Meningitis and Sub-arachnoid haemorrhage Flashcards
What are the 3 layers od the meninges?
Dura Mater
- Endosteal layer
- Meningeal layer
Arachnoid Mater
Pia Mater
- thin layer closesly adhered to brain
What makes up the leptomeninges?
The arachnoid + pia mater
What are the 4 important dural septa?
- Falx cerebri (between cerebral hemispheres)
- Falx cerebelli (between cerebellar hemispheres)
- Tentorium cerebelli
- Diaphragma sella
Between what layers do epidural bleeds (extradural) occur?
Between the endosteal layer of the dura and the skull
Between what layers do subdural bleeds occur?
Between the meningeal and arachnoid layer
Where is the subarachnoid space?
Between the arachnoid and pia
What are cisterns?
- Enlarged areas that occur in the subarachnoid space when the brain moves away from the skull
- Filled with CSF
What are the functions of CSF?
- Physical support of neural structures
- Excretion of brain metabolites
- Intracerebral transport (hormone releasing factors)
- Control of chemical environment
Describe the flow of CSF through the ventricles of the brain
- Formed in the choroid plexus
- Into lateral ventricles
- Through interventricular foramina to third ventricle
- Through cerebral aqueduct to 4th ventricle
- Through lateral and median aperture (Lushka and Megande) to subarachnoid space and small amount into spinal cord
How is CSF reabsorbed?
By arachnoid granulations that project into dural sinuses
How do spontaneous subarachnoid haemorrhages usually occur?
Rupture of saccular aneurysm (berry aneurysm) (80% of non traumatic)
Usully occur at bifurcation points of cerebral vasculature
In which demographics are subarachnoid haemorrhages more common?
- More likely in females (1.6: 1)
- More likely in black, Finnihs and Japanese populations
- Average age onset 50-55yrs
How will a subarachnoid haemorrhage present?
- Headache (48%) thunderclap- from nowhere
- Dizziness
- Orbital plan
- Diplopia
- Visual loss as aneurysms compress visual pathways
What is one of the most common sites for a berry aneurysm to occur?
The anterior communicating artery
Give some risk factors for develping saccular aneurysms?
- Same as cardiovascular- hypertension, smoking etc
- Alcohol +++
- Connective tissue disorders (dilate aneurysm)
What do you do with small aneurysms (<5mm)?
Unlikely to rupture
Manage with surveillance
What might you find on examination of someone with a subarachnoid haemorrhage?
History: sudden onset thundercalp heache, nausea and vomiting, may have LOC on onset
On examination:
- Normal mental state
- Signs of meningism (due to bleeding irritating meninges) → neck stiffness, photophobia
- Right third nerve palsy if posterior communicating artery aneurysm (compresses 3rd nerve)
- No motor or sensory deficits
What can happen after a subarachnoid haemorrhage?
- Microtrhombi can occlude smaller distal arteries
- Vasoconstriction from CSF irritant
- Cerebral oedema in response to hypoxia
- Sympathetic activation → myocardial damage
- Early rebleeding is quite common
- Acute hydrocephalus
- Global cerebral ischaemia
What is the first line investigation for subarachnoid haemorrhage?
CT Scan
Detects 93% of bleeds if done within 24 hours of bleed
What should you do if you have a convincing history of subarachnoid haemorrhage, but the CT scan is negative?
Lumbar puncture
- wait 6 hrs (12+ preferable)
- Need time for lysis of red blood cells to take place and release bilirubin
- Gives CSF yellow tinge - xanthochromia
What will you see in the CSF results if there is a subarachnoid haemorrhage?
- High protein
- WCC not raised
- Glucose normal
What do you do once a diagnosis of subarachnoid haemorrhage is confirmed?
Angiography
Performed to confirm and locates the site of the aneurysm
How do you treat subarachnoid haemorrhage?
- Asses for airway support
- Monitor cardiovascular parameters
- Calcium channel blockers (Nimodipine → selective for cerebral vasculature) prevents vasopasm and secondary iscehmia
-
Operate on patients with good neurological stats within 72 hours to prevent re-bleeds
- clamping neck of aneurysm
- coiling (neuro-radiologists) inserting wire into aneurysm which causes thrombosis of blood
What is the prognosis for subarachnoid haemorrhage?
