Lecture 15 - Subarachnoid Haemorrhage And Meninges Flashcards
What are the 3 meningeal layers form most superficial to deep?
Dura mater
Arachnoid mater
Pia mater
What is the dura mater?
Tough outer later surrounding and supporting the dural sinuses
What are the 2 layers to the dura mater?
Periosteal layer
Meningeal layer
What is the Pia mater?
Thin layer that adheres closely to the cerebal hemispheres
What are the leptomeninges?
Arachnoid mater + Pia mater
The meningeal layers affected in meningits
What structures are produced when the 2 layers of the dura mater separate?
Dural venous sinuses
Dural folds
What layer of dura separates from the other to produce dural venous sinuses and dural folds?
Meningeal dural layer
What are the 4 main dural folds formed by the meningeal layer of dura separating from the periosteal layer of dura?
Falx cerebri (separates the cerebral hemispheres)
Tentorium cerebelli (seperates cerebrum from cerebellum)
Falx cerebelli (between cerebellar hemispheres)
Diaphragma sella (covers superior surface of pituitary, infundibulum passes through it)
How does an Extradural bleed/haemorrhage appear on a CT head?
Lentiform appearance
What blood vessel is ruptured in an extra dural bleed?
Middle meningeal artery
Where does the bleed occur for an Extradural haemorrhage?
Between periosteal layer of dura and the skull
What is the typical patient presentation for a patient with an Extradural bleed?
Trauma to lateral side of head (pterion)
Loss of consciousness then is conscious/apparently fine, this is the LUCID INTERVAL
Then they deteriorate and lose consciousness as blood builds up in extra dural space
How does a subdural haemorrhage appear on CT head?
Banana shape (concave towards brain)
What blood vessel is ruptured in a subdural haemorrhage?
Bridging veins
What space does blood accumulate in as a result of the bridging veins rupturing in a subdural haemorrhage?
Meningeal layer of dura and arachnoid mater
Where is the subarachnoid space located?
Betweeen arachnoid mater and Pia mater
What are the enlarged regions in the subarachnoid space where the arachnoid separates from the brain called?
Cisterns
What is contained within the sub arachnoid space and cisterns?
CSF
What are the functions of CSF?
Physical support
Excretion of brain metabolites
Intracererbal transport (hormone releasing factors)
Control of chemical environment
Controlling blood volume intracranially
What structure forms CSF?
Choroid plexi
How does CSF flow from most superior to inferior?
Lateral ventricle choroid plexuses
Lateral ventricle -> 3rd ventricle via Interventricular foramina
Then from 3rd ventricle -> 4th ventricle via cerebral aqueduct
4th ventricle -> subarachnoid space to arachnoid granulations via lateral and median apertures
Then from arachnoid granulations to dural venous sinuses
What drives the flow of CSF through the ventricles of the brain?
Pressure from newly formed fluid
Ciliary action of ventricular Ependyma
Vascualr pulsations
What type of disease is a subarachnoid haemorrhage?
Stroke (usually non traumatic)
Who do subarachnoid haemorrhage most commonly affect?
More females (1.6:1)
50-55yrs onset
Black, Finnish and Japanese most likely
What are the main risk factors for subarachnoid haemorrhage??
Vascular disease risk factors:
-hypertension
-smoking
-alcohol
-FHx
-predisposition to aneurysm formation
Marfan’s syndrome (inc risk of aneurysm formation)
CKD
Trauma
Cocaine use
What is the pathophysiology of a subarachnoid haemorrhage?
Saccular/berry aneurysms most commonly in the anterior circulation of the circle of Willis (ant + middle cerebral arteries) RUPTURE
What is an aneurysm?
When theres a weakness in the arterial vessel wall which can cause an abnormal bulge
What is likely to be the cause of the formation of saccular/berry aneurysms that lead to a subarachnoid haemorrhage?
-Intracranial arteries lack external elastic lamina and have thin adventitia
-pressure on arterial wall due to haemodynamic turbulence at branch points
-genetic predisposition
Where do the majority of berry aneurysms form in the circle of Willis?
Anterior communicating artery/proximal arterial cerebral artery
Posterior communication artery
Bifurcation of middle cerebal artery
What structure can be affected if an aneurysm forms on the anterior communicating artery/proximal anterior cerebal artery?
Optic chiasm
Frontal lobe
Pituitary
What structure can be affected by a posterior communicating artery aneurysm?
