The brain is the pilot of the incredibly complicated system that we refer to as a person. The brain is responsible for controlling just about everything we do, whether it’s done consciously, like kicking a soccer ball, or unconsciously, like digesting a meal. Because the brain is so important, it should come as no surprise that the body goes to great extents to protect it, just like an army goes out of its way to protect its general or The United States bends heads-over-heels to protect our President. The skull is an incredibly tough vault that encapsulates the brain in solid bone. However, the skull wouldn’t be worth a whole lot if the brain was allowed to bounce around inside of it. Think about it. If you hit your head and your brain was free to move around inside the skull then it would smack itself back and forth against the skull bones, quite possibly doing more damage than conking your noodle outright in the first place!
This is a dissection of a human brain from the front (“the coronal axis” for you fancy medical folks out there). Essentially, this cadaver had its face cut off and this is a view of the brain along the same plane that you see every day when you look someone in the eyes — this is just a little bit deeper in the old noggin. The outermost layer is the scalp and the skull bones are right underneath. The sponge-looking thing in the middle is your brain, the organ that is processing and making sense out of these words for you as you read my medical blog!
This is another cadaveric dissection, except this time we’re looking down on the cadaver at the top of their noggin (which obviously has been removed). The flappy layer on the outside is the scalp. Underneath that is the bone. The white bone is tough cortex while the darker colored stuff in the middle is bone marrow. The brain is white and brownish colored in this preparation and it is sitting inside the skull.
The body prevents this dangerous scenario from occurring (in most instances) by stabilizing the brain inside the skull with fibrous “support ropes” that are called “the meninges.” The rope analogy is actually fairly accurate, by the way. In a cadaver the consistency of the meninges feels very much like rubbing a thin piece of wet hemp rope, albeit without the rope splinters! In addition to its meningeal “support rack,” the brain is surrounded and filled internally with a fluid called CSF that cushions the brain and acts as a biological shock absorber. Overall, the human brain is very well protected indeed.
This is an MRI of the head and brain. You can see the meninges if you know what you’re looking at, but what I really want you to notice here is the CSF. See that black stuff in the middle of the brain (in the lateral, third, and fourth ventricles to be precise)? That’s CSF. The layer of black directly around the brain and the spinal cord (located underneath the brain) is also CSF.
Okay, here’s a good picture of the meninges. In this illustration, which was based on an actual cadaveric dissection, everything inside the skull vault except the meninges has been removed. See that big fibrous band? That’s the meninges! The blue structures are “dural venous sinuses,” large veins that run inside the meningeal layers and that return blood from the brain back to the heart.
The defenses of the human brain don’t end with the mechanical protections of the CSF and the meninges. The brain is also garrisoned against bacteria and viruses by specialized adaptations of the blood vessels that provide it was oxygen and nutrition. Unlike the relatively “leaky” blood vessels in the rest of the body, that allow cells and nutrients from the blood to freely pass back and forth between the blood and the body tissues, the blood vessels in the brain are tightly lined with a “blood-brain barrier” that specifically regulates what can and cannot pass into and out of the brain via the bloodstream. As formidable as the blood-brain barrier is, every once in a while the blood-brain barrier is infiltrated by a bacteria or a virus and the result is meningitis, encephalitis, or both.
This is an illustration of the blood-brain barrier. Don’t perseverate over this complicated cartoon! The point is that nothing is supposed to get into the brain from the bloodstream that the body doesn’t want there — and most of the time the blood-brain barrier keeps things that way.
Meningitis is an infection of the meninges and it is frequently accompanied by encephalitis, an infection of the brain proper. Meningitis causes a high fever, a severe headache with light sensitivity, confusion, nausea and vomiting (often projectile), and sometimes seizures that can be fatal. On physical examination patients with meningitis often have an extremely stiff neck and this is called “nuchal rigidity.” Meningitis can only be definitively diagnosed with a lumbar puncture, the dreaded “spinal tap” procedure that is so often portrayed in the movies and on television. A lumbar puncture is performed by placing the patient on their side with their legs flexed and then inserting a long needle through the layers of the lower back and into the meningeal layers that line the spinal cord [the brain + the spinal cord = the “central nervous system (CNS)” and both parts of the CNS are surrounded by supporting meningeal layers). The point of a lumbar puncture is to obtain CSF so that this special fluid can be analyzed in a laboratory. The reason that CSF is so important is that meningitis can be caused by several very different types of pathogens, all of which require a different type of treatment by the medical team.
A lumbar puncture…good times are not waiting. In reality it’s not as bad as it looks, but I still wouldn’t volunteer to let someone practice a lumbar puncture on me (I let folks stick my veins for practice all the time).
Most cases of meningitis are caused by viruses and these infections, while they make you feel really lousy for a week or two, are usually fought off by the body on its own with no residual effects. One specific type of viral meningitis is herpetic viral meningitis and it is treatable with an antiviral drug called acyclovir. CSF evaluation is pretty good at showing whether a case of meningitis is caused by a virus, but really lousy at determining which specific virus is the guilty party. Because of this many physicians treat all patients who have viral meningitis with acyclovir just in case they happen to have herpetic meningitis, which is a fairly common disease because the herpes viruses (there are lots) are much more prevalent than most folks realized. Remember that herpes viruses don’t only cause the notorious genital disease, the also cause cold sores, which most of us have from time-to-time.
An electron micrograph of one of the many, many, many types of herpes viruses that are floating around in our environment.
