Ali Hosin
Anatomy of Head, Neck & Spine
CRANIUM AND BRAIN
Definitions
Skull
– skeleton of head
Cranium
– bones which enclose the brain
Vault (calvarium) – part of cranium which covers the superior and lateral aspects of the brain
Base of skull – part of cranium which holds the base of the brain
Bones of the skull
- Cranium (further subdivided into vault and base)
- Facial skeleton
Bones of the cranium
- 2x temporal bones
- 2x parietal bones
- Frontal bone
- Sphenoid bone
- Ethmoid bone
- Occipital bone
Bones of the facial skeleton
- 2x nasal bones
- 2x palatine bones
- 2x lacrimal bones
- 2x zygomatic bones
- 2x maxillae
- 2x inferior nasal conchae
- 1x vomer
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Anterior view of the skull
Mandible (strictly not part of the f.s.)
Lateral view of the skull
Bones of cranial base
superior view
Meninges
3 layers of meninges:
- Dura mater
- Arachnoid membrane
- Pia mater
CSF:
flows through the
subarachnoid space
Dura mater
- The outer layer of the dura mater is adherent to the inside of the cranium
- The inner layer forms double folds, which:
o Divide the cranial cavity into compartments
o Stabilise the brain within the cranium
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Falx cerebri – crescent-shaped; separates the cerebral hemispheres
Tentorium cerebelli separates occipital lobes and posterior temporal lobes from cerebellum
The brainstem (midbrain) passes through the tentorial notch (incisura) in the midline
Diaphragma sellae – surrounds the pituitary stalk in the sella turcica of the sphenoid bone.
Herniation
A space-occupying lesion (e.g. blood, tumour, oedema, cyst) in any compartment may lead to increased intracranial
pressure and lead to herniation of part of the brain.
3 main types:
1. Subfalcine herniation – not usually clinically significant
2. Uncal herniation – affects midbrain (pushed against edge of tentorium) – unconsciousness
3. Tonsilar herniation – affects medulla (pushed against foramen magnum) – cardiorespiratory failure
Dural folds
Dural sinuses – note relations with dural folds
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Dural sinuses are like veins but without valves
Superior sagittal sinus – upper margin of falx cerebri
Inferior saggital sinus – lower margin of falx cerebri
Straight sinus – at junction of falx / tentorium
-
They anastomose with extracranial veins via emissary veins
Straight sinus  transverse sinuses sigmoid sinuses  internal jugular vein – key drainage
Cavernous sinuses
- two pairs of cavernous sinuses
- Located against lateral aspect of body of sphenoid bone; either side of sella turcica
- Of clinical significance due to the structures passing through them
- Receive blood from:
o cerebral veins
o ophthalmic veins
o emissary veins
- pathway for infection to pass from extracranial sites into intracranial locations.
- As structures pass through the cavernous sinuses, and are located in the walls of
these sinuses, they are particularly vulnerable to injury due to inflammation
- Structures passing through each cavernous sinus:
o Internal carotid artery
o Abducens nerve (VI)
- Structures in lateral wall of each cavernous sinus – superior to inferior:
o Oculomotor nerve (III)
o Trochlear nerve (IV)
o Ophthalmic nerve (V1)
o Maxillary nerve (V2)
- The intercavernous sinuses connect the right and left cavernous sinuses – around the pituitary stalk
Internal organisation of the forebrain
-
Coronal and horizontal sections through the middle of
the forebrain show a very similar relationship of the
internal structures.
-
This is because there are two structures at the core, surrounded by several structures, forming an arc:
o Thalamus on either side of the 3rd ventricle
o lentiform nucleus (putamen and globus pallidus) lateral to the thalamus.
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The encircling structures are:
o Lateral ventricles
o Associated structures e.g. caudate nucleus; limbic structures
Coronal section through hypothalamus
Horizontal section