L16 - Meningitis and subarachnoid haemorrhage Flashcards
Dural septa
Falx cerebri
Falx cerebelli
Tentorium cerebelli
Diaphragma sella - layer of dura with a hole for the pituitary stalk
Cisterns
Enlarged spaces between the brain and the skull where CSF can collect
Functions:
- Render brain weightless
- Excretion of brain metabolites
- intracerebral transport of hormone releasing factors
What percentage of strokes are subarachnoid
6%
Who is more likely to get a subarachnoid stroke?
Women 1.6:1
50- 55 yr olds
Black, Finnish and Japanese’s people
Prognosis of subarachnoid haemorrhage
50% mortality
60% longer term morbidity
Risk factors of subarachnoid haemorrhage
Hypertension Smoking Trauma Cocaine Family history Excess alcohol consumption Predisposition to aneurysm formation - Marfan’s
Presentation of subarachnoid haemorrhage
Thunderclap headache Nausea and vomiting Dizziness Orbital pain Diplopia Visual loss Meningism - bleeding into the subarachnoid space cause if inflammation
Pathophysiology of subarachnoid haemorrhage
Rupture of berry aneurysm in the circle of Willis usually at bifurcation points
Common sites of Berry aneurysms
Anterior communicating artery - 40%
- can compress the optic chiasm
Posterior communicating artery - 25%
- compress CN III
Middle cerebral artery as it bifurcates into superior and inferior - 20%
Why are intracerebral arteries prone to aneurysm
Lack external elastic lamina
Thin adventitia
Sentinel headaches
Headaches month prior to the subarachnoid haemorrhage due to small leaks from the aneurysm
What happens after a subarachnoid bleed?
Microthrombi can occlude distal arteries
Vasoconstriction of cerebral arteries as the CSF is irritated
Cerebral oedema
Myocardial damage due to sympathetic activation
Early rebleeding
Acute hydrocephalus - blood blocks CSF drainage
Global cerebral ischaemia
How does cerebral oedema occur?
Decreased oxygen delivery to an area of the cerebral cortex causes ischaemia
Less ATP produced therefore less Na+/K+ ATPase activity
Higher Na+ conc inside the cell causes depolarisation
Na+ influx
K+ efflux
Water follows sodium therefore influx of water causing oedema
Investigations of a subarachnoid haemorrhage
1st line - CT without contrast
If there is a convincing Hx but negative CT, do a lumbar puncture at L3/L4 or L4/L5
Lumbar puncture
Wait at least 6 hours
Preferably 12+ hours
For the blood in the CSF to lyase, therefore can detect the bilirubin
CSF has a yellow tinge after centrifugation - xanthochromia
Traumatic tap
Needle inadvertently enters an epidural vein
Xanthochromia
Yellow tinge of the CSF due the presence of bilirubin
CSF contents of subarachnoid haemorrhage
High protein (plasma proteins from blood)
No WCC ( not infection)
Normal glucose
High RBC
After diagnosis
Angiography is performed to confirm the location of the aneurysm
Treatment of a subarachnoid haemorrhage
Stabilisation
Airways - Assess whether they need airway support
Breathing- Give oxygen
Circulation - fluids and nimodopine
Possibly operate
When to operate
Within 72 hours of bleed
On patients with good neurological status
Prevents rebleeding
Types of surgical procedures
Decompression - craniotomy
Clipping - surgeon clamps base of the aneurysm with spring clip (open craniotomy) cutting off the blood supply causing it to shrivel
Coiling - neuro radiologists insert a platinum wire into the aneurysm sac which causes thrombosis of blood within the aneurysm which doesn’t occlude the artery
Subarachnoid CT
Prominent filling of the basal cisterns in a 5 point star pattern
Blood may be seen within the ventricles - reflux from subarachnoid space
Nimodopine
Calcium channel blocker prevents secondary vasospasm and secondary ischaemia
Meningitis
inflammation of the meninges commonly due to infection
Often the leptomeninges
Encephalitis
Infection (often viral) of the brain parenchyma
