Cerebrospinal fluid (CSF) plays a role in homeostatic hormonal signaling, chemical buffering, circulations of nutrients, and neurodevelopment. The two lateral ventricles drain into the third ventricle through the foramina of Monro. The third ventricle subsequently drains into the fourth ventricle through the narrowest portion of the ventricular system called the cerebral aqueduct. The roof of the fourth ventricle is bounded by the vermis of the cerebellum and the fastigium. CSF production is to a degree dependent on blood perfusion. In instances of increased intracranial pressure (ICP) with subsequent decreased cerebral perfusion, there will be a decrease in CSF production. CSF flows through net bulk flow from the lateral ventricles through the foramen of Monro into the third ventricle, then on into the fourth ventricle through the cerebral aqueduct. The pathways of CSF reabsorption include the ependymal layer of the ventricular system, and endothelial layer of the brain parenchyma.