Session 2 Flashcards
Which suture can be found between the parietal bones?
Sagittal Suture
Which suture can be found between the frontal bone and parietal bones?
Coronal Suture
What suture can be found between the occipital bone and parietal bone?
Lambdoid suture
Which 2 groups can the bones of the skull be broadly divided into?
Neurocranium - 8 bones
- Encase and protect brain
- Has the Calvaria, Cranial floor base and Cranial cavity
Viscercranium - 14 bones
- Facial skeleton and the jaw
- Surround the oral cavity, pharynx and upper respiratory passages
What does the Calvaria begin as and how does it ossify?
Begins as membrane and undergoes intramembranous ossification
What does the floor of the neurocranium begin as and by which process does it ossify?
- Cartilage
- Undergoes endochondrial ossification
How do structures within neurocranium communicate with other head and neck structures?
- Cranial floor has holes that enable cranial nerves to allow communication between the brain and brain stem and the structures of the face and neck they innervate.
- Blood vessels also pass between these holes
What are the 3 bowl shaped depression formed on the cranial floor?
- Anterior Cranial Fossae
- Middle Cranial Fossae
- Posterior Cranial Fossae
What is the trilaminar arrangement of the calvaria?
Outer Table (compact bone) Diploeic Cavity (spongy bone) Inner table (compact bone)
Why are the edges of the bones of the skull serrated?
To prevent slippage and movement
When does growth at sutures stop?
Puberty
What covers the surface of the outer table of bone?
Periosteum
-Strongly adhered at suture line
Periosteum covering the outer table is continuous through to the periosteum covering the inner table. True/False
True
Where does a cephalohaematoma occur?
Occurs between he periosteum and the bones.
Can bleeding in a cephalohaematoma pass the suture lines?
No it cannot.
What are fontanelles?
Areas of membrane between bones that are particularly large.
What are the purposes of fontanelles?
- To allow for altering of the skull size and shape during child birth
- To permit growth of infant brain
When the fontanelles fuse?
Posterior - 1 month to 3 months
Anterior - 18 months to 2 years
What is early fusion of fontanelles and sutures called?
Craniosyntosis
What is the shape of the fontanelles?
Slightly convex shape in a healthy baby
What should be performed in all partients with known or suspected skull fractures?
CT scanning should be performed to identify intra cranial injuries
What are the two main types of fractures?
Linear - pass full thickness of skull. It is failed strains and involve no bone displacement
Depressed - Fragment is displaced inwards towards the brain
What are basilar skull fractures and what are their risks?
Fractures involving the cranial base
- Associated with cranial nerve injuries
- Prone to causing cerebrospinal fluid leaks
Which artery is underlying the Pterion?
Middle meningeal artery
Why is the pterion particularly at risk of fracture?
It is the thinnest area of the skull
What is the risk with the pterion?
Intracranial Haemorrhage due to the injury to the middle meningeal artery
What are some signs of basilar skull fractures?
- Raccoon eyes
- Battle signs
- Hemotympanum
What the 3 sacs around the brain and their properties?
Dura: tough fibrous membrane
Arachnoid: soft translucent membrane
Pia: microscopically thin, delicate and closely adherent to surface of brain
Which membranous layers of the brain can be pulled away easily?
Dura and Arachanoid
The dura is translucent. True/False
False. The arachnoid is translucent
What are the layers of the dura?
Periosteal = endosteum lining the inner bones of skull Meningeal = Layers adjacent to arachnoid
What is formed by separation of the two layers of the dura?
- Dural folds
- Dural venous sinuses
What is the purpose of the dural folds?
Helps to stabilise the brain and act as Rigid dividers
What are these signs associated with?
A. Sunken fontanelles
B. Bulging fontanelles
C. Enlarged fontanelles
A. Sign of dehydration
B. Symptom of serious illness such as meningitits
C. Sign of Down syndrome or premature birth
Where can the falx cerebri be found?
In the sagittal place. It lies in the midline of the brain
Where can the tentorium cerebella be found?
In the transverse plane of the brain. It slips between the cerebellum and the brain.
What can a rise in pressure inside the skull lead to?
Compression and displacement of the brain against the rigid folds and/or through foramen magnum. (herniation)
What are the effect of a rise in pressure on the cranial nerves?
Their roots have a close relationship with the dural folds so they can get squashed
What are dural venous sinuses?
Venous blood filled spaces created by separation of meningeal from periosteal layer of the dura.
Where do the major venous sinuses lie?
At the border of the falx cerebri, falx cerebelli and also on the cranial floor.
Where does venous blood from the brain drain to?
Venous sinuses via the cerebral veins
Where do the dural venous sinuses eventually drain to?
Internal jugular vein
Which venous sinus runs in the sagittal plane?
- Superior sagital sinus
- Inferior sagital sinus
Which venous sinus runs in the transverse plane?
-Transverse venous sinus
What does the transverse venous sinus change to when it reaches the petrous bone?
Sigmoid sinus
When does the sigmoid sinus become the internal jugular vein?
When it reaches the jugular foramen
Where is the confluence of sinuses found?
Deep to the protuberance of the occipital bone
What is the confluence of sinuses?
A meeting point of the straight sinus, superior sagittal sinus and inferior sagittal sinus.
How do cerebral veins within the subarachnoid space drain into the dural venous sinuses?
Bridging veins
What is a common cause of extradural haemorrhage?
Arterial bleed via the middle meningeal artery. Bleeding occurs between the bone and periosteal
What is a common cause of subdural haemorrhage?
Venous bleed through the bridging veins.
Why doesn’t the bleed form a subdural haemorrhage spread across the brain?
Falx cerebri stops the spread across the side of the brain
Why are older people more susceptible to subdural haemorrhage?
- The Brian gets smaller as you get older
- Increase tension of the bridging veins
- A slight knock could cause the veins to rupture as a result
What usually cause a subarachnoid haemorrhage?
-Usually a branch of the circle of willis
Secondary to trauma or spontansous rupture of the blood vessel
