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
If convincing history but negative CT scan do a lumbar puncture (LP)
- Should wait at least 6 hours (12+ is preferable)- need time for lysis of red blood cells to take place (release of bilirubin)
- This gives the CSF a yellow tinge after centrifuging (this can differentiate this from traumatic tap) called Xanthochromia
- 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
Infections of the CNS can be divided into two broad categories
- Infections focused on parenchyma (encephalitis)
- Infections focused on the meninges (meningitis)
meninigitis
- Inflammation of the dura (rare)
- Inflammation of the Leptomeninges (essentially arachnoid tissue and subarachnoid space) more common
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)
The triad of meningism with a fever (44%
Develops overs hours in bacterial causes, days with viral cause
- Headache
- Neck stiffness
- Photophobia
other symptoms of meningitis
- Flu like
- Joint pains
- Rash
- Reduced GCS/seizures
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
where is petechial or purpuric rash usualyl found
- A petechial or purpuric rash usually is found on the trunk, legs, mucous membranes, and conjunctivae. Occasionally, it is on the palms and soles
Community acquired bacterial meningitis
- Pyogenic inflammation of the meninges and underlying subarachnoid
- Prior to antibiotics meningitis was almost always fatal
- Mortality still very high (25%)
Common bacterial causes (adults and children)
-
Streptococcus pneumonia (pneumococcal meningitis)
- Most common cause in US and UK
- This has decreased by 32% since pneumococcal conjugate vaccine (PCV13-pneumococcal conjugate vaccine))
-
Neisseria meningitides (meningococcal meningitis)
- Note- Meningococcal sepsis can occur without meningitis (with high mortality)
-
Haemophilus influenza (Hib meningitis)
- Until Hib vaccine introduced (1990s) this accounted for 45% of bacterial meningitis
risk factors for community acquired bacterial meningitis
- Young and old the most affected (<5 years, >65 years)
- Crowding
- Immune problems (non immunised infants, cancer, asplenia)
- Cochlear implants- mastoiditis
pneumococcal meningitis- bacteria reaches the CNS via
- Colonisation of the nasopharynx
- Colonisation of the lower resp tract
- Neonates can get pathogens from maternal source
Pneumonoccal colonisation of the nasopharynx
- Ascent of bacteria through Eustachian tube to middle ear (otitis media)
- Prolonged infection in this area can lead bacteria to spread directly into CSF (through mastoid sinuses)
Colonisation of the lower resp tract
- Seeding to lower respiratory tract (pneumonia)
- Lung inflammation allows bacteria to enter blood (bacteraemia)
- Invasion of CSF via capillaries that traverse choroid plexus or Subarachnoid space
Neonates can get pathogens from maternal source
- Placenta/reproductive (tract secretions)
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%)
1st line investigation of meningitis
Lumbar puncture is most important investigation
- In untreated bacterial meningitis CSF is usually:
- Cloudy- high numbers of white cells (lymphocytes and neutrophils)
- Elevated protein (immune proteins)
- Low glucose (bacteria metabolise it)
- Positive gram stain
In viral meningitis CSF is usually:
- Clear or cloudy (immune cells and protein)
- Normal or raised protein
- Normal glucose
what do you do with blood and CSF sample
- Do PCR from blood and CSF
- Helpful to diagnose pts who received empirical antibiotic treatment
- Distinguishing from bacterial from viral causes
- Blood cultures
lumbar puncture usually done between
L3/4
when to beware of lumbar puncture
If there is raised ICP there is a possibility of brain herniation occurring.
- 5% of patients with acute bacterial meningitis
- Performing an LP increases chances of this occurring
- Sudden decrease in pressure (removal of CSF)
Clinical signs of raised ICP are best predictors of when to delay an LP:
- Decreasing consciousness
- Brainstem signs
- Recent seizure
- CT head can be useful to find contraindications to doing an LP
- But a normal CT may not mean that an LP is safe to perform
Meningitis treatment
- Admit to hospital
- Empirical antibiotics (broad spec)
- Eg Vancomycin + (Ceftriaxone or Cefotaxime)
- Supportive therapy
- Intubation if altered consciousness
- Fluids if shocked (caution with raised ICP)
- Oxygen
- Dexamethasone (to prevent hearing loss)
- If viral Aciclovir for Herpes
