Lecture 18- The meninges and subarachnoid haemorrhage Flashcards
3 layers of the meninges
dura mater
x2 leptomeninges
- arachnoid mater
- pia mater
Dura mater
- ‘Tough mother’
- Surround and supports dural sinuses
- Endosteal layer
- Meningeal layer
Arachnoid mater
‘Spider’ -arachnoid trabeculae pass through space and blend with pia
Pia mater
- Thin layer that adheres closely to the brain- pierced by blood vessels
- ‘shrink wrapped’ to the cerebral hemispheres
dural folds
The two layers of the dura mater (periosteal and meningeal) are firmly adhered to each other except where they split:
- To enclose venous sinuses
- To form dural septa (4 important ones)
4 important dural septa
- Falx cerebri (between cerebral hemispheres)
- Falx cerebelli (between cerebellar hemispheres)
- Tentorium cerebelli
- Diaphragma sella
extra dural haemorrhage
(epidural)
- between endosteal layer and skull
- CT scan= biconvex bleed (lemon)
- trauma
- MMA
- loss of consciousness and then consciousness and then LOC (lucid intervals)
subdural bleed
- between meningeal layers and arachnoid
- trauma
- more common in elderly (atrophy)
- torn bridging veins
- concave towards (banana)
subarachnoid (below arachnoid) space
- Located between arachnoid and pia
- Contains enlarged regions called cisterns
- Occur where brain moves away from skull
- Filled with CSF
function of Cisterns (subarachnoid space)
- Filled with 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 i.e. Blood
how is CSF formed
- Formed by choroid plexuses within the ventricular system- capillaries that filter plasma from the blood to produce CSF (and extra-choroidal structures)
flow of CSF through the ventricles
- Flow:
- Lateral ventricles (interventricular foramen)
- 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
sybarachnoid haemorrhage
Extravasation of blood into the subarachnoid space
- Can occur in trauma but we are going to be talking about non-traumatic (spontaneous)
- 9000 cases in uk/year
- 6% of all strokes
- More likely in females(1.6:1)
- More likely in black, Finnish and Japanese populations
- Average age of onset is 50-55 yrs
Subarachnoid haemorrhage presents with
- Headache(48%) - thunderclap
- Dizziness
- Orbital pain
- Diplopia
- Visual loss (anterior communicating artery aneurysm)
causes of subarachnoid haemorrhage
- arteriovenous malfgormation (AVM)- 10%
- saccular aneurysms (berry aneurysms)
saccular/berry aneurysms
- 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
- Intracranial arteries lack external elastic lamina and have thin adventitia
- Small aneurysms(<5mm) unlikely to rupture
risk factors for developing aneurysms (not conclusive)
- Same as cardiovascular- hypertension, smoking etc
- Alcohol++
where are berry aneurysms most commmon
posterior communicating arteries
Subarachnoid haemorrhage- what happens after a bleed
- Microthrombi which can occlude smaller distal arteries
- Vasoconstriction from CSF irritant (blood in CSF) (cerebral arteries)
- Cerebral oedema
- Response to hypoxia and extravasated blood
- Sympathetic activation
- Myocardial damage e.g. MI
- Early rebleeding
- Acute hydrocephalus (blood in subarachnoid space may block normal drainage of CSF)
- Global cerebral ischaemia
1st line investigation of subarachnoid bleed
CT scan
- Will detect 93% if done within 24 hours of bleed
- Small amounts of blood can be hard to see
- If convincing history but negative CT scan do a lumbar puncture (LP)
- CSF will have high protein, WCC not raised, glucose normal
once diagnosis of subarachnoid haemorrhage is made..
- Angiography is performed to confirm location of aneurysm
stabilisation of subarachnoid haemorrhage patient
Stabilisation
- Assessment of whether they need airway support
- Monitoring of cardiovascular parameters
- Calcium channel blockers- Nimodipine (to prevent vasospasm and secondary ischaemia)
- Operate on patients who have good neurological status within 72 hours -to prevent re-bleeding
- Clipping (surgeons)à Clamping neck of aneurysm (with spring clip)
- Coiling (neuro-radiologists) à Insertion of wire into aneurysm sac which causes thrombosis of blood within aneurysm
most common cause of meningitis
- is infection (bacterial (worse prognosis) or viral (more common))
- Gain access to meninges from other parts of the body
- Can occasionally be caused by fungal disease or non infectious modalities (trauma/surgery)
meningitis in Babies
- Inconsolable crying/ high pitched
- Reduced feeds
- Floppy
- Bulging fontanelle
meningitis rash
Most common with meningococcal meningitis
- The rash is caused by bleeding into skin or mucosa (microvascular thrombosis)
- This produces a non blanching rash
- Larger lesions called termed purpuric
- Smaller lesions (1-2 mm) termed petechial
- Older patients have rash less commonly than younger
- A petechial or purpuric rash usually is found on the trunk, legs, mucous membranes, and conjunctivae. Occasionally, it is on the palms and soles
pneumococcal meningitis- bacteria reaches the CNS via
- Colonisation of the nasopharynx
- Colonisation of the lower resp tract
- Neonates can get pathogens from maternal source
signs specifically related to meningitis
Kernig sign
brudzinski
Kernig sign
- Supine patient
- With thigh flexed to 90 degrees
- Extension of knee is met with resistance
- More common in children (up to 53%)
Brudzinski sign
- When neck is Flexed there is an involuntary flexion of knees and hips
- More common in children (up to 66%)
lumbar puncture usually done between
L3/4