Occulomotor nerve (CN III) can be compressed causing Ipsilateral CNIII palsy
How do patients with subarachnoid haemorrhages present? (Signs and symptoms)
Thunderclap headache (worst headache ever)
Dizziness
Orbital pain
Diplopia
Visual loss (anterior communicating artery aneurysm may have ruptured)
Meningism
Nausea and vomitng
Loss of consciousness
Sentinel headaches
Cardiac arrest (if ICP rises rapidly can lead to profound Cushing’s response)
What can happen after bleeding has occured into the subarachnoid space from a subarachnoid haemorrhage?
-Microthrombi form blocking more smaller arteries
-vasoconstriction due to CSF irritating the cerebral arteries
-cerebral oedema due to general inflammatory response to tissue hypoxia and damaged blood vessels
-MI due to increased sympathetic activation also called Cushings response
Early rebleeding
Acute hydrocephalus
Global cerebal ischaemia
How does subarachnoid haemorrhage cause an MI?
Rapid rise in intracranial pressure leads to profound Cushing response (increasing sympathetic drive) to the point where MI occurs since the workload/demand of the heart is so high
What some signs of menignism that can be seen in subarachnoid haemorrhage?
Neck stiffness
Photophobia
What artery aneurysm can compress occulomotor nerve?
Posterior communicating artery anureysm
What is the first line investigation done for subarachnoid haemorrhage?
Urgent non contrast CT (blood is contrast)
What may be visible on a noon contrast CT head with subarachnoid haemorrhage?
5pointed star pattern in basal cisterns
Blood in ventricles
What investigation is done if a CT for subarachnoid haemorrhage doesn’t show SAH but Hx is convincing?
Lumbar puncture
Why should a lumbar puncture be delayed to at least 6/12 hours after thinking it’s a subarachnoid haemorrhage?
Need time for RBCs to undergo lysis to release bilirubin in the CSF indicating SAH
What is the yellow tinge called in CSF that is indicative of a Subarachnoid haemorrhage?
Xanthochromia
What is the traumatic tap and why is xanthochromia able to differentiate this to indicate a subarachnoid haemorrhage?
Traumatic tap = may be blood in CSF after redoing lumbar puncture due to iatrogenic damage to blood vessels when doing LP
Xanthochromia = yellow tinge indicates that the blood cells have been in the CSF long enough to be lysed showing bilirubin
Apart from xanthochromia, what should be in the CSF indicating subarachnoid haemorrhage?
High protein
WCC normal
Glucose normal
High red cell count
What investigation must be done to locate aneurysm after a subarachnoid haemorrhage has been diagnosed?
CT angiogram
What vertebral level is a lumbar puncture done?
L4/L5
What is the route of a needle for a lumbar puncture?
Skin
Subcutaneous tissue
Supraspinous ligament
Interpsinous ligament
Ligamentum flavum (pop)
Dura mater
Arachnoid mater
Subarachnoid space
What are some general treatments for subarachnoid haemorrhage?
Support airway
Give O2
Support circulation by giving fluids
What drug can be given in a subarachnoid haemorrhage to help reduce cerebral vasospasm and secondary ischaemia?
What type of drug is this?
Nimodipine
Calcium channel blocker (dihdyropyridine)
What are the neurosurgical interventions done for subarachnoid haemorrhage?
Clipping (place clip at neck of aneurysm so it loses supply and shrivels up)
Coiling (insert platinum wire into sac causing thrombosis of blood in aneurysm)
Decompressive surgery (Craniectomy)
What is an infection of the parenchyma of the brain (functional tissue) called?
Encephalitis
What is meningitis?
Infection of the meninges (most commonly the leptomeninges)
What are some signs and symptoms of meningitis?
Triad of meningism with fever
Flu like
Joooint pains
Rash
Reduced GCS/seizures
Babies:
-inconsolable crying
-reduced feeds
-floppy/reduced tone
-bulging fontanelle (inc ICP)
What is the triad of menigism?
Headache
Neck stiffness
Photophobia
Accompanied by fever in meningitis
What type of rash is associated with meningitis?
Non blanching rash
So when pressure applied it doesn’t disappear
What type of meningitis is the non blanching rash most common in?
Meningococcal meningitis
What is the pathophysiology of the non blanching rash seen in meningococcal meningitis?
Bleeding in skin or mucosa (micro vascular thrombosis)
What is a petechia?
