Subarachnoid haemorrhage and meningitis Flashcards
What is the epidemiology of subarachnoid haemorrhage?
- Cause around 6% of all strokes
- Slightly more females affected
- Most are under 50
- 50% mortality
- 60% of patients suffer some longer term morbidity
What are the risk factors for subarachnoid haemorrhage?
- Hypertension
- Smoking
- Excess alcohol consumption
- Predisposition to aneurysm formation
- Family history
- Associated conditions
- Trauma
- Cocaine use
What are some conditions associated with subarachnoid haemorrhage?
- Chronic kidney disease (resultant effect on vessel wall)
- Marfan’s syndrome (effect on connective tissues of vessels)
- Neurofibromatosis (unclear mechanism, if any link)
Why do subarachnoid haemorrhages usually occur?
- Rupture of an aneurysm in the circle of Willis
What is an aneurysm?
- Aneurysm is a weakness in a vessel (usually artery) wall which can cause an abnormal bulge
- May be a genetic predisposition to aneurysm formation
What are the causes of aneurysms?
- May be caused by haemodynamic effects at branch points in the circle of Willis
- Higher resulting flow rate in progressively smaller branches, turbulence
What are the majority of aneurysms?
- Berry aneurysms
- Make up 75% of all aneurysms
What are the common sites of berry aneurysms?
- Anterior communicating / proximal anterior cerebral artery (30%)
- Posterior communicating artery (25%)
- Bifurcation of the middle cerebral artery as it splits into superior and inferior divisions (20%)
What parts of the brain are affected by a berry aneurysm in the anterior communicating/proximal anterior cerebral artery?
- Can compress the nearby optic chiasm
- May affect frontal lobe or even pituitary
What parts of the brain are affected by a berry aneurysm in the posterior communicating artery?
- Can compress the adjacent oculomotor nerve causing an ipsilateral third nerve palsy
What does bleeding into the subarachnoid space cause?
- Early brain injury
- Cellular changes
- Systemic complications
What are the features of early brain injury caused by bleeding into the subarachnoid space?
- Microthrombi (may occlude more distal branches)
- Vasoconstriction as a result of blood in the CSF irritating the cerebral arteries
- Cerebral oedema - general inflammatory response to tissue hypoxia and extravasated blood
What are the cellular changes caused by bleeding into the subarachnoid space?
- Oxidative stress
- Release of inflammatory mediators can activate many pathways as well as activation of microglia
- Platelet activation (formation of thrombi)
What are the systemic complications caused by bleeding into the subarachnoid space?
- Sympathetic activation - early Cushing response
- Myocardial necrosis due to sympathetic activation
- But subarachnoid haemorrhage has typical ECG features
- Systemic inflammatory response can affects multiple systems
What are the clinical features of subarachnoid haemorrhage?
- Thunderclap headache
- Frequently loss of consciousness and confusion
- Meningism
- May be focal neurology
- May be history of sentinel bleed
- May present as cardiac arrest (due to profound Cushing response)
What are the features of thunderclap headache?
- Explosive in onset and severe
- Often reported as the worst headache ever or like being hit on the head with a cricket bat
- Diffuse pain
- Can last from an hour to a week
What are the features if meningism?
- Neck stiffness
- Photophobia
- Headache
What are the investigations for subarachnoid haemorrhage?
- CT head
- CT angiogram
- Lumbar puncture
What is a classical CT finding for subarachnoid haemorrhage?
- Prominent filling of the basal cisterns in a five pointed star pattern
- Blood may be seen within the ventricles (may be due to reflux from the subarachnoid space)
What does CT angiogram show in the case of a subarachnoid haemorrhage?
- Will allow direct visualisation of bleeding aneurysm of aneurysm sac
- Vital planning surgery
What is the technique for lumbar puncture?
- Identify iliac crests at L4-L5 level
- Give local anaesthetic
- Insert LP needle between spinous processes
- Through the supraspinous and interspinous ligaments
- Feel give as pass through ligamentum flavum and dura
- Remove needle stylet and collect CSF in sterile containers (allow it to drip, don’t aspirate)
What are the lumbar puncture findings in subarachnoid haemorrhage?
- Increased opening pressure (as there is now additional volume in the subarachnoid space)
- Frank blood or xanthochromia may be seen
- High protein
- White cells often not raised
- Glucose not affected
- High red cell count
What is xanthochromia?
