Pyogenic meningitis, also referred as bacterial meningitis, is a life-threatening CNS infectious disease affecting the meninges, with an elevated mortality and disability rates. Three bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis) account for the majority of cases 4,5.
The epidemiological spectrum of pyogenic meningitis has changed in the last two decades in some countries due 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 on 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 decades as a result of children 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 were common predisposing factor for bacterial meningitis among adults, such as 5:
- elderly patients (>65 years)
- splenectomy and hyposplenic state
- diabetes mellitus
- anatomical defect (related with recurrent meningitis)
- organ transplant recipients
In older children and adults there are typical symptoms and signs, such as: fever, headache, stiff neck, committing and mental dysfunction hanging from lethargy to coma. The signs are less clear in infants, being related to non-specific signs of sepsis and seizures 2.
The diagnosis is usually confirmed by lumbar puncture.
Bacteria may arise at 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.
- group B streptococcus (GBS): is the major cause of bacterial meningitis in infants under 2 months of age
- Neisseria meningitidis: is the major cause of bacterial meningitis in older children and young adults
- Streptococcus pneumoniae: is the the most common pathogen in adults
As the response to these insults are limited and follows a stereotypical fashion, the imaging findings are mostly nonspecific with respect to the causative pathogen. Nevertheless, imaging findings are helpful in detecting an abnormality and making differential diagnosis with other noninfectious causes 1.
CT and MRI
- typically shows thin and linear leptomeningeal enhancement
The complications of meningitis can be remembered using the mnemonic HACTIVE 6.
- H: hydrocephalus
- A: abscess
- C: cerebritis / cranial nerve lesion
- T: thrombosis
- I: infarct
- V: ventriculitis / vasculopathy
- E: extra-axial collection: empyema and hygroma
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 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.
- 1. Mohan S, Jain KK, Arabi M et-al. Imaging of meningitis and ventriculitis. Neuroimaging Clin. N. Am. 2012;22 (4): 557-83. doi:10.1016/j.nic.2012.04.003 - Pubmed citation
- 2. Kennedy P. Infections of the Nervous System: Butterworths International Medical Reviews (Butterworths International Medical Reviews/Neurology, Vol 8). Butterworth-Heinemann. ISBN:B00IPDIYXE. Read it at Google Books - Find it at Amazon
- 3. Thigpen MC, Whitney CG, Messonnier NE et-al. Bacterial meningitis in the United States, 1998-2007. N. Engl. J. Med. 2011;364 (21): 2016-25. doi:10.1056/NEJMoa1005384 - Pubmed citation
- 4. McIntyre PB, O'Brien KL, Greenwood B et-al. Effect of vaccines on bacterial meningitis worldwide. Lancet. 2012;380 (9854): 1703-11. doi:10.1016/S0140-6736(12)61187-8 - Pubmed citation
- 5. Adriani KS, Brouwer MC, van de Beek D. Risk factors for community-acquired bacterial meningitis in adults. Neth J Med.73 (2): 53-60. Pubmed citation
- 6. Hughes DC, Raghavan A, Mordekar SR, Griffiths PD, Connolly DJ. Role of imaging in the diagnosis of acute bacterial meningitis and its complications. Postgrad Med J. 2010 Aug;86(1018):478-85. doi: 10.1136/pgmj.2010.097022. Review. PubMed PMID: 20709770.