L10: Osteology and radiographic appearance of the skull Flashcards
What are the 2 divisions of the bones of the skull?
- neurocranium (encases the brain, consists of 8 bones-usually flat ones)
- viscerocranium (facial skeleton and jaw, consists of 14 bones)
How many bones does the skull consist of?
22 individual bones
What are fossae?
Shallow depressions or hollows
What are canals?
Bony tunnels
What are the technical names for holes in the skull?
Round holes: foramina
Narrow slits: fissures
What is the neurocranium split into?
- calvaria (skull cap/vault)
- cranial floor
- cranial cavity between the floor and cap (where you find the brain)
What is the vault of the cranium?
Top and sides of the cranium, known as the calvaria
How is the neurocranium developed?
Vault: membranes which begin to ossify via intramembranous ossification
Floor: begin as cartilage which ossifies via endochondrial ossification
How is the viscerocranium developed?
Bones begin as membranes/cartilage and ossify
-most structures here develop from the pharyngeal arches
Why are there holes in the cranial floor?
To permit cranial nerves and blood vessels to enter into and out of the neurocranium
What bones form the calvaria?
- 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)
In which bone of the neurocranium does the mastoid process lie?
Temporal bone (has a flat part forming the vault, but has other shapes inside the skull forming part of the floor)
What are the names of the sutures in the neurocranium?
-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
What are the intersections between the sutures called?
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
How do sutures ossify?
Sutures tend to ossify from the inside outwards
What are fontanelles?
Large areas of unossified membranous gaps between flat bones of calvaria
What are the 2 important fontanelles and their function?
Anterior/posterior fontanelle
- allow for alteration of skull size during child birth
- permit growth of the infant brain
When do the fontanelles fuse?
Anterior: 18 months-2 years
Posterior: 1-3 months
What is craniosynotosis?
Early fusion of fontanelles and sutures (rare)
Why is the anterior fontanelle clinically useful?
You can palpate it
- slightly convex in healthy baby
- if bulging can indicate increased intercranial pressure
- appears sunken if baby is dehydrated
What is the cross-sectional arrangement of the flat bones of the skull?
Trilaminar arrangement Outer table: compact bone Spongy bone in middle: diploe Inner table: compact bone Provides protective strength without significant weight
What covers the bones in neurocranium?
Periosteum
- wraps round entire bone
- some blood vessels run b/w periosteum and inner table
What does an intracranial haemorrhage look like?
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
What vessel does an extradural intracranial haemorrhage usually occur from?
Usually rupture from middle meningeal artery
What forms the inner and middle ear structures?
Petrous part of the temporal bone
