Osteology of the Skull

Question 1

Which structures can be seen on an open mouth x-ray?

Answer 1

C1 either side of dens

Question 2

What does foramina mean?

Answer 2

Round-ish hole

Question 3

What does fissure mean?

Answer 3

Narrow slit hole

Question 4

What are the main large bones of the skull?

Answer 4

• Frontal bone – contain metopic suture, forehead, part of orbital cavity
• Temporal bone –
• Spenoid bone – great wing + lessor wing
• Parietal bones
• Zygomatic – with temporal bone forms zygomatic arch
• Occipital bone –
• Maxilla bones – 2 make up upper jaw,
• Mandible – jaw bone

Question 5

What is a suture in the skull?

Answer 5

• Fibrous joint between bones in the skull
• Serrated
• Periosteum cover and lies between the sutures
• Eventually they completely ossify = from inside to out

Question 6

What is the suture between the parietal bones?

Answer 6

Sagittal

Question 7

What is the suture line between the parietal bones and the frontal bone?

Answer 7

Coronal

Question 8

What is the suture line between the occipital bone and the parietal bones?

Answer 8

Lamdoid

Question 9

What is the name for the point at which the sagittal and lambdoid suture meet?

Answer 9

lambda

Question 10

What is the name for the point at which the coronal and sagittal sutures meet?

Answer 10

bregma

Question 11

What 2 groups can the skull be divided into?

Answer 11

Neurocranium = 8 bones, protect brain, calvaria + cranial floor + cranial cavity

Viscerocranium = 14 bones, facial skeleton, jaw

Question 12

What is the calvaria?

Answer 12

Vault, top of the skull

Begins as membranes (intramembranous ossification)

Question 13

Discuss the cranial floor

Answer 13

Bottom of the skull bowl

Begins as cartilage (endochondrial ossification)

Needs to permit cranial N, brainstem and blood vessels = via foramina, fissures, canals

Question 14

Where is the cranial cavity?

Answer 14

Inside the calvaria and the cranial floor

Question 15

What are the 3 bowl-shaped depression that form the cranial floor?

Answer 15

Anterior cranial fossa

Middle cranial fossa

Posterior cranial fossa

Question 16

What do grooves on the inner surface of the skull carry?

Answer 16

Dural venal sinuses

Question 17

What are the layers of the calvaria?

Answer 17

Outer table = compact bone

Diploeic cavity = spongy bone

Inner table = compact bone

Question 18

What does the tri-laminar arrangement of the calvaria confer?

Answer 18

Protective strength without adding significant weight

Question 19

What are the common injuries to the skull?

Answer 19

Fracture of zygomatic bone and arch

Fracture of the nasal bones

Mandible fracture

Risk of intracranial injury = CT should be performed

Question 20

What are the types of skull fracture?

Answer 20

Linear = full thickness, straight, no bone displacement

Depressed = displacement inwards

Basilar = involves cranial base, cranial N injury, CSF leaks (nose, ear), racoon eyes, battle’s sign

Question 21

What is the thinnest part of the skull and therefore the easiest part to fracture?

Answer 21

Pterion = region where frontal, parietal, temporal, sphenoid join together

Can tear middle meningeal artery

Blows to the side of the head

Question 22

What is blood behind the eardrum called and indicative of?

Answer 22

Hemotympanum

Fracture the petrous bone = basilar skull fracture

Question 23

Differences in foetal and adult skull

Answer 23

Large areas of unossified membranous gaps = fontanelles

Anterior fuse = 18m – 2 years

Posterior fuse = 1-3m

Question 24

What do we call early fusion of the fontanelles and sutures?

Answer 24

craniosyntosis

Question 25

Outline a jeffersons fraction

Answer 25

Fracture of anterior and posterior arches of atlas

Axial load

May damage arteries at the base of the skull

Question 26

Outline a hangmans fracture

Answer 26

Hyperextension of head on neck

Axis fracture through par interarticularis

Forward displacement of C1 and body of C2 on C3

Question 27

Outline an odontoid peg fracture

Answer 27

Hyperextension/flexion

Visualise via open mouth AP x-ray

Question 28

What is a cephalohaematoma?

Answer 28

Sub-periosteal

Bleeding between the periosteum and the bone

Cant pass suture line = cant pass intra-cranially

Question 29

What is a subgaleal haemorrhage?

Answer 29

Bleed between aponeurosis and periosteum

Sub-Aponeurotic

Not limited by suture lines

Question 30

Key features of the C spine

Answer 30

Bifid spinous process except C7

Foramen transversarium

Atlas – no vertebral body, no spinous process

Axis – dens, large spinous process

C1-C7

Question 31

What can be seen on a CT head (bone window)?

Answer 31

Inner table and outer table – grey outlines

Diploic cavity = dark area between inner/outer table

Suture lines