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 Bones of the facial skeleton - 2x temporal bones - 2x nasal bones - 2x parietal bones - 2x palatine bones - Frontal bone - 2x lacrimal bones - Sphenoid bone - 2x zygomatic bones - Ethmoid bone - 2x maxillae - Occipital bone - 2x inferior nasal conchae - 1x vomer
- Mandible (strictly not part of the f.s.)
Anterior view of the skull Lateral view of the skull
Bones of cranial base superior view Meninges 3 layers of meninges: CSF: - Dura mater flows through the - Arachnoid membrane subarachnoid space - Pia mater
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
- 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
- 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.
- The encircling structures are:
o Lateral ventricles
o Associated structures e.g. caudate nucleus; limbic structures
Coronal section through hypothalamus Horizontal section