Session 2 - Skull Anatomy

Question 1

What is the Neurocranium?

Answer 1

The part of the skill that protects the brain (8 bones)

• Calvaria (skull cap)
• Cranial Floor (base)
• Cranial Cavity

Question 2

What is the Viscerocranium?

Answer 2

Facial Skeleton & Jaw
(14 bones)

Surrounds oral cavity, pharynx & upper respiratory tract.

Question 3

How do neurocranial structures communicate with other head & neck structures?

Answer 3

‘Holes’ in the cranial floor, for the brain stem, nerves and vessels.

Question 4

Which structures form the cranial floor?

Answer 4

Anterior, middle & posterior cranial fossae.

Question 5

Describe the structure of the bones of the Calvaria (skull cap)

Answer 5

1. Outer table (compact bone)
2. Diploeic cavity (trabecular bone)
3. Inner table (thinner layer of compact)

Question 6

What is a Fontanelle?

Answer 6

The anatomical feature in infants.

The soft membranous gaps between the cranial bones.

Question 7

What are suture lines? Name three important ones.

Answer 7

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.

Question 8

Describe the structure of the suture lines through life.

Answer 8

Serrated and interlocked to prevent slippage.

Growth stops at puberty.

Gradually ossify from inside out.

Question 9

How is the periosteum adhered to the outer table of bone?

Answer 9

Adheres closely to the bone, though continuous, it adheres STRONGLY to suture lines.

Question 10

What is a cephalohaematoma? How is it diagnosed?

Answer 10

A sub-periosteal bleed.

Will be over only ONE bone, as periosteum is tightly adhered to suture lines.

Question 11

What is a subgaleal haemorrhage?

Answer 11

Sub-aponeurotic bleed, between skull aponeurosis and periosteum.

Can spread over whole skull.
Patients can form raccoon eyes.

Question 12

What is the purpose of the fontanelles?

Answer 12

Allow for alteration of skull size and shape in child birth, and allow growth in infant brain.

Question 13

What is Craniosyntosis?

Answer 13

Early fusion of fontanelles and sutures (rare)

Question 14

When do the fontanelles usually fuse?

Answer 14

Early infancy

Anterior= ~18 Months - 2 Years

Posterior= ~1-3 Months

Question 15

How is the anterior fontanelle clinically relevant?

Answer 15

In examining newborns.

• Slightly convex shape.
• Inspection & gentle palpation can asses Intracranial pressure and state of hydration.

Question 16

What is an important clinical test for any suspected skull injury or fracture?

Answer 16

Risk of intracranial injury!

CT scanning on ALL patients with know/suspected skull fracture.

Question 17

Name and describe the two main types of skull fracture.

Answer 17

Linear:
Pass full thickness of skull, straight, no bone displacement.

Depressed:
Fragment is displaced inwards towards brain/

Question 18

What are basilar skull fractures?

Answer 18

Fractures involving cranial base.

Question 19

What are some common signs of basilar skull fractures?

Answer 19

-Cerebrospinal fluid leaks.
(Ears/nose)
-Racoon eyes
-Bruising around mastoid process (Battle’s sign)
- Cranial nerve injuries

Rare!

Question 20

What is the Pterion?

Answer 20

The thinnest area of the skull, where the parietal, frontal, sphenoid and temporal bones join.

Question 21

Why is a blow to the pterion particularly dangerous?

Answer 21

If fractured, the middle meningeal artery lies under this structure.
Can cause intracranial haemorrhage.

Question 22

Describe the layers of the meninges.

Answer 22

Three layers surrounding the brain.

1. Dura - thick tough outer
2. Arachnoid - in between, transparent
3. Pia - tightly adhered to the brain

Question 23

What are the layers of the dura?

Answer 23

1. Outer periosteal layer (endosteum lining inner skull bones)
2. Meningeal layer - adjacent to arachnoid

Question 24

Where do the dural layers separate?

Answer 24

Dural folds

Dural venous sinuses

Question 25

Which two dural folds are important? Why?

Answer 25

Rigid dividers of the brain!

• Falx Cerebri
  Protects/separates hemispheres.

-Tentorium Cerebelli
Protect cerebellum.

Question 26

How would a pressure increase due to e.g. a bleed affect the brain?
(dural folds)

Answer 26

Compression and displacement against the rigid folds! No space for fluid to go.

Can cause herniation, e.g. into brain stem.

Question 27

What are dural venous sinuses?

Answer 27

Sections where the periosteal and meningeal dura is separated forming channels, allowing venous blood to drain from the vein.

Question 28

Where do dural venous sinuses drain to?

Answer 28

Drain to the internal jugular vein.

Question 29

Where are the major venous sinuses?

Answer 29

At the margins of borders of the Falx cerebri and Falx cerebelli.

On the cranial floor.

Question 30

What are bridging veins?

Answer 30

Veins traversing the sub dural space and draining into dural venous sinuses.
(Cerebral veins within subarachnoid space)

Question 31

Name the three types of haemorrhages in the meningeal layers?

Answer 31

Extradural
Sub dural
Subarachnoid

Question 32

What is an extradural haemorrhage?

Answer 32

An arterial bleed between the bone and the dura (periosteal layer stripped away)

Can cause increase in intracranial pressure.

Question 33

What is a sub dural haemorrhage, what are common causes?

Answer 33

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)

Question 34

What can cause a subarachnoid haemorrhage? How do they occur?

Answer 34

Secondary to trauma, or rupture of vessel (aneurysm).

Blood leaks in subarachnoid space, mixes with CSF.

Question 35

What is the outlook of a subarachnoid haemorrhage?

Answer 35

Sudden, often fatal.

CT image!
93% picked up within 24 hours
100% picked up within 6 hours

Question 36

Which procedure can confirm a subarachnoid haemorrhage has occurred?

Answer 36

A lumbar puncture.

Sample the CSF and identify presence of blood.