Small lesion 1-2mm
What are purpura?
Larger lesions over 2mm
Where are the petechia or purpuric non blanching rashes most commonly seen with meningitis?
Trunk
Legs
Mucous membranes
Conjunctiva
What are the most common causative organisms for neonatal meningitis?
Escherichia coli
Group B streptococcus
Listeria moncytogenes
What are the most common causative organisms for childrens meningitis?
Haemophilus influenzae
Neisseria meningitidis
What are the most common causative organisms for elderly meningitis?
Streptococcus pneumoniae
Listeria monocytogenes
What are the 3 most common causes of bacterial meningitis?
Pneumococcal meningitis (streptococcus pneumonia)
Meningococcal meningitis (Neisseria meningitides)
Hib meningitis (Haemophilus influenzae)
What vaccine helps prevent pneumococcal meningitis?
Pneumococcal conjugate vaccine (PCV13)
What vaccine helps prevent Hib meningitis?
Hib vaccine
What are the risk factors for community aquried meningitis?
Crowded housing
Asplenic
Immunosuppressed
Cochlear implants
Alcoholism
spina bifida
Endocarditis
Lumba puncture, surgery
What are the ways by which pneumococci can reach the CNS leading to pneumococcal meningitis?
Commensals in nasopharynx travelling to Eustachian tube causing otitis media, prolonged infection hear can lead to spread into CSF via the mastoid air cells/sinuses
Or
Commensals in nasopharynx can seed to lower resp tract (pneuma) then lung inflammation can let bacteria in blood (bacteriaemia) invade CSF via capillaries
How can neonates get pnuemococcal meningitis?
Maternal source
Placenta
Reproductive tract secretions
What is the pathophysiology of meningitis?
Bacteraemia occurs likely from commensals in the nasopharynx
Bacteraemia damages vessel walls in brain and meninges so pathogen can enter subarachnoid space/CSF
Rapidly multiplies in CSF leading to severe meningeal inflammation
What other negative effects can occur as result of bacteria in CSF causing mengitis?
Cerebal oedema
Raised ICP
Septic shock
DIC
Coma
Seizures (brain parenchyma irritated)
Hearing loss (vestibulocochlear nerve damage)
Hydrocephalus
Focal Paralysis (Cerebral abscess)
SIADH. (Hypothalmus/pituriatry effectd)
Intellectual deficits
How can meningitis cause hydrocephalus?
Meningeal inflammation can block the CSF drainage pathway
Why does micro vascular thrombosis causing the non blanching. Rash occur in mengiits?
Sluggish circulation
Impaired fibronlysis
Inc tissue factor in endothelial cells
What are the 2 examination signs that can be done to find meningitis?
Kernig sign
Bruzinski sign
What is the Kernig sign?
Patient supine with hip flexed at 90 degrees
Try and extend knee and its met with resistance
Most common in kids
Indicates meningitis
What is brudzinski sign??
Patient lies supine
When neck is flexed, knees and hips involuntarily flex
More common in kids
Indicates meningitis
What is the first line investigation for meningitis?
Lumbar puncture
Then blood cultures
PCR
How will CSF from a lumbar puncture appear with bacterial meningitis?
Cloudy CSF
High protein
High white cells (neutrophils)
Low glucose
How will CSF from a lumbar puncture appear with viral meningitis?
Clear (can be cloudy)
Protein normal or raised
High white cells (lymphocytes)
Normal glucose
Why may you want to delay doing a lumbar puncture with suspected meningitis?
What are the signs indicating this may be an issue?
Sudden decrease in pressure cause by doing LP can increase risk of brain herniation
Signs:
Brainstem signs
Decreasing consciousness
Recent seizure
What empirical antibiotics are immediately given when suspecting meningitis while you’re waiting for blood cultures back?
IV Vancomycin + Ceftriaxone or cefotaxime
What is an empirical antibiotic?
Broad spectrum antibiotics given when we dont know the microbial cause of an infection
What supportive treatments are given for meningitis?
Analgesia
Antipyretics
Fluids
What drug would be given to help prevent hearing loss with meningitis?
What type of drug is this?
Dexamethasone
Steroid helps reduce swelling of vestibulocochlear nerve
What drug is given if meningitis is thought to be viral (herpes)?
Aciclovir
What drug is given if the viral cause of meningitis is cytomegalovirus?
Ganciclovir
