Osteology And Radiographic Appearance Of The Skull

Question 1

What are the following:
Fossae
Canals 
Foramina 
Fissures

Answer 1

Fossae- shallow depressions

Fissures - narrows slits

Round holes - foramina

Narrow slits- fissures

Question 2

How many bones make up the neurocranium? What did they develop from?

Answer 2

8 bones

Calvaria (skull cap/ vault) - begin as membranes (intramembranous ossification)

Floor/ base begin as cartilage (endochondrial ossification)

Question 3

How many bones make up the viscerocranium? What did they develop from?

Answer 3

14 bones

Facial skeleton and jaw

Begin as membranes or cartilage and ossify

Structures mostly develop from the 1st and 2nd pharyngeal arches

Question 4

What bones make up the neurocranium?

Answer 4

Anterior = frontal

Inferior to frontal and lateral= sphenoid bone

Posterior = parietal

Inferior to parietal= temporal

Most posterior = occipital

Question 5

What separates the frontal and parietal bones?

Answer 5

Coronal suture

Question 6

What separates the parietal bones?

Answer 6

Sagittal suture

Question 7

What separates the parietal bones from the occipital bone?

Answer 7

Lambdoid suture

Question 8

Where do the coronal suture and Sagittal suture meet? What did this develop from and at what age?

Answer 8

Bregma

In newborn it’s a gap filled with fibrous tissue - anterior fontanelle

Changes from 18months - 2yrs

Question 9

Where do the Sagittal suture and lambdoid suture meet? What did this develop form and at what age?

Answer 9

Lambda

From the posterior Fontanelle - gap filled with fibrous tissue until 1-3months

Question 10

What is the function of fontanelles?

Answer 10

Areas of membrane between flat bones of calvaria which allow for alteration of skull size and shape during childbirth

Question 11

What is craniosynostosis?

Answer 11

Rare condition where there is early fusion of fontanelles and sutures

Question 12

What can inspection and gentle palpation of the anterior fontanelle tell you about a newborn/ infant?

Answer 12

If bulging can mean ICP is high

If sunken can mean dehydrated

Normal baby should be slightly convex

Used alongside other signs and symptoms

Question 13

What is the trilaminar arrangement of bones in the calvaria? What’s the purpose of this arrangement?

Answer 13

Compact bone for outer table

Spongy bone = diploe (middle)

Compact bone is inner table

Confers protective strength without adding significant weight

Question 14

Describe the periosteum arrangement on the calvaria bones. What can occur between the periosteum and dura mater?

Answer 14

Covers the outer table of skull bones, strongly adhered to the edges and continuous through suture and onto inner table of the same bone

(All the way around the bone)

An extradural haemorrhage can occur where a bleed from most commonly the medial meningeal artery strips periosteum from inner table but is too strong to strip the edges of suture so stops

Question 15

What bone(s) form the anterior cranial floor only?

Answer 15

Frontal bone up to orbital plates

Ethmoid bone (separates nasal cavity from brain) a.k.a Cribriform plate and cribriform foramina

(Sphenoid also)

Question 16

What bones from the anterior and middle cranial floor?

Answer 16

Sphenoid bone
Anterior: lesser wings
Middle: Lesser and greater wings, Dorsum sella and sella turcica (where pituitary gland sits)

Question 17

What bones form the middle and posterior cranial fossa?

Answer 17

Temporal bones

Squamous part
Zygomatic process
Mastoid process
Petrous bone

Slide 19

Question 18

What bone(s) form the posterior cranial floor only?

Answer 18

Occipital bone

External occipital protuberance

Superior nuchal lines

Foramen magnum

Slide 21

Question 19

2 types of skull cranial vault fractures

Answer 19

Linear- straight, no bone displacement

Comminuted - multiple fractures lines, fragments may displace inwards towards the brain (depressed or non-depressed)

Question 20

Where is the most likely place to fracture your cranial vault and what structure could this damage?

Answer 20

Pterion- thinnest area of skull

Underlying is middle meningeal artery

Blows to side of head can fracture bone -> intracranial extra-Dural haemorrhage

Question 21

What is a skull base fracture called and what are some signs this has occurred?

Answer 21

Basilar fracture

Rarer

Raccoon eyes - bilateral periorbital ecchymosis

Battle sign- bruise behind ear

Haemotympanum - Blood in tympanic cavity of middle ear

Question 22

What bones make up the facial skeleton?

Answer 22

Lateral superior - 2 zygomatic bones

Inferior- mandible

Central - maxilla

Above nose- nasal

Inner eyes- lacrimal

Question 23

What facial fractures can occur?

Answer 23

Supraorbital ridge of frontal bone (superior orbital fossa) very tough so can splinter skin

Fractures of nasal bones, zygomatic bone and arch, mandible (always fractures at 2 places) are common

Maxillae fracture is rare

Question 24

What type of joint is the temporomandibular joint?

Answer 24

Synovial hinge joint divided into two synovial cavities by fibrocartilaginous disc

Question 25

What conditions can occur at the TMJ? What’s its innervation?

Answer 25

TMJ disorder (pain often in ear, jaw, lateral side of head

Dislocation (yawning or blow to side of jaw)

Arthritis

Innervated by auriculotemporal Nerve (mandibular division of trigeminal N) Vc

Question 26

What parts of the temporal and mandible bone make up the TMJ? What stabilises it?

Answer 26

temporal:Articular tubercle
Mandibular/ glenoid fossa

Fibrocartilaginous disc central between two synovial cavities filled with synovial fluid

Mandibular: Mandibular condyle

Stabilised by a joint capsule and 3 EXTRACAPSULAR ligaments

Question 27

What two movements are involved in depression of the mandible and where do these occur? What muscles are involved?

Answer 27

Depression: hinge/ rotational action at inferior half of joint cavity

Gliding forward action at superior half of joint capsule- condyle slides onto articular tubercle

Lateral pterygoid against resistance

Question 28

Where does retraction and protraction take place in the TMJ? What muscles are involved?

Answer 28

Gliding action at superior joint capsule

Retraction: posterior fibres of temporalis

Protrusion/ protraction: lateral pterygoid and medial pterygoid

Question 29

Which muscles are involved in elevation of the mandible at the TMJ joint?

Answer 29

Masseter, temporalis, medial pterygoid

Question 30

Which muscles are involved in grinding of the mandible?

Answer 30

Lateral and rotational movement, alternate protrusion and retraction

Muscles of 2 sides working co-operatively (lateral pterygoids laterally deviate mandible)

Question 31

How does dislocation of the TMJ occur?

Answer 31

Yawning/. Bow to side of jaw

Jaw locks as joint fixes in open position due to anterior dislocation of condyle over the articular tubercle

Contraction of muscles around joint keep joint locked in anterior displacement