Neuropathology - raised ICP and SOL's (pie) Flashcards
What are the 3 main things found in the cranium?
Within the cranium, the brain takes up 80%, CSF 8% and blood 12%.
How does the body try to compensate for enlargement of the brain ?
- Some blood +/- CSF must escape from cranial vault to avoid rise in pressure.
- Once this process is exhausted, any further increase in brain volume results in rapid increase in ICP.
What are the causes of raised ICP ?
- Increased CSF (hydrocephalus)
- Focal lesion in brain (Space Occupying Lesions) e.g. tumour, abscess, chronic subdural haematoma, granuloma, cyst
- Diffuse lesion in brain (e.g. oedema)
- Increased venous volume
- Physiological (hypoxia, hypercapnia, pain)
Define hydrocephalus
Accumulation of excessive CSF within the ventricular system of the brain.
What are the normal values for CSF fluid ?
Clear fluid containing:
- Lymphocytes <4 cells/ml
- Neutrophils 0 cells/ml
- Protein <0.4g/l
- Glucose >2.2mmol/l
- No RBCs
What are the causes of hydrocephalus ?
- Obstruction to flow of CSF (e.g. inflammation, pus and tumours)
- Decreased resorption of CSF (post SAH, or meningitis)
- Overproduction of CSF (v. rare: tumours of choroid plexus)
How is hydrocephalus classified ?
Hydrocephalus can be congenital or acquired and:
- Communicating - Obstruction to flow of CSF occurs within ventricular system
- Or non-communicating - Obstruction to flow of CSF outside of the ventricular system e.g. in subarachnoid space or at the arachnoid granulations
What is the difference in the presentation of hydrocephalus between it arising when the cranial sutures haven’t closed over (i.e. before 2-3yrs old) and it arising after the cranial sutures have closed over ?
If hydrocephalus develops before closure of cranial sutures, then cranial enlargement occurs (as seen in the pic with baby), bulging fontanel
If hyrocephalus occurs after closure of the sutures, you get:
- Expansion of the ventricles
- Flattening of the gyrae (as seen on the left)
- Fullness of the sulci
- And raised ICP
What are the direct effects of raised ICP (not talking about the signs/symptoms, meaning the effects on the brain etc)?
- Intracranial shifts and herniation
- Midline shift
- Distortion & pressure on cranial nerves
- Impaired blood flow
- Decreased consciousness
Where is the cingulate gyrus located ?
Immediately above the corpus callosum
Describe the 4 main types of shifts/ herniations that can occur due to raised ICP ?
1) Subfalcine herniation: - Unilateral or asymmetric expansion of cerebral hemisphere displaces the cingulate gyrus under the falx cerebri
* Assoc. compression of ACA: manifested by weakness and/or sensory loss in leg, because of ischaemia to the primary motor and/or sensory cortex in these areas.
2) Tentorial herniation - Medial aspect of temporal lobe (hippocampal uncus and parahippocampal gyrus) herniates over the tentorium cerebelli.
* Compression of ipsilateral third cranial nerve and its parasympathetic fibres -> pupillary dilation and impairment of ocular movements on the side of the lesion.
3) Tonsillar herniation - Displacement of cerebellar tonsils through the foramen magnum.
* Life-threatening as it causes brainstem compression and compromises vital respiratory centres in medulla oblongata.
Transcalvarium – a swollen brain will herniate through any defect in the dura and skull.
- Reduction in level of consciousness
- Dilatation of pupil on same side as mass lesion
- Bradycardia, increase in pulse pressure and increase in mean arterial pressure,
- Cheyne-Stokes respiration
What are the core clinical signs of raised ICP ?
- Papilloedema – occurs due to pressure on optic nerve
- Nausea and vomiting
- Headache – (worse on lying down, coughing, sneezing, and straining) – thought due to compression and distortion of the dura.
- Neck stiffness – due to pressure on dura around cerebellum and brainstem.
- May also get mental changes
What are the main causes of space occupying lesions ==> raised ICP ?
- Tumours – primary brain tumours, metastases
- Abscess – single/multiple
- Haematomas
- Localised brain swelling – e.g. swelling and oedema around cerebral infarct
What are the 2 main classes of abscesses in the brain ?
Single abscesses and multiple abscesses
Single abscesses:
- Due to local extension e.g. secondary to mastoiditis, chronic otitis media, or mastoiditis, paranasal sinusitis, nasal, facial and dental infections
- Or by direct implantation e.g. skull fracture
- They tend to occur adjacent to source
Multiple abscesses:
Indicate haematogenous spread e.g. from bronchopneumonia, bacterial endocarditis
What is the pathological appearance of abscesses ?
Central necrosis, oedema fibrous capsule
