Session 2 - Osteology of the Skull Flashcards
The skull consists of how many individual bones?
22
The bones of the skull can be broadly divided into what two groups?
Neurocranium (calvaria, cranial floor)
Viscerocranium (facial skeleton, jaw)
What are the names of the three depressions that form the cranial floor?
Anterior cranial fossa
Middle cranial fossa
Posterior cranial fossa
What are the layers in the trilaminar arrangement of the bones of the calvaria?
Outer table (cortical bone) Diploeic cavity (cancellous bone) Inner table (cortical bone)
What is the benefit of the trilaminar arrangement in bones of the calvaria?
Gives protective strength without adding significant weight
What are sutures in the skull?
Fibrous joints found at intersections between the bones of the skull.
What are the three main suture lines?
Coronal
Sagittal
Lambdoid
What are fontanelles?
Large areas of unossified membranous gaps between flat bones of the calvaria, found in infants.
When do anterior and posterior fontanelles fuse?
Anterior: 18 months - 2 years
Posterior: 1-3 months
What is craniosyntosis?
Rare condition where there is early fusion of fontanelles and sutures
How can the anterior fontanelle be clinically useful when examining new borns and infants?
Inspection and gentle palpation of the anterior fontanelle can be used to assess the intracranial pressure and state of hydration.
What are the two main types of skull fracture?
Linear - through the full thickness of the skull, fairly straight, no bone displacement
Depressed - fragment is displaced inwards towards the brain
Fractures involving the cranial base are known as what?
Basilar skull fractures
What clinical signs indicate a basilar skull fracture?
Cerebrospinal fluid leaks (e.g. from the nose (CSF rhinorrhea) or from the ears (CSF otorrhea))
Raccoon eyes
Battle’s sign (bruising over the mastoid process)
Haemotympanum (blood behind the ear drum)
What is the pterion?
The thinnest area of the skull. Relatively easy to fracture.
What blood vessel underlies the pterion?
Middle meningeal artery (anterior branch)
Bleeding from the middle meningeal artery will result in what kind of haematoma?
Extradural haematoma
The large number of foramina found in the cranial floor increase its vulnerability to what?
Fracture, if significant force is transmitted through the skull base
What are the different types of intracranial heamatoma?
Epidural/extradural
Subdural
Subarachnoid
Intracerebral
What is the only moveable joint of the skull?
Temporomandibular joint (TMJ)
Facial fractures most commonly involve which bones?
Nasal bones (because of the prominence of the nose), the zygomatic bone and the mandible.
What structures run through the foramen magnum?
Medulla Meninges Vertebral arteries Spinal accessory nerve (ascending) Duran veins Anterior and posterior spinal arteries
What structures run through the internal acoustic meatus?
Facial nerve (CN VII) Vestibulocochlear nerve (CN VIII) Labrynthine artery
What structures run through the jugular foramen?
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)
Spinal accessory nerve (descending) (CN XI)
Internal jugular vein
Inferior petrosal sinus
Sigmoid sinus
Meningeal branches of the ascending pharyngeal and occipital arteries
What structure runs through the hypoglossal canal?
Hypoglossal nerve (CN XII)
The crista galli is found in the midline of which bone?
Ethmoid bone
What structures run through the cribriform foramina?
Olfactory nerve fibres (CN I)
Other than the cribriform foramina, what other two foramina are found in the cribriform plate?
Anterior ethmoidal foramen
Posterior ethmoidal foramen
What structures run through the superior orbital fissure?
Oculomotor nerve (CN III) Trochler nerve (CN IV) Ophthalmic branch of the trigeminal nerve (CN Va) Abducens nerve (CN VI) Ophthalmic veins Sympathetic fibres
What structures run through the optic canals?
Optic nerves (CN II) Ophthalmic arteries
What groove runs transversely between the two optic canals?
Chiasmatic sulcus
Foramen rotundum transmits what structure?
The maxillary branch if the trigeminal nerve (CN Vb)
Foramen rotundum opens into what fossa?
Pterygopalatine fossa
Foramen ovale transmits what structures?
Mandibular branch of the trigeminal nerve (CN Vc)
Accessory meningeal artery
Foramen ovale opens into what fossa?
Infratemporal fossa
Foramen spinosum transmits what structures?
Middle meningeal artery
Middle meningeal vein
A meningeal branch of CN Vc
Foramen spinosum opens into what fossa?
Infratemporal fossa
The carotid canal transmits what structures?
Internal carotid artery
Deep petrosal nerve
Through which foramina do the different branches of the trigeminal nerve run?
Opthalmic (CN Va) - superior orbital fissure
Maxillary (CN Vb) - foramen rotundum
Mandibular (CN Vc) - foramen ovale
Which two foramina provide a connection between the infratemporal fossa and the cranial cavity?
Foramen ovale
Foramen spinosum
