Anatomy of Space Occupying Lesions Flashcards
What is a space occupying lesion?
Abnormal tissue taking up space in the skull
Both acute and subacute (expanding) intracranial pathologies can be considered as SOLs
How and why does a space occupying lesion cause raised ICP, which may cause brain herniation?
The skull has limited space and holds many structures
Usually only capable of slow rate expansion. Acute and subacute SOLs can result in increase ICP and cause herniation through foramen magnum
What are layers of the scalp from superficially to skull bone?
SCALP Skin Connective tissue Aponeurosis Loose connective tissue Pericranium
Which layer of the scalp has a rich anastomotic arterial blood supply?
Layer 2- connective tissue
Lacerations can cause excessive bleeding
What is the clinical significance of sutures in the skull?
Prevent fractures from spreading
N.B. Fibrous joints
What is the significance of the ‘H-shaped’ pterion?
This is where frontal, parietal, temporal and sphenoid bones meet
Thinnest part of skull
Why is the pterion clinically relevant?
Close proximity to middle meningeal artery
What is meningitis?
Bacterial or viral infection of the meninges
Name the meninges from superficial to deep
Dura Mater (Hard mother) Arachnoid Mater (Spidery mother) Subarachnoid space (contains CSF) Pia Mater (Faithful mother)
What is the role of dura mater?
Tough/fibrous
Has sensory nerve supply mainly from CN V
Encloses the dural venous sinuses
What is the role of arachnoid mater?
Arachnoid granulations reabsorb CSF
What is the role of Pia mater?
Adherent to the brain and the blood vessels & nerves entering or leaving brain
What is the name of the dura mater covering the cerebellum?
Tentorium cerebelli
Where does the tentorium cerebella attach?
Attaches to ridges of petrous temporal bones
Has central gap to permit the brainstem to pass through
What is the name of the dura mater forming a roof (diaphragm) over the pituitary fossa?
Diaphragm sellae
How are the dural venous sinuses formed?
Split between dura mater layers
The dura mater forms a midline structure that separates the right & left cerebral hemispheres, what is the name of it?
Falx cerebri
Where does the flax cerebri attach to the skull?
The crista galli of the ethmoid bone anteriorly
Internal occipital protuberance of the occipital bone posteriorly
What are sinuses that drain the brain?
Superior sagittal sinus Left sigmoid sinus- drains into internal jugular at jugular foramen Confluence of the sinuses Inferior sagittal sinus Cavernous sinuses
What is the clinical significance of the danger triangle?
Potenital for venous spread of infection in facial vein
Facial vein is atypical- much thicker walls that remain open rather than collapse and have no valves allowing spread of bacteria
Which veins of the face connect with the cavernous sinus?
Ophthalmic veins
Which arteries supply the brain?
Right vertebral artery passes through cervical vertebrae then foramen magnum
Right common carotid gives rise to right external carotid artery and right internal carotid artery
Circle of Willis
Picture
Where does the subarachnoid space lie?
Between arachnoid mater and pia mater
What is the role of the subarachnoid space?
Cushions and protects
How many mls of CSF are produced per day?
400-500mls
Where is CSF produced?
Inside the brain
Choroid plexus of the ventricles
Where is CSF reabsorbed?
In the dural venous sinuses via arachnoid granulations
Where can CSF be samples from?
Via lumbar puncture at L3/L4 or L4/5 IV disc levels to obtain a sample of CSF
Where does the subarachnoid space end?
Level of S2 in sacrum
How does CSF move through the ventricles?
- Secreted by choroid plexus
- Lateral ventricles via foraminae of Monro
- Midline of 3rd ventricle
- Via cerebral aqueduct into..
- 4th ventricle then..
- Subarachnoid space of brain & spinal cord
- Reabsorbed from subarachnoid space via arachnoid granulations
- Into dural venous sinuses
What is hydrocephalus?
Excessive production, obstruction to flow or inadequate reabsorption leads to an increased CSF volume
How can hydrocephalus be treated surgically?
Shunt catheter “tunnelled” beneath the skin of the neck and chest then sited within the peritoneal cavity
What is an extradural haemorrhage?
Between bone and dura
Example: ruptured middle meningeal artery, trauma to the pterion
What is a subdural haemorrhage?
Separates dura from arachnoid
Torn cerebral veins
Common in falls in the elderly and those with drinking problems
What is a subarachnoid haemorrhage?
Haemorrhage into CSF of subarachnoid space
Ruptured circle of Willis (“berry”) aneurysm
Congenital aneurysm
Describe the pathway of an epidural catheter vs lumbar puncture as it passes through the skin
Supra and then interspinous ligaments Ligamentum flavus Epidural space (fat + veins)
Lumbar puncture then continues through the dura mater + arachnoid mater to reach subarachnoid space to obtain CSF sample
Damage to the extradural venous plexus can result in what?
Epidural haematoma compressing spinal cord or cauda equina
What are the two directions of an infratentorial herniation?
Upward
Downward or tonsillar herniation
(herniation of cerebellar tonsils into foramen magnum)
What are the four types of supratentorial herniation?
Cingulate (subfalcine)
Central
Uncal- the uncut (medial part) of temporal lobe herniates inferior to tentorium cerebella
Transcalvarial
What is the clinical sign seen when the oculomotor nerve is compressed by an uncle herniation?
Ipsilateral fixed dilated pupil (a “blown” pupil)