Meningitis can lead to encephalitis
Signs and symptoms of meningitis
Signs: Non blanching rash Fever Reduced GCS Kernig sign Brudzinski sign
Symptoms: Photophobia Neck stiffness Headache Joint pains Seizures
Meningitis in children
Insoluble crying
Reduced feeds
Floppy
Bulging fontanelle
Non blanching rash
Due to bleeds into the skin or mucosa - microvascular thrombosis
- slow circulation
- impaired fibrinolysis
- increased tissue factor expression in endothelial cells
1-3mm - petechia (pin prick like)
Larger than 3mm - purpura
Usually found on legs, trunk, mucosal membranes and conjunctivae
Occasionally palms and soles
More common in younger patients
Conjugate vaccine for meningitis
PCV13 - pneumococcal conjugate vaccine for 13 worst variants
- given to under 60s
PCV20 - given to the elderly
Risk factor for community acquired meningitis
Young and old - less that 5 yrs old and over 65 years old
Crowding
Immunocompromised- non vaccinated, asplenic, cancer, diabetes
Cochlear implants - physical conduit to meninges
CSF defects - spina bifida
Spinal procedures - lumbar puncture
Endocarditis - bacteraemia
Alcoholism
How does pneumococcal bacteria reach the meninges
- commensal of nasopharynx
- ascends through the Eustachian tube to middle ear (otitis media)
- prolonged otitis media can lead to bacteria spread directly to CSF through the mastoid sinus
- seeds to the lower resp tract (pneumonia)
- lung inflammation causes vessels to become more leaky therefore bacteria enters the blood stream causing bacteraemia
- invasion of CSF via capillaries the traverse the choroid plexus or subarachnoid space
- neonates can get pathogen from mother (Ecoli)
Effects of meningitis
Once bacteria is in the subarachnoid space, it multiplies exponentially as no resistance
- inflammatory mediators are induced
- leukocytes enter the CSF
- inflammatory cascade causes cerebral oedema and raised ICP
Complications of meningitis
Septic shock - meningococcal sepsis due to bacteraemia
DIC - disseminated intravascular coagulation - bacteraemia
Coma - raised ICP
Seizures - irritation of brain parenchyma
Hearing loss - cochlea swelling or CN VIII lesion
Hydrocephalus
Focal paralysis - cerebral abscess
Positive Kernig sign
Supine patient with thigh flexed to 90 degrees
Resistance to knee extension as stretches meninges
More common in children
Positive brudzinski sign
When neck is flexed, involuntary flexion of the knees and hips
More common in children
Investigations of meningitis
Lumbar puncture - compare with blood culture
PCR
- blood and CSF
- distinguishes between viral and bacterial
Blood culture - May be influenced by antibiotic treatment
Sepsis screen
If septic:
- mid stream urine sample
- CXR
CSF in meningitis
Bacterial:
- WCC present - lymphocytes and neutrophils
- cloudy due to WCC
- elevated protein - immune proteins
- low glucose - bacteria metabolism it
- positive gram stain
Viral meningitis:
- clear of cloudy
- WCC
- normal or raised protein
- normal glucose
Risk of lumbar puncture
Raised ICP increases the likelihood of brain herniation
Performing the LP increases this chance due to a sudden decrease in pressure from removal of the CSF
When should a lumbar puncture be delayed
- decreased consciousness
- brainstem signs
- recent seizures
CT can identify contraindications but a normal CT may not mean LP is safe
Meningitis treatment
Admit to hospital
- empirical antibiotics asap - vancomycin + IV ceftriaxone or cefotaxime (neonatal meningitis)
Supportive therapy:
- airways - intubation - altered consciousness
- breathing - oxygen
- circulation - fluids if sepsis shock - caution with raised intracranial pressure
Dexamethosone (corticosteroid) - prevents hearing loss by reducing swelling
Viral
- acyclovir for herpes
- ganciclovir - CMV
Supportive:
- fluids if sepsis shock
- analgesia
- antipyretic