The biggest concern that a doctor has when they are confronted with someone who has meningitis is to determine if the meningitis is cause by bacteria. Bacterial meningitis is bad news because it is fatal about 10% of the time and responsible for brain damage or limb amputations in up to 20% (that’s 1-in-5) of the survivors. Limb amputations? Yep, I said that right. Bacterial meningitis frequently causes shock and DIC, two deadly conditions in which the whole body more or less shuts down in response to an infection. When this occurs the body tries to shunt its blood supply to its most important organs, namely the heart and the brain, and this comes at the expense of the limbs in particular. Because the limbs no longer are being supplied with an adequate amount of blood they die and the treatment for a necrotic limb is to amputate it before it becomes infected because otherwise the infection of the dead limb is likely to spread to the rest of the body and result in death.
Gangrene. What doctors are trying to prevent when they amputate a dead limb, hopefully before it becomes infected.
Bacterial meningitis is treated with potent antibiotics, antiepileptic drugs to prevent seizures, and with powerful anti-inflammatory drugs to decrease damage to the brain. With that said, the best treatment for bacterial meningitis is to prevent it in the first place and the medical establishment is actually pretty good at this if people will vaccinate their kids! Pneumococcus and Haemophilus influenza type b were formerly very common causes of very serious cases of bacterial meningitis in young children. The incidence of meningitis caused by these two nasty bugs has greatly decreased due to the Conjugated Pneumococcal Vaccine (PCV7) and the Hib Vaccine, both of which are routinely given to young children with the first dose of Hib being given at the age of 2 months. In addition, the most notorious cause of meningitis in teenagers and young adults is Meningococcus and we have a pretty good vaccine that covers most strains of this nasty killer and that is now routinely given to children at age 12 (with a booster at age 16), thus saving many otherwise young healthy lives. The take home message is to please vaccinate your children!
Pneumococcal meningitis. The band of tissue being held back by the metal forceps is the meninges. That yellow stuff underneath the meninges, but on top of the brain, is puss. There is a vaccine that covers the most common strains of pneumococcus, which is also a common cause of (big surprise) pneumonia, a disease that is still one of the leading causes of death in America today.
An 11-year-old boy with meningitis being held down by his physicians as he suffers a violent seizure. This photograph was taken in the pre-antibiotic era.
There are two other uncommon, but exceedingly nasty, other types of organisms that are potential causes of meningitis: fungi and parasites. Fungal meningitis most commonly afflicts people who are immunocompromised, e.g. people with AIDS and people suffering from cancer. Though usually uncommon in healthy persons, there was an outbreak in 2012 that was spread by contaminated corticosteroid injections (often used for joint injections in people with arthritis) that unnecessarily killed a lot of people. An even more scary cause of meningitis is the parasite Naegleria fowleri, an ameba that can swim up the nose of people who are swimming in warm fresh water and that causes a form of meningitis that has a 95% mortality (death) rate! Fortunately Naegleria meningitis is rare; unfortunately, when it does strike it is usually in young healthy teenagers because this is the age group that most commonly swims in warm lakes and rivers.
Naegleria. On the left is the cyst form. When inhaled through the nose the cyst transforms into the nasty buggers seen on the right. The Naegleria ameba literally eats your brain.
Dr. Leonardo Noto
Physician and Author of Medical School 101, Intrusive Memory, The Life of a Colonial Fugitive, and The Cannabinoid Hypothesis. Amazon Link to Doc’s Writing: http://www.amazon.com/Leonardo-Noto/e/B00ATVOMCW/ref=ntt_dp_epwbk_0
NOTE: The Life of a Colonial Fugitive — my dark historical thriller — is free for your e-reader at http://www.smashwords.com/books/view/215272. Thanks for reading!
Author Bio: Dr. Leonardo Noto is the nom de plume of a former airborne battalion surgeon who is now in civilian practice. Dr. Noto is the author of four books and he also writes for a medical education corporation that assists medical students, interns, and residents as they prepare for the medical board examinations. Dr. Noto is the proud father of an extremely spoiled 16-month-old American Bulldog who enjoys slobbering everywhere and tearing up things that he is not supposed to! Dr. Noto is an amateur practitioner of muay Thai and Brazilian jiu jitsu and he recently began learning to play the guitar (but he is currently a quite terrible musician, as his neighbors will readily attest).
Remember to discuss all health concerns with your personal physician (I don’t count!) before making any medical decisions. www.leonardonoto.com is intended to present general medical information for entertainment purposes and not as specific guide to any medical treatment. The author has made every effort to present accurate information; however, due to the ever-changing nature of medicine and the intrinsic caveats that are inherent in any particular case, no medical decisions should ever be made based on information gleaned from the internet (duh!). The internet and self-education are great, but they don’t replace your Doc!
The opinions voiced on this medical blog are solely the author’s own and they do not reflect the opinions or values of Dr. Noto’s employers, past or present. Dr. Noto’s medical blogs should never be used as supporting evidence for legal testimony — this is of course obvious to anyone who isn’t a complete moron, but some people are rather stupid.
- www.flickr.com Courtesy of Liz Henry.
- www.wikipedia.org. Brain Dissections.
- www.ilearnttoday.com – 507 × 444 – Search by image. Blood-Brain Barrier Illustration.
- www.wikipedia.org. Lumbar Puncture.
- www.flickr.com. Herpes Virus.
- www.wikipedia.org. Gangrene.
- www.wikipedia.org. Pneumococcal Meningitis.
- www.wikipedia.org. Boy with Meningitis.
- www.wikipedia.org. Naegleria.