L10: Osteology and radiographic appearance of the skull

Question 1

What are the 2 divisions of the bones of the skull?

Answer 1

• neurocranium (encases the brain, consists of 8 bones-usually flat ones)
• viscerocranium (facial skeleton and jaw, consists of 14 bones)

Question 2

How many bones does the skull consist of?

Answer 2

22 individual bones

Question 3

What are fossae?

Answer 3

Shallow depressions or hollows

Question 4

What are canals?

Answer 4

Bony tunnels

Question 5

What are the technical names for holes in the skull?

Answer 5

Round holes: foramina

Narrow slits: fissures

Question 6

What is the neurocranium split into?

Answer 6

• calvaria (skull cap/vault)
• cranial floor
• cranial cavity between the floor and cap (where you find the brain)

Question 7

What is the vault of the cranium?

Answer 7

Top and sides of the cranium, known as the calvaria

Question 8

How is the neurocranium developed?

Answer 8

Vault: membranes which begin to ossify via intramembranous ossification
Floor: begin as cartilage which ossifies via endochondrial ossification

Question 9

How is the viscerocranium developed?

Answer 9

Bones begin as membranes/cartilage and ossify

-most structures here develop from the pharyngeal arches

Question 10

Why are there holes in the cranial floor?

Answer 10

To permit cranial nerves and blood vessels to enter into and out of the neurocranium

Question 11

What bones form the calvaria?

Answer 11

• frontal bone (forms part of the roof of the orbit of the eye) (start as a pair and they fuse- sometimes it doesn’t fully fuse so can be mistaken for a fracture)
• parietal bone: flat bone which is paired and extend laterally down sides
• temporal bone: seen on lateral view, underneath the parietal bone (paired)
• occipital bone: not paired, found at posterior base of skull (has occipital condyles at bottom which articulate with the cerival vertebrae)
• sphenoid bone (only seen lateral view, where you see the greater wing of the sphenoid)

Question 12

In which bone of the neurocranium does the mastoid process lie?

Answer 12

Temporal bone (has a flat part forming the vault, but has other shapes inside the skull forming part of the floor)

Question 13

What are the names of the sutures in the neurocranium?

Answer 13

-coronal suture: b/w the singular frontal bones and the paired parietal bones behind it
-sagittal suture: b/w the paired parietal bones
-lamboid suture: b/w occipital bone and parietal bones
These sutures are very irregular, to help prevent slippage and movement

Question 14

What are the intersections between the sutures called?

Answer 14

Bregma: intersect b/w coronal and sagittal suture
Lambda: intersect b/w sagittal and lambnoid suture
These points remain membranous in infants skull for up to 2 years

Question 15

How do sutures ossify?

Answer 15

Sutures tend to ossify from the inside outwards

Question 16

What are fontanelles?

Answer 16

Large areas of unossified membranous gaps between flat bones of calvaria

Question 17

What are the 2 important fontanelles and their function?

Answer 17

Anterior/posterior fontanelle

• allow for alteration of skull size during child birth
• permit growth of the infant brain

Question 18

When do the fontanelles fuse?

Answer 18

Anterior: 18 months-2 years
Posterior: 1-3 months

Question 19

What is craniosynotosis?

Answer 19

Early fusion of fontanelles and sutures (rare)

Question 20

Why is the anterior fontanelle clinically useful?

Answer 20

You can palpate it

• slightly convex in healthy baby
• if bulging can indicate increased intercranial pressure
• appears sunken if baby is dehydrated

Question 21

What is the cross-sectional arrangement of the flat bones of the skull?

Answer 21

Trilaminar arrangement
Outer table: compact bone 
Spongy bone in middle: diploe
Inner table: compact bone
Provides protective strength without significant weight

Question 22

What covers the bones in neurocranium?

Answer 22

Periosteum

• wraps round entire bone
• some blood vessels run b/w periosteum and inner table

Question 23

What does an intracranial haemorrhage look like?

Answer 23

B/w the periosteum and inner table, bulges inwards as it strips the periosteum away from the bone. As soon as you reach the ends of the bone the blood can no longer strip away the periosteum as it is tightly adhered here. (You can easily idenitfy the blood vessel it has occured from)
LENTIFORM SHAPE

Question 24

What vessel does an extradural intracranial haemorrhage usually occur from?

Answer 24

Usually rupture from middle meningeal artery

Question 25

What forms the inner and middle ear structures?

Answer 25

Petrous part of the temporal bone