Pyogenic meningitis, also referred as bacterial meningitis, is a life-threatening CNS infectious disease affecting the meninges, with elevated mortality and disability rates. Three bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis) account for the majority of cases 4,5.
On this page:
Epidemiology
The epidemiological spectrum of pyogenic meningitis has changed in the last two decades in some countries due to routine vaccination. Largely the use of the H. influenzae type b (Hib) conjugate vaccine for infants and the heptavalent protein-polysaccharide pneumococcal conjugate vaccine (PCV7) are good examples that explain the significant reduction in H. influenza and pneumococcal disease incidences. Near elimination of serogroup C meningococcal meningitis and H. influenzae meningitis has been documented in wealthy nations 3,4.
The median age at diagnosis of bacterial meningitis has increased in the last few decades as a result of childhood vaccination, although infants under 2 months of age have not experienced this incidence reduction 3.
It is important to note that chronic and immunocompromising conditions are common predisposing factors for bacterial meningitis among adults, including 5:
elderly patients (>65 years)
splenectomy and hyposplenism
alcoholism
anatomical defect (related to recurrent meningitis)
organ transplant recipients
Clinical presentation
In older children and adults there are typical symptoms and signs, such as:
fever
headache
stiff neck
vomiting
mental dysfunction ranging from lethargy to coma.
The signs are less clear cut in infants, with non-specific features including sepsis and seizures 2.
The diagnosis is usually confirmed by lumbar puncture.
Pathology
Bacteria may arise in the CNS as a result of direct implantation, contagious infection from a local septic process (e.g. sinusitis) or an infected foreign body (e.g. a shunting catheter), or by haematogenous spread 2.
Aetiology
group B streptococcus (GBS): the major cause of bacterial meningitis in infants under 2 months of age
Neisseria meningitidis: the major cause of bacterial meningitis in older children and young adults
Streptococcus pneumoniae: the most common pathogen in adults
Staphylococcus aureus: post neurosurgical procedures, penetrating head trauma or haematogenous spread secondary to infection outside the nervous system 9
Listeria monocytogenes: known to affect immunocompromised patients as well as high-risk groups such as neonates and the elderly 8
Radiographic features
As the response to these insults is limited and follows a stereotypical fashion, the imaging findings are mostly non-specific with respect to the causative pathogen. Nevertheless, imaging findings are helpful in detecting an abnormality and making differential diagnoses with other non-infectious causes 1. Overall cross-sectional imaging is neither sensitive nor specific for diagnosing meningitis 7.
CT
Reported CT findings include sulcal effacement and slight hyperattenuation on unenhanced CT but false positives are common 7.
MRI
Increased FLAIR signal relative to normal cortex may be seen but this is not specific for meningitis 7.
On post-contrast MRI, the most common positive findings are thin and linear leptomeningeal enhancement (only seen in 50% of patients 7). More specifically, if seen, smooth or linear enhancement is more characteristic of acute pyogenic (bacterial) and lymphocytic viral meningitis. If a more nodular thick enhancement pattern is seen especially involving the basal cisterns, leptomeningeal carcinomatosis or granulomatous disease is more likely 7.
Other findings on MRI may include cerebral sulcal restricted diffusion relative to normal cortex 7.
Treatment and prognosis
Empirical antimicrobial therapy for purulent meningitis is guided by the age of the patient 3.
The adult case fatality has a straight correlation with increasing age, the overall rate is estimated at around 16% in the USA, ranging from ~9% among patients 18 to 34 years of age vs. ~23% among those older than 65 years 3.
Complications
The complications of meningitis can be remembered using the mnemonic HACTIVE 6:
A: abscess
C: cerebritis / cranial nerve lesion
T: thrombosis
I: infarct
V: ventriculitis / vasculopathy
E: extra-axial collection: empyema and/or hygroma
Differential diagnosis
fungal meningitis: usually exhibit a thicker, lumpy or nodular enhancement 1
Unable to process the form. Check for errors and try again.