Meningitis and other meningeal infections
How bacteria, viruses, mycobacteria and fungi reach the CSF, why bacterial meningitis fills it with pus and injures the brain, how tuberculous and cryptococcal infection smoulder at the base, and how CSF findings and meningococcal sepsis follow.
By the end, you can
- Explain how bacteria reach and multiply in the CSF, and relate the likely organisms to age and defences.
- Describe the purulent exudate of bacterial meningitis and explain how it causes oedema, infarcts, deafness and hydrocephalus.
- Compare viral, tuberculous and cryptococcal meningitis, and explain the CSF pattern of each.
- Explain the rash, shock and adrenal haemorrhage of meningococcal sepsis.
- Recognise the classic appearances and tests of meningitis, and explain how antimicrobials, corticosteroids and conjugate vaccines act on the mechanism.
What it is
Meningitis is inflammation of the leptomeninges (the arachnoid and pia) and of the cerebrospinal fluid (CSF) in the subarachnoid space between them, usually caused by infection. Bacterial meningitis fills the space with pus and is an emergency; viral (aseptic) meningitis causes a milder lymphocytic reaction; tuberculous and fungal meningitis develop over weeks with a thick exudate at the base of the brain.
4 types to tell apart
- Acute bacterial (purulent) meningitis
- Neutrophils and pus in the CSF; meningococci and pneumococci beyond infancy, with other organisms in newborns and older or immunosuppressed people.
- Viral (aseptic) meningitis
- Lymphocytes with a normal CSF glucose; enteroviruses are the usual cause, and most people recover fully.
- Tuberculous meningitis
- Subacute; a gelatinous basal exudate with granulomas that traps cranial nerves, blocks CSF and narrows arteries.
- Fungal meningitis
- Mainly Cryptococcus in weak T-cell immunity, such as advanced HIV infection; chronic, with very high CSF pressure.
US spelling: microlitre → microliter.
Normal function
The meninges, the CSF and its barriers
Three meninges cover the brain and spinal cord. The tough lines the skull; beneath it the thin and the delicate pia on the brain surface form the leptomeninges. Between them, the subarachnoid space is filled with CSF and crossed by the arteries and veins of the brain surface and the roots of the cranial nerves. Meningitis is inflammation of this space and its membranes.
CSF is made by the choroid plexus in the ventricles, flows out over the brain and spinal cord, and is absorbed into the venous sinuses, such as the , through the arachnoid granulations. Two barriers control what enters it: tight junctions between the endothelial cells of brain capillaries (the blood–brain barrier) and between the epithelial cells of the choroid plexus (the blood–CSF barrier). Glucose is carried across, so CSF glucose is normally more than half the blood level, but most protein and cells are kept out.
Normal CSF is clear, with up to about 5 lymphocytes per microlitre and little protein, antibody or complement. That spares the brain from inflammation, but it also means that microbes crossing the barrier meet almost no defence at first.
Underlying change · Step 1 of 5
How bacteria reach the CSF
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Bacterial meningitis: pus in the subarachnoid space
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 3 of 5
Viral, tuberculous and fungal meningitis
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
How meningitis injures the brain and nerves
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
When bacteria flood the blood: meningococcal sepsis
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .