T1 post contrast MRI study in axial view. The leptomeninges enhance post gadolinium contrast injection.
Meningoencephalitis: Bacterial
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Bacterial
Overview
- Acute, purulent meningitis (the most dangerous).
- On gross brain inspection, this classically causes opacity of the leptomeninges.
- On microscopic inspection, we see neutrophilic infiltration.
- Abscess/empyema (often iatrogenic).
- See: Brain Abscess
- On gross inspection, we see central, liquefactive necrosis and granulation tissue.
- On microscopic inspection, we see reactive astrocytes surrounding a fibrous capsule.
- Chronic meningitis (which often acts like fungal meningitis).
- < 10 cells, 70% of which are lymphocytes
- Glucose is 60% of that of the serum glucose
- Protein is from 15 to 45
- CSF pressure is usually 70 to 180 mmH2O.
- Cell counts are typically > 1,000, the majority of cells are usually polymorphonuclear cells (PMNs)
- Glucose is low
- Protein is elevated
- Intracranial pressure is elevated from CSF obstruction
- Group B. strep and E. Coli are notable causes of neonatal meningitis.
- Group B strep is more common, whereas E. coli is more fatal.
- Listeria is most often found in those older than 50 who are immunocompromised.
- Meningococcal meningitis (from Neisseria meningitidis) occurs most often in teens and young adults.
- Pneumococcal meningitis from Streptococcus pneuomniae is the most common cause of bacterial meningitis across all ages.
- Waterhouse-Friderichsen syndrome can occur in meningococcal and pneumococcal meningitis, wherein patients present with septicemia, cutaneous petechiae and purpura, and adrenal gland hemorrhagic infarcts.
Abscess/empyema
- Typically polymicrobial (eg, staphylococcus aureus and streptococcus).
- Direct implantation (most commonly from surgery)
- Hematogenous causes, notably, are: tooth extraction, immunosuppression, bronchiectasis, endocarditis, and congenital heart disease.
- Local extension occurs most commonly from mastoiditis and sinusitis.
Chronic meningitis
- Mycobacteria, most notably: tuberculosis (TB).
- Causes a basilar meningitis, which manifests with hydrocephalus (swelling of the ventricles from CSF obstruction).
- Commonly causes tuberculomas (mass lesions) and typically occurs in immunosuppressed individuals.
- Spirochete causes: Neurosyphilis and Lyme disease
- Neurosyphilis also causes a basilar meningitis and causes gummas. It manifests with obliterative endarteritis (often presenting with sensori-neuronal hearing loss).
- Lyme disease is a rare cause of meningitis. Indicate that it is one of the few causes of bilateral facial palsies. It is caused by the Ixodes tick.
- Rickettsia rickettsi
- Causes Rocky mountain spotted fever, which notably manifests with a non-itchy red rash that starts on the wrists and ankles.