16. Subarachnoid haemorrhage and meningitis Flashcards
what are the 3 layers of the meninges?
- Dura mater
- Arachnoid mater
- Pia mater
function of dura mater and two divisions?
- (Tough mother)- surround and supports dural sinuses
- Endosteal layer
- Meningeal layer
which two layers make the Leptomeninges?
- Arachnoid mater
* Pia mater
what are dural folds?
The two dura mater layers are firmly adhered to each other except
where they split:
•To enclose venous sinuses
•To form dural septa
what are the 4 important dural septa?
- Falx cerebri (between cerebral hemispheres)
- Falx cerebelli (between cerebellar hemispheres)
- Tentorium cerebelli
- Diaphragma sella
where does extradural bleeds occur and what can cause it?
- Between endosteal layer and skull
- Trauma
- Middle meningeal artery
presentation and imaging of extardural bleed?
- LOC, consciousness, LOC (lucid interval)
* CT scan- biconvex bleed (lemon)
where does subdural bleeds occur and what can cause it?
- Between meningeal layer and arachnoid
- Trauma
- Torn bridging veins
imaging of subdural bleed?
• Concave towards brain (banana)
what is the subarachnoid space?
Located between arachnoid and pia
what are enlarged areas of subarachnoid space called and what do they contain?
- enlarged regions called cisterns
- Occur where brain moves away from skull
- Filled with CSF
function of CSF?
- Physical support of neural structures
- Excretion (of brain metabolites)
- Intracerebral transport (hormone releasing factors)
- Control of chemical environment
- Volume changes reciprocally with volume of intracranial contents to control ICP
where is CSF produced?
- Formed by choroid plexuses (and extra-choroidal structures)
- choroid plexuses are capillaries and loose connective tissue that filter plasma from blood to form CSF
describe flow of CSF
- Lateral ventricles
- -3rd ventricle-(aqueduct of Sylvius)
- -4th ventricle (median and lateral apertures)
- subarachnoid space (small amount into spinal cord)
- Propelled by newly formed fluid,ciliary action of ventricular ependyma, vascular pulsations
What percent of strokes are subarachnoid haemorrhages?
6% of all strokes
What is the mortality of subarachnoid haemorrhage?
50% mortality, 60% suffer some longer term morbidity following the event
who are subarachnoid haemorrhages more common in?
• More likely in females (1.6:1)
• More likely in black, Finnish and Japanese
populations
• Average age of onset is 50-55 yrs
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 the associated conditions that increase risk of SAH?
o Chronic kidney disease (resultant effect on vessel
wall)
o Marfan’s syndrome (effect on connective tissues of
vessels)
o Neurofibromatosis (unclear mechanism, if any link)
What usually cause SAH?
- Rupture of aneurysms (80% of non-traumatic cases)
- Rupture of AVMs (arteriovenous malformations) -10%
What causes aneurysm to develop?
Aneurysms develop due to pressures on the arterial wall (vessels in subarachnoid space)
• Usually at bifurcation points
• Large cerebral arteries in anterior circle of Willis most affected
• genetic predisposition
• haemodynamic effects at branch points in the circle of Willis (e.g. higher resulting flow rate in progressively smaller branches, turbulence)
- cerebral arteries lack elastic lamina and have thin adventitia
What are the risk factors for developing aneurysms?
- Same as cardiovascular- hypertension, smoking etc
* Alcohol++
Where are the common site for aneurysms to develop?
- Anterior communicating (30%)
- posterior communicating (25%)
- bifurcation of MCA into superior and inferior divisions (20%)
What can an aneurysm at the anterior communicating artery cause?
Can compress the nearby optic chiasm and may affect frontal lobe or even pituitary
What can an aneurysm at the posterior communicating artery cause?
Can compress the adjacent oculomotor nerve causing an ipsilateral third nerve palsy
4 things that bleeding into SAS cause that lead to early brain injury?
- microthrombi: occlude more distal branches
- vasoconstriction
- cerebral oedema: general inflammatory response to tissue hypoxia and extravasated blood
- apoptosis of brain cells
Why does vasoconstriction
As a result of blood in CSF irritating cerebral arteries
WHat are the cellular changes after SAH? (3)
- oxidative stress (related to reperfusion)
- release of inflammatory mediators
- platelet activation (form thrombi)
What are the systemic complications after a SAH? (3)
- sympathetic activation (cushings response)
- myocardial necrosis (due to sympathetic activity)
- systemic inflammatory response
- Acute hydrocephalus (blood in subarachnoid space may block normal drainage of CSF)
What are the clinical features of SAH?
- Thunderclap headache
- Frequently loss of consciousness and confusion
- meningism
- may be focal neurology
- history of sentinel headaches/bleed - Minor leaks from aneurysm
- may present as cardiac arrest
Describe the headache in SAH.
Thunderclap headache
• Explosive in onset and severe, often reported as worst headache ever or even ‘like being hit on the head with a cricket bat’
• Diffuse pain
• Can last from an hour to a week
What are the features of meningism?
• Neck stiffness • Photophobia • Headache