The Meninges and the Deadly “Itis”

Your Meninges and You

"Whoah, play that back..whose heart is gonna stop?"

“Whoa, play that back…whose heart is gonna stop?”

It doesn’t seem fair about the brain does it…all the E-Hollywood, red carpet attention it gets? I mean there isn’t a single one of us out there in this crazy world that can survive if our heart stops beating and that’s just as true for snow leopards, crickets, Glen Beck, and 3-toed sloths as it is for foxy human-beings like you and me. However, the brain is treated like the commander and chief of the body (which it pretty much is). By that I mean consider the level of security and protection the body invests in its head of state. Not only is some of the densest sections of bone in the body (contained in the skull) there to protect it from impact like a souped up, Seattle Seahawks NFL helmet but there is layer upon layer of security measures in place to maintain this safe, warm, cozy, zen-like environment surrounding the brain and spinal chord as well. One of those layers of security is a super fancy barrier of connective tissue between the brain and skull referred to as the “meninges.”

Your meninges has 3 layers of its own, the dura mater, arachnoid mater, and subarachnoid space, which all kind of sound to me like strange galaxies of the Star Trek universe in old episodes of the Next Generation. (just saying, I’m a nerd like that)

Oh yeah, that's what I'm talking about.

Oh yeah, that’s what I’m talking about.

No, I’m not going to compare them to layers of a cake. We all know that’s really gross, but it is a fairly dynamic, intricate space. The Dura mater is the outermost layer. It’s thick, tough stuff just like you would imagine the outer layer of a barrier to be. Just beneath the dura is a single layer called the arachnoid mater that has thousands of spindly little projections that connect to the layer below, like scaffolding to a building under construction. The third layer is really more of a space, the subarachnoid space, that contains blood vessels, arachnoid spindles, and cerebrospinal fluid that basically coats the brain and spinal chord.

MeningesBlum

the subarachnoid space is a mesh of branching vasculature within a matrix of CSF fluid

Meningitis

Just like other tissues of the body the meninges is susceptible to infection and can become infiltrated by pathogens like bacteria, viral particles, or any other bad boy microbe within our circulation that makes it past our immune system or the blood brain barrier. When this happens the meninges becomes inflamed (e.g. Meningitis) and it’s about as bad news as bad news gets. Picture the meninges as a continuous inflatable mattress wrapped around the brain and spinal cord that suddenly gets blown up, squeezing and pressing on the delicate wiring of your central nervous system. Not exactly the best summer ever.

Hey, don't get distracted. I'm talking about meningitis here

Hey, don’t get distracted. I’m talking about meningitis here

Meningitis sufferers typically complain of a biggie-sized headache coupled with neck stiffness along with a fever. Other symptoms mimic that of a migraine…light sensitivity, confusion, disorientation, and a general sense of “something just ain’t right!” Now meningitis is an inflammatory process and you know that there are about a bazillion microbes out there that can trigger an inflammatory response upon infection. So when a patient, or even worse, when multiple patients display clinical features of meningitis the clock is ticking for medical detectives to seek out the “infectious agent.”

The Usual Suspects

N. meningitidis, pain in the butt, gram negative staining diplococci that looks like tiny coffee beans under the scope

N. meningitidis, pain in the butt, gram negative staining diplococci that looks like tiny coffee beans under the scope

When we want to point the finger at bacterial causes of Meningitis three misfits come to my mind almost immediately; Neisseria meningitidis aka meningococcus, Streptococcus pneumoniae aka pneumococcus, and Hemophilus influenzae. All three of these shady characters like to hang out in the nasopharynx of our upper respiratory tract. So they typically spread from infected individuals by means of “respiratory secretions” as in kissing, coughing, and sneezing. Of course, if the infected is an infant the mode of transmission can include just about anything they can put in their mouths and pass on. S. pneumoniae and H. influenzae are opportunistic little bastards. That means don’t go spraying everything and everyone down with lysol just yet, because these guys typically only spring into action when we are already immunocompromised in some way. Meningococcus, on the other hand, is the only known bacteria to cause meningitis on an epidemic level.

You may have noticed that I didn’t dive into viral causes of meningitis. Are you kidding..that list is like 3 pages long! Viruses pose an even greater threat in that they are much much smaller, mutate at the drop of a hat, and have more modes of transmission than…Lil Jon has bling.

Lil+Jon

Exactly, more than that.

A lumbar puncture is typically the diagnostic procedure of choice when meningitis is suspected. This undeniably scary, long needle is inserted into the patient’s back to extract Cerebrospinal fluid from the spinal canal, usually through access to the lumbar vertebrae. Remember that your brain and spinal chord are suspended in fluid 24/7 that should be vacant of things like, viruses, bacteria, and even your own blood cells. So those few precious drops of CSF are like diagnostic gold to the folks working the clinical lab. They will make microscope slides to look for white cells and microbe hitchhikers and perhaps most importantly culture that CSF sample on clean, nutrient rich agar plates to see what pathogens grow. Many times they can positively ID the culprit like a closed case file in an episode of “The First 48.”

Stay curious, stay classy, and never stop learning my friends 🙂

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