Cerebrospinal Fluid

What is Cerebrospinal Fluid (CSF)?

Cerebrospinal fluid (CSF) is a clear, colorless liquid that circulates within and around the central nervous system (CNS), which includes the brain and spinal cord. CSF cushions the brain and spinal cord, helps maintain their chemical environment, and participates in nutrient transport and waste removal. Its volume and movement also affect pressure inside the skull.

What is CSF made of?

CSF contains glucose, proteins, lipids, and electrolytes. Its composition differs from blood plasma; for example, it normally contains less protein. The StatPearls overview of cerebrospinal fluid describes these constituents and their roles.

Production and Circulation of Cerebrospinal Fluid

• Choroid Plexuses

  CSF is primarily produced by specialized structures called choroid plexuses, located within the brain's ventricular system. These vascular structures consist of a network of capillaries and specialized ependymal cells that secrete CSF into the ventricles.

• Ventricular System

  The ventricular system is a series of interconnected, fluid-filled cavities within the brain. CSF flows through the ventricles, starting from the two lateral ventricles, then into the third ventricle, and finally the fourth ventricle, before entering the subarachnoid space that surrounds the brain and spinal cord.

• Subarachnoid Space and Reabsorption

  After circulating through the ventricular system, CSF enters the subarachnoid space, a fluid-filled cavity between the arachnoid mater and pia mater layers of the meninges. CSF flows around the brain and spinal cord, providing mechanical support and delivering nutrients. Outflow includes routes associated with arachnoid structures, exiting nerves and lymphatic vessels. Researchers are still working out how much each route contributes. Drainage is not limited to arachnoid granulations and the venous bloodstream.

Functions of Cerebrospinal Fluid

• Mechanical Support

  CSF provides cushioning and buoyant support. This reduces the effective weight of the brain and the load it places on surrounding structures.

• Nutrient Delivery and Waste Removal

  CSF plays a vital role in maintaining the brain's chemical environment by facilitating the exchange of nutrients, hormones, and other substances between the brain and the bloodstream. It also helps remove metabolic waste products, which can leave through several fluid-clearance pathways.

• Regulation of Intracranial Pressure

  The skull has limited space for brain tissue, blood, and CSF. Changes in CSF production, circulation, or drainage can therefore alter intracranial pressure.

Clinical Significance of Cerebrospinal Fluid

• Lumbar Puncture

  A lumbar puncture, or spinal tap, is a medical procedure in which a small sample of CSF is collected from the subarachnoid space in the lower back. This sample can be analyzed for the presence of pathogens, abnormal cells, or biochemical markers, aiding in the diagnosis of various neurological disorders, infections, and cancers.

• CSF Disorders

  Disrupted CSF circulation or drainage can contribute to hydrocephalus, while CSF leakage can cause intracranial hypotension. Meningitis is inflammation of the meninges, often due to infection; it is not simply a result of altered CSF flow. Diagnosis and treatment of these conditions may involve neuroimaging, lumbar puncture, medications, or surgical intervention.

• Neurological Biomarkers

  CSF can be a valuable source of biomarkers for neurological diseases such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. The clinical value of a CSF biomarker depends on the disease, assay and intended use; not every research marker is validated for diagnosis or treatment monitoring.

Sources and evidence

• Steven T. Proulx: Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics. Reviews evidence for arachnoid, nerve-associated, and lymphatic drainage routes.