Session 2: Osteology and Radiographic Appearance of the Skull Flashcards
What can the cranium be broadly divided into?
Into the neurocranium and the viscerocranium.
Broadly explain the neurocranium.
8 bones which encases and protects the brain. It is roughly divided into three parts: The calvaria, the cranial floor and the cranial cavity.
Origin of the calvaria.
The bones of the calvaria being as membranes and thereof intramembranous ossification.
Origin of the cranial floor.
Begin as cartilage and thereof endochondrial ossification.
Broadly explain the viscerocranium.
14 bones which makes up the facial skeleton and jaw. Bones begin either as membranes or cartilage. Structures mostly develop from the pharyngeal arches.
What are the ‘holes’ (foramina, fissure and canals) in cranial floor important for?
They permit cranial nerves and blood vessels to enter into and out of neurocranium.
Bones of the calvaria.
Frontal bone Parietal bones (2) Sphenoid bone Temporal bone (2) Occipital bone Ethmoid bone
What is the coronal suture?
The joint connecting the frontal bone to the parietal bones.
What is the sagittal suture?
The joint connecting the two parietal bones.
What is the lambdoid suture?
The joint connecting the parietal bones and the occipital bone.
What is bregma?
An intersection of where the frontal bone meet both the parietal bones.
What is lambda?
An intersection of where the occipital bone meet both the parietal bones.
What is bregma and lambda remnants of?
In an infant this is where the fontanelles were.
What are fontanelles?
Large areas of unossified membranous gaps between flat bones of calvaria aka soft spots.
Purpose of the fontanelles.
Allow for alteration of the skull size and shape during childbirth. Allows the brain to fully develop and grow.
When do the fontanelles fuse?
Early childhood. Bregma fuses at around 18months to 2 years. Lamdba fuses at around 1-3 months.
What is a complication of early fusion of fontanelles and sutures?
A condition called craniosynostosis which can result in a malformed head shape and underdeveloped cognitive abilites.
How is the anterior fontanelle clinically useful?
To examine newborns and infants to see whether it is normal, sunken or bulging.
What is a sunken fontanelle an indication of?
Dehydration
What is bulging fontanelle an indication of?
Elevated intracranial pressure.
How is the bone of the calvaria arranged.
It has a trilaminar arrangement with a compact bone called the outer table, a diploe which is a spongy bone and yet another compact bone on the inside called the inner table.
Where does the middle meningeal artery run in relation to the calvaria?
It runs between the bone of the calvaria and the dura mater.

Clinical significance of the route of the middle meningeal artery.
The anterior branch of the middle meningeal artery runs by the pterion which is the weakest point of the calvaria. Trauma here can cause rupture of the anterior branch of the middle meningeal artery.
Since the middle meningeal artery runs inside the skull, between the dura mater and the trilaminar arrangement it will cause an haematoma in that space. Since the calvaria is tough and rigid the haematoma can’t expand externally so it will do so internally instead and increase intracranial pressure.
What is an extradural haematoma?
Due to extradural haemorrhage meaning it is between the dura and the bone.