Poor prognosis - 40% mortality within the first month if you reach hospital
33% survivors hae major neurological haemorrhage
What are the classical signs and symptoms you would see in meningitis?
Triad of meningism with fever (44%)
- Heache
- Neck stiffness
- Photophobia
What associated symptoms do you see in meningitis?
- Flu like symptoms
- Joint pain
- Rash
- Reduces GCS/ seizure
What features of menigitis would you specifically see in babies?
- Insolable crying/ high pitched
- Reduced feeds
- Floppy
- Bulging fontanelle
In what type of meningitis would you see a rash?
Most commonly in meningococcal meningitis
Describe the rash seen in meningitis
- Bleeding into the skin/ mucosa causes non blanching rash
- Larger lesions are pupuric, smaller lesions petechial
- Usually found on trunk, legs, mucous membranes and conjunctivae
- Occasionally on tehe palms and soles
- Older patients can have rash less commonly than younger patients
Why is rash not definitively a disgnostic criteria for meningitis?
- can show up a lot later in the infection
- petechiae can occur from screaming children without illness
What are the common bacterial causes of meningitis in adults and children?
Streptococcus pneumonia (pneumococcal meningitis)
- most common in UK and US
Neisseria meningitides (meningococcal meningitis)
- meningococcal sepsis can occur without meningitis
Haemophilis influenza (Hib meningitis)
What vaccines are given to try to reduce rates meningitis in the UK?
PCV13- pneumococcal conjugate vaccine
- 13 variants of pneumococcal strep vaccinated against
Hib vaccine against haemophilus influenza
- introduced in 1990s
What are some of the risk factors for developing community aquired menigitis?
- Young and old most affected (<5 and >65 years)
- Crowding
- Immune problems (non immunised, cancer, asplenia)
- Cochlear implants (creates a pathway to meninges)
How can bacteria reach the CNS to cause meningitis?
- Colonisation of nasopharynx is normal
- can ascend through eustacian tube to middle ear (otitis media)
- prolonged infection can lead to bacteria spreading to CSF through mastoid sinuses
- Pnemococcus can also spread to the lower respiratory tract causing pneumonia
- Lung inflammation allows bacteria to enter blood (bacteraemia)
- invades CSF via capillaries that transverse choroid plexus
How can neonates get pathogens from the mother?
- Placenta/ reprodctive tract secretions
What are the effects of having a bacterial infection in the subarachnoid space?
- Inflammation → lots of leucocytes enter CSF
- Inflammatory cascade results in cerebral oedema and raised ICP
What are some of the complications of meningitis?
- Septic shock due to bacteraemia (multi organ failure
- Disseminated intravascular coagulation
- Coma (rICP)
- Seizures (irritation of brain parenchyma)
- Hearing loss (CN VIII nerve involved/ cochlea swelling)
- Hydrocephalus (blockage of CSF drainage)
- Focal paralysis (due to potential cerebral abscess)
What is the Kernig sign for diagnosing meningitis?
- Patient supine with thigh flexed to 90 degrees
- Extension of knee is met with resistance
- Common in children
What is the Brudzinski sign?
When the neck is flexed there is involuntary flexion of knees and hips
More common in children (66%)
What is the first line investigation for meningitis?
Lumbar puncture
What will you see in the CSF in untreated bacterial meningitis?
- Cloudy - high numbers of white cells
- Elevated protein (immune proteins)
- Low glucose (bacteria metabolise glucose)
- Positive gram stain
What will you see in the CSF in untreated viral meningitis?
- Clear or cloudy (immune cells and protein)
- Normal or raised protein
- Normal glucose
What is the benefit of lumbar puncture if menigitis is suspected (apart from diagnosis)?
Lumbar puncture will reduce ICP if raised by removing CSF
What are clinical signs of rICP?
- Decreasing conciousness
- Brainstem signs
- Recent seizure
What other tests can be done to diagnosis meningitis?
PCR blood + CSF
- helpful to diagnosie patients who recieved empirical antibiotic treatment
- distinguishes bacterial from viral causes
Blood culture
- but results can be influenced by previous antibiotic treatment
How do you treat meningitis?
Admit to hopsital
- Empirical antbiotics e.g vancomycin + (Ceftriaxone or Cefotaxime)
- Supportive therapy
- intubate if altered conciousness
- fluids if shocked
- oxygen
- Dexamethasone to prevent hearing loss
If viral
- Aciclovir for herpes
