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
what may SAH patient present with?
- Headache (48%)
- Dizziness
- Orbital pain
- Diplopia
- Visual loss (anterior communicating artery aneurysm)
- Nausea and vomiting
WHat focal neurological signs may be present?
- compression of optic chiasm (bitemporal hemianopia)
- compression of third nerve (down and out and open)
WHat is the first line investigation for SAH?
CT head
What is seen in CT of SAH?
- Prominent filling of the basal cisterns in a five pointed ‘star’ pattern
- Blood may be seen within the ventricles (maybe due to reflux from subarachnoid space)
WHat are cisterns?
- Large, expanded subarachnoid spaces, between arachnoid and pia mater
If bleeding is confirmed what should be done?
CT angiogram if bleed confirmed
• Will allow direct visualisation of bleeding aneurysm of aneurysm sac
• Vital for planning surgery
If the CT is negative with convincing history what should be done?
lumbar puncture
WHat is the technique for LP?
- Identify iliac crests (giving L4-L5 level)
- Give local anaesthetic
- Insert LP needle between spinous processes and 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 to drip, don’t aspirate!)
WHat are the typical findings of a LP in SAH?
- Increased opening pressure
- Frank blood or xanthochromia may be seen
- High protein (blood constituents and haemoglobin)
- White cells often not raised
- Glucose not affected
- High red cell count
What is xanthochromia, how long after SAH presentation is it seen?
Yellow colouring of the CSF due to metabolism of haemoglobin to bilirubin within the subarachnoid space
• Seen at least 12 hours post bleed
Why is presence of xanthochromia better than frank blood?
More specific than frank blood for SAH - helps exclude a bloody/traumatic tap
how long should you wait before LP and why?
- 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)
- Xanthochromia
What is the initial (non-surgical) treatment for SAH? (3)
ABC approach
• Support airway if diminished conscious level
• Give oxygen
• Support circulation
What can be given to support circulation?
- Fluids
- Maybe nimodipine to alleviate cerebral vasospasm
What neurosugical treatment is available?
- decompressive surgery (craniectomy)
- coiling
- clipping
WHat is involved in clipping in SAH, who is it performed by?
- Placement of a spring clip around the neck of the aneurysm, causing it to lose blood supply and ‘shrivel up’
- Performed by neurosurgeons
WHat is involved in coiling in SAH, who is it performed by?
- Insertion of (frequently) a platinum wire into the aneurysm sac, which causes thrombosis of blood within the aneurysm itself
- Performed by neuroradiologists
within how many hours should patients be operated and why?
Operate on patients who have good neurological status within 48 hours
• To prevent re-bleeding
How often does rebleeding occur after SAH?
30% within 2 weeks in unoperated patients
What is the most common cause od death following aneurysmal SAH?
Delayed ischaemia from cerebral vasospasm
compare encephalitis and meningitis
- Infections focused on parenchyma (encephalitis)
* Infections focused on the meninges (meningitis)
which parts of the meninges are affected in meningitis?
• Inflammation of the dura (rare)
• Inflammation of the Leptomeninges (essentially arachnoid tissue
and subarachnoid space) more common
Most common cause of meningitis?
infection (bacterial or viral)
•Can occasionally be caused by fungal disease or non infectious modalities (trauma/surgery)
What are the typical organisms that cause meningitis in neonates?
- E. coli
- Group B streptococcus (ahalactiae)
- 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 elderly?
- Streptococcus pneumoniae (vaccines now given)
- Listeria monocytogenes
What are the typical organisms that cause meningitis in adults?
- Streptococcus pneumonia (pneumococcal meningitis)
- Neisseria meningitides (meningococcal meningitis)
- Haemophilus influenza (Hib meningitis)
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)
- Cochlear implants
what is The triad of ‘meningism’ with fever associated with meningitis?
- Headache
- Neck stiffness (nuchal rigidity)
- Photophobia
What symptoms are associated with meningitis?
• Flu-like symptoms • Joint pains and stiffness • Seizure • Meningococcal rash (non blanching) • Drowsiness • Patient may be in shock • Babies: o Inconsolable crying / off feeds o Rigidity / floppiness o Bulging fontanelle (late sign)
How might bacteria reach the CNS?
