Lecture 4 - Osteology & Radiographic Appearance of the Skull

Question 1

What are:

• Fossae
• Canals
• Foramina
• Fissures

Answer 1

Fossae = shallow depressions or hollows
Canals = bony tunnels 
Foramina = round-ish holes
Fissures = narrow slits

Question 2

What does the neurocranium and viscerocranium consist of?

What do both these structures begin as?

Answer 2

Neurocranium:

• 8 bones which encase/protect brain
• Calvaria (vault), Cranial floor (base) & Cranial cavity
• Vault begins as membranes (intramembranous ossification), floor begin as cartilage (endochondral ossification)

Viscerocranium:

• 14 bones of the facial skeleton & jaw
• Bones begin either as membranes or cartilage and ossify

Question 3

What structures in the cranial floor allow CN’s and blood vessels to enter in and out the neurcranium?

Answer 3

Holes - foramina, fissures and canals

Question 4

List + Locate the 5 main bones of the neurocranium
What sutures separate these bones?
What is the bregma and lambda?

Answer 4

• Frontal bone, Parietal bones, Temporal bone, Occipital bone & Greater wing of sphenoid bone
• Coronal suture separates frontal and parietal, Sagittal suture separates parietal bones L+R, Lamboid suture separates parietal and occipital bones
• Intersections of sutures, bregma = sagittal + coronal, lambda = sagittal + lamboid

Question 5

What are fontanelles and their purpose?
What are the two important fontanelles?
What is early fusion of fontanelles and sutures known as?
What can the anterior fontanelle be used to asses clinically in infants?

Answer 5

• Large areas of unossified membranous gaps between flat bones of calvaria. They allow for alteration of skull size/shape during growth of infant brain.
• Anterior + Posterior (at bregma and lambda)
• Craniosynostosis
• Slightly convex shape in healthy baby, will bulge if high intracranial pressure, will depress if dehydrated.

Question 6

What is the trilaminar arrangement flat bone of the calvaria have?
What does this arrangement confer?

Answer 6

1) Outer + Inner layer = compact bone (dense & thick)
2) Middle layer = diploe (spongy bone)

Confers protective strength without adding significant weight

Question 7

What are the outer and inner surface of skull bone?

What runs between the bone and this structure?

Answer 7

• Periosteum, they are “shrink-wrapped” by it, it runs continous through suture.
• Middle meningeal artery, which can be ruptured and lead to intracranial haemorrhage.

Question 8

What are the 3 ‘bowl-shaped’ depressions that form the cranial floor?

Answer 8

1) Anterior cranial fossae
2) Middle cranial fossae
3) Posterior cranial fossae

Question 9

Which bones form the anterior cranial fossae of the cranial floor?

Answer 9

• Large portion is formed by the frontal bone
• Very posterior part is formed by the sphenoid bone
• Also the ethmoid bone (highlighted in green)

Question 10

Which bone forms parts of both the anterior and middle cranial fossae?
Describe the structure of this bone and which parts form the anterior and middle part of the floor

Answer 10

• The sphenoid bone
• Has lesser wings which form the posterior part of the anterior cranial fossae
• Has greater wings which from part of the middle cranial fossae
• Has the sella turcica (Turkish saddle) upon which the pituitary gland sits

Question 10

Which bone forms parts of both the anterior and middle cranial fossae?
Describe the structure of this bone and which parts form the anterior and middle part of the floor

Answer 10

• The sphenoid bone
• Has lesser wings which form the posterior part of the anterior cranial fossae
• Has greater wings which from part of the middle cranial fossae
• Has the sella turcica (Turkish saddle) upon which the pituitary gland sits

Question 11

Which bone forms middle and lateral parts of the middle and posterior cranial fossae?
What part of this bone houses middle and inner ear structures?

Answer 11

• Temporal bone

- Petrous part of temporal bone, very hard as it houses important aural structures such as cochlea and CN8

Question 12

Which bone forms the majority of the posterior cranial fossae?

Answer 12

Occipital bone

Question 13

What type of fractures can occur to the cranial vault? (2)
Which area of the vault is particularly susceptible to fracture?
Are skull base (basilar) fractures less or more common?

Answer 13

1) Linear - straight, involve no bone displacement
2) Comminuted - multiple fracture lines, may be depressed or non-depressed

Pterion (where 4 skull bones meet) - can cause rupture of MMA leading to intracranial haemorrhage

Less common, but important not to miss

Question 14

FINISH LAST 6/7 SLIDES

Answer 14

K