Skull Osteology - Cranial Base Flashcards
What are the 3 regions (fossa) of the cranium?
- anterior
- house for frontal lobes - middle
- house for temporal lobes - posterior
- house for occipital lobes, cerebellum and medulla oblongata
The anterior cranial fossa is formed by?
- Frontal bone (orbital parts)– anteriorly
- Ethmoid bone – middle
- Sphenoid bone (body and lesser wing) – posteriorly
Describe the surface of the anterior cranial fossa?
brain markings of orbital gyri
What does the frontal bone form in the anterior cranial fossa?
- Frontal crest – median bony extention
- Foramen caecum – base
What does the ethmoid bone form in the anterior cranial fossa?
- Crista galli – median ridge posterior to foramen caecum
- Cribriform plate – sieve-like passage for olfactory nerves to olfactory bulb
What does the ethmoid bone contribute to?
- Perpendicular Plates
- Superior & Middle Nasal Concha
- Cribriform Plate
- Crista Galli
N.B. the ethmoid bone is the deppest skull bone
Describe a common anterior cranial fossa fracture and subsequent signs + symptoms?
- Cause
The cribriform plate may be fractured - Consequence
- Usually results in tearing of the overlying meninges - Signs and symptoms
- The patient will have bleeding from the nose and leaking of CSF into the nose (rhinorrhea)
- Battles sign
- unequal pupils
- discoloration of soft tissue under eyes - Potential treatment
- if any sinus is involved in a fracture antibiotics must be given prophylatically as the sinus renders it a compound fracture even if the skin is intact.
What are Raccoons eyes?
Periorbital edema and bruising suggestive of Frontal-basal fracture
What is the middle cranial fossa composed of?
- Large depressions on each side
- Small depression called sella turcica
What are the 3 bony parts that form the middle cranial fossa?
- Greater wing of sphenoid bone
- Squamous part of temporal bone – laterally
- Petrous part of temporal bone – posteriorly
What separates the middle and anterior cranial fossae?
- Sphenoid crest – laterally
- Sphenoid limbus – medially
What separates the middle and posterior cranial fossae?
- Pretrous crest of temporal bones – laterally
- Dorsum sellae of sphenoid – medially
What is the function of the middle cranial fossa?
Supports temporal lobes of the brain
Describe the sella turcica?
- Surrounded by anterior and posterior clinoid processes
- Lesser wings of sphenoid overhangs the fossa
The sella turcica is composed of which 3 parts?
- Tuberculum sella –anteriorly
- Hypophysial fossa (pituitary fossa)
- Dorsum sellae
Describe the sphenoid bone?
A prominent, irregular, wedge-shaped bone at the base of the skull.
Note: The sphenoid bone has been called the “keystone” of the cranial floor since it is in contact with all of the other cranial bones.
What are the landmarks of the sphenoid bone?
- Greater wings: large lateral projections of bone that help to form the lateral border of the skull
- Lesser wings: smaller lateral projections of bone above the greater wings
- Pterygoid processes: two long downward projections from the greater wings that act as a point of muscle attachment.
- Sella turcica: known as the Turkish Saddle which cradles the pituitary gland
What are the 5 foramina of the sphenoid bone?
- Superior orbital fissure
- Foramen rotundum
- Foramen Ovale
- Foramen spinosum
- Foramen lacerum
Describe the superior orbital fissure and what it transmits?
- between the lesser and greater wings
- Transmits opthalmic veins and nerves entering the orbit
> oculomotor nerve CNIII
> trochlear nerve CNIV
> ophthalmic CNV1
> abducens CNVI
> sympathetic fibers
Describe the Foramen rotundum and what it transmits?
- posterior to the medial end of superior orbital fissure.
- Transmits maxillary nerve (CN V2)
Describe the foramen ovale and what it transmits?
- posterolateral to foramen rotundum
- opens in infratemporal fossa
- Transmits mandibular nerve (CN V3) and small accessory meningeal artery
Describe the foramen spinosum and what it transmits?
- postlateral to foramen ovale
- Transmits middle meningeal vessels and meningeal branch of mandibular nerve
Describe the foramen lacerum and what it transmits?
- artefact of dried skull
- In life covered by cartilage.
- Posteriorly and laterally the re is a groove for greater petrosal nerve
What is the consequence of fractures to the middle cranial fossa?
- Consequence
Otorrhea - Clinical presentation
- Leakage of blood and CSF from the ear is common in middle cranial fossa fractures . - Treatment
- Drainage of CSF from the ear - Cause
- Suggestive of a Fracture of the temporal bone with torn meninges
What part of the middle cranial fossa is usually fractured?
The base of the skull is more fragile than the vault and is thus commonly involved in fractures
What part of the middle cranial fossa is rarely involved in fractures?
The petrous part of the temporal bone is rarely involved
> Which fits with it’s name
– petrous = rock like i.e. Strong
Describe the posterior cranial fossa and it’s contents?
- Largest and deepest
- Contains cerebellum, pons and medulla oblongata
The posterior cranial fossa is formed by?
- occipital bone
- Dorsum sella of sphenoid – medially
- Petrous and mastoid parts of temporal bone –anterolaterally
Note: Clivius – centrally inclined part of occipital bone
Describe the landmarks of the posterior cranial fossa?
- Divided by internal occipital crest into two crebellar fossae
- Internal occipital fossa ends up in internal occipital protuberance ( confluence of dural venous siunuses
- Transverse and sigmoid dural venous sinuses – grooves anterolaterally
Name the foramina of the posterior cranial fossa?
- foramen magnum
- jugular foramen
- hypoglossal canal
- internal acaustic meatus
What does the foramen magnum of the posterior cranial fossa transmit?
- Medulla and meninges
- Vertebral arteries
- Spinal roots of CN XI
- Dural veins
- Anterior and posterior spinal arteries
What does the jugular foramen of the posterior cranial fossa transmit?
- CNs IX (glossopharyngeal), X (vagus), and XI (accessory)
- Superior bulb of internal jugular vein,
- Inferior petrous and sigmoid sinuses
- Meningeal branches of pharyngeal and occipital arteries.
What does the hypoglossal canal of the posterior cranial fossa transmit?
hypoglossal nerve (CNXII)
What does the internal acaustic meatus of the posterior cranial fossa transmit?
facial, and vestibulocochlear nerves (CNXII)
Describe the walls of the cranial cavity?
- Vary in thickness in different regions
- Thinner in females than men
- Thinner in children than elderly
- Bones contains internal and external tables of compact bone
> Tables separated by diploe
Diploe of the walls of the cranial cavity contains?
- Red bone marrow
- Canals containing diploic veins
Describe the clinical correlations of the clivus?
formed from sphenoid and occipital bones
- the spheno occipital synchodrosis can be seen in children and young adults (not a fracture)
- accounts for majority of skull base growth
- normal fate signals in adult (late teens) in MRI
Describe the consequence of posterior cranial fossa fractures?
Blood may reappear from under muscles near the mastoid process days afterwards
