Infections, tumours and ICP control Flashcards
How do pathogens gain entry to CNS
Direct - otitis media, base of skull fracture
Blood borne - sepsis, infective endocarditis
Iatrogenic - VP shunt, surgery, LP
What is inflamed in meningitis
Leptomeninges (pia and arachnoid)
Causative organisms of meningitis in each age group
Neonates: Ecoli, listeria monocytogenes
2-5: haemophilus influenzae B
5-30: Neisseria meningitidis
>30: strep pneumoniae
Complications of meningitis
Raised intracranial pressure Cerebral infarction Cerebral abscess Subdural empyema Epilepsy
Causative organism in chronic meningitis and complication of this type of infection
Mycobacterium tuberculosis
Can cause fibrosis of leptomeninges around brainstem leading to focal CN lesions
What is encephalitis
Inflammation of brain parenchyma causing neurone death
Causative organisms of encephalitis for different parts of brain
Temporal lobe: herpes virus
Spinal cord motor neurones: polio
Brainstem: rabies
What commonly causes encephalitis in elderly/immunocompromised
Herpes zoster
Can be mild to severe
What are prions
Normal soluble proteins found in neuronal synapses
How do prions become mutated
Sporadically
Familial
Ingesting mutated prions
Why are prions not pathogens
Only fulfil 1 of Koch’s postulates (found in all organisms suffering from disease)
What do mutated prions cause and how
Spongiform encephalopathies
Mutated prions interact with normal prions causing a post translational conformational change leading to a mutated prion aggregate.
Thee aggregates cause neuronal death and lead to holes in the grey matter.
Examples of spongiform encephalopathies
BSE
Scrapie
Variant Creutzfeldt-Jacob disease
Definition of dementia
Acquired global impairment of intellect, reason and personality without impairment of consciousness
What damages cholinergic neurones in AD
Neurofibrillary tangles - twisted filaments of Tau protein formed by hyperphosphorylation
Senile plaques - abnormal BV due to amyloid deposition in centre of plaque. Foci contain synaptic terminals, dendrites and enlarged axons
Why does early onset AD have a higher prevalence in trisomy 21
3 genes are mutated:
Amyloid precursor protein
Presenilin 1 + 2 (make secretase to break down amyloid)
Normal ICP
5-15 mmHg
When is an above normal ICP pathological
Raised for at least several minutes
Up to what ICP can compensatory mechanism work to maintain cerebral blood flow
60 mmHg
How does the brain maintain blood flow in high ICP
Decreased blood volume
Decreased CSF volume
Brain atrophy (in chronic)
What is a space occupying lesion of the brain
Deform or destroy brain around lesion leading to loss of symmetry and eventual herniation
3 types of brain herniation
Subfalcine
Tentorial
Tonsilar
Describe a subfalcine herniation
Ipsilateral cingulate gyrus is pushed under free edge of falx cerebri
Anterior cerebral artery occlusion so ischaemia of frontal, parietal and corpus collosum
Describe a tentorial herniation
Uncus herniates through tentorial notch
Damages ipsilateral CNVIII and occludes posterior cerebral and superior cerebellar arteries
What is a duret haemorrhage
Haemorrhage into brainstem (fatal)
Can be secondary to tentorial herniation
Describe a tonsilar herniation
Cerebellar tonsils pushed into foramen magnum which compresses brainstem (rapidly fatal)
Features of primary brain tumours
Very rare as cells don’t divide
Never metastasise
Examples of benign brain tumours
Meningioma
Neurofibroma
Example of malignant brain tumour
Astrocytoma
Where do astrocytomas spread to
Along nerve tracts
Sub arachnoid space
Percentage occurrence of types of stroke
85% infarction
15% haemorrhage (10% intracerebral and 5% subarachnoid)
Describe causes of intracerebral haemorrhage
Hypertensive vessel damage
Charcot-Bouchard aneurysm rupture
BV amyloid deposition in elderly
Causes of subarachnoid haemorrhage
Rupture of berry aneurysm (at branching points of circle of Willis)
