrocephalus corresponds to an increased exclusively due to cerebrospinal fluid pressure intracranial fluid volume and can be difficult to distinguish from cerebral atrophy, in which passive expansion of CSF On closure of the rostral and caudal neuropores at the first spaces compensates for the reduction of brain volume. month of intrauterine life, the choroid plexuses are not The distribution of fluid overload depends on the site of yet functional [6]. However, CSF pressure increases in the obstruction. In obstructive hydrocephalus, the obstruction lumen of the neural tube and the volume of the cephalic is situated in the ventricular system, while in communicat- extremity increases, suggesting secretion of CSF by struc- ing hydrocephalus, the ventricular system and subarachnoid tures other than the choroid plexuses. The subarachnoid spaces freely communicate. spaces appear on the 32nd day at the ventral aspect of the The mechanisms of ventricular dilatation remain hypo- rhombencephalon, then extend caudally and dorsally [7]. thetical, but include hydrodynamic factors (secretion and Anatomy and physiology of cerebrospinal fluid 311 absorption rates, fluid pressure and cerebral compliance), The composition of cerebrospinal fluid is not hormonal neuropeptides, Atrial Natriuretic Peptide (ANP), simply a plasma ultrafiltrate and prostaglandin F2 (PGF2) [12]. Na, Cl and Mg concentrations are higher and K and Ca con- Cerebrospinal fluid secretion centrations are lower than those of plasma. The CSF cell count usually does not exceed five cells per milliliter. Varia- tions in the closely regulated composition of CSF can be used Cerebrospinal fluid secretion in adults for diagnostic purposes. Studies have demonstrated the exis- tence of chronobiological cycles of Na content with peaks CSF secretion in adults varies between 400 to 600 ml per day, Na concentrations at 8:00 a.m. and at 6:00 p.m., with no depending

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