May 25, 2022
Layers of Meninges of the Brain

MENINGITIS

Welcome to Medical Advice Channel. This article is going to be on Meningitis. Meningitis is an infection that causes inflammation of the Meninges of the brain. The inflammation causes swelling, and is the reason for the development of signs and symptoms, for example, headaches. It is a rare disease to come across but can be life-threatening or lead to severe conditions if urgent medical treatment is not provided.

Before we dig deep, let have a brief look at what Meninges are.

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What are Meninges?

These are membranous covering that provides a cover to the brain and spinal cord. They provide a covering that separates the brain and the spinal cord from the bony structures surrounding them, therefore, we can say that it’s most important function to protect the Central Nervous System. The Meninges are made up of three layers, namely;

  1. Dura Mater
  2. Arachnoid Mater
  3. Pia Mater.

Layers of Meninges of the Brain

Note that they are arranged in their respective order from Superficial to Deep.

        Dura Mater.

This is the most superficial of all the 3 layers of Meninges of the brain and consists of dense irregular connective tissues. It consists of two-layers;

  1. The Endosteal Layer – This is closest to the skull
  2. The inner meningeal layer lies closer to the brain.

These two layers are attached to each other and the fold to form four fibrous septa within the cranium;

  1. Falx cerebri.
  2. Tentorium cerebelli.
  3. Falx cerebelli.
  4. Diaphragma sellae.

         Arachnoid Mater.

This is the middle layer of the meninges of the brain. It is a spiderweb-like in shape. Between the Dura Mater and the Arachnoid mater, there is a formation of a space that is called the subarachnoid space, which contains blood vessels that supply the cerebral area, and most importantly, it contains Cerebrospinal Fluid (C.S.F).

The superficial layer (Outer layer) of the Arachnoid mater is important as it prevents The Cerebrospinal fluid from leaking out into the subdural space. Arachnoid trabeculae are present in the inner surface of the Arachnoid mater and transverse through the subarachnoid space to attach themselves to the superficial surface of the Pia mater. You might notice that in some books, the Pia mater and the Arachnoid mater are referred to as Leptomeninges, this is because they both display similarity in their embryological and cellular structure.

There is also the presence of Arachnoid granulation, whose functions to ensure that there is continuous drainage of CSF into the vascular system. This Arachnoid granulation can also be known as Pacchionian bodies. These bodies play a big role in the cranial vault, because, as you know, the skull is enclosed, therefore pressure builds up in the skull. The Arachnoid granulation plays an important role in trying to ensure this level is well balanced. This is done by draining it, to give way to new Cerebrospinal fluid, which by the way, is produced by the Choroid Process.  

         The Pia Mater.

This is the layer closest to the brain. It is rich in the number of blood vessels around it and forms shapes according to the contours of the brain. The functions of the Pia mater include;

  • Separating blood vessels in the subarachnoid space from neural tissues.
  • Contributes by making the Blood-Brain Barrier stronger and more efficient.
  • Helps in the degradation of neurotransmitters produced to ensure that they do not stay active for a period longer than required.

Spinal Meninges.

There also exists spinal meninges. These are;

  •  Spinal Dura mater

Has only one layer (The meningeal layer), unlike the one in the brain which has three layers. It extends up to the level of S2 vertebral level, thus extending below the spinal cord termination(L1/L2).

It is also important to note that it has its own Periosteum and the space formed between the Spinal dura mater and the periosteum is called the Epidural space.

  • Spinal Arachnoid mater.

The Arachnoid mater of the brain continues to form the spinal Arachnoid mater.

There is also the formation of the subarachnoid space, which is formed as a result of the space between the spinal arachnoid mater and the spinal pia mater. The subarachnoid space expands to form the lumbar cistern.

  • Spinal pia mater.

The spinal pia mater continues onto the cranial pia. This continuation occurs at the level of the foramen magnum (T-12). It closely encloses the spinal cord and contains a vascular plexus that supply the spinal cord tissue.

Meningeal Spaces.

