CNS Infections.pdf

CNS INFECTIONS C Bacteria gain access to the CNS by : 1. direct spread from an adjacent focus of infection, ( the paranasal sinuses or middle ear; 2. direct spread from outside the body, (open skull fractures 3. septicaemia or septic emboli (bacterial endocarditis and bronchiectasis) 4. iatrogenic i...

CNS INFECTIONS C Bacteria gain access to the CNS by : 1. direct spread from an adjacent focus of infection, ( the paranasal sinuses or middle ear; 2. direct spread from outside the body, (open skull fractures 3. septicaemia or septic emboli (bacterial endocarditis and bronchiectasis) 4. iatrogenic infection,: following introduction of organisms into the CSF at lumbar puncture; meningitis may occur in 20% of patients with a ventriculo-peritoneal shunt, (S.epidermidis,) Bacterial meningitis inflammation in the subarachnoid space involving the arachnoid and pia mater, i.e. leptomeningitis. inflammation involve predominantly the dura mater (pachymeningitis). Pachymeningitis direct spread of infection from the bones of the skull following otitis media or mastoiditis, or complication of skull fracture. Gram-negative bacilli from the middle ear, α or β haemolytic streptococci from paranasal sinuses, or mixed organisms, often with Staphylococcus aureus, from skull fractures. An epidural or subdural abscess may then occur. are usually required before healing can occur Epidural abscess. suppuration between the dura mater and the skull or vertebral column. act as space-occupying lesions, require surgical drainage and antibiotic therapy healing by fibrosis Subdural abscess. a localized lesion, (subdural empyema). surgical drainage and antibiotic therapy Leptomeningitis result of blood-borne spread of infection. in neonates: Escherichia coli, Streptococcus agalactiae, Listeria monocytogenes, Salmonella spp. 2-5 years: Haemophilus influenzae type B 5-30 years: Neisseria meningitides over 30 years: Streptococcus pneumoniae type 3. Tuberculosis and syphilis Meningococcal meningitis is the commonest variety; occur in sporadic or as an epidemic outbreak Subgroups A and C of Neisseria meningitidis are associated with epidemic disease, while subgroup B is usually responsible for solitary cases. The organism is spread in droplets from asymptomatic nasal carriers; The organism reaches the CNS by haematogenous spread, A petechial rash may herald the onset of disseminated intravascular coagulation accompanied by adrenal haemorrhage (Waterhouse-Friderichsen syndrome), which is often fatal. Diagnosis and complications of bacterial meningitis Examination of the CSF by lumbar puncture is essential in each case; pus is present in the cerebral sulci and around the base of the brain, extending down around the spinal cord Common complications of bacterial meningitis are: cerebral infarction obstructive hydrocephalus cerebral abscess subdural empyema epilepsy. Cerebral abscess develops from an acute suppurative encephalitis following: 1. direct spread of Gram-negative bacilli, from the paranasal sinuses or middle ear 2. septic sinus thrombosis, due to spread of infection from the mastoid cavities or middle ear 3. haematogenous spread, for example in patients with infective endocarditis or bronchiectasis. most often found in the parietal lobes, and are often multiple. The clinical presentation is similar to that of acute bacterial meningitis, but focal neurological signs, epilepsy and fever are common manifestations. Abscesses act as space-occupying lesions Complications of cerebral abscesses include: meningitis intracranial herniation focal neurological deficit epilepsy. CNS Tuberculosis always secondary to infection elsewhere in the body; the lungs are the commonest site. CNS involvement takes two main forms: tuberculous meningitis and tuberculomas. Tuberculous meningitis result of haematogenous spread from a primary or secondary complex in the lungs Tuberculomas lesions consist of focal areas of granulomatous inflammation with caseation, and are surrounded by a dense, fibrous capsule. occur most frequently in the cerebellum and present with signs and symptoms of raised intracranial pressure; CNS infection by viruses can occur by the following mechanisms: haematogenous spread as part of a systemic infection with viraemia, usually causing meningitis or encephalitis neural spread along peripheral sensory nerves by retrograde axonal transport. Certain viruses exhibit neurotropism-a tendency to spread specifically to the CNS from the initial site of infection, for example polio virus from the gut. Viruses can cause neurological dysfunction either as a result of viral multiplication within cells of the CNS, or as a result of an immunological response to a viral infection Viral meningitis clinically less severe than bacterial meningitis. the viruses reach the CNS by haematogenous spread. Common organisms are: echovirus 7, 11, 24, 33 coxsackie B1-5 coxsackie A9 mumps virus other enteroviruses. Viral encephalitis Most cases are mild, self-limiting conditions rabies and herpes simplex type I infections, result in extensive tissue destruction and are often fatal. Herpes simplex encephalitis is the commonest cell lysis (cytolytic viral infection) and phagocytosis of cell debris by macrophages; when neurones are involved,, this process is known as neuronophagia viral inclusions, which can often be detected in infected neurones or glial cells; occasionally, these can be of diagnostic value, for example, 'owl-eye' inclusions in cytomegalovirus infection, or Negri bodies in rabies uncommon; haematogenous spread from the lungs, direct spread of infection from the nose and paranasal sinuses also occurs. in immunosuppressed patients Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus are usually accompanied by pulmonary infection Uncommon Toxoplasma gondii, which may be congenital Plasmodium falciparum, causing one form of malaria Trypanosoma rhodesiense, causing chronic meningoencephalitis Entamoeba histolytica, causing solitary amoebic abscess Taenia solium, causing cerebral cysticercosis Echinococcus granulosus, causing solitary hydatid cyst Toxocara canis, causing eosinophilic meningitis, with granulomas around larvae. Infections in immunosuppressed patients CNS infections are common in immunosuppressed patients, atypical mycobacteria cytomegalovirus papovaviruses Candida albicans Aspergillus fumigatus Cryptococcus neoformans Toxoplasma gondii Entamoeba histolytica.