Session 1 - Ventricular System And CSF Flashcards
What is the venous drainage of the brain?
The venous drainage of the brain is unique in that venous blood is drained from smaller cerebral veins into large dural venous sinuses before passing back into veins to be returned to the heart.
• Cerebral venous blood first drains into internal cerebral veins, which are located deep within the brain tissue.
• The internal cerebral veins then drain into larger external cerebral veins which can be seen on the surface of the brain.
• The external cerebral veins then drain into the dural venous sinuses.
o These are discussed in the meninges section above, under Dura Mater.
Where do dural venous sinuses drain into?
• The dural venous sinuses can drain the blood into extracranial veins via two routes:
o The sigmoid sinuses become the internal jugular veins as they exit the skull.
o Emissary veins cross the endosteal layer of dura and drain the venous blood into the bones of the skull.
What is venous sinus thrombosis?
Venous sinus thrombosis
Like other vessels in the body, blood can clot within the dural venous sinuses. If this occurs, drainage of venous blood will be compromised, meaning there will be an increase in intracranial pressure causing a headache and potentially compression of intracranial structures.
What is the cavernous sinus?
Cavernous sinus
One of the dural venous sinuses that is found behind the orbit (eye socket) on both sides is called the cavernous sinus. It is clinically relevant because the internal carotid artery and several important nerves pass through it: the oculomotor nerve (CN III), trochlear nerve (CN IV), ophthalmic nerve (CN V1), maxillary nerve (CN V2) and abducens nerve (CN VI). Venous blood draining from the face can potentially drain into the cavernous sinus, thereby providing a connection for superficial infection of the face to reach intracranial structures. Infection in the cavernous sinus can lead to meningitis or thrombosis. A thrombosis here will cause an increase in pressure and compress these nerves leading to problems with eye movements and sensation over the face.
Where is CSF?
There are central cavities within the brain that are filled with cerebrospinal fluid (CSF). These cavities are called ventricles and are joined to each other. They are continuous with the subarachnoid space meaning the CSF can surround the brain and spinal cord. In this way, the brain is submerged in a thin layer of CSF which provides a degree of physical protection, and mechanism for transfer of certain substances in and out of the brain tissue.
Where is CSF made?
CSF is primarily produced in the lateral ventricles by a group of specialised cells called the choroid plexus. The lateral ventricles are located within the cerebral hemispheres. The CSF then flows out of the lateral ventricles via the interventricular foramen to reach the third ventricle. The third ventricle is a very thin chamber in the midline separating the two sides of the diencephalon.
What is the path of the CSF?
CSF then passes out of the third ventricle via the cerebral aqueduct into the fourth ventricle which is diamond-shaped and located posterior to the brainstem, but anterior to the cerebellum.
CSF finally leaves the ventricular system either by passing inferiorly via the central canal to fill the subarachnoid space around the spinal cord, or posteriorly and laterally (via the median aperture of Magendie and lateral apertures of Luschka, respectively) to enter the subarachnoid space that surrounds the brain.
What are subarachnoid cisterns?
In certain areas around the brainstem and diencephalon, there are larger pockets of CSF in the subarachnoid space called subarachnoid cisterns. The names of individual cisterns are not important at your stage. On a CT scan, blood may be identified in the subarachnoid cisterns if there is bleeding into the subarachnoid space.
How is the CSF recycled back into the bloodstream?
Ultimately, CSF is recycled back into the bloodstream by arachnoid granulations. These are outpouchings similar in shape to a mushroom, that push out of the subarachnoid space around the brain into the dural venous sinuses. CSF diffuses across the wall of the arachnoid granulations to enter the bloodstream here.
What is hydrocephalus?
Hydrocephalus
Hydrocephalus (meaning ‘water in the head’ or ‘water on the brain’) is the term used to describe the accumulation of CSF, often characterised by enlarged lateral ventricles. This is most often caused by a blockage to the flow of CSF through the ventricular system. The compression of the rest of the brain may cause headache, vomiting, drowsiness, reduced conscious level or seizures. It can be relieved by placing a ‘shunt’ which is a device that diverts the CSF around the obstruction. A common type of shunt is known as a ‘VP’ (ventriculo-peritoneal) shunt, that diverts the CSF from the cerebral ventricles to the peritoneal cavity in the abdomen through a tube that is buried under the skin.