As the name suggests, these are spaces between the Meninges. These spaces include;

  1. The Epidural space.
  2. The Subdural space.
  3. The subarachnoid space.

 

Clinical significance

Injuries to the meninges, often result in;

  • Hemorrhage –  Subarachnoid hemorrhage.
  • Hematoma – The word Hematoma means a collection of blood. There are two types of hematoma that might occur; subdural hematoma and Epidural Hematoma.

Other medical conditions that affect the meninges include;

  • Meningitis (Can occur either from a bacterial, viral or fungal type of infection). 
  • Meningioma.

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TYPES OF MENINGITIS.

Now that you are familiar with what Meninges are, we can now go back to our main article of the day, which was about Meningitis. You have to take note that Meningitis is a very serious condition and is life-threatening.

A patient with Meningitis should receive urgent medical assistance to avoid death, other related complications like brain damage, and learning problems. Meningitis can be caused by three types of infections. These are;

  • Fungal Infections.
  • Bacterial infections.
  • Viral infections.

         Fungal Meningitis

If you are a healthy person and your immunity is good, then the risk of getting Fungal Meningitis is really low. People who have a weakened immune system for example in HIV, are more susceptible. This is the reason why it is rare to come across, compared to Bacterial and viral Meningitis.

The condition comes to life when someone has had a Fungal infection that was able to penetrate into the bloodstream and able to find its way to the Brain or the Spinal cord.

Some of the most common fungal infections that cause fungal Meningitis with Cryptococcus being the most common include;

  1. Cryptococcus.

Also known as Cryptococcus neoformans

Cryptococcus neoformans can be found in the soil or even in a bird dropping. It is the most common cause of Fungal Meningitis. It infects a person when inhaled.

  1. Histoplasma

Causes a fungal disease known as Histoplasmosis. It can also be found in soil, bird droppings, or decaying wood. Its mode of transmission is through inhaled air.

  1. Blastomyces.

It is the cause of Blastomycosis infection. The mode of transmission is the same as the above infections.

     4. Coccidioides.

It is the known cause of the Valley Fever infection which is also transmitted when a person breaths in the spores from the air.

    5.  Candida.

        This is a type of fungus, a yeast to be precise, which causes Candidiasis. Candida live on the skin and inside the body of human being as normal flora, and it is known to be opportunistic when the immunity of the person is weakened in Immunodeficiency diseases. A candida infection can sometimes grow excessively and evade the brain and spinal cord causing Fungal Meningitis. This type of condition is not common.

These infections can be treated with antifungal medications.

Bacterial Meningitis.

Bacterial Meningitis is the second most common cause of Meningitis (but it is the most severe), and could lead to very serious complications and even death if no urgent medical attention is provided as soon as possible. The most common complication of this type of Meningitis is Brain damage.

Because this is a medical emergency, the doctor will often treat the patient with broad-spectrum antibiotics before the blood samples can be taken to the lab. This is done because there are many types of bacteria that might be causing the infection, and therefore this may take up a bit of time before the lab results are back.

The Broad-spectrum antibiotics are given to try and fight any type of bacterial infection that may be causing the bacterial infection.

The most common types of bacteria causing bacterial meningitis include;

  •  Pneumococcus

          It can also be known as Streptococcus pneumoniae. Pneumococcus is a gram-positive bacteria                that can be found mostly in the respiratory tract and nasal cavity. This bacteria is the most                        commonly known cause of bacterial meningitis in infants.

  • Haemophilus influenzae (Type B (Hib). It was once the most common cause of bacterial meningitis before vaccines were developed. Vaccines have greatly reduced the number of infections caused by these bacteria.
  • Neisseria meningitides. This is one of the most common causes of upper respiratory system infections.
  • Listeria monocytogenes. Pregnant women can easily infect newborns because Listeria can cross the placental barrier to cause Listeriosis. Infections in late pregnancy may be very fatal to the infant.

We use Antibiotics to treat these bacterial infections.

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Viral Meningitis

Viral causes of meningitis account for between 80 – 85% of Meningitis, making it the most common cause of Meningitis. It occurs due to a viral infection.

