[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Central nervous system](https://durgical.com/en/general-pathology/areas/cns/) › Acute meningitis: pyogenic vs aseptic # Acute meningitis: pyogenic vs aseptic - Lesion Meningitis is infection of the brain's coverings; bacteria give pus and an emergency, viruses usually a milder illness. Updated Nov 12, 2026 ## Key points - Newborns: group B streptococcus, Escherichia coli and Listeria monocytogenes. - Children and adults: Streptococcus pneumoniae and Neisseria meningitidis; Haemophilus influenzae type b fell sharply with vaccination. - Older adults and the immunosuppressed: pneumococcus and Listeria. - Pyogenic CSF: many neutrophils, high protein, low glucose; viral: lymphocytes, mildly raised protein, normal glucose. - Meningococcemia can cause adrenal hemorrhage and shock (Waterhouse-Friderichsen syndrome). - Enteroviruses are the most common cause of viral meningitis. ## What it is Acute meningitis is inflammation of the leptomeninges and CSF. Bacterial (pyogenic) meningitis fills the subarachnoid space with neutrophils and fibrin and can kill within hours through raised pressure, vasculitis and sepsis. Aseptic meningitis, usually viral, gives a lymphocytic CSF and is generally self-limited. The organism depends on age and setting, and the CSF profile separates the main causes. ## Structure - Pyogenic: creamy purulent exudate over the convexities (pneumococcus) or base (Haemophilus), with congested vessels. - Micro: neutrophils fill the subarachnoid space and spread along vessels; phlebitis and arteritis can cause venous thrombosis and infarcts. - Late: leptomeningeal fibrosis can block CSF flow and cause hydrocephalus. ## Step by step - Bacteria colonise the nasopharynx or reach the blood from another focus. - They cross the blood-brain barrier at the choroid plexus or meningeal vessels. - Bacterial products trigger cytokines; neutrophils pour into the CSF. - Inflammation raises pressure, damages vessels and injures cranial nerves. - Without treatment: cerebral edema, infarction, herniation and death; survivors may be deaf. ## CSF in the main types of meningitis | Type | Cells | Protein | Glucose | Other clue | | --- | --- | --- | --- | --- | | [Bacterial (pyogenic)](https://durgical.com/en/conditions/bacterial-meningitis/) | Many neutrophils | High | Low | Gram stain and culture positive | | [Viral (aseptic)](https://durgical.com/en/conditions/viral-meningitis/) | Lymphocytes | Normal or mildly high | Normal | PCR for enterovirus, herpesviruses | | [Tuberculous](https://durgical.com/en/conditions/tuberculosis/) | Lymphocytes (neutrophils early) | Very high | Low | Acid-fast stain, molecular tests; basal exudate | | [Cryptococcal](https://durgical.com/en/conditions/cryptococcal-meningitis/) | Few to moderate lymphocytes | High | Low or normal | Cryptococcal antigen, India ink; high opening pressure | ## Clinical notes - Fever, headache, neck stiffness and altered mental state; a petechial rash suggests meningococcus. - Sensorineural hearing loss is a common sequel, especially after pneumococcal meningitis in children. ## Memory aid Bacteria eat the sugar and leave pus; viruses leave the sugar and send lymphocytes. ## Test yourself Think of the answer, then tap the question to see it. ## Which three bacteria cause most neonatal meningitis? Group B streptococcus, Escherichia coli and Listeria monocytogenes. ## How does the CSF glucose differ between bacterial and viral meningitis? Low in bacterial meningitis because bacteria and neutrophils consume it; normal in viral meningitis. ## What is Waterhouse-Friderichsen syndrome? Bilateral adrenal hemorrhage with shock in fulminant meningococcal septicemia. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/acute-meningitis-pyogenic-vs-aseptic/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Meningeal syndrome](https://durgical.com/en/clinical-exam/meningeal-syndrome/) - [Meningeal signs: neck stiffness, Kernig and Brudzinski](https://durgical.com/en/clinical-exam/meningeal-signs-neck-stiffness-kernig-and-brudzinski/) ## Connections ## Related 6 - [Brain abscess and empyema](https://durgical.com/en/general-pathology/brain-abscess-and-empyema/) - [Chronic bacterial meningoencephalitis: TB, syphilis, Lyme](https://durgical.com/en/general-pathology/chronic-bacterial-meningoencephalitis-tb-syphilis-lyme/) - [Viral encephalitis: the shared pattern](https://durgical.com/en/general-pathology/viral-encephalitis-the-shared-pattern/) - [Fungal infections of the CNS](https://durgical.com/en/general-pathology/fungal-infections-of-the-cns/) - [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/) - [How septic shock develops](https://durgical.com/en/general-pathology/how-septic-shock-develops/) ## Related conditions 6 - [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/) - [Viral (aseptic) meningitis](https://durgical.com/en/conditions/viral-meningitis/) - [Meningococcal disease (meningococcemia)](https://durgical.com/en/conditions/meningococcal-disease/) - [Cryptococcal meningitis](https://durgical.com/en/conditions/cryptococcal-meningitis/) - [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/) - [Hydrocephalus](https://durgical.com/en/conditions/hydrocephalus/) ## Microorganisms 7 - [Neisseria meningitidis](https://durgical.com/en/microbiology/neisseria-meningitidis/) - [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/) - [Streptococcus agalactiae](https://durgical.com/en/microbiology/streptococcus-agalactiae/) - [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/) - [Listeria monocytogenes](https://durgical.com/en/microbiology/listeria-monocytogenes/) - [Haemophilus influenzae](https://durgical.com/en/microbiology/haemophilus-influenzae/) - [Enteroviruses](https://durgical.com/en/microbiology/enteroviruses/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Bacterial Meningitis](https://www.ncbi.nlm.nih.gov/books/NBK470351/) (StatPearls (NCBI Bookshelf), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/acute-meningitis-pyogenic-vs-aseptic/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/acute-meningitis-pyogenic-vs-aseptic/