I'm a former pharmacy technician and certified medical office assistant. I'm also a health nerd/ hypochondriac and knowledge eases my fears.
What Is Cerebrospinal Fluid?
To better understand how cerebrospinal fluid affects the body, it helps to gain a deeper understanding of the anatomy of the brain.
Our brain is enclosed by a protective skull and an interior membrane known as the dura mater. This membrane surrounds the brain and spinal cord.
Both the brain and spinal cord are surrounded by cerebrospinal fluid (CSF) which is constantly produced by the brain. This fluid plays a protective role as a shock absorber in case of trauma and the dura mater prevents it from leaking out.
Cerebrospinal fluid surrounds the optic nerve that travels to the eye and also reaches into the spine where it surrounds the spinal cord.
Continuously, this fluid produced by the brain circulates through the brain's ventricles, then exits the brain and returns to surround the brain.
The dura mater also has a drainage system, which allows blood to leave the brain and cerebrospinal fluid to re-enter circulation.
How Much Cerebrospinal Fluid Is Made Inside the Brain?
In general, about 120 to 150 ml of fluid is found inside the brain at any time. The total amount produced is around 400 to 600 ml per day.
Because the brain can only hold 120 to 150 ml, the 400 to 600 ml is recycled about three times a day.
Did you know? When cerebrospinal fluid is drained through a spinal tap, it is replaced in a relatively short period of time, usually within a few hours.
What's the Normal Flow of Cerebrospinal Fluid?
In a normal, healthy functioning body, CSF fluid is produced continuously by the brain and it's reabsorbed as well continuously so that the brain maintains its ideal level of 120 to 150 ml.
Problems arise when the drain holes are blocked or if the pipes become partially clogged. This leads to slower drainage and buildup of CSF within the brain, with its associated increased pressure.
Fluctuations of Cerebrospinal Pressure During the Day
The levels of cerebrospinal pressures tend to fluctuate throughout the day and to a good extent are related to movements of our head.
In particular, temporary rises are seen when we do things such as cough, sneeze, and strain or bend down to tie our shoes.
Increases of pressure in the head also take place when laying flat. In particular, when laying down during sleep, increases are seen since our breathing slows down and we retain carbon dioxide.
Further increases in pressure may be seen in people suffering from sleep apnea.
Levels instead decrease upon standing and after waking up, walking around, and standing for some time in the morning.
Can Cerebrospinal Fluid Cause Pulsatile Tinnitus?
Yes, increases in pressure due to the cerebrospinal fluid can trigger symptoms such as pulsatile tinnitus.
Pulsatile tinnitus is often described as a whooshing sound accompanied by the sound of the heartbeat. Sufferers often describe it as "hearing the heartbeat in the ear."
The sound may be continuous or present only in certain circumstances.
Coincidentally, many sufferers lament hearing the sound in situations known for increasing cerebrospinal fluid pressure such as when laying in bed, straining, or bending down.
Interestingly, these same situations are also known for causing headaches in sufferers of idiopathic intracranial hypertension.
A Matter of Narrowed Veins
There are chances that the pulsatile, whooshing sound, is the result of narrowed sinus veins. Stenosis is the medical term for narrowing.
Every time, with each heartbeat the blood is forced into the narrowed vein, and the sound is heard.
This is due to turbulent flow. For sake of an example, imagine a river. In the areas of narrowing, the water flow will be more turbulent due to the concentration of water found in such a tight place as it flows through.
Such narrowing is believed to occur due to high cerebrospinal fluid exerting pressure on the outside of the vein.
Intracranial Hypertension: High Venous Sinus Pressure
In a condition known as idiopathic intracranial hypertension, high pressure of the cerebrospinal fluid is due to higher than normal pressures in the venous sinuses.
Basically, in normal cases, the pressure stays around 16 to 18 mmHg, whereas, in people affected by this condition it stays around 20–40 mmHg with values up to 60 or 70 mmHg in the most severe cases.
Indeed, this is proven by the fact that, upon lowering the venous pressures, there is an immediate reduction in cerebrospinal fluid pressure. Treatment of intracranial hypertension, therefore, revolves around lowering this pressure.
This condition can be diagnosed by having the eyes checked for the presence of a swollen optic disc (papilledema) since this can be a sign of increased cerebrospinal pressure. After all, the optic nerve is surrounded by cerebrospinal fluid.
Next, an MRI or CT scan may be ordered to see whether there may be signs of abnormalities such as brain tumors, hydrocephalus, or bleeding in the brain. If nothing shows up, the next step may be performing a spinal tap to measure the levels of pressure.
A diagnosis is therefore made when brain imaging comes clear and the spinal tap reveals 25 cm of water or higher.
The Importance of Treatment
One main concern of having elevated intracranial hypertension is loss of vision. The increased pressure causes damage to the optic nerve and loss of vision over time if the pressure is high.
In general, the higher the pressure (like over 40), the more likely vision is at risk. It is therefore paramount to take steps to prevent vision loss.
- Chen J, Wall M. Epidemiology and risk factors for idiopathic intracranial hypertension. Int Ophthalmol Clin. 2014 Winter;54
- Fargen KM. Idiopathic intracranial hypertension is not idiopathic: proposal for a new nomenclature and patient classi- fication. J Neurointerv Surg. 2020
- Kyle M. Fargen Idiopathic Intracranial Hypertension Explained, 1st ed. 2021
- Wall M, George D. Idiopathic intracranial hypertension. A prospec-tive study of 50 patients. Brain 1991
- Akçakaya et al.; Idiopathic Intracranial Hypertension Turk J Neurol 2017;23:43-50
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2022 Adrian Rolla