Osteology Flashcards
What is the neurocranium
Neurocranium (8 bones)
– Encase and protect brain
– Calvaria (“skull cap” or “vault”), cranial floor (base) and cranial cavity
– ‘Vault’ bones begin as membranes (intramembranous
ossification): floor/base begin as cartilage (endochondrial
ossification)
What is the viserocranium
Viscerocranium (14 bones)
– Facial skeleton and the jaw
– Surrounds oral cavity, pharynx and upper respiratory passages
– Bones begin as membranes or cartilage and ossify
– Structures (most) develop from the pharyngeal arches
(1&2)
What passes though the neurocranium
Cranial floor needs ‘holes’ that permit cranial nerves to leave or reach the brain and brainstem to/from structures of the face (including viscerocranium) and neck that they innervate.
Blood vessels also need to pass between inside/outside the neurocranium
Foramina, fissures and canals
What are the bones and joints of the calvaria
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What are the fontanelles
Large areas of unossified membranous gaps between flat bones of calvaria
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• Fontanelles are areas of membrane between bones, that are particularly large
• Allow for alteration of the skull size and shape during childbirth
• Permit growth of infant brain
• Fontanelles fuse in early infancy
*
Note there are a number of other features specific to the fetal/infant skull…
• Anterior ~18 months- 2 years
• Posterior ~1-3 months
• Early fusion of fontanelles and sutures
= craniosyntosis (rare condition)
Describe the anterior fontanelle and assessment
• 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
Assessment of the fontanelles is taken in the context of how the infant appears (unwell/well) and the presence of other clinical signs and symptoms.
What are the layers of the bones of the calvaria
A trilaminar arrangement in cross-section
Compact bone on either side - outer is thigh and tough,inner is thin dense and brittle
Diploe (spongy bone) in the centre
Right frontal bone cut in horizontal plane
Tri-laminar arrangement confers protective strength without adding significant weight
How does the periosteum determine the extent of haematoma
Periosteum covers surface of outer and inner table of skull bones Strongly adhered at suture line and continuous through suture and onto inner table
of same bone
In an extra dural haemorrhage, the periosteum strips away from bone
Sure lines restrict how much it is stripped away
Describe teh structure of the cranial floor
• Anterior, middle and posterior cranial fossae
• Seat different parts of the brain and its associated structures
• Made up of numerous bones
• Numerous foramina, canals and fissures (learn and explore in Session 3 SGW)
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What boens form the cranial floor
Frontal bone, ethmoid bone, sphenoid bone, temporal bone, occipital bone
Descrive how skull fractures can involve the vault/floor
• Significant trauma and force required to fracture skull
– Thickness of cranial bones varies, resistance to fracture therefore varies
• Main concern is risk of injury to intracranial structure (i.e. brain, blood
vessels, cranial nerves)
– Presence of skull fracture associated with higher incidence of intracranial
pathology, neurological deficits and poorer outcomes
• BUT can still have intracranial injury following head injury, even in
absence of skull fracture
Describe cranial vault fractures
• Linear fairly straight, involve no bone displacement
Or
• Comminuted (multiple fracture lines)
-Fragments may or may not displace inwards towards the brain (depressed vs non-depressed)
What is the pterion
Thinnest area of skull: relatively easy to fracture
• Important relationship between pterion
and an underlying blood vessel: MMA (anterior branch)
• Blows to the side of the head can fracture bone in area of pterion and injury blood vessel lying immediately below
• Intracranial haemorrhage (extra-dural)
Descrbe basilar fractures
Rarer type of skull fracture but important not to miss!
Describe the facial skeleton
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