- Yellow colouring of the CSF due to metabolism of haemoglobin to bilirubin within the subarachnoid space
- Seen at least 12 hours post bleed
- More specific than frank blood for subarachnoid haemorrhage
What is the treatment for subarachnoid haemorrhage?
- ABC approach
- Neurological observations - look for trends which may suggest increasing ICP
- Neurosurgery
Outline the ABC approach used to treat subarachnoid haemorrhage?
- Support airway if diminished consciousness level
- Give oxygen
- Support circulation - fluids and maybe nimodipine to alleviate cerebral vasospasm
What are the different types of neurosurgery used to treat subarachnoid haemorrhage?
- Decompressive surgery (craniectomy)
- Coiling
- Clipping
- All performed by neurosurgeons
How does coiling happen?
- Insertion of a platinum wire into the aneurysm sac, which causes thrombosis of blood within the aneurysm itself
How does clipping happen?
- Placement of a spring clip around the neck of the aneurysm, causing it to lose blood supply and shrivel up
What are the typical organisms that cause meningitis in neonates?
- E. coli
- Group B streptococcus
- Listeria monocytogenes
What are the typical organisms that cause meningitis in children?
- Haemophilus influenzae type B (HiB vaccine given, ‘meningococcus’)
- Neisseria meningitidis (vaccines given for some strains)
What are the typical organisms that cause meningitis in the elderly?
- Streptococcus pneumoniae (vaccines now given)
- Listeria monocytogenes
What are the risk factors for meningitis?
- CSF defects (e.g. spina bifida)
- Spinal procedures (e.g. surgery, lumbar puncture)
- Endocarditis (as a focus of bacteraemia)
- Diabetes (immunosuppression)
- Alcoholism
- Splenectomy (immunosuppression)
- Crowded housing (students at risk)
What are the clinical features of meningitis?
- The triad of meningism with fever
- Associated symptoms
What are the features of the triad of meningism?
- Headache
- Neck stiffness (nuchal rigidity)
- Photophobia
What are the associated symptoms of meningitis?
- Flu-like symptoms
- Joint pains and stiffness
- Seizure
- Meningococcal rash (non blanching)
- Drowsiness
- Patient may be in shock
What are the symptoms of meningitis in babies?
- Inconsolable crying/off feeds
- Rigidity/floppiness
- Bulging fontanelle (late sign)
How does infection enter the meninges?
- Bugs which normally live in the nose gain entry to the circulation and cause a bacteraemia
- This causes damage to vessel walls in the brain and meninges, allowing the pathogen to enter the subarachnoid space
What happens once infection gets into the meninges?
- Once in the subarachnoid space, pathogens multiply rapidly
- This causes purulent CSF and severe meningeal inflammation
- Vasospasm of cerebral vessels can cause cerebral infarction
How does meningitis cause raised ICP?
- Oedema of brain parenchyma
Why does meningococcal septicaemia cause maculopapular rash?
- Caused by microvascular thrombosis due to many factors including:
- Sluggish circulation
- Impaired fibrinolysis
- Increased tissue factor expression in endothelial cells
What investigations are done to diagnose meningitis?
- Bloods including sepsis screen and PCR
- Maybe chest X-ray or midstream urine if you suspect a particular septic focus
- Lumbar puncture findings
What are the lumbar puncture findings in bacterial meningitis?
- Cloudy CSF
- High protein
- High white cells, primarily neutrophils
- Low glucose (metabolised by bacteria and white cells)
What are the lumbar puncture findings in viralnmeningitis?
- May be clear but can be cloudy (due to immune cells and proteins)
- Protein level may be normal or raised
- High white cells, primarily lymphocytes to mount an adaptive response
- Normal glucose
What is the supportive treatment for meningitis?
- Analgesia
- Antipyretics
- Fluids if shocked
What is the medical treatment for meningitis?
- IV ceftriaxone
- Dexamethasone to prevent hearing loss
- If viral, give acyclovir for herpes or ganciclovir for CMV
Why can meningitis lead to hearing loss?
- Due to swelling of vestibulocochlear nerve or effect on cochlea
What are some of the complications of meningitis?
- Septic shock and disseminated intravascular coagulation (due to bacteraemia)
- Coma (due to raised ICP)
- Cerebral oedema (due to cerebral inflammation)
- Death
- Seizures (due to irritation of brain parenchyma)
