CNS Infections and Meningitis

CNS Infections: Routes of Infections/Meningitis

• The brain and its coverings can be sites of infection
• Meningitis is caused by inflammation of the protective membranes covering the brain and spinal cord
• The annual incidence of meningitis is higher than 2.5 cases per 100,000 population
• Meningitis incidence is declining because of vaccinations
• Damage to the nervous tissue can be a consequence of infectious agents, microbial toxins, or host immune responses

Routes of Entry for Infectious Agents

• Hematogenous spread is the most common route of entry
• Direct implantation
• Local extension
• Peripheral nerve is the least common route of entry

Terminologies

• Meningitis is an inflammatory process involving the leptomeninges located within the subarachnoid space
• Meningoencephalitis refers to inflammation of the meninges and the brain parenchyma
• Infectious meningitis can be divided into three types: acute pyogenic, aseptic, and chronic (usually tuberculous)
• Examination of the CSF is useful to identify the cause of meningitis

Acute Pyogenic (Bacterial) Meningitis

• Many bacteria including Escherichia coli and group B streptococci can cause it depending on the age
• In neonates, common organisms are Escherichia coli and group B streptococci
• In adolescents and young adults, Neisseria meningitidis is the most common pathogen
• In older individuals, Streptococcus pneumoniae and Listeria monocytogenes are more common
• Lumbar puncture reveals increased pressure, CSF containing abundant neutrophils, elevated protein, and reduced glucose

Morphology

• Exudate is evident within the leptomeninges over the surface of the brain.
• The meningeal vessels are engorged
• Tracts of pus can be found along blood vessels on the brain surface.
• Fulminant meningitis, focal cerebritis and Ventriculitis

Microscopy

• Neutrophils fill subarachnoid space in affected areas, found near leptomeningeal blood vessels in less severe cases
• Phlebitis can lead to venous occlusion and hemorrhagic infarction.
• Early treatment can leave little damage
• Leptomeningeal fibrosis may follow pyogenic meningitis and cause hydrocephalus
• Pneumococcal meningitis leads to gelatinous exudate that promotes arachnoid fibrosis, referred to as chronic adhesive arachnoiditis

Clinical Features

• Adults may experience headache, nuchal rigidity, fever, photophobia, irritability, and clouded consciousness
• Positive Kernig's and Brudzinski's signs may be present
• Neonates may exhibit poor feeding, lethargy, irritability, apnea, apathy, fever, bulging frontanelle, and hypoglycemia

Aseptic Meningitis (Viral Meningitis)

• Aseptic meningitis is where bacterial cultures are absent, but the patient shows manifestations of meningitis (meningeal irritation, fever, altered consciousness)
• Viral etiology accounts for 80% of cases like Enteroviruses like Echovirus & Coxsackie
• Other causes can be bacterial, rickettsial, or autoimmune
• Viruses can include Measles and influenza

Aseptic Meningitis

• CSF profiles include : lymphocytic pleocytosis, mild protein increase; normal glucose
• Viral aseptic meningitis normally is self limiting
• Resolves from the treatment of the symptoms
• Exposure to chemical irritants may cause an aseptic like reaction to be developed
• Ruptured epidermal and subarachnoid cysts may cause the disease

Fungal Meningitis

• Fungalinfections in the CNS are mostly within immunocompromised individuals
• Common offenders include Candida albicans, Mucor species, and Cryptococcus neoformans
• Brain damage often occurs following the hematogenous spread of fungi.
• Cryptococcal meningitis is an opportunistic diseases that can occur with AIDS patients. Fatal in two weeks, or progressivley evolving for months and years
• CSF with few cells but great quanitites of potein is common sign
• Can be visualized with special stains or assays

Chronic Bacterial Meningitis

• It may be caused by Mycobacterium tuberculosis.
• Tuberculosis of the CNS may be part of active disease
• The CSF shows pleocytosis with mononuclear or mixed cells, elevated protein, and reduced/normal glucose
• Serious complications include arachnoid fibrosis leading to hydrocephalus
• Also obliteration of the arteries may be a cause

Morphology

• Subarachnoid space characterized by gelatinous/fibrinous with effacing cisterns and cranial nerves
• Discrete areas can be covered with white inflamation
• Microscopically mixed inflamation present containing macrophages, plasma cells and lymphocytes

Morphology (cont)

• Florid cases, well formed granulomas develop containing caseaus necrosis (giant cells)

Acute Focal Suppurative Infections

• Acute focal suppurative infections can lead to a brain abscess, subdural empyema, or an extradural abscess

Brain Abscess

• Localised necrosis located in the brain tissue with accompanied inflammation
• Happens due to bacterial infaction
• Brain abcesses occur due to direct implantation of organisms, local extension and hematogenous spread
• Predisposing conditions include endocarditis and congenital heart disease

Brain Abscess (cont.)

• The CFS white cell count and the protein levels high however glucose levels normal
• Abscesses are destructive
• Patients often times present with general signs related to high intracranial pressure Surgical and medicinal treatment with antibiotics can help reduce death of patients leading to even better outcomes

Morphology

• Forms discrete lesions with central liquefactive necrosis
• Fibrous casule
• Under examination the neurotic enter is commonly surounded by edema and granulation
• The outisde the fiors capsule characterized by reaction gliosis

Subdural empyema

• Bacteria rarely fungal infections of the skull bones or air space can move in due to subdural space
• May cause a a thromobophlebitis
• Patients display headaches and neck stiffness
• Treatment involves a surgical drain for quick resolutions

Extradural Abcess

• Commonly associated with osteomyelitis
• May be caused by sinusitis or other surgeries procedures
• In the spinal epidural space the procedure may cause spinal compression and constitute a neuro suericial emergency

Other important CNS infections

• Subacute sclerosing panencephalitis is caused by the measles virus characterized by viral inclusion in CSF
• HIV causes cognitive dysfunction ranging from mil to full blown dementia or HIV-associated neurocognitive disorder(HAND)
• Poliomyelitis: Damages motor neurons

Other Important CNS Infections:

• Poliomyelitis caused by poliovirus: damages the peripheral nerve of motor neurons, and brain stem (paralysis)

Conclusion

• The central nervous system is vital to the functioning of the human body thus infection may cause compromise