Session 2: Osteology and Radiographic Appearance of the Skull

Question 1

What can the cranium be broadly divided into?

Answer 1

Into the neurocranium and the viscerocranium.

Question 2

Broadly explain the neurocranium.

Answer 2

8 bones which encases and protects the brain. It is roughly divided into three parts: The calvaria, the cranial floor and the cranial cavity.

Question 3

Origin of the calvaria.

Answer 3

The bones of the calvaria being as membranes and thereof intramembranous ossification.

Question 4

Origin of the cranial floor.

Answer 4

Begin as cartilage and thereof endochondrial ossification.

Question 5

Broadly explain the viscerocranium.

Answer 5

14 bones which makes up the facial skeleton and jaw. Bones begin either as membranes or cartilage. Structures mostly develop from the pharyngeal arches.

Question 6

What are the ‘holes’ (foramina, fissure and canals) in cranial floor important for?

Answer 6

They permit cranial nerves and blood vessels to enter into and out of neurocranium.

Question 7

Bones of the calvaria.

Answer 7

Frontal bone Parietal bones (2) Sphenoid bone Temporal bone (2) Occipital bone Ethmoid bone

Question 8

What is the coronal suture?

Answer 8

The joint connecting the frontal bone to the parietal bones.

Question 9

What is the sagittal suture?

Answer 9

The joint connecting the two parietal bones.

Question 10

What is the lambdoid suture?

Answer 10

The joint connecting the parietal bones and the occipital bone.

Question 11

What is bregma?

Answer 11

An intersection of where the frontal bone meet both the parietal bones.

Question 12

What is lambda?

Answer 12

An intersection of where the occipital bone meet both the parietal bones.

Question 13

What is bregma and lambda remnants of?

Answer 13

In an infant this is where the fontanelles were.

Question 14

What are fontanelles?

Answer 14

Large areas of unossified membranous gaps between flat bones of calvaria aka soft spots.

Question 15

Purpose of the fontanelles.

Answer 15

Allow for alteration of the skull size and shape during childbirth. Allows the brain to fully develop and grow.

Question 16

When do the fontanelles fuse?

Answer 16

Early childhood. Bregma fuses at around 18months to 2 years. Lamdba fuses at around 1-3 months.

Question 17

What is a complication of early fusion of fontanelles and sutures?

Answer 17

A condition called craniosynostosis which can result in a malformed head shape and underdeveloped cognitive abilites.

Question 18

How is the anterior fontanelle clinically useful?

Answer 18

To examine newborns and infants to see whether it is normal, sunken or bulging.

Question 19

What is a sunken fontanelle an indication of?

Answer 19

Dehydration

Question 20

What is bulging fontanelle an indication of?

Answer 20

Elevated intracranial pressure.

Question 21

How is the bone of the calvaria arranged.

Answer 21

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.

Question 22

Where does the middle meningeal artery run in relation to the calvaria?

Answer 22

It runs between the bone of the calvaria and the dura mater.

Question 23

Clinical significance of the route of the middle meningeal artery.

Answer 23

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.

Question 24

What is an extradural haematoma?

Answer 24

Due to extradural haemorrhage meaning it is between the dura and the bone.

Question 25

Why is the trilaminar arrangement of the calvaria important and beneficial?

Answer 25

It confers protective strentgh to protect the brain without adding significant weight.

Question 26

What is the skull bones wrapped in?

Answer 26

Periosteum which covers both the outer and inner table of skull bones.

Question 27

What can skull fractures involve?

Answer 27

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.

Question 28

Types of skull fractures of the calvaria.

Answer 28

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.

Question 29

Clinical presentation of skull base (basilar) fractures.

Answer 29

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.

Question 30

Important bones of the viscerocranium.

Answer 30

Zygomatic

Maxilla

Nasal

Lacrimal

Mandible

Question 31

Common facial injuries and fractures.

Answer 31

Fractures of the nasal bones, zygomatic bone and arch and mandible are common.

Question 32

If you get struck by your eye brow, what might happen?

Answer 32

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.

Question 33

How will a fracture of the mandible usually present on an x-ray.

Answer 33

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.

Question 34

What is the temporomandibular joint?

Answer 34

An articulation between the temporal bone and the mandible allowing us to open and close our mouths.

Question 35

What kind of joint is the temporomandibular joint?

Answer 35

A synovial hinge-type joint divided into two synovial cavities by fibrocartilaginous disc.

Question 36

Common conditions of the TMJ.

Answer 36

Dislocation secondary to trauma or yawning

Arthritis

Question 37

Symptoms of TMJ disorders.

Answer 37

Pain often referred to the ear, jaw and lateral side of the head.

Clicking and locking of the jaw.

Question 38

Innervation of the TMJ.

Answer 38

Auriculotemporal nerve which is a branch of the mandibular division of trigeminal (CN V, Vc)

Question 39

What stabilises the TMJ?

Answer 39

A joint capsule and a series of 3 extracapsular ligaments. Also the articular tubercle of the joint prevents anterior displacement.

Question 40

What kind of movement occurs at the inferior joint capsule?

Answer 40

Rotation which only happens when you open and close your mouth slightly.

Question 41

What kind of movement occurs at the superior joint capsule?

Answer 41

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.

Question 42

What happens if the condyle moves anterior to the articular tubercle?

Answer 42

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.

Question 43

How to treat anterior dislocation of the jaw.

Answer 43

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.