S2- Osteological and Radiographic Appearance of the Skull

Question 1

what are foramina?

Answer 1

holes in the skull

Question 2

what are fissures ?

Answer 2

narrows slit

Question 3

how many bones are in the skull ?

Answer 3

22

Question 4

How are the bones of the skull divided into two groups ?

Answer 4

Neurocranium and Viscerocranium

Question 5

How many bones are in the Neurocranium ?

Answer 5

8 bones

Question 6

Describe Neurocranium

Answer 6

Provides strength but lightweight and divided into A, M , P cranial fosse
Calavaria : skullcap - superior portions of frontal , occipital and L AND R parietal bones
Cranial base : provide articulation points for atlas and facial bones - made up of ethmoid, sphenoid , occipital ,L and R temporal and frontal bones

Question 7

How do skull cap bones ossify and how do base bones ossify ?

Answer 7

skull cap - begin as membranes (intramembranous ossification)
Floor/base - as cartilage ( endochondrial ossification )

Question 8

How many bones are in the Viscerocranium ?

Answer 8

14 bones , nasal, lacrimal, maxilla, zygomatic, inferior nasal conchae, mandible, vomer and palatine

Question 9

How do structures develop in the skull ?

Answer 9

pharyngeal arches

Question 10

What is the pterion and its clinical significance?

Answer 10

thinnest part of the skull , thin meeting part of frontal, parietal, temporal and sphenoid bones. Anterior branch of the middle meningeal artery is immediately beneath so fracture of this bone can cause an extradural heamorrhage

Question 11

What is the arrangement in cross section of the bones of the skull cap ?

Answer 11

trilamina arrangement
outer table - compact hard bone
diploid cavity - spongy bone
inner table - compact hard bone

Question 12

what are sutures ?

Answer 12

fibrous joints between bone, prevails prevent spillage , ossify in approx 20 years , potential weak points

Question 13

name some examples of some sutures

Answer 13

coronal - frontal fusions with parietal
sagittal - fusion of both parietals
lambdoid - fusion of occipital of both parietals
squamous - separates squamous part of temporal from parietal
bregma - fusion of frontal and parietal ( anterior fontanelle)
lambda - fusion of parietal and occipital ( posterior fontanelle )

Question 14

what is fontanelle and what is its clinical significance

Answer 14

large areas of unossified membranous gaps between flat bones of calvaria - allow for alteration of skull size and shape in infants
Anterior fuses - fuses 18 months - 2 years
posterior - 1 - 3 months

Question 15

what its the early fusion of fontanelles and sutures known as ?

Answer 15

Craniosynostosis

Question 16

what is the pooling of blood between the periosteum and the bone known as ?

Answer 16

cephalohaematoma
does not pass suture lines so cannot leave the skull
most commonly occurs in parietal bones

Question 17

how are intracranial injuries identified

Answer 17

ct scanning

Question 18

what the two main fracture types ?

Answer 18

linear - pass full thickness of skull and involve no bone displacement
depressed - fragment is displaced inwards towards the brain causing skull indentation and potential Brian injury

Question 19

what are fractures involving the cranial base ?

Answer 19

basilar skull fractures - associated with cranial nerve injuries
prone to causing cerebrospinal fluid leaks

Question 20

what are the clinical signs that indicate their presence of basilar skull fractures ?

Answer 20

battles signs - bruising over the mastoid process

raccoon eyes - ( periorbital ecchymosis) - bruising around both eyes

Question 21

what is the infra - temporal fossa ?

Answer 21

large space inferior and medial to zygomatic arch, medial and lateral pterygoid muscles are here

Question 22

what is the pterygopalatine fossa ?

Answer 22

very small space on the inferior surface of the skull between sphenoid and maxilla

Question 23

what is the middle cranial fossa ?

Answer 23

has pituitary gland, made up of sphenoid and temporal bones

Question 24

what is the posterior cranial fossa ?

Answer 24

deepest, made up of occipital and temporal bones, has brainstem

Question 25

what is the anterior cranial fossa ?

Answer 25

most shallow , over nasal and orbital cavities, accommodates anterioinferior portions of the frontal lobes of the brain

Question 26

what is meninges ?

Answer 26

three membranous layers that surround and protect the brain

Question 27

what are the three layers of meninges ?

Answer 27

Dura - tough outermost fibrous membrane Arachnoid - soft translucent membrane Pia- microscopically thin, delicate closely adherent to surface of brain

Question 28

how many layers do dura consist of ?

Answer 28

2 Periosteal - endosteum lining inner bones of skull meningeal - layer adjacent to arachnoid

Question 29

what are dural folds and dural venous sinuses ?

Answer 29

separation of two layers forms dural folds and dural venous sinuses( venous blood filled spaces created by seperation of meningeal from periosteal layer of dura )

Question 30

what are some examples of dural folds ?

Answer 30

Falx Cerebri | Tentorium Cerebelli

Question 31

what are the attachment of the dural folds ?

Answer 31

FC - crista gali | TC- sits above cerebellum

Question 32

what is the function and clinical significance of dural folds ?

Answer 32

help to stabilise the brain and act as a rigid divider a rise in pressure inside the skull can lead to compression and displacement of brain against rigid dural folds or through foramen magnum causing herniation

Question 33

what is the function of dural venous sinuses ?

Answer 33

major dural venous sinuses lie at the margins of borders of falx cerebri and on cranial floor. Venous blood from brain drains into the sinuses and eventually DVS drain into IJV

Question 34

how do cerebral veins within subarachnoid space drain into the DVS ?

Answer 34

bridging veins connect between the subarachnoid space into the dural venous sinuses

Question 35

what does the carvenous sinus drain into ?

Answer 35

drain into sigmoid sinus which goes through the jugular foramen, the skull becoming the IJV

Question 36

what does the carvenous sinus drain into ?

Answer 36

drain into sigmoid sinus which goes through the jugular foramen, the skull becoming the IJV

Question 37

what is a intracranial haemorrhage ?

Answer 37

head trauma can lead to bleeding in spaces between meningeal layers and blood vessels run along between the meningeal layers. Injury and bleeding from these blood vessels will cause accumulation of blood in the space between the meningeal layers

Question 38

what are the three types of intracranial haemorrhage ?

Answer 38

Extradural ( arterial blood, pear shaped on CT,MMA) Subdural ( venous blood from a bridging vein, banana shaped on CT, falx cerebri prevents it going to other part of the skull) Subarachnoid ( caused by trauma or spontaneous rupture of vessel - circle of willis, blood leaks into the subarachnoid space and mixes with CSF

Question 39

what is a intracerebral haemorrhage ?

Answer 39

blood can also occur within the brain tissue itself addition of volume such as a bleed, to an already fixed space( the skull )leads to a rise in pressure and damage to brain tissue, brainstem and other important structures e.g cranial nerves