Space Occupying Lesions & Raised ICP Flashcards
Define hydrocephalus
Accumulation of excessive CSF within the ventricular system of the brain
State three mechanisms of hydrocephalus
- overproduction of CSF (rare choroid plexus tumours)
- decreased resorption of CSF by arachnoid granules (arachnoiditis after haemorrhage/meningitis)
- obstruction of CSF flow (pus, tumour, congenital, SOL)
Name two types of hydrocephalus
Communicating and non-communicating
What is communicating hydrocephalus?
Obstruction to flow outside of the ventricular system e.g subarachnoid space or granulations
What is non-communicating hydrocephalus?
Obstruction to flow occurs within the ventricular system
When do cranial sutures close?
Between 2 and 3 years of age
What happens if hydrocephalus occurs before cranial sutures close?
Cranial enlargement, increase in occipital- frontal circumference
What happens if hydrocephalus occurs after cranial sutures close?
Expansion of ventricles, flattening of gyri and increased ICP
What is ex vaco?
Loss of brain parenchyma, not due to an increase in pressure but expansion of CSF and ventricle e.g alzheimers, infarct
What is normal ICP?
5-13mmHg
What can cause increased ICP?
Increased CSF Focal lesions (SOL) Diffuse lesion (oedema) Increased venous volume Physiological (hypoxia, pain, hypercapnia)
What are the effects of increased ICP?
Intracranial shifts and herniation Midline shift Distortion and pressure on cranial nerves and brain centres Impaired blood flow Reduced consciousness
Name four types of herniation
- subfalcine/cingulate
- tentorial/uncal
- cerebellar
- transcalvarial
Describe subfalcine herniation
Displacement of cingulate gyrus under falx cerebri, anterior cerebral artery branches may be compressed- contralateral leg symptoms
Describe tentorial herniation
Compression of ipsilateral third cranial nerve - pupillary dilatation, uncus of the temporal lobe is pushed against the midbrain
Describe cerebellar/tonsillar herniation
Cerebellar tonsils are pushed through the foramen magnum, compresses vital respiratory centres and causes loss of consciousness
Describe transcalvarial hernation
Associated with a defect in the dura/skull
What are the clinical signs of increased ICP?
- papilloedema
- headache
- nausea/vomiting
- reduced consciousness
- neck stiffness
How do brain tumours often present?
Focal symptoms, headache - retain CO2 during sleep, increase in bloodflow means it will be worse in the morning, seizures and increased ICP
How do single abscesses in the brain arise?
Local extension - chronic otitis media, sinusitis, tooth infections
Direct implantation - skull fracture
How do multiple brain abscesses arise?
Haemtogenous spread - IV drug use, respiratory/cardiac infections, congenital heart disease
Where do brain abscesses often occur?
Grey/white matter boundary
Describe the pathology of a brain abscess
Oedema, can cause midline shift, surrounding ischaemia and excitotoxic injury
What does an abscess look like on imaging?
Central necrosis with oedematous fibrous capsule - ring enhancing lesion
What are the organisms associated with brain abscesses?
Staph, strep (aerobic and anaerobic)
Immunocompromised - fungi and protozoa
Name three types of skull fracture
Linear
Compound
Depressed
Describe a linear skull fracture
Straight, sharp fracture line that may cross sutures, associated with haematoma - if it occurs at the squamous portion of temporal bone it can rupture the middle meningeal artery causing a subdural haematoma
Describe a compound fracture
Full thickness scalp lacerations usually open - base of skull fractures are an example as paranasal sinus injury is presumed
What are surface contusions?
Bruises due to damage of tissue, they predominate in cortices but can move into white matter
What part of the skull is susceptible to contusions?
Under surface of temporal and frontal lobes due to sharp bony prominences
Describe the difference between coup and contra coup
coup - side of impact
contra-coup - non-impact side may occur at the same time or as rebound
What provokes diffuse axonal injury?
Rotational movement
Where does diffuse axonal injury tend to occur?
- brainstem
- corpus collosum
- parasagittal area
- interventricular septum
- hippocampal formation
What signs can be seen in axonal injury?
Microglia accumulation
Shear strain and transection of axons
Axonal bulging and blabbing
Name types of secondary brain injury
- haematoma
- reduced blood flow
- hypoxia
- excitotoxicity
- oedema
- raised ICP
- infection
- reduced auto regulation
