S2- Osteological and Radiographic Appearance of the Skull Flashcards
what are foramina?
holes in the skull
what are fissures ?
narrows slit
how many bones are in the skull ?
22
How are the bones of the skull divided into two groups ?
Neurocranium and Viscerocranium
How many bones are in the Neurocranium ?
8 bones
Describe Neurocranium
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
How do skull cap bones ossify and how do base bones ossify ?
skull cap - begin as membranes (intramembranous ossification)
Floor/base - as cartilage ( endochondrial ossification )
How many bones are in the Viscerocranium ?
14 bones , nasal, lacrimal, maxilla, zygomatic, inferior nasal conchae, mandible, vomer and palatine
How do structures develop in the skull ?
pharyngeal arches
What is the pterion and its clinical significance?
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
What is the arrangement in cross section of the bones of the skull cap ?
trilamina arrangement
outer table - compact hard bone
diploid cavity - spongy bone
inner table - compact hard bone
what are sutures ?
fibrous joints between bone, prevails prevent spillage , ossify in approx 20 years , potential weak points
name some examples of some sutures
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 )
what is fontanelle and what is its clinical significance
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
what its the early fusion of fontanelles and sutures known as ?
Craniosynostosis
what is the pooling of blood between the periosteum and the bone known as ?
cephalohaematoma
does not pass suture lines so cannot leave the skull
most commonly occurs in parietal bones
how are intracranial injuries identified
ct scanning
what the two main fracture types ?
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
what are fractures involving the cranial base ?
basilar skull fractures - associated with cranial nerve injuries
prone to causing cerebrospinal fluid leaks
what are the clinical signs that indicate their presence of basilar skull fractures ?
battles signs - bruising over the mastoid process
raccoon eyes - ( periorbital ecchymosis) - bruising around both eyes
what is the infra - temporal fossa ?
large space inferior and medial to zygomatic arch, medial and lateral pterygoid muscles are here
what is the pterygopalatine fossa ?
very small space on the inferior surface of the skull between sphenoid and maxilla
what is the middle cranial fossa ?
has pituitary gland, made up of sphenoid and temporal bones
what is the posterior cranial fossa ?
deepest, made up of occipital and temporal bones, has brainstem
what is the anterior cranial fossa ?
most shallow , over nasal and orbital cavities, accommodates anterioinferior portions of the frontal lobes of the brain
what is meninges ?
three membranous layers that surround and protect the brain
what are the three layers of meninges ?
Dura - tough outermost fibrous membrane
Arachnoid - soft translucent membrane
Pia- microscopically thin, delicate closely adherent to surface of brain
how many layers do dura consist of ?
2
Periosteal - endosteum lining inner bones of skull
meningeal - layer adjacent to arachnoid
what are dural folds and dural venous sinuses ?
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 )
what are some examples of dural folds ?
Falx Cerebri
Tentorium Cerebelli
what are the attachment of the dural folds ?
FC - crista gali
TC- sits above cerebellum
what is the function and clinical significance of dural folds ?
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
what is the function of dural venous sinuses ?
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
how do cerebral veins within subarachnoid space drain into the DVS ?
bridging veins connect between the subarachnoid space into the dural venous sinuses
what does the carvenous sinus drain into ?
drain into sigmoid sinus which goes through the jugular foramen, the skull becoming the IJV
what does the carvenous sinus drain into ?
drain into sigmoid sinus which goes through the jugular foramen, the skull becoming the IJV
what is a intracranial haemorrhage ?
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
what are the three types of intracranial haemorrhage ?
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
what is a intracerebral haemorrhage ?
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