You will also find that some books refer to it as Aseptic Meningitis. In viral Meningitis, there is no evidence of bacterial in the CSF (Cerebrospinal fluid).

The most common cause of Viral Meningitis is Enteroviruses, including coxsackievirus and Echo viruses, which are commonly found in the gastrointestinal system (GIT).

Other viruses that can cause Viral Meningitis are;

  • Herpes simplex viruses (Type I and II).
  • Human Immunodeficiency Virus (HIV).
  • Varicella virus.

It is very hard to treat viral infections, therefore there is no treatment for Viral Meningitis. It is usually a self–limiting the type of infection and it will clear by itself. The treatment is therefore what we call a supportive type of treatment. In this treatment, the patient may be prescribed anti-inflammatory drugs to reduce the pain, and corticosteroids because of the inflammation (Remember that Meningitis is because of the inflammation of the Meninges).

However, if the patient’s cause of the Viral Meningitis is the Herpes Virus, then the doctor might be able to treat the condition using Antiviral medication.

Mechanism of Action (Simplified)

Let us discuss briefly the Mode of Action of Meningitis. The cause of Meningitis is an infectious organism that has been able to colonize another part of the body.

Normally, the body is able to fight infectious agents that attack any part of the body to try and prevent this colonization, but in persons with an already weakened immune system, like in Cancer patients, the immunity is not strong enough. Therefore the infectious microorganism finds it easy to colonize and infect the body.

Commonly infected body sites are the skin and the gastrointestinal system, just to name a few

After the invasion, they penetrate the submucosa by invading the defense mechanism, for example, Macrophages. Then can now access the bloodstream where they are able to move into the CNS. Their invasion causes activation of the immunity, which produces cytokines and other chemicals.

The Blood-Brain – Barrier, which is very important in shielding the brain from the body’s Immune system, plus providing very limited access for materials required by the brain e.g. Glucose and some medications. Cytotoxic reactive oxygen species released by the endothelial cells and meninges that have undergone damage due to the infection, disrupt the Blood-Brain Barrier.

 Disruption of the Blood-Brain – Barrier prevents the immune system from reaching the infection, therefore the body’s immune system is unable to fight off the infection. This isolation from the immune system means the infection can spread and do more harm, leading to increased Cranial pressure or even neurological death.

SIGNS AND SYMPTOMS

The incubation period of Meningitis is between 2 to 10 days, this means that signs and symptoms may appear between these time periods. Signs and symptoms include;

  • Seizures
  • Headaches accompanied by nausea and vomiting. Headaches are more severe than usual.
  • Confusion
  • Loss of appetite
  • Constant crying in newborns.
  • High fever.
  • Poor feeding in children.
  • The patient complains of a stiff neck.
  • Skin rash.

 

Risk Factors for Meningitis.

Anyone can get Meningitis, but the following group of people is at a higher risk of developing the disease;

  • Immunosuppressed individuals.

These include cancer patients with HIV infection, on Chemotherapy, patients using immunosuppressing drugs like Calcineurin Inhibitors: Tacrolimus and Cyclosporine.

Patients who have undergone splenectomy are also at risk and require frequent vaccination to minimize the risk of contracting Meningitis.

  • Unvaccinated individuals

Children who missed their required vaccination during their infancy period are also at risk. If your child did not receive the recommended vaccine, make sure you visit the hospital so that they can receive it as fast as possible. This also applies to adults.

  • Expectant women.

Pregnant women are at risk of infection by a bacteria called Listeria, which is the cause of a disease we call Listeriosis.  This increases their chances of having a miscarriage or even stillbirths.

  • Young age.

Children between the ages of 5 – under 20 years are at a higher risk of getting Meningitis.

  • Environment one lives in.

 Army personnel, college students who living in crowded hostels, and children in boarding school have a higher risk of contracting Meningococcal Meningitis, which is spreads through inhalation.

 

Diagnosis.

A good history from the patient is key in the treatment of Meningitis. The patient’s history will enable to you to know a lot of things which might be helpful to you as a doctor. for example, in the past medical history, you may be able to find out that the patient was never immunized, making high at a higher risk of contracting the disease.

