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.
Why is the trilaminar arrangement of the calvaria important and beneficial?
It confers protective strentgh to protect the brain without adding significant weight.
What is the skull bones wrapped in?
Periosteum which covers both the outer and inner table of skull bones.
What can skull fractures involve?
The cranial vault (calvaria) or the cranial floor (calvaria is more common).
It can also involve intracranial structures like brain, blood vessels and cranial nerves.
Remember that intracranial injury can still follow head injury even in the absence of a skull fracture.
Types of skull fractures of the calvaria.
They can be linear which means they are fairly straight, light and involve no bone displacement.
They can be comminuted with multiple fracture lines and those fracture lines might be depressed or non-depressed.
Clinical presentation of skull base (basilar) fractures.
Depending on in which fossa the fracture is the signs may present differently.
From the anterior cranial fossa you may present with bilateral periorbital ecchymosis or also known as raccoon eyes.
From the middle cranial fossa you may present with bleeding from ears.
From the middle cranial fossa or posterior cranial fossa you may present with Battle’s sign or haemotympanum.
Important bones of the viscerocranium.
Zygomatic
Maxilla
Nasal
Lacrimal
Mandible
Common facial injuries and fractures.
Fractures of the nasal bones, zygomatic bone and arch and mandible are common.
If you get struck by your eye brow, what might happen?
Since the supraorbital ridge of the frontal bone is very rigid and tough it is more common for the skin over the supraorbital ridge to splinter.
How will a fracture of the mandible usually present on an x-ray.
If you see a fracture line on an x-ray of the mandible you should look for another fracture as well. The mandible usually fractures in two places.
What is the temporomandibular joint?
An articulation between the temporal bone and the mandible allowing us to open and close our mouths.
What kind of joint is the temporomandibular joint?
A synovial hinge-type joint divided into two synovial cavities by fibrocartilaginous disc.
Common conditions of the TMJ.
Dislocation secondary to trauma or yawning
Arthritis
Symptoms of TMJ disorders.
Pain often referred to the ear, jaw and lateral side of the head.
Clicking and locking of the jaw.
Innervation of the TMJ.
Auriculotemporal nerve which is a branch of the mandibular division of trigeminal (CN V, Vc)
What stabilises the TMJ?
A joint capsule and a series of 3 extracapsular ligaments. Also the articular tubercle of the joint prevents anterior displacement.
What kind of movement occurs at the inferior joint capsule?
Rotation which only happens when you open and close your mouth slightly.
What kind of movement occurs at the superior joint capsule?
A gliding movement where the condyle slides onto articular tubercle (but never infront of it). This motion is in action when you open your mouth extensively.
This action is simple retraction and protraction of mandible.
What happens if the condyle moves anterior to the articular tubercle?
This causes anterior dislocation of the jaw. The lateral pterygoid will now pull the jaw even further (protraction-wise) and it won’t possible to close one’s jaw and keeps the joint locked in the anterior displacement.
How to treat anterior dislocation of the jaw.
Reduction technique where you massage and try to relax the mastication muscles (lateral and medial pterygoid muscles) in order to make them stop protracting.
Once they are relaxed the jaw can easily slide into the TMJ again.
