When pressure in the skull builds up, whether due to swelling, a bleed, a tumor, or some other problem, the compression of brain tissue can lead to permanent damage. Elevated intracranial pressure (ICP) is considered a neurologic emergency, and needs to be addressed as soon as possible.
Detecting high ICP
The first way to detect high ICP is to pay attention to someone’s symptoms. Blurry vision, headache, or changes in thinking can all indicate that someone’s intracranial pressure is too high. In general, symptoms are worse when laying flat.
Sometimes, though, the person loses consciousness, in which case other indicators are needed. Fundoscopy, where the doctor looks in the back of your eye while shining a bright light, can show changes in the optic nerve due to elevated ICP. These changes don’t always occur right away, though, so sometimes other methods of investigating intracranial pressure are required if physicians are suspicious that intracranial pressure might be climbing.
One of the most reliable ways of measuring ICP is to place a monitor beneath the skull. This has the added benefit of being able to measure ICP constantly rather than just getting a single measurement, so changes in ICP can be captured. This is especially important in cases where one could predict the ICP to get worse, such as swelling after brain trauma.
Placing such a monitor is an invasive procedure, however. While they are normally safe, these monitors can lead to infection or bleeding. They are only placed when there is a clear need for close monitoring of ICP.
When neurologists feel ICP is high, steps are taken to lower that pressure. There are basically three components to the intracranial space under the skull: blood, brain, and cerebrospinal fluid (CSF). If pressure is building, reducing volume of blood or CSF can make more room for the brain to prevent compression and permanent injury.
CSF volume can be reduced by slowing production. CSF is normally made in the ventricles of the brain. Some medications like acetazolamide can slow CSF production and lower ICP as a result. However, the strength of this affect isn’t very strong, and acetazolamide has side effects such as changing the acidity of the blood.
Blood volume in the brain can be reduced by positioning the head up to encourage the veins of the head to return blood quickly to the heart. If the patient is intubated, the breathing rate can be increased to change the acidity of the patient’s blood, which can cause the arteries in the brain to constrict, reducing blood flow and giving the brain a little bit more room—however, this is only a temporary solution at best.
Sometimes the brain is swelling due to edema, where fluid leaks out of blood vessels and into brain tissue. Certain substrates like mannitol, or even saline, can encourage that fluid to return from the brain into the blood vessels where it causes less damage. Steroids like dexamethasone can also help reduce brain swelling.
When medical management isn’t enough, sometimes more aggressive measures are called for.
If the brain is being compressed by something in the skull that doesn’t belong there, like an abscess or tumor, sometimes it’s possible to remove the problem. Other times, though, this is impossible, either because the risk of surgery is too great, or because the problem isn’t easily removed.
For example, if the main problem is that the brain is swelling due to inflammation, it would obviously not be the best solution to just remove part of the brain itself. In this case, more room somehow has to be made in order to allow room for the swelling.
As we’ve discussed, CSF volume can also be reduced in order to free up room for the brain. If medications like acetazolamide aren’t effective enough, CSF can be removed by draining it through a shunt. This involves a tube being placed into the ventricles of the brain to drain CSF. If an ICP monitor has been placed already, CSF may be drained through that monitor to keep the pressure at a certain goal.
However, there are side effects to shunting. In addition to the risks of infection and bleeding that comes from inserting something into the body, there’s also a risk that too much CSF will be removed from the wrong places, leading to pressure shifts that lead to herniation-- movement of part of the brain to where it doesn't belong.
There’s another to solve the problem of too much competition between blood, brain, and cerebrospinal fluid for the tight space in the skull. You can make that space bigger. That’s the ultimate goal of a craniectomy, in which part of the skull is removed in order to allow more room for brain to swell.
Part of the skull is removed, but the tissue surrounding the brain is still kept as intact and clean as possible to prevent infection. Although infections and other complications can occur, by the time a craniectomy is called for, there are few other options. A craniectomy is a major surgery with some serious risks, but can it can nevertheless be useful in drastic situations.
Allan H. Ropper, Daryl R. Gress, Michael .N Diringer, Deborah M. Green, Stephan A. Mayer, Thomas P. Bleck, Neurological and Neurosurgical Intensive Care, Fourth Edition, Lippicott Williams & Wilkins, 2004
Braunwald E, Fauci ES, et al. Harrison's Principles of Internal Medicine. 16th ed. 2005.