Cranium- anatomy of basi-cranium, dural venous sinus

Cranium is the skeleton of the head.
Neurocranium is the bony case of the brain and meninges. It is formed by a series of eight bones:
Unpaired: Frontal, Ethmoid, Sphenoid & Occipital
Paired : Temporal, Parietal
Ethmoid bone relatively minor contribution

1. BASICRANIUM DURAL FOLDS DURAL VENOUS SINUS BY RAMAGOPALAN S

2. CRANIAL CAVITY: Cranium is the skeleton of the head. Neurocranium is the bony case of the brain and meninges. It is formed by a series of eight bones: Unpaired: Frontal, Ethmoid, Sphenoid & Occipital Paired : Temporal, Parietal Ethmoid bone relatively minor contribution

3. CRANIAL CAVITY: Cranial cavity is a space enclosed by neurocranium that contains the brain, the intracranial portions of the cranial nerves and spinal nerves and blood vessels, meninges and CSF The base of the cranial cavity is dived into three distinct fossae. Namely, Anterior cranial fossa Middle cranial fossa Posterior cranial fossa Anterior cranial fossa is at the highest level and Posterior cranial fossa is at the lowest level.

4. Landmarks in Basicranium :

5. Anterior cranial fossa: Shallowest of the three cranial fossae Formed by the frontal bone anteriorly, the ethmoid bone is the middle, and the lesser wings of the sphenoid posteriorly Greatest part of the fossa – orbital plate of the frontal bone Support the frontal lobes of the brain and form the roofs of the orbit Crista galli - thick, median ridge of ethmoid, which project superiorly and each of ridge is the sieve-like cribriform plate of the ethmoid Olfactory bulbs of the brain, which lie on cribriform plate

6. Landmarks and Foramina/Apertures: Foramen cecum: Site: base of the frontal crest Structures: emissary vein of frontal bone(1%) Anterior and posterior ethmoidal foramina: Structures: vessels and nerves with same name Cribriform foramina: Structures: Axons of olfactory cells in the olfactory epithelium that form olfactory nerves

7. Middle cranial fossa: Butterfly shaped fossa It is bounded by: In front by sphenoid crest of lesser wing and part of the body of the sphenoid Behind superior border of the petrous part of temporal bone dorsum sellae Laterally by the squamous parts of the temporal bone Communicates with the orbits by the superior orbital fissures

8. Middle cranial fossa: Sphenoid crests end medially in two sharp bony projection, anterior clinoid processes Optic canal is lateral to the sulcus chiasmatis which transmits the optic nerve Centrally the floor of the fossa is narrower and formed by the sphenoid bone which contains the sphenoidal sinuses Roof of the sphenoid sinus is deeply concave and houses the pituitary fossa(aka sella turcica ) between turberculum and dorsum sellae that gives attachment to the tentorium cerebelli.

9. Foramina of Middle cranial fossa: Optic canal: Bone: Lesser wing of the sphenoid Structures: Optic nerve and ophthalmic artery Superior orbital fissure: Bone: Between lesser and greater wings Structures: Oculomotor, Trochlear, Lacrimal, Frontal, Nasociliary and abducent nerve & Superior ophthalmic vein Foramen rotundum: Bone: Greater wings of sphenoid Structures: Maxillary division of the trigeminal nerve

10. Foramina of middle cranial fossa: Foramen ovale : Bone: Greater wing of the sphenoid Structures: Mandibular(V3) nerve, lesser petrosal nerve, accessory meningeal artery, Emissery veins Foramen spinosum: Bone: Between lesser and greater wings Structures: Middle meningeal artey Foramen lacerum : Bone: Between the petrous part of the temporal and the sphenoid Structures: Internal carotid artery

11. Posterior cranial fossa: The largest and deepest of the three cranial fossa, contains the cerebellum, pons, and medulla oblongata Mostly by the occipital bone an sloping surface of the basilar part, called clivus . Bounded anteriorly by dorsum sellae and superior border of petrous part of temporal Corresponds extracranially with the posterior part of the cranial base Most prominent feature – foramen magnum

12. Posterior cranial fossa: The jugular foramen at the posterior end of the petro -occipital fissure Jugular foramen: Upper border- notch for the glossopharyngeal nerve Posteriorly it is grooved by the sigmoid sinus which continues into foramen as the internal jugular vein Jugular tubercle lie between the inferior petrosal and sigmoid sinus

13. Posterior cranial fossa: Sigmoid sulcus which runs forwards and downwards and finally forwards to the jugular foramen Median internal occipital crest in the squamous part of the occipital and gives attachment to the falx cerebelli and grooved by occipital sinus The groove for the transverse sinus runs laterally from internal occipital protuberance Internal occipital crest separates two shallow fossae which house the cerebellar hemispheres

14. Foramina of posterior cranial fossa: Foramen magnum: Bone: Central area of the floor Structures: Medulla oblongata and its meninges, ascending spinal parts of the accessory spinal nerves and two vertebral arteries Hypoglossal canal: Bone: Close to the anterolateral boundary of the foramen magnum Structures: Hypoglossal nerve

15. Foramina of posterior cranial fossa: Jugular foramen: Bone: Between the petrous part of the temporal bone and the condylar part of the occipital bone Structures: Glossopharyngeal, Vagus and accessory nerves & internal jugular vein Internal acoustic meatus: Bone: Posterior surface of the petrous of the temporal bone Structures: Vestibulocochlear and facial nerves

