H&N4 - Osteology & Radiographic Appearance of the Skull

Question 1

4 features of the neurocranium

Contents
Ossification
Bone Arrangement
Periosteum

Answer 1

1. ) Contents - calvaria (skull cap or vault), cranial floor, and cranial cavity
2. ) Ossification - vault bones is intramembranous whilst cranial floor bones is endochondral
3. ) Trilaminar Arrangement - present in vault bones.
   - compact:spongy (diploe):compact bone
   - this provides protective strength w/out adding significant weight
4. ) Periosteum - covers surface of the outer and inner table of skull bones
   - MMA runs underneath the periosteal layer

Question 2

3 features of the viscerocranium

Ossification
Development
Facial Skeleton Bones x5

Answer 2

1. ) Ossification - intramembranous or endochondral ossification
2. ) Development - from the pharyngeal arches
3. ) Facial Skeleton Bones - zygomatic, maxilla, nasal, lacrimal, mandible

Question 3

6 Bones and 3 Joints of Calvaria

Answer 3

1. ) Bones - frontal, parietal (x2), sphenoid, temporal, occipital
2. ) Joints - serrated, immobile joints known as sutures
   - coronal (frontal and parietal), sagittal, (parietals), lamboid (occipital and parietal)
   - interlocking nature makes it difficult to dislocate

Question 4

6 features of fontanelles

Description
Function
Position
Fusion
Examination
Clinical Condition

Answer 4

1. ) Description - large areas of unossified membranous gaps between flat bones of calvaria
   2.) Function - allow for alteration of the skull size and shape during childbirth and permit growth of infant brain
   3.) Position - anterior = bregma (frontal + parietals)
   posterior = lambda (occipital + parietals)
   4.) Fusion - anterior fuses in 18-24 months, posterior fuses in 1-3 months
   5.) Examination - gentle palpation of anterior fontanelle used to assess intracranial pressure and state of hydration in infants
   - bulging suggests increased intracranial pressure
   - sunken suggests dehydration
   6.) Craniosynostosis - early fusion of fontanelles which affects brain development since no room to grow

Question 5

4 features of the cranial floor

Divisions
Bones making up the divisions

Answer 5

1. ) Divisions - consists of anterior, middle and posterior cranial fossa
2. ) Anterior Floor - frontal, ethmoid, and sphenoid bone
3. ) Middle Cranial Floor - sphenoid, temporal, parietal
   - sella turcica is where the pituitary gland sits in the sphenoid bone
4. ) Posterior Cranial Floor - temporal and occipital bone
   - temporal bone houses inner and middle ear structures
   - contains the large foramen magnum

Question 6

4 features of skull fractures affecting the cranial vault or floor

Injury Risk
Type of Fractures
Common Fracture Location
Basilar Skull Fracture

Answer 6

1. ) Injury Risk - to intracranial structures (brain and neurovasculature)
   - you can still have intracranial injury w/out a skull fracture
2. ) Fracture Types - linear or comminuted
   - comminuted fragments can be depressed or non depressed (displaced inwards towards the brain)
3. ) Pterion - thinnest area of the skull so easy to fracture
   - fracture can damage the MMA leading to an extradural haematoma
   - bones forming this region are frontal, parietal, temporal

4.) Basilar Skull Fracture - fracture involving bones of the cranial floor.

Question 7

4 features of facial injuries and fractures

Common Fractures x3
Supraorbital Ridge Injuries
Mandibular Fractures
Imaging

Answer 7

1. ) Common Fractures - nasal, zygomatic, mandible
2. ) Supraoribtal Ridge Injuries - corner of eye is very tough so doesn’t fracture and just splinters the skin
3. ) Mandibular Fractures - usually fractures in 2 places
4. ) Imaging - CT scans are used for skull fractures

Question 8

5 features of the temporomandibular joint (TMJ)

Joint Type
Innervation
Movements x4
Disorders
Dislocation

Answer 8

1. ) Joint Type - synovial hinge joint divided into 2 synovial cavities by fibrocartilaginous disc
2. ) Innervation - auriculotemporal nerve (mandibular division of trigeminal)
3. ) Movements - hinge (rotational) action (inferior half), gliding forward action (superior half)
   - retraction and protraction of mandible (gliding action at superior half)
4. ) TMJ Disorders - often refers to pain in ear, jaw and lateral side of head
   - can also get dislocation and arthritis
5. ) Dislocation - caused by facial trauma or yawning
   - joint fixes in open position due to anterior dislocation of mandibular condyle over the articular tubercle
   - contraction of muscles around joint keeps it locked in anterior displacement

Question 9

What are the 4 Clinical Signs of a Basilar Skull Fracture?

Answer 9

1. ) Battle’s Sign - bruising over mastoid
2. ) Raccoon Eyes - (bruising around both eyes)
3. ) Haemotympanum - (blood behind ear drum)
4. ) CSF Leakage - nose (rhinorrhoea) or ear (otorrhoea)

Question 10

3 features of note on the frontal bone

Answer 10

• Suparorbital ridge and supraorbital notch (foramen)

- Orbital plate

Question 11

6 features of note on the ethmoid bone

Answer 11

• crsita galli - superior spike
• cribriform plate - forms roof of nasal cavity
• cribriform foramina - holes in the cribriform plate
• perpendicular plate - inferior spike
• superior and middle conchae - protrudes into the passage of the nose

Question 12

6 features of note on the sphenoid bone

Body
Greater Wing
Lesser Wing
Superior Orbital Fissure
Pterygoid Process
Clinoid Processes

Answer 12

1. ) Sphenoid Body - posterior aspect contains the sella turcica which is a just a depression
   - hypophyseal fossa is the deepest part and is where the pituitary gland sits
2. ) Greater Wing - contains 3 real foramen and 1 other
   - foramen rotundum (maxillary nerve)
   - foramen ovale (mandibular nerve)
   - first 2 communicates with the pterygopalatine fossa
   - foramen spinosum (MMA and vessels)
   - foramen lacerum (empty)
3. ) Lesser Wing - contains the optic canal
4. ) Superior Orbital Fissure - gap formed between the greater and lesser wing
5. ) Pterygoid Process - consists of lateral and medial plate
6. ) Anterior and Posterior Clinoid Processes - attachment points for the tentorium cerebelli
   - anterior comes from lesser wing, posterior from sella turcica

Question 13

5 features of note on the temporal bone

Squamous Part
Zygomatic Process
Petromastoid
Tympanic Part
Carotid Canal

Answer 13

1. ) Squamous Part - flat and plate-like located superiorly
   - site of origin of temporalis muscle
2. ) Zygomatic Process - articulates with temporal process of zygomatic bone forming zygomatic arch
   - forms articular tubercle of TMJ
   - attachment of masseter muscle
3. ) Petromastoid - posterior and made up of petrous part and mastoid part
   - petrous part houses structures of the middle and inner ear
   - petrous part also surrounds part of foramen lacerum
   - mastoid process is site of attachment of SCM
4. ) Tympanic Part - leads into external auditory meatus
   - styloid process projects outwards

5.) Carotid Canal - where ICA enters the middle cranial fossa

Question 14

3 features of note on the mandible

Answer 14

1.) Body –> Ramus –> Neck and Head (posterior) or Coronoid Process (anterior)

2. ) Mandibular Foramen - internal surface of the ramus
   - contains inferior alveolar nerve and artery
   - mandibular foramen –> mandibular canal –> mental foramen
3. ) Mental Foramen - external surface of the body
   - contains mental nerve (continuation of inferior alveloar nerve)