4 - Osteology of the Skull

Question 1

How can we divide the bones of the head up?

Answer 1

- Cranium: Neurocranium (vault, floor, cavity) and Viscerocranium

- Mandible

Question 2

In broad terms how do each part of the cranium form embryologically?

Answer 2

Question 3

What is the structure of the calvaria?

Answer 3

• Trilamina
• Two layers of compact bone separated by a layer of spongy bone called the diploe
• Adds strength without adding significant weight

Question 4

Label the bones of the calvaria part of the neurocranium

Answer 4

Question 5

Label the important joints of the calvaria.

Answer 5

Bregma and Lambdoid are where the fontanelles wrere as an infant. They are points of intersection between different sutures.

Question 6

What are the different types of skull fracture?

Answer 6

• Linear fractures radiate away from the point of injury
• Comminuted can be depressed or non-depressed
• Basillar have signs (see later flashcard)

Question 7

What is a fontanelle and where are they found?

Answer 7

• Large areas of unossified membranes between flat bones of the calvaria
• Allow for alteration of skull and brain size and birth
• Anterior fuses 18months-2years, Posterior fuses 1-3months

Question 8

What can fontanelles be used for?

Answer 8

Anterior: slightly convex in infant, can palpate to assess intra-cranial pressure and hydration state.

• If baby crying or vomiting and it is bulging this is normal, if not crying not normal
• If sunken may be dehydrated

Question 9

What is craniosynostosis?

Answer 9

• Early fusion of fontanelles and sutures
• Head can have an usual shape and may need surgery to reshape it

Question 10

How does the periosteum of the skull run and what is the importance of this anatomy?

Answer 10

• Covers inner and outer table of the skull, strongly adhered to edges of suture and continous through sutures
• Fracture to pterion can blow middle meningeal artery (anterior branch), haemorraghe pulling periosteum away from the bone up to the sutures

The periosteum is the sheath outside your bones that supplies them with blood, nerves and the cells that help them grow and heal.

Question 11

How is the cranial floor divided up?

Answer 11

- Anterior Fossa: frontal, ethmoid and small bit of sphenoid

- Middle Fossa: sphenoid and temporal

- Posterior Fossa: occipital

Question 12

Where is the ethmoid bone and label it’s different parts.

Answer 12

Question 13

Label the parts of the sphenoid bone.

Answer 13

Question 14

Label the parts of the temporal bone.

Answer 14

Question 15

Label the parts of the occipital bone.

Answer 15

Question 16

What should we do if we suspect a skull fracture and why?

Answer 16

• CT scan as significant force and trauma needed for a fracture so may be injuries intracranially
• Even if no fracture could still be something going on intracranially after head trauma so need to look at cervical spine, brain, look in ears and behind ears, neurological assessment

Question 17

What type of fractures are these CT scans showing?

Answer 17

• Comminuted has mutiple fracture lines and bone displacement inwards but linear does not
• Main concern is brain not fracture

Question 18

What are some signs of a basilar skull fracture and what fossa would be fractured in each case?

Answer 18

• Rhinorrhea or CSF fluid leakage from nose
• Battle’s = bruising over mastoid

Question 19

Label the bones of the viscerocranium.

Answer 19

Frontal bone forms part of the orbit (supraciliary arch), cranial floor and calvarium

Question 20

What injury would occur if there was trauma to the top of the orbit and why?

Answer 20

Skin would splinter over the supraciliary arch (supraorbital ridge) with blunt force injury

Question 21

What are the most common fractures of the face?

Answer 21

Zygomatic bone and arch, mandible and nasal bones. Maxillae rare

Question 22

When looking at a mandible x-ray with a suspected fracture what should you think about?

Answer 22

There is usually two fracture lines

Question 23

What is the anatomy of the TMJ joint and what is it innervated by?

Answer 23

- Synovial hinge joint
- Disc splits the joint into two
- Innervated by auriculotemporal nerve (mandibular division of trigeminal Vc) . This nerve also sensory which is why pain radiates here

Question 24

What is TMJ disorder?

Answer 24

• Pain around jaw, ear and temple
• Clicking, popping, grinding when moving jaw
• Lock jaw
• Headache around temples
• Pain mostly due to ear so this can throw you off

Question 25

What are some conditions affecting the TMJ?

Answer 25

• Arthritis
• TMJ disorder
• Dislocation

Question 26

What movements can the TMJ do and what muscles perform these movements?

Answer 26

Condyle does not pass in front of the articular process

Question 27

How does the TMJ dislocate and how do you reduce it?

Answer 27

• Facial trauma (particularly open mouth side of face) and yawning
• Jaw locks in open position as condyle moves anterior over articular tubercle
• Pterygoids and mastication muscles spasm and pull forward locking it

Question 28

How do you classify midfacial injuries and why are they concerning?

Answer 28

Le Fort Classification

Fractures can seperate face from skull base so issues with patients airways

Question 29

Where does the carotid sheath extend to and from?

Answer 29

Base of skull to aortic arch

Question 30

Where is the cribriform plate?

Answer 30

Question 31

Where is the orbital plate of the frontal bone?

Answer 31

Question 32

Label this AP x-ray of the cervical vertebrae and how would you get a better view of C1 and C2?

Answer 32

Open mouth image

Question 33

By what process do the fontanelles ossify?

Answer 33

Question 34

What features of a fetal skull are different to an adult skull?

Answer 34