3.1.2 Bones Forming Cranial Floor Flashcards
Describe the structure of the cranial floor
3 bowl-shaped depression
Anterior, middle and posterior cranial fossae
Why are there 3 cranial fossae?
Seat different parts of the brain
Elevation decreases, anterior most elevated (similar to steps)
What bones form the anterior cranial floor?
Frontal bone- vast majority
Ethmoid bone (middle part)
Sphenoid bone (posterior)
Why does the cribriform plate have foramina?
Allows olefactory nerves to enter nasal cavity
Label the image
Perpendicular plate helps form nasal septum
What bones form the middle cranial fossa?
Temporal bone (squamous part)
Zygomatic process of temporal bone
Mastoid process
Petrous bone (part of temporal bone)
Label the image
Sella turcica contains the pituitary gland in the pituitary fossa
Why is the petrous part of the temporal bone extremely strong?
Contains middle ear structures such as branches of the facial nerve and vestibulocochlear nerve
Label the image
What bone forms the posterior cranial fossa?
Occipital bone
Identify the osteology of the occipital bone
- External occipital protuberance
- Superior nuchal line (trapezius attaches here)
- Foramen magnum (conducts the brainstem)
What can skull fractures involve?
Cranial vault (calvaria)
Cranial floor
Why are skull fractures so concerning?
Significant trauma and force required to fracture the skull, therefore higher risk of injury to intracranial structures, e.g.brain, blood vessels, cranial nerves
Can still have intracranial injury following head injury with no skull fracture
What are the different types of fracture to the cranial vault?
Linear- fairly straight, no bone displacement
Comminuted- multiple fracture lines, fragments may displace inwards to the brain
What are the two types of comminuted fractures?
Depressed-fragments displaced inwards
Non-depressed- no inwards displacment
What is the thinnest part of the skull?
Pterion, relatively easy to fracture
Where frontal,parietal, temporal and greeater wing of sphenoid meet together
What blood vessel runs beneath the pterion?
Middle meningeal artery, can cause MMA ruputre, leading to intracranial extradural haemorrhage
Lemon shaped
What are basilar fractures?
Fractures of the skull base
Rarer type of skull fracture
What are some signs of anterior fossae fractures?
Periorbital ecchymoses / racoon eyes - severe bruising around eyelids.
Frontal bone forms roof of orbit, blood escapes and pools in eyes
CSF leakage from nose - ethmoid bone damaged, communication between subarachnoid space and nasal cavity
What are some signs of middle fossa - petrous bone damage
- CSF/blood leakage from ear
- Battles sign - bruised mastoid process
- Blood pooling behind tympanic membrane
