Raised ICP Flashcards
what is raised ICP
increase in pressure within the cranial cavity caused by an increased pressure in fluid surrounding the brain or increase in pressure within the brain itself. Can be acute or chronic.
What is the monro-kellie hypothesis
Pressure volume relationship that aims to keep a dynamic equilibrium. ie the intracranial volume in adults in 1700- 1400 brain tissue, 150 CSF and 150 blood so a decrease in any should be compensated with an inc in another
what is CN II
An extension of the brain covered in meninges- optic nerve
what are the meninges
Protective covering of the brain and spinal cord- dura mater, arachnoid mater and pia mater
What is the dura mater? Features and innervation.
Outermost layer of the meninges- directly underneath the bones of the skull and vertebral column. thick and tough. contains a dural venous sinuses- responsible for the venous vasculature of the cranium and drains into internal jugular veins.
Innervated by trigeminal nerve (V1, V2 and V3)
Vasculature: middle meningeal artery and nerve
What is the arachnoid mater?
middle layer directly underneath the arachnoid dura mater. It is avascular and has no innervation- consists of sheets of connective tissue.
What is the subarachnoid space
Underneath the arachnoid layer there is a space filled with CSF to cushion the brain. there are small projections of arachnoid mater into the dura mater called arachnoid granulations that allow CSF to re-enter circulation via the dural venous sinuses
What is the Pia mater
Underneath the sub arachnoid space and thin. It is tightly adhered to the brain and spinal cord and follows the contours of gyri and fissures. HIghly vascularised.
What is the tentorial notch
allows the passage of brainstem
What is the flex cerebri
descends vertically in the human brain between cerebral hemispheres. its a double fold of dura mater through the inter hemispheric fissure.
What is the tentorium cerebelli
Dura mater that is perpendicular to the flex cerebri (ie its in the axial plane) and divides it into superior and inferior compartments.
What are the ventricles in the brain lined with?
ependymal cells which form a choroid plexus and produce CSF
What are the ventricles derived from?
Lumen of the neural tube
How many ventricles are there and what are they called?
4:
right and left lateral ventricles
3rd ventricle
4th ventrcile
Lateral ventricles structure
right and left lateral ventricles
They have horns which project into the temporal, occipital and frontal lobes.
volume of lateral ventricle increases with age
What connects the lateral and 3rd ventricle
foramen of monro/ interventricular foramina
Location of the 3rd ventricle
between the right and left thalamus- midline in the diencephalon
what connects the 3rd and 4th ventricles
Cerebral aqueduct
Location of the 4th ventricle
in the brainstem @the junction between the pons and medulla oblangata
How is CSF drained from the brain
Draingae occurs in the subarachnoid space. Arachnoid granualtions project into the dura mater allowing CSF to drain into the dural venous sinuses and then into the Internal jugular veins
How does CSF drain from the 4th ventricle
via the apertures: 1 median aperture and 2 lateral aperture
Effects of raised ICP on the optic nerve
will compress the optic nerve in the subarachnoid space (also will compress the central artery and vein of the retina). can lead to a bulging or swollen optic disc (papillodema) and visual symptoms.
What do the parasympathetic fibres of CNIII innervate?
Sphincter pupillae fibres and ciliary msucles of the eye
What are the effects of compression of CNIII
paralysis of somatic motor innervation: extraocular muscles
paralysis of parasympathetic innervation of sphincter pupillae
Clinical signs of CNIII injury
- no /slow pupillary light reflexes
- dilated pupil due to unopposed action of dilator pupillae
- ptosis- due to loss of LPS innervation
- postion of eye- looking down and out due to unopposed action of LR and SO
3 main causes of oculomotor nerve lesion
- increasing ICP
- aneurysm of posterior cerebral artery
- cavernous sinus infection
What are the effects of CN IV damage
paralysis of superior oblique so the IO is unopposed. eye cannot move inferomedially
Presentation of CNIV damage
diplopia especially when looking down eg reading or going down stairs
Pateint may develop head tilt
Most common cause of CN IV damage
microvascular damage from DM or HT
Function of abducens nerve (CN VI)
somatic motor innervation of lateral rectus
Presentation of damage to CN VI
medial rotation and diplopia
what is the choroid plexus
network of capillaries which filter blood to from CSF
