Session 2 - Skull Anatomy Flashcards
What is the Neurocranium?
The part of the skill that protects the brain (8 bones)
- Calvaria (skull cap)
- Cranial Floor (base)
- Cranial Cavity
What is the Viscerocranium?
Facial Skeleton & Jaw
(14 bones)
Surrounds oral cavity, pharynx & upper respiratory tract.
How do neurocranial structures communicate with other head & neck structures?
‘Holes’ in the cranial floor, for the brain stem, nerves and vessels.
Which structures form the cranial floor?
Anterior, middle & posterior cranial fossae.
Describe the structure of the bones of the Calvaria (skull cap)
- Outer table (compact bone)
- Diploeic cavity (trabecular bone)
- Inner table (thinner layer of compact)
What is a Fontanelle?
The anatomical feature in infants.
The soft membranous gaps between the cranial bones.
What are suture lines? Name three important ones.
The intersections between the bones of the skull.
Saggital= between the two parietal.
Coronal= between the parietals and frontal.
Lambdoid= Between the parietals and the occipital.
Describe the structure of the suture lines through life.
Serrated and interlocked to prevent slippage.
Growth stops at puberty.
Gradually ossify from inside out.
How is the periosteum adhered to the outer table of bone?
Adheres closely to the bone, though continuous, it adheres STRONGLY to suture lines.
What is a cephalohaematoma? How is it diagnosed?
A sub-periosteal bleed.
Will be over only ONE bone, as periosteum is tightly adhered to suture lines.
What is a subgaleal haemorrhage?
Sub-aponeurotic bleed, between skull aponeurosis and periosteum.
Can spread over whole skull.
Patients can form raccoon eyes.
What is the purpose of the fontanelles?
Allow for alteration of skull size and shape in child birth, and allow growth in infant brain.
What is Craniosyntosis?
Early fusion of fontanelles and sutures (rare)
When do the fontanelles usually fuse?
Early infancy
Anterior= ~18 Months - 2 Years
Posterior= ~1-3 Months
How is the anterior fontanelle clinically relevant?
In examining newborns.
- Slightly convex shape.
- Inspection & gentle palpation can asses Intracranial pressure and state of hydration.
What is an important clinical test for any suspected skull injury or fracture?
Risk of intracranial injury!
CT scanning on ALL patients with know/suspected skull fracture.
Name and describe the two main types of skull fracture.
Linear:
Pass full thickness of skull, straight, no bone displacement.
Depressed:
Fragment is displaced inwards towards brain/
What are basilar skull fractures?
Fractures involving cranial base.
What are some common signs of basilar skull fractures?
-Cerebrospinal fluid leaks. (Ears/nose) -Racoon eyes -Bruising around mastoid process (Battle’s sign) - Cranial nerve injuries
Rare!
What is the Pterion?
The thinnest area of the skull, where the parietal, frontal, sphenoid and temporal bones join.
Why is a blow to the pterion particularly dangerous?
If fractured, the middle meningeal artery lies under this structure.
Can cause intracranial haemorrhage.
Describe the layers of the meninges.
Three layers surrounding the brain.
- Dura - thick tough outer
- Arachnoid - in between, transparent
- Pia - tightly adhered to the brain
What are the layers of the dura?
- Outer periosteal layer (endosteum lining inner skull bones)
- Meningeal layer - adjacent to arachnoid
Where do the dural layers separate?
Dural folds
Dural venous sinuses
Which two dural folds are important? Why?
Rigid dividers of the brain!
- Falx Cerebri
Protects/separates hemispheres.
-Tentorium Cerebelli
Protect cerebellum.
How would a pressure increase due to e.g. a bleed affect the brain?
(dural folds)
Compression and displacement against the rigid folds! No space for fluid to go.
Can cause herniation, e.g. into brain stem.
What are dural venous sinuses?
Sections where the periosteal and meningeal dura is separated forming channels, allowing venous blood to drain from the vein.
Where do dural venous sinuses drain to?
Drain to the internal jugular vein.
Where are the major venous sinuses?
At the margins of borders of the Falx cerebri and Falx cerebelli.
On the cranial floor.
What are bridging veins?
Veins traversing the sub dural space and draining into dural venous sinuses.
(Cerebral veins within subarachnoid space)
Name the three types of haemorrhages in the meningeal layers?
Extradural
Sub dural
Subarachnoid
What is an extradural haemorrhage?
An arterial bleed between the bone and the dura (periosteal layer stripped away)
Can cause increase in intracranial pressure.
What is a sub dural haemorrhage, what are common causes?
Venous bleed between dura and arachnoid layer.
Often due to bleed from bridging vein.
Spread over one half of the skull.
(Falx cerebri prevent spread)
What can cause a subarachnoid haemorrhage? How do they occur?
Secondary to trauma, or rupture of vessel (aneurysm).
Blood leaks in subarachnoid space, mixes with CSF.
What is the outlook of a subarachnoid haemorrhage?
Sudden, often fatal.
CT image!
93% picked up within 24 hours
100% picked up within 6 hours
Which procedure can confirm a subarachnoid haemorrhage has occurred?
A lumbar puncture.
Sample the CSF and identify presence of blood.