- colonisation of the nasopharynx
- ascent through eustachian tube to middle ear and then into CSF through mastoid air cells
or
• Colonisation of nasopharynx
• 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
describe the pathophysiology of meningitis
- The bacteraemia causes damage to vessel walls in the brain and meninges, allowing pathogen to enter the subarachnoid space
- pathogens multiply rapidly causing purulent CSF and severe meningeal inflammation
- Vasospasm of cerebral vessels can cause cerebral infarction
- Oedema of brain parenchyma can cause raised intracranial pressure
when is Maculopapular rash seen in ?
meningococcal septicaemia
Why is a maculopapular rash seen in meningococcal septicaemia?
Caused by microvascular thrombosis ( bleeding into skin or mucosa) due to many factors, including
- Sluggish circulation
- Impaired fibrinolysis
- Increased tissue factor expression in endothelial cells
describe the features of rash in meningitis
a non blanching rash
• Larger lesions called termed purpuric
• Smaller lesions (1-2 mm) termed petechia
where is the rash commonly found and who?
- A petechial or purpuric rash usually is found on the trunk, legs, mucous membranes, and conjunctivae. Occasionally, it is on the palms and soles
- Older patients have rash less commonly than younger
What are the complications of meningitis?
▪ Septic shock (due to bacteraemia)
▪ DIC (due to bacteraemia)
▪ Raised ICP
▪ Coma (due to raised ICP)
▪ Cerebral oedema (due to cerebral inflammation)
▪ Death (due to brain herniation, sepsis)
▪ SIADH (maybe direct effect on hypothalamus/pituitary?)
▪ Seizures (due to irritation of brain parenchyma)
▪ Hearing loss (due to swelling of vestibulocochlear nerve or cochlea itself. Perilymph is continuous with subarachnoid space)
▪ Intellectual deficits (due to direct brain damage)
▪ Hydrocephalus (due to interruption of CSF drainage pathways and effect on arachnoid granulations)
▪ Focal paralysis (maybe due to cerebral abscess)
What signs may be present on physical examination?
- Kernig sign
- Brudzinsk
What is Kernig sign?
- Supine patient With thigh flexed to 90 degrees
- Extension of knee is met with resistance
- More common in children (up to 53%)
What is brudzinsk sign?
- When neck is Flexed there is an involuntary flexion of knees and hips
- More common in children (up to 66%)
What is the most important investigation for meningitis?
lumbar puncture
What is the most important investigation for meningitis?
- Cloudy CSF
- High protein (immune proteins etc.)
- High white cells, primarily neutrophils (which phagocytose bacteria)
- Low glucose as bacteria (and white cells) metabolise it
What is seen in LP in a viral meningitis?
- Maybe clear but can be cloudy (due to immune cells and proteins)
- Protein level may be normal or raised (as above)
- High white cells, primarily lymphocytes to mount an adaptive response
- Normal glucose (>60% plasma)
When may doing a LP be dangerous?
When there is raised ICP
What may happenn by doing an LP while there is raised ICP?
Precipitates the risk of brain herniation
What are the best predictors to delay doing an LP?
Signs of raised ICP:
• Decreasing consciousness
• Brainstem signs
• Recent seizure
CT head may be useful
What other investigations are done for meningitis?
- bloods (compare to LP)
- blood culture
- PCR (from blood and CSF)
- sepsis screen:
- CXR and mid stream urine for septic focus
What supportive treatment is given for meningitis?
- Oxygen
- Intubation in altered consciousness
- Analgesia
- Antipyretics
- Fluids if shocked
When should there be caution when giving fluids in meningitis?
Raised ICP
What medical treatment is given for meningitis, what is given if viral cause?
- IV Vancomycin + (Ceftriaxone or Cefotaxime)
- Dexamethasone to prevent hearing loss (due to swelling of vestibulocochlear nerve or effect on cochlea
- If viral: Aciclovir for Herpes, Ganciclovir for CMV
