Transcript Middle cranial fossa Bones

Anterior cranial fossa
Bones: Orbital plate of frontal bone,
cribriform plate of ethmoid and lesser
wing of sphenoid bone.
Features: Frontal crest, foramen cecum,
crista galli, anterior and posterior
ethmoidal foramina and anterior clinoid
process.
Foramina: foramen cecum, foramina for
olfactory nerves, foramina for anterior and
posterior ethmoidal nerves and vessels.
Middle cranial fossa
Bones: Sphenoid bone (body and greater
wing), Temporal bone (squamous part, petrous
part) and parietal bone.
Features: Middle and posterior clinoid
processes, sulcus chiasmaticus, tuberculum
sellae, hypophyseal fossa, dorsum sellae, sella
turcica, arcuate eminenca, tegmen tympani.
Foramina: optic canal, superior orbital fissure,
foramen rotundum, foramen ovale, foramen
spinosum, foramen lacerum, hiatus for greater
petrosal nerve and hiatus for lesser petrosal
nerve.
Posterior cranial fossa
Bones: basilar part of sphenoid and
basilar part of occipital (clivus), lateral
part of occipital, squamous part of
occipital and petrous part of temporal
bones.
Features: internal occipital crest, internal
occipital protuberance, .
Foramina: Foramen magnum, jugular
foramen, internal acoustic meatus,
hypoglossal canal, .
The meninges
The brain and spinal cord are
surrounded by three layers of
meninges which are:
1. Dura mater.
2. Arachnoid mater.
3. Pia mater.
Dura mater
 Layers:
A. Endosteal layer: periosteum of the inner surface of
the skull bones. Strongly adherent to the bone.
B. Meningeal layer: dense strong fibrous membrane,
continues through the foramen magnum with dura
covering the spinal cord. It send inward four septa
that divide the cranial cavity into communicating
spaces and act to restrict the rotatory displacement
of the brain during movement. They are:
1. Falx cerebra.
2. Tentorium cerebelli.
3. Falx cerebelli.
4. Diaphragma sellae.
1. Falx Cerebri
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A sickle-shaped dural fold, lies in the midline
between the two cerebral hemispheres.
Attachment:
1. Anteriorly: its narrow anterior end is
attached to the crista galli and frontal crest.
2. Superiorly: it is attached to borders of the
groove for superior sagittal sinus.
3. Posteriorly: it blends with the upper surface
of the tentorium cerebelli.
Related venous sinuses: Superior and inferior
sagittal sinuses and straight sinus.
2. Tentorium Cerebelli
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A crescent tent-shaped dural fold that roofs the
posterior cranial fossa. It covers the upper surface
of the cerebellum and supports the occipital lobes
of the cerebral hemispheres. It has tentorial notch
for the passage of the midbrain.
Attachment:
1. Free border: to the anterior clinoid process.
2. Attached border: to posterior clinoid process,
superior border of petrous part of temporal bone
and margin of the groove for the transverse
sinus.
Related venous sinuses: Straight sinus, superior
petrosal sinus, transverse sinus.
3. Falx Cerebelli
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A small sickle-shaped dural fold, attached to
internal occipital crest and project between
the two cerebellar hemispheres.
Related venous sinuses: occipital sinus.
4. Diaphragma sellae
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A small circular dural fold which form the roof
of the sella turcica. It has a small opening
that allow the passage of the stalk of the
hypophysis cerebri (infundibulum of the
pituitary gland).
Nerve supply of the dura mater
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Dura is sensitive to stretch which
produces the sensation of headache or
referred pain in the back of the neck and
scalp.
Nerves are branches of:
1. Trigeminal nerve.
2. Vagus nerve.
3. Hypoglossal nerve.
4. Upper three cervical nerves.
5. Sympathetic nerves.
Blood supply of the dura mater
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Arterial supply come from branches of:
1. Internal carotid artery.
2. Maxillary artery.
3. Ascending pharyngeal artery.
4. Occipital artery.
5. Vertebral artery
Middle meningeal artery is the clinically most
important artery. It a branch of the first part of
maxillary artery. It enters through the foramen
spinosum and grooves the inner aspect of the
squamous temporal bone. In cases of fracture of
the pterion area, this artery is injured causing
bleeding and hematoma formation.
Intracranial venous sinuses
 They are blood-filled spaces between the
layers of the dura mater. They are lined
with endothelium. They posseses no valves
and drain brain, diploe, orbit and internal
ear and communicate with the extracranial
veins through emissary veins. They are:
 Single sinuses: Superior sagittal, inferior
sagittal, straight, intercavernous and basilar
plexus of veins.
 Paired sinuses: Sphenoparietal, cavernous,
superior petrosal, inferior petrosal,
transverse, sigmoid and occipital sinuses
Cavernous sinus
 Position: in middle cranial fossa, on each side of
the body of sphenoid bone.
 Extent: from the superior orbital fissure to the
apex of the petrous part of temporal bone.
 Contents :
A. Inside the sinus: 1. internal carotid artery
surrounded by sympathetic plexus and 2.
abducent nerve. These structures are
separated from the sinus by endothelial layer.
B. On its lateral wall: 1. oculomotor nerve, 2.
trochlear nerve, 3. ophthalmic nerve and 4.
maxillary nerve (between the endothelial lining
and the dura mater.
Cavernous sinus
 Tributaries: from 1. Superior and inferior
ophthalmic veins, 2. cerebral veins, 3.
sphenoparietal sinus and 4. central vein of the
retina.
 Drainage: to 1. superior and 2. inferior petrosal
sinuses.
 Communications :
1. With each other through intercavernous
sinuses (anterior, middle and posterior).
2. With pharyngeal plexus of veins by emissary
veins running through foramen ovale.
3. With the facial veins through deep facial vein
and superior ophthalmic vein.
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