L4: osteology and radiographic appearance of the skull Flashcards
Describe the key osteological features of the skull
Neurocranium – consists of the calvaria (roof of the cranium) and the cranial floor
Viscerocranium – bones forming the facial skeleton
Cranial cavity – space within the cranium, which holds the brain
Describe the bones of the calvaria
Two layers of compact bone separated by a layer of spongy bone (diploe)
The tri-lamina arrangement of compact and spongy bone conveys protective strength to the skull without adding significant weight
-severe blows to the neurocranium may still result in fractures
What is the pterion?
Thinnest part of the calvaria
Area of clinical importance – risk of fracture at this site
-can injure the middle meningeal artery -> bleeding from this artery will cause an extradural haematoma
-blood will accumulate between the periosteal layer of the dura mater and bone
-growing haematoma exerts pressure on the brain
What are between the large flat bones forming the calvaria?
Serrated, immobile joints = SUTURES
-coronal, sagittal and lambdoid
Interlocking nature of these joints makes it very difficult for the bones forming the joint to dislocate
-as we age -> suture lines begin to ossify
What are the three fossae of the cranial floor?
Anterior
Middle
Posterior
What are the boundaries of the anterior fossa?
Consists of three bones – frontal bone, ethmoid bone and sphenoid bone
Anteriorly and laterally – inner surface of the frontal bone
Posteriorly and medially – lumbus of the sphenoid bone
Posteriorly and laterally – lesser wings of the sphenoid bone
Floor – frontal bone, ethmoid bone and anterior aspects of the body & lesser wings of the sphenoid bone
What are the boundaries of the middle fossa?
Consists of three bones – sphenoid bone and two temporal bones
Anteriorly and laterally – lesser wings of the sphenoid bone
Anteriorly and medially – limbus of the sphenoid bone
Posteriorly and laterally – superior border of the petrous part of the temporal bone
Posteriorly and medially – dorsum sellae of the sphenoid bone
Floor – body and greater wing of the sphenoid & squamous and petrous parts of the temporal bone
What are the boundaries of the posterior fossa?
Consists of three bones – occipital bone and two temporal bones
Anteriorly and medially – dorsum sellae of the sphenoid bone
Anteriorly and laterally – superior border of the petrous part of the temporal bone
Posteriorly – internal surface of the squamous part of the occipital bone
Floor – mastoid part of the temporal bone & squamous, condylar and basilar parts of the occipital bone
What is the significance of the foramina in the cranial floor?
Allow passage for structures such as cranial nerves and blood vessels between extra- and intra-cranial compartments
What causes an intracranial haematoma?
Bleeding within the cranial cavity -> can compress and damage the underlying brain tissue
When there is clinical suspicion of intracranial haemorrhage, CT imaging of the head will be necessary
List clinical signs associated with a basilar skull fracture
Battle’s sign – bruising over the mastoid process
Racoon eyes – bruising around both eyes
Haemotympanum – blood behind the eardrum
CSF rhinorrhoea – CSF leaking from the nose
CSF otorrhoea – CSF leaking from the ear
What bones make up the facial skeleton?
Zygomatic Maxilla Nasal Lacrimal Mandible
Describe the temporomandibular joint
Synovial hinge-type joint divided into two synovial cavities by a fibrocartilaginous disc
Articulation between mandible and the cranial base
Number of conditions – TMJ disorder (pain, clicking, locking), dislocation and arthritis
Innervated by the auriculotemporal nerve (branch of mandibular division of trigeminal)
Describe injury to the facial skeleton
Most common facial fractures – nasal bones, zygomatic bone and/or mandible
Hard blow to the lower jaw often results in a fracture of the neck of the mandible and its body & may be associated with TMJ dislocation
Fractures to the bones of the midface are particularly concerning -> separation of some or all of the midface from the skull base -> can present problems for the patient’s airway
-Le Fort classification
Outline the differences between the fetal/infant and adult skull
Fontanelles = large areas of unossified membranous gaps between flat bones of calvaria
-allow for alteration of the skull size and shape during childbirth -> permit growth of infant brain
-fuse in early infancy (anterior – 18 months to 2 years, posterior – 1 to 3 months)
-early fusion = CRANIOSYNOSTOSIS (rare)
NB: anterior fontanelle useful in examining newborns and infants -> can be used to assess intracranial pressure and state of hydration
