Osteology of the Head

Question 1

Identify the main neurocranium bones of the skull

Answer 1

Look at onenote

Question 2

Neurocranium vs viscerocranium location

Answer 2

• Neurocranium encase and protect the brain

- Viscerocranium are the facial skeleton and jaw

Question 3

What are the 3 components of the neurocranium

Answer 3

Calvaria, cranial floor, cranial cavity

Question 4

State the difference in development between calvaria and cranial floor

Answer 4

• Calvaria bones begin as membrane (intramembranous ossification)
• Cranial floor bones begins as cartilage (endochondral ossification)

Question 5

Describe the cranial floor structure

Answer 5

• 3 bowl shaped depressions form the cranial floor
  
  • Anterior cranial fossae higher than middle which is higher than posterior cranial fossae
  • Each fossae has series of foramina, some have fissures and canals
    
    • Allow communication with other areas of the head and neck
  • Bone grooved by location of dural venous sinuses

Question 6

State the components of the trilaminar arrangement of calvaria and describe its purpose

Answer 6

• Trilaminar arrangement confers protective strength without adding significant weight
• Inner and outer table made of compact bone
• Diploeic cavity made of spongy tissue surrounded by compact bone from outer and inner table

Question 7

What are sutures

Answer 7

• Fibrous joints called sutures exist between bones

- Sutures are intersections between bones of skull

Question 8

What is the purpose of sutures

Answer 8

• Edges of bones forming suture joint are ‘serrated’ to prevent slippage and movement
  
  • They stop growing in puberty and ossification occurs over time
  • Gradually disappear from inside to outside

Question 9

How is the periosteum and sutures related

Answer 9

• Periosteum covers surface of outer table of bone

- Strongly adhere at suture line but continuous through to periosteum covering inner table

Question 10

Identify the features of the skull listed on onenote

Answer 10

Good luck

Question 11

State the sutures on a skull

Answer 11

• Coronal
• Sagittal
• Lamboid

Question 12

State the sutural intersections and their locations

Answer 12

• Bregma - anterior fontanelle

- Lambda - posterior fontanelle

Question 13

Describe cephalohaematoma

Answer 13

• Sub-periosteal
• Bleeding from periosteum and bone
• Sheering/torsion injury
• Only bleed in shape of bone - cannot pass through suture lines
  
  • Cannot bleed intracranially

Question 14

Describe subgaleal haematoma

Answer 14

• Sub-aponeurotic
• Above periosteum
• Bleeding not limited

Question 15

What is the major risk of intracranial injury

Answer 15

Injury to brain, blood vessels, cranial nerves

Question 16

What investigation should be performed on suspected skull fracture patients

Answer 16

• CT scan should be performed in all patients with known or suspected skull fractures to identify intracranial injuries
• X-ray only examines skull, not brain

Question 17

Describe the two main fracture types of skull

Answer 17

• Linear - pass full thickness of skull, straight, no bone displacement
• Depressed - fragment displaced inwards towards brain

Question 18

What are the consequences of basilar skull fractures

Answer 18

• Associated with cranial nerve injuries
• Nerves that run through foramina most vulnerable
• Prone to causing cerebrospinal fluid leaks
• Blood escapes from skull and accumulates
  
  • Can cause haematoma, haemotympanum (blood behind ear lobe), Racoon eyes (black eye), battle’s sign (bruising over mastoid process)

Question 19

What is the link between pterion and skull fractures

Answer 19

• Thinnest area of skull and easy to fracture
  
  • Middle meningeal artery passes underneath pterion
  • Blows to side of head can fracture at pterion

Question 20

Why are facial injuries and fractures less common

Answer 20

• Supraorbital ridge and supra ciliary arch very tough - injury normally involves cut to eyebrow
• Fractures of nasal bones, zygomatic bone and arch and mandible are common

Question 21

What are fontanelles

Answer 21

Large areas of unossified membranous gaps between flat bones of calvaria

Question 22

What is the purpose of fontanelles

Answer 22

• Allow for alteration of the skull size and shape during childbirth
• Permit growth of infant brain

Question 23

When do fontanelles fuse

Answer 23

• Anterior: 18 months - 2 years to become bregma

- Posterior: 1-3 months to become lambda

Question 24

What is it called when fontanelles fuse early

Answer 24

Craniosyntosis

Question 25

What is the significance of examining anterior fontanelle

Answer 25

• Slightly convex shape in a healthy baby
• Inspection and gentle palpation of anterior fontanelle can be used to assess intracranial pressure and state of hydration