16. Fracture of the anterior cranial fossa causes anosmia, periorbital bruising, and CSF leakage from the nose Fracture of the anterior cranial fossa causes anosmia, periorbital bruising, and CSF leakage from the nose A blow to the chin with the mouth closed, causing fracture of the middle cranial fossa

17. DURAL FOLDS

18. Dural folds of cranial cavity: The meningeal layer of the dura is reflected inwards to form four septa, namely Falx cerebri Falx cerebelli Diaphragma sellae Tentorium cerebelli Partially divide the cranial cavity into compartment

19. Falx cerebri: Sickle shaped double layer of dura mater, lying between the cerebral hemispheres Is attached anteriorly to the crista galli and posteriorly to the tentorium cerebelli Has a free inferior concave border that contains the inferior sagittal sinus and its upper convex margin encloses the superior sagittal sinus

20. Falx cerebelli: Is a small sickle-shaped projection between the cerebellar hemispheres Is attached superiorly to the posterior-inferior parts of the tentorium and posteriorly to the internal occipital crest Contains the occipital sinus in its posterior border

21. Tentorium cerebelli: Is a crescentic fold of dura mater that supports the occipital lobes of the cerebral hemispheres and covers the cerebellum Has a free internal concave border , which bounds the tentorial notch, whereas its external convex border encloses the transverse sinus posteriorly and the superior petrosal sinus anteriorly. Free border is anchored to the anterior clinoid process , whereas the attached border is attached to the posterior clinoid process

22. Diaphragma sellae: Is a circular, horizontal fold of dura that forms the roof of the sella turcica , covering the pituitary gland. Has a central aperture for the hypophyseal stalk or infundibulum

23. Pain sensitive intracranial structures are: Large cranial venous sinuses Dural arteries Dural floor of anterior and posterior cranial fossae Arteries at the base of the brain

24. DURAL VENOUS SINUSES

25. Dural venous sinuses form a complex network of venous channels which drain the blood from the brain and cranial bones Lie between the endosteal and meningeal layer of the dura matter Lined by endothelium, have no valves and their walls are devoid of muscular tissue. Arachnoid granulations drain CSF from the subarachnoid space into the dural venous sinuses Dural venous sinuses:

26. Classification of the dural venous sinus: Dural venous sinuses: Unpaired venous sinuses Paired venous sinuses 1. Superior sagittal Cavernous 2. Inferior sagittal 2. Superior petrosal 3. Straight 3. Inferior petrosal 4. Occipital 4. Transverse 5. Anterior intercavernous 5. Sigmoid 6. Posterior intercavernous 6. Sphenoparietal 7. Basilar venous plexus 7. Petrosquamous *Along with middle meningeal sinus/ veins in the paired venous sinus group

27. Cavernous sinus: the cavernous sinuses are two large venous plexus that lie on either side of the body of the sphenoid bone Extending from the superior orbital fissure to the apex of the petrous temporal bone Average length of 2cm and width of 1cm

28. Cavernous sinus: Relations Superiorly: Optic tract Optic chiasma Olfactory tract Internal carotid artery Anterior perforated substance Inferiorly: Foramen lacerum Junction of the body and greater wings of the sphenoid bone

29. Cavernous sinus: Relations Anteriorly: Superior orbital fissures Apex of the orbit Posteriorly: Apex of the petrous temporal The crus cerebri of the midbrain

30. Cavernous sinus: Relations Medially: Hypophysis cerebri Sphenoidal air sinus Laterally: Temporal lobe with uncus Below laterally: Mandibular nerve

31. Cavernous sinus: Structure within the sinus Lateral aspect (from above downwards): Oculomotor nerves Trochlear nerve Ophthalmic nerve Maxillary nerve Trigeminal ganglion Medial aspect : Internal carotid artey Abducent nerve

32. Cavernous sinus:

33. Cavernous sinus thrombosis: Caused by bacterial infections Usually from a spreading infection in the nose, sinuses, ears or teeth Produce: headache, papilledema, exophthalmos, diplopia, vision loss, meningitis, ophthalmoplegia

34. Superior sagittal sinus: Lies in the midline along the convex border of the falx cerebri Begins at the crista galli Receives the cerebral, diploic meningeal, and parietal emissary vein Interior of the sinus shows: Opening of the superior cerebral veins Opening of the venous lacunae Arachnoid villi and granulations Fibrous band

35. Inferior sagittal sinus: Lies in the free edge of the falx cerebri Ends in the strainght sinus Receives veins from the falx and medial surface of the cerebral hemisphere Straight sinus: Runs along the line of attachment of the falx cerebri to the tentorium cerebelli Is formed by union of the inferior sagittal sinus and the great vein of Galen Ends at the internal occipital protuberance by continuous as the transverse sinus usually left Also receives a few of the superior cerebral vein

36. Transverse sinus: Begins at the internal occipital protuberance Right, continuous with superior sagittal sinus and the left with straight sinus Course along the posterolateral attached margins of the tentorium cerebelli and then becomes sigmoid sinus Its tributaries are: Superior petrosal sinus Inferior cerebral veins Inferior cerebellar veins Diploic (posterior temporal) vein Inferior anastomotic vein

37. Sigmoid sinus: Is a continuation of the transverse sinus; arches downwards and medially in an S- shaped groove on the mastoid part of the temporal bone Becomes the superior bulb of the internal jugular vein Its tributaries are: The mastoid & emissary veins Cerebellar veins Internal auditory vein

38. Other sinuses:

39. Other sinuses: