Cerebrospinal Fluid Leak

Excerpt

Cerebrospinal fluid (CSF) is a clear, colorless fluid found in the subarachnoid space (SAS) that fills the neuroaxis spaces and surrounds the central nervous system (CNS). CSF consists primarily of water (99%), with 1% comprising electrolytes, proteins, neurotransmitters, and glucose. According to the Cushing and Weed seminal theory, CSF is produced by the choroid plexus, a network of blood vessels located within the ventricles of the brain, and circulates throughout the CNS until it is reabsorbed back into the venous sinuses through the arachnoid granulation. However, controversy remains regarding the basic CSF physiology. Some researchers dispute the conventional theory and propose alternative homeostatic mechanisms for regulating CSF.

The volume of CSF in the SAS is estimated to be 125 to 150 mL, with 25 mL located in the ventricular system. This volume has equivalent production and reabsorption rates of approximately 420 to 530 mL/day in adults. The CSF regulates CNS temperature and cushions the brain and spinal cord, providing a balanced, buoyant force that maintains the brain's shape and circulatory integrity despite its weight and absence of intrinsic rigid support. The CSF also forms the blood-CSF barrier, removing waste products and metabolites through continuous renewal.

A CSF leak occurs when there is a breach in the dura mater, the outermost layer of the meninges that protects the CNS, allowing the SAS to communicate with the epidural space and occasionally with the skin, thereby establishing a connection between the CNS and the external environment. This connection can cause headaches, neck pain, ear ringing, and, occasionally, loss of smell or taste due to low pressure. A CSF leak can be detrimental to brain blood flow and function and can increase the risk of direct trauma to brain parenchyma due to loss of the protective fluid cushion. Direct entry into the SAS from a CSF leak also creates a pathway for life-threatening infections, such as meningitis (see Image. Cerebrospinal Fluid Pathway). Signs and symptoms of a CSF leak indicate the need for further evaluation and treatment.