CRANIAL CAVITY

1. CRANIAL CAVITY

2. 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.

3. 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.

4. 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, .

5. The meninges • The brain and spinal cord are surrounded by three layers of meninges which are: • Dura mater. • Arachnoid mater. • Pia mater.

6. Dura mater • Layers: • Endosteal layer: periosteum of the inner surface of the skull bones. Strongly adherent to the bone. • 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: • Falx cerebra. • Tentorium cerebelli. • Falx cerebelli. • Diaphragma sellae.

7. 1. Falx Cerebri • A sickle-shaped dural fold, lies in the midline between the two cerebral hemispheres. • Attachment: • Anteriorly: its narrow anterior end is attached to the crista galli and frontal crest. • Superiorly: it is attached to borders of the groove for superior sagittal sinus. • Posteriorly: it blends with the upper surface of the tentorium cerebelli. • Related venous sinuses: Superior and inferior sagittal sinuses and straight sinus.

8. 2. Tentorium Cerebelli • 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: • Free border: to the anterior clinoid process. • 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.

9. 3. Falx Cerebelli • 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 • 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).

10. Nerve supply of the dura mater • 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: • Trigeminal nerve. • Vagus nerve. • Hypoglossal nerve. • Upper three cervical nerves. • Sympathetic nerves.

11. Blood supply of the dura mater • Arterial supply come from branches of: • Internal carotid artery. • Maxillary artery. • Ascending pharyngeal artery. • Occipital artery. • 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.

12. 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

13. 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 : • 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. • 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.

14. 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 : • With each other through intercavernous sinuses (anterior, middle and posterior). • With pharyngeal plexus of veins by emissary veins running through foramen ovale. • With the facial veins through deep facial vein and superior ophthalmic vein.

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