The doctor will also do a physical examination to see any evidence of an infection, maybe in the Mouth, throat, ears, or even the skin.

The patient will then undergo the following diagnostic tests which will help in the diagnosis and treatment. These tests include;

         Lumbar Puncture.

This the best diagnostic test we do to determine if the patient has bacterial Meningitis. If viral meningitis is a suspect, the doctor will order a Polymerase Chain Reaction test (PCR). We perform the Lumbar Puncture on your lower back, in the lumbar region.

Lumbar Puncture PROCEDURE

During the Spinal Tap procedure, we insert a needle between two lumbar bones (vertebrae) to remove a sample of cerebrospinal fluid. In a person who has Meningitis, the following will be found in the test results;

  1. During the lumbar puncture, we might notice increased pressure of the CSF draining. This is because of increased intracranial pressure caused by the infection.
  2. There is an increased number of White Blood Cells. As you know, white blood cells are the body’s soldiers that fight infections. Their numbers will be elevated by the body’s immunity to fight off the infection. (Normal White Blood Cell Count : 0 – 5)
  3. There will be a decrease in glucose levels (Slow sugar levels). Normal glucose levels in the CSF are between 50 – 80 mg/mL. These values might differ from one laboratory to the other.
  4. The color of the CSF fluid will be turbid in bacterial Meningitis while clear in the other two types of Meningitis.

         Imaging tests.

An MRI may be requested to show if there is any inflammation or swelling. On the other hand, the doctor can request a chest X-ray to look for any Meningitis related infection.

An MRI Scanning Machine used to diagnose Meningitis

         Blood culture.

We use this test to identify the type of organism present. One important thing to note is that the sample should be taken before administration of any medication, for example, antibiotics in a critically ill patient. We do this to get accurate results.

 

Treatment.

Treatment of Bacterial Meningitis.

Meningitis caused by Bacterial are often life-threatening and should be handled swiftly. The doctor will have to admit the patient to the hospital for a few days for close monitoring.

In Patients with acute meningitis, we immediately give broad-spectrum antibiotics intravenously. We do this before the lab results come back. If you wait for the lab results before starting treatment, the patient might not make it.

The doctor can administer Corticosteroids to reduce the occurrence of complications e.g. Seizures.

The doctor will also drain the Infected mastoid and sinuses.

Treatment of Viral Meningitis.

Like I said before, viral meningitis is usually self-limiting, meaning it will clear all by itself. We give supportive treatment, which entails;

  • Getting lots of rest.
  • Medications to reduce pain and inflammation.
  • Getting a lot of fluids.

In the case of Meningitis caused by Herpes infection, the doctor will prescribe antiviral drugs. Finally, Swelling will also be reduced through the administration of Corticosteroids.

Treatment of Fungal Meningitis

Treatment of Fungal Meningitis will include the use of Antifungal drugs. The course of treatment depends on the patient’s immune system – The weaker the system, the longer the treatment. Fungal meningitis will require a long course of high-dose antifungals.

We can administer these drugs intravenously. After that, the doctor might decide to now give the antifungal medications orally.

 

Prevention of Meningitis

  1. First of all, remember to cover your mouth when sneezing or coughing. Always sneeze into your elbows, disposable tissue, or a clean handkerchief.
  2. Secondly, always eat a balanced diet with all the required vitamins, carbs, and proteins, while more importantly drinking enough water. This boosts the strength of your immune system.
  3. Expectant women should always have regular checkups to ensure they are in good health. Also, they should also eat a balanced diet, which has to be properly cooked. This will ensure that they are not at risk of contracting Listeriosis.
  4. Ensure children get the recommended immunization as recommended by your doctor.
  5. Similarly, wash your hand and maintain good hygiene in order to reduce the spread of germs.

 

Vaccines Available for Meningitis

Meningococcal conjugate vaccine.

Pneumococcal conjugate vaccine (PCV13).

Haemophilus influenzae type b (Hib) vaccine.

Pneumococcal polysaccharide vaccine (PPSV23).

 